save your money.. many use poly locks. many need taller valve covers.. The stock cam and springs are so mild, you are not going to gain much of anything.. other than a lighter wallet They work well when you have aggressive cam lobe ramps and heavy springs to control the valves and lifter over the nose of the lobe.. not an issue with the mild stuff. yes you'll gain a few hp.. but that is from the ratio being more spot on than the oem stamped rockers.. When we have to use stamped rockers for a class of racing we will go through 40-60+ rockers to get a matching set that truly = the rated ratio.. of 1:52
Are you building a race engine? If not, then you're probably better off using the Comp Cams roller-tip rockers. They can use the stock rocker studs and nuts, so no clearance issues. Plus, you'll be saving a lot of money vs full-roller rockers.
Also, why the 1.5 rockers? IMO, if you're gonna buy rockers, might as well upsize to 1.6.
[This message has been edited by Blacktree (edited 04-04-2017).]
I bought a semi-personalised cam+lifters+springs+retainers kit from Crower for my engine rebuild project.
During our discussions, we had settled on a 1.5 ratio. This recipe is "supposed to work", so I don't want to mess with the recipe by deviating from the Crower-specified 1.5 ratio.
Also, I don't want to buy 1.6 rockers, find out I have a piston-to-valve clearance problem, and then need to spend $$$ again for 1.5 rockers.
I'm using their 68301X1-12 spring: Seat: 1.700" @ 101 lbs Nose: 1.200" @ 297 lbs Coil bind: 1.130"
I will have up to 0.449" lift on the intake.
Is my new valve spring much stiffer than a Fiero valve spring?
My concern is overheating/galling of the ball and socket.
I may run up to 6500 RPM, so that will also play into the overheating. The time I spend at high revs depends on how hard the engine pulls up there (I'll only know when the engine is installed in the Fiero).
With a roller trunnion, these ball and socket durability concerns will pretty much vanish.
If that's not a concern, then I'll just buy the Comp Cams roller-tipped 1.52 ratio rockers, and have the precise ratios.
[This message has been edited by pmbrunelle (edited 04-04-2017).]
Those valve springs are a little stiffer than stock, but not by much. The camshaft lift doesn't seem to be very aggressive either. So piston-to-valve clearance won't be a concern. Rocker ball wear won't be a concern either, as long as your oil pump works.
If Crower says to get 1.5 rockers, then I would follow their recommendation. Your build doesn't seem to be "hard core" enough to warrant full-roller rockers. So you can get the Comp Cams rockers and save some cash.
[This message has been edited by Blacktree (edited 04-04-2017).]
use factory type stamped rockers, rockers with roller tips don't do much of anything.. the gains are again with higher lifts, that have the rocker sliding more on the tip.. if you use the correct length pushrods the rocket contact should stay in the center of the valve tip.. if it is sliding across the tip you need different length pushrods..
Originally posted by Blacktree: So piston-to-valve clearance won't be a concern.
Kind of what I think, but rather than guessing, I'll be checking this with clay. I also bought the Cloyes double-row timing chain set, with 4° advance/retard keyways, so if I had a piston-to-valve clearance issue, I would have a way to mess with it, rather than just be screwed.
Off on a tangent, how does one inspect an oil pump? I took one apart, and there's a gasket on the end cover. However, this gasket seems to be unobtainium.
I have a "good used" oil pump lying around, but I can't open it up, because I don't have the gasket to close it up after inspection.
If we summarize, heating of the ball and socket is proportionally affected by three factors:
Spring pressure
Lift
RPM
Valve spring pressure change: don't know, presumed to be negligible Lift change: stock: 0.410", new: 0.449" 10% increase Redline change: stock: 5500 RPM, new: 6500 RPM 18% increase
So there's up to 30% more heat being dissipated in the ball and socket's friction than stock. I'll need to think about how I feel about that, doesn't seem like much more than stock, I guess. Anyway, right now I'm working on the bottom end, I only need to answer these valvetrain questions when I get to the heads.
As far as the usefulness of roller tips, the LS7 has plain tipped rockers (but roller trunnions), and it has 0.591" of lift... so we know that plain tips can work well. But the roller trunnions seem commonplace for any sort of performance applications.
