Thoughts on compression/build

[cuisinartvette]

Let me pick your collective brains on a build...

First off Ive "heard" (yeah, I know...) that the LT5 is not a true 11:1 motor, is really closer to 10:1. NOW-If thats the case.....

-Options
1) Mill heads
2)Custom piston
3)What are the stock CCs on these?
4)Would add a slight bit of cam timing to take advantage of porting. Not 100% on this but heavily leaning towards it. Spring pressures may only increase a slight bit so longevity shouldnt be a problem.
5)Longer/lighter rods....
6)Wont be stroked

Now, for a real zinger....

How difficult would it be to create a solid type lifter, how would that work in terms to adjustment, lash ramps, etc??? Dont Porsche and Ferarri use somethign like this?

Kind of know the direction I want to go, just wanted some input..It never ends.
I promise Im sober posting this

[jonszr1]

the thing with trying to increase compression , if the knock sensor is activated now on premium pump gas wouldn't it defeat the reason for increasing comp? what if you actually thought of increasing the cc by 1or2 in matching all the combustion chambers . you might be able to put more total in instead of what corey did with mine 24.5 total down from factory 27-28. lighter rods ok but longer means shorter skirts. which is great on women but sucks on pistons . rod stroke ratio in outr engines not the greatest stk. Cams really dont seem to mke more power unless you put a 4in piston in it to unshroud the valves. cams seem to do alot for the 402-415 and unles you just want the lope , most say cams arent worth it . pete has trid all kinds of cam in his totally ported 350 with out making any more power. thats what ive heard hope it helps. get headers and port your stuff first just might like her that way. i know i do mine

[A26B]

Originally Posted by cuisinartvette

Let me pick your collective brains on a build...
Now, for a real zinger....

How difficult would it be to create a solid type lifter, how would that work in terms to adjustment, lash ramps, etc??? Dont Porsche and Ferarri use somethign like this?

Kind of know the direction I want to go, just wanted some input..It never ends.
I promise Im sober posting this

Solid lifters with required lash would wreak havoc with the knock sensor to the extent you would never be able to open the secondaries. Even if you removed the secondary butterflys, it would not go into open loop with the high knock count being registered by the solid lifters.

Not sure why you would want solids as the Lt5 is good for 8 grand anyway.

[cuisinartvette]

Just thinking out loud, so to speak . These do rev well, just love the sound and feel that a solid lifter motor has. No bleed down from oil thinning out when it get s hot...all the lift and duration 100% of the time. These (LT5) lifters do run on the same principle as a typicl hydraulic lifter would, no?

[32valve]

Originally Posted by A26B

Not sure why you would want solids as the Lt5 is good for 8 grand anyway.

Is it? I wonder how much stroke you could go with to reliably reach these RPM levels? 4"? It seems that with the right intake and cam setup this would be the way to more power. The strokers have been limited to just under 600rwhp for a long time now and maybe the answer is 8k+ rpm.

[8upZR1]

I like the idea of solids. It wouldn't require too much work to fab the lifters. Shimming the deal for proper clearance would be a pain but only cause its 32 valves, and if you have to play with it a few times, thats 64, or 128 or just a headache, but do able. Also you dont need absolute perfect lash for street motor. Once its done though, it aint gonna change like a 16V 350. As for the knock issue, it can be turned off or tuned to be not so sensitive. I wouldn't rev my LT5 to 8K on a regular extended period with stock lifters. No one seems to have a clue about which audi lifters work so the solids seem to be a logical choice. Also with solids you could probably rev way past 8K & you would know that its OK.

After valvetrain what is the limiting factor for these motors in terms of RPM potential?

As for milling the heads for more compression, I have been told by a reputable LT5 specialist that it is worthwhile but that there is a limit cause the timing chain tensioner can't take up slack properly when you mill the head more than 10 thousandths or something like that.

[tpepmeie]

All this talk about 8K is entertaining, but nobody has mentioned the cam chains. If I recall, they were the failure point for the World Challenge cars, when they were sustaining 7500 for extended periods. JVD could chime in here, I'm sure.

Maybe stronger chains are available these days?

The other limiting factor to making power that high (8000+), is the port cross-section. Especially as you increase the stroke. As the piston speed goes up, the port choke rpm is reduced. The best you're going to get at the intake throat is about 38mm, or 1.5" diameter just under the valve seat. I think Rod has gone to 39, but with very thin port walls.

Finally, not least, the intake tuned length (about 13" total) is perfect for 7000 rpm. That is where the wave tuning is strongest