Is machinist's blue the hot ticket to check if the rocker is touching in the middle of the valve stem?
[This message has been edited by pmbrunelle (edited 04-04-2017).]
I don't mean to be condescending, but the setup you're describing isn't "hard core". It's more of a medium performance build. You don't have to start throwing race parts in it, unless you just want to do it for the heck of it. There's no need to worry about your valvetrain melting down, or pistons smacking the valves, or whatever.
As far as the usefulness of roller tips, the LS7 has plain tipped rockers (but roller trunnions), and it has 0.591" of lift... so we know that plain tips can work well. But the roller trunnions seem commonplace for any sort of performance applications.
Is machinist's blue the hot ticket to check if the rocker is touching in the middle of the valve stem?
You are comparing your engine to a titanium valved supercharged v8 with titanium rods and such..? Yes they use roller trunnions.. and roller lifters.. both because todays oils don't have the zinc and prosperous (sp?) for sliding metal to metal contact.. The LS7 was built and put in a VETTE.. they know the car will be used, and used hard.. many will be used as track cars.. long run times at high rpm use.. If you are going to drive at 5000-7800 rpm for 20 minutes to a few hours.. then yes.. you'll need roller trunnion rockers, they don't have roller tips as the engineers have set the valvetrain up correctly so the rocker tip is not sliding across the tip.. it is not side loading the valve in the guide.. Not as easy to get in production parts without special length valves and pushrods. and adjustable valvetrain.. The ls7 cam isn't that high of lift, why because the heads flow so well they don't need to open it more.. the gains are out weighted by the loads.. You are comparing apples to oranges.. Yes roller trunnuns will lower friction.. do you need it.. Not really.. Are you running a rollercam?? if not you should be using an oil made for flat tappet cams, that will limit the friction as it has the zinc/etc to coat the parts for metal to metal sliding.. You'll do no harm.. adding full roller rockers.. will you gain anything.. doubt it.. only you know if you'll be spinning this engine to 5000-7000+ rpm and not just a run up to it then shift.. I mean running down a road or a straight at 5000+rpm for an 1/8th mile or better.. Now if you had a hyd roller or solid with huge lift or at least very aggressive cam lobes that required heavy spring pressure it be different.. and that includes using it hard.. I'm sure you can find a set of full rockers to fit under the stock valve covers with a little grinding on the covers.. but do you NEED them.. most likely not..
If I was to build an engine and use roller rockers.. I'd get 2 sets of valve covers, and cut them. and then have them welded together to make factory looking tall valve covers.. For that oem look and everyone to look and go something isn't stock but I just can't put my finger on it.. as they look at an engine with valve covers an1"to 1.5" taller than stock.. welded,body worked(if needed), and painted oem red..
I don't mean to be condescending, but the setup you're describing isn't "hard core". It's more of a medium performance build. You don't have to start throwing race parts in it, unless you just want to do it for the heck of it. There's no need to worry about your valvetrain melting down, or pistons smacking the valves, or whatever.
Just trying to measure twice, cut once. My first engine build ever, so everything needs to be measured; I don't have the experience to glance and know without checking that something will or will not be a problem.
As far as the LS7 goes, I don;t think anyone can argue that it's well-done; that's why I think it can serve as a good benchmark. They have an open pressure of 310 lbs. Titanium valves actually make it easier on the valvetrain; less spring is needed to control them.
By the RPM and lift differences, an LS7 would dump 83% more heat into its ball and sockets, if it were so-equipped. So somewhere between the stock Fiero (0% heat increase), and the LS7 (83% heat increase), there is a line that was crossed... when this line (for severe duty) was crossed, Chevrolet added roller trunnions to the LS7. I'm trying to figure out where this line is.
In the foreseeable future, the hardest duty that the engine will see is tuning. I will be staying at high RPM (and holding it there) for a couple minutes at a time, in order to reach every cell of my Speed-Density VE table. Don't want to grenade the engine while tuning it!
My cam is a flat tappet cam; probably going to use Shell Rotella T oil.
Is a Fiero valvetrain (with its stamped rockers) reliable for minutes at a time at 6000 RPM? If the Fiero valvetrain works up to redline, then that gives me confidence for my new valvetrain, which is not much (well, estimated 30%) harder on the ball-and-sockets than stock.
By the RPM and lift differences, an LS7 would dump 83% more heat into its ball and sockets, if it were so-equipped. So somewhere between the stock Fiero (0% heat increase), and the LS7 (83% heat increase), there is a line that was crossed... when this line (for severe duty) was crossed, Chevrolet added roller trunnions to the LS7. I'm trying to figure out where this line is.
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The vette is their halo car.. the line was crossed when failure was not an option.. and they expect the car to be run at high rpm for long stints.. On a track... on the us roadways illegally speeding.. and overseas.. on roads made to high speed running.. The oil used today.. don't have the stuff to let sliding metal on metal live.. it was removed because it kills emission parts (o2 sensor and cats) that are required by law to last 100-150k.. This is the ONLY reason for roller cams.. the more a to b vehicles would have flat tappets to save mony if they live.. they don't.. Shell Rot. won't help you.. diesel oils have had it removed since 2010.. when the epa mandated egr and exhaust scrubing cats.. If you are truly going to run this engine at 5000rpm+ for a minute or more.. you will need to use oil made for flat tappet and ball and socket rockers.. off the shelf oil and most racing oils are not made for this anymore.. Going to full roller rockers or, trunnun roller rockers and keeping a flat tappet cam is odd.. as you'll lower the heat generated at the rocker, but do nothing to the cam.. Cam lobes fail much more than rockers.. and it's easy to check for the rocker cup and ball "blueing" and replace.. not so much the cam.. Will you hurt anything adding roller trunnun rockers.. nope.. will you gain anything.. nope.. other than 1-2* oil temp.. and maybe "3-5" hp.. at the peak.. Any friction you are worrying about at the rocker, it's worse at the flat tappet.. push rod caps /or oil drippers that direct the oil to the ball and socket flood the rocker with oil.. = less friction and cooler oil temps.. those "worried "about it, run spray bars in the valve cover to spray the rocker ball and the springs to cool them.. Go look at circle track valve covers.. on the inside..
The vette is their halo car.. the line was crossed when failure was not an option.. and they expect the car to be run at high rpm for long stints.. On a track... on the us roadways illegally speeding.. and overseas.. on roads made to high speed running.. The oil used today.. don't have the stuff to let sliding metal on metal live.. it was removed because it kills emission parts (o2 sensor and cats) that are required by law to last 100-150k.. This is the ONLY reason for roller cams.. the more a to b vehicles would have flat tappets to save mony if they live.. they don't.. Shell Rot. won't help you.. diesel oils have had it removed since 2010.. when the epa mandated egr and exhaust scrubing cats.. If you are truly going to run this engine at 5000rpm+ for a minute or more.. you will need to use oil made for flat tappet and ball and socket rockers.. off the shelf oil and most racing oils are not made for this anymore.. Going to full roller rockers or, trunnun roller rockers and keeping a flat tappet cam is odd.. as you'll lower the heat generated at the rocker, but do nothing to the cam.. Cam lobes fail much more than rockers.. and it's easy to check for the rocker cup and ball "blueing" and replace.. not so much the cam.. Will you hurt anything adding roller trunnun rockers.. nope.. will you gain anything.. nope.. other than 1-2* oil temp.. and maybe "3-5" hp.. at the peak.. Any friction you are worrying about at the rocker, it's worse at the flat tappet.. push rod caps /or oil drippers that direct the oil to the ball and socket flood the rocker with oil.. = less friction and cooler oil temps.. those "worried "about it, run spray bars in the valve cover to spray the rocker ball and the springs to cool them.. Go look at circle track valve covers.. on the inside..
I thought that flat tappet lobes, when properly broken in and lubricated with ZDDP, don't get wiped, leaving the ball and socket as the next weakest link. Am I wrong?
While it is easy to inspect rockers for bluing, by simply removing the valve covers, if the remedy is to change to roller rockers, then that's going to be a cradle drop to work on the engine properly...
Is bluing of the ball and socket affected by the presence of ZDDP? My understanding is that ZDDP helps where extreme pressures are present. At the camshaft lobe, there is a very small contact zone between the lobe and lifter. Therefore, for the lobe-lifter contact, ZDDP is essential.
At the ball and socket, the contact area is much larger, so I would not characterize it as extreme pressure.
So for the ball and socket, if regular oil doesn't cut it (overheating, bluing), then I doubt that ZDDP additive will help anything (on the premise that ZDDP is beneficial for extreme pressures only).
Or, does ZDDP have a beneficial effect even for low-pressure contact between metal surfaces? If so, then that may be the safety cushion I need to run ball and sockets.
That would be a good idea... either that or regular oil with some ZDDP additive.
E.Furgal thinks that the Rotella T is watered down... I'm not sure how to confirm that.
The one for sale locally at Canadian Tire meets API CJ-4, which came into effect for 2007 diesel engines.
So if there was an EPA cleanup in 2010:
quote
Originally posted by E.Furgal: Shell Rot. won't help you.. diesel oils have had it removed since 2010.. when the epa mandated egr and exhaust scrubing cats..
Then the CJ-4 oil wouldn't be affected, correct? Since it precedes 2010
Need to do a whack of head and intake (and exhaust) manifold work before you get the flow to take advantage of more bump stick. You didn't go into whether or not you were doing that.
One of the big mistakes people make is to source valve train components from more than one manufacturer. If you use some one else's (other than the cam manufacturer's) springs or rockers etc. and it screws the engine you get no come back.
Having said all that, you rebuild sounds moderate enough and I think you can forget about the roller rockers.
FWIW I went all Comp Cams on my turbo build, after making sure they were willing to do e up a custom camshaft. Their pressed roller rockers are cost effective.
Need to do a whack of head and intake (and exhaust) manifold work before you get the flow to take advantage of more bump stick. You didn't go into whether or not you were doing that.
One of the big mistakes people make is to source valve train components from more than one manufacturer. If you use some one else's (other than the cam manufacturer's) springs or rockers etc. and it screws the engine you get no come back.
Having said all that, you rebuild sounds moderate enough and I think you can forget about the roller rockers.
FWIW I went all Comp Cams on my turbo build, after making sure they were willing to do e up a custom camshaft. Their pressed roller rockers are cost effective.
I didn't specify the overall plan, but rocker durability has nothing to do with airflow/hp. It's all to do with the valve springs, lift, and RPM. I didn't initially feel the need to pollute this post with superfluous information.
That said, I may as well share some more information regarding the powertrain rebuild project. The Crower bumpstick (114° LSA, along with lifters, springs, retainers) has already been purchased a while ago, so that's already set in stone.
My plan for the intake is to do nothing. Exhaust, I was going to buy Sprint headers, they are now unobtainum, so probably going to end up building my own exhaust (and for sure costing way more). I'm going to slap a TO4B H-trim clone turbo on this thing. Sunbird 3-port boost control solenoid Lumina APV knock sensor and knock module 30 lbs/hr injectors, EP-381 fuel pump LC-1 wideband #459 block 3.1 crank, most probably going to use the crank sensor to trigger the MegaSquirt 2 computer Block bored to 89.80 mm, giving 3192 cc displacement Hypereutectic pistons, approx. 7.5 compression (precise value depends on head gasket choice) Head gasket thickness to be determined based on quench distance (once bottom end is assembled and I know how far the pistons stick out from the deck), probably MLS. Fiero Store 9.75" HD clutch set Refreshed Muncie gearbox, complete 1984 Performance gearset, 85 V6 ribbed case
So it's a basic turbo build.
I agree that the valvetrain is a kind of "engineered package". That's why I don't want to mess with the 1.5 rocker ratio. But the rocker pivot's durability is outside of the scope of Crower's responsiblity in this case, since I didn't buy any rockers from them (they don't seem to have any for the V6).
Therefore, it's on me to ensure that the rocker pivots are reliable. The prevailing opinion is that my valvetrain is mild, so that's reassuring. It's just the extended time at higher revs (to datalog the entire VE table) that's outside of normal use. Maybe the zinc-laden oil will be enough.
Basic turbo build.. Nothing basic there.. As the springs have to be strong enough to not open under boost.. And will require a higher seat pressure than a non boosted engine.. Higher spring pressure puts more pressure on the ball and socket.. Your lack of not bringing up the fact that it is a turbo (boosted) build polluted your thread to no end
I'm using Crower's standard spring for 2.8s with hydraulic flat tappets. Same spring as for N/A applications. I posted the spring pressures above.
The ball and socket load is only affected by the spring pressures. If you don't increase the spring pressures for boost, the ball and socket doesn't see any more load with boost.
They knew I would like 15 psi of boost... yet specified this spring anyway. So I assume it's OK. 15 psi on a 1.72" intake valve gives up to 35 lbs of additional force trying to open the intake valve.
Once the engine is assembled I'll find out if these valve springs are good enough for real
[This message has been edited by pmbrunelle (edited 04-07-2017).]
I'm using Crower's standard spring for 2.8s with hydraulic flat tappets. Same spring as for N/A applications. I posted the spring pressures above.
The ball and socket load is only affected by the spring pressures. If you don't increase the spring pressures for boost, the ball and socket doesn't see any more load with boost.
They knew I would like 15 psi of boost... yet specified this spring anyway. So I assume it's OK. 15 psi on a 1.72" intake valve gives up to 35 lbs of additional force trying to open the intake valve.
Once the engine is assembled I'll find out if these valve springs are good enough for real
You DID tell crower that this will be boosted.. and the amount.. and they matched those springs to that cam, with boost..and the red line you plan on ? I'm done.. but I'd make sure crower gives the ok for those springs and boost.. hate to blow the intake off it because the boost held the valve open. Boost cams are not the same as n/a.. sure you can run them.. but if you are installing a new one.. I'd use a grind designed for it.. why give up power using a n/a cam..
[This message has been edited by E.Furgal (edited 04-07-2017).]
Originally posted by pmbrunelle: The ball and socket load is only affected by the spring pressures. If you don't increase the spring pressures for boost, the ball and socket doesn't see any more load with boost.
Actually, the ball and socket will see less load under boost, because the boost pressure will counteract some of the spring pressure. So I'll say once again that ball and socket wear/heat/whatever will not be a concern. However, spring tension under boost might become a concern.
Edit to add: The stated spring pressures are 101 lb closed, 297 lb @ .500" lift. Under 15 psi of boost, you could potentially be losing about 30 lb of spring pressure on the intake valves, and about 20 lb on the exhaust valves. That's just a quick estimate. But hopefully you get the point.
So the fact that your engine is turbocharged is definitely NOT superfluous. When someone is trying to help you, you shouldn't insult them by stringing them along.
Have fun with your project.
[This message has been edited by Blacktree (edited 04-07-2017).]
You DID tell crower that this will be boosted.. and the amount.. and they matched those springs to that cam, with boost..and the red line you plan on ? I'm done.. but I'd make sure crower gives the ok for those springs and boost.. hate to blow the intake off it because the boost held the valve open. Boost cams are not the same as n/a.. sure you can run them.. but if you are installing a new one.. I'd use a grind designed for it.. why give up power using a n/a cam..
It is a customized boost cam. That's why it has a 114° LSA; wider than their NA off-the-shelf products. They didn't think any of their off-the-shelf grinds were suitable for my Fiero. They told me I could run to 6500 RPM, so that's why I want my rockers to handle 6500 RPM. They recommended their standard 2.8 springs for it... I hope they're not wrong!
quote
Originally posted by Blacktree:
Actually, the ball and socket will see less load under boost, because the boost pressure will counteract some of the spring pressure. So I'll say once again that ball and socket wear/heat/whatever will not be a concern. However, spring tension under boost might become a concern.
Edit to add: The stated spring pressures are 101 lb closed, 297 lb @ .500" lift. Under 15 psi of boost, you could potentially be losing about 30 lb of spring pressure on the intake valves, and about 20 lb on the exhaust valves. That's just a quick estimate. But hopefully you get the point.
So the fact that your engine is turbocharged is definitely NOT superfluous. When someone is trying to help you, you shouldn't insult them by stringing them along.
Have fun with your project.
Consider that the most load on the ball and socket is at the nose of the lobe. Presumably, the maximum load is what causes damage. So lets focus on this.
With an open intake valve, air/fuel mixture rushing around it drags the valve in towards the piston. How much force? Theoretically, up to 35 lbs, but probably much less in reality.
So suppose that we consider this force: 297 lbs - 35 lbs = 262 lbs
If we use 262 lbs for our calculations, then we are underestimating the load on the ball and socket. It could be 270 lbs in reality. Or maybe 290 lbs.
Underestimating loads is a good way to break things... this is why in the absence of hard information, we assume the worst case (NA engine), and neglect the presence of the turbo.
Originally posted by pmbrunelle: ...They recommended their standard 2.8 springs for it... I hope they're not wrong!
Just make sure that there won't be any coil bind at whatever lift you end up with. (FWIW, the stock Fiero springs will bind somewhere between .45 and .48 valve lift. Makes the difference between running a Crane 260 or 272 cam.)
Without going back over all the other comments, I'll just say that given the option of choosing a cam, from scratch, and using the 1.52 rockers, or choosing a milder cam, and then using the 1.6s, I'll always try to do the more agressive cam and the 1.52s, simply because that's what the cam and the engine are designed for. I consider the 1.6s a bandaid, for when you don't want to go into the engine and change the cam. If you're already in there, just do it right.
I also prefer the Comp Cams roller tipped rockers.
[This message has been edited by Raydar (edited 04-08-2017).]
Just make sure that there won't be any coil bind at whatever lift you end up with. (FWIW, the stock Fiero springs will bind somewhere between .45 and .48 valve lift. Makes the difference between running a Crane 260 or 272 cam.)
Without going back over all the other comments, I'll just say that given the option of choosing a cam, from scratch, and using the 1.52 rockers, or choosing a milder cam, and then using the 1.6s, I'll always try to do the more agressive cam and the 1.52s, simply because that's what the cam and the engine are designed for. I consider the 1.6s a bandaid, for when you don't want to go into the engine and change the cam. If you're already in there, just do it right.
I also prefer the Comp Cams roller tipped rockers.
The oem was a mild cam, and used parts bin thinking (been counters) The you spec cam and 1.6 rockers puts the valve down on the seat smoother, and opens it smoother, as the lobe ramp isn't as aggressive. making it easier to control the valve and valve train . Also the reason they don't use it today.. and have moved to 1.7 I'd not call sticking with parts because the been counters did, "just do it right". but ymmv.
1 - you are leaving some power on the table by failing to address the intake - even though you are boosting it, you can get significant gains with a couple of hours with a grinder.
2 - assume you are fitting an intercooler (which is a pain in these cars due to routing to the front of the car) otherwise don't bother with boosting past about 12 psi
3 - if you run a knock sensor with suitable software you can run 8.5 compression with 12-13 psi. You want as much as you can get without getting into trouble as it helps the pick up at lower rpm
4 - you won't need to run higher rpm (except maybe for testing). Depending on turbo sizing you may run out of poop at high end anyway, but in any case, with the turbo you can shift near stock red line and the engine drops back right near the torque peak in the next gear, so there is no benefit to punishing it by running it any higher as it won't significantly improve your times.
I'd not call sticking with parts because the been counters did, "just do it right". but ymmv.
The stock cam is relatively mild, and will work just fine with 1.6s, with no other changes. It's a common mod. I even did that myself. (Because, as I said, I didn't want to go into the engine to change the cam. Which I ended up doing later, anyway, and went back to 1.5s.) My point was that aftermarket cams for the 2.8 and 3.4 iron head V6 are designed to work with 1.5 rockers. 1.6s may help to put more stress on the cam lobes (and lifters and pushrods.) If you're already into the engine for a cam swap, best to just stick with what the engineers who designed the cam had in mind. It's easy enough to buy a cam that has the specs you want. Now if they recommend 1.6 (or whatever) rockers with their cam, and designed it all to work together as a system, then that's another story altogether.
I still remember a few years ago, when people were wiping out 272 cams, and lifters, with stunning regularity, even with 1.5 rockers. People who had built numerous engines. Maybe it was the fault of the cam, or maybe installation or break-in issues, but I certainly wouldn't want to tempt fate by inducing more stress than they were supposedly designed for.
[This message has been edited by Raydar (edited 04-09-2017).]
Just make sure that there won't be any coil bind at whatever lift you end up with. (FWIW, the stock Fiero springs will bind somewhere between .45 and .48 valve lift. Makes the difference between running a Crane 260 or 272 cam.)
Without going back over all the other comments, I'll just say that given the option of choosing a cam, from scratch, and using the 1.52 rockers, or choosing a milder cam, and then using the 1.6s, I'll always try to do the more agressive cam and the 1.52s, simply because that's what the cam and the engine are designed for. I consider the 1.6s a bandaid, for when you don't want to go into the engine and change the cam. If you're already in there, just do it right.
I also prefer the Comp Cams roller tipped rockers.
At some point, you will hit a limit trying to increase lift by reducing the base circle of the cam. The ramps become too steep, and the edges of the tappet will dig into the side of the lobe. There is a limit with roller lifters as well, but it's not easily as reached.
The solution to this is to increase the overall size of the lobe, and to increase the diameter of the tappet face (or increase roller diameter if applicable). However, changing the diameter of the lifter is a major change to the architecture of the engine...
Even in a so-called "clean-sheet" design such as the LS, some things such as the 4.4" bore spacing, and the 0.842" lifter diameter are unchanged from the old-school small block V8s. These are carryovers... if the designers were to design a V8 from scratch in isolation, the chances that they would have picked exactly the same dimensions are next to nil.
So if the diameter of your lifters limits the possible lobe lift, yet you still wish to increase valve lift, the only way to accomplish this is by increasing the rocker ratio.
Increasing the rocker ratio has downsides... the load on the lobe and on the rocker pivot are increased. But if you have roller lifters and roller trunnions, then I suppose that this becomes a non-issue. So maybe the GM 1.7 rocker ratio is some kind of compromise resulting from the 0.842" lifters, but we can't argue that the final result works!
Anyway, I'm sticking with the 1.5s, because that's the ratio needed for my cam+lifter+spring system. As for coil bind, I haven't yet thought about how to check that. I was thinking of trying to stick a feeler gauge between the coils at full lift. I don't know if this is the proper procedure.
quote
Originally posted by BillS:
Couple of comments.
1 - you are leaving some power on the table by failing to address the intake - even though you are boosting it, you can get significant gains with a couple of hours with a grinder.
2 - assume you are fitting an intercooler (which is a pain in these cars due to routing to the front of the car) otherwise don't bother with boosting past about 12 psi
3 - if you run a knock sensor with suitable software you can run 8.5 compression with 12-13 psi. You want as much as you can get without getting into trouble as it helps the pick up at lower rpm
4 - you won't need to run higher rpm (except maybe for testing). Depending on turbo sizing you may run out of poop at high end anyway, but in any case, with the turbo you can shift near stock red line and the engine drops back right near the torque peak in the next gear, so there is no benefit to punishing it by running it any higher as it won't significantly improve your times.
I know it's better to port the intake, but I want to drive the car this summer, not next year! On the other hand, if I cut too many corners, then I'll be disappointed with the result.
I was thinking of putting an air-air intercooler in the location of the stock catalyst (I will have a rear-exit exhaust). Not sure how the air circulation will be though... For the first summer, I might skip the intercooler, and stay low boost. Intercooling (and more boost) may come next year; I don't have a super-defined plan.
Compression will be 7.5 (pistons in my possession, block already bored to match). The detonation resistance is particularly important considering the inexperienced tuner that will be tuning the engine. The safety cushion is more important to me than off-boost performance. I will have a knock sensor to act as a guardian angel.
To tune the engine, I'll be accelerating the car down a dragstrip, recording engine acceleration (laptop) for each RPM. Kind of like an inertia dyno. I'll pick my shift points according the the pseudo-power curves I get. -1st: 3.53 -2nd: 1.95 With the large gap between 1st and 2nd, I expect to need to hold 1st for a long time to avoid bogging down in 2nd.
1 - if you responded to my statement that it will require a knock sensor I didn't see it.
2 - port matching the intake manifold won't take you until 'next year' it should take you part of one day.
3 - the compression is fine if you ever do go to the higher boost, but will kill some of your bottom end if you are only using 12 psi, which is all you CAN use until you put in an IC - which as I said, is a pretty challenging job. Most people accept the 10-12psi cap, forget about an IC and run compression of 8.0-8.5.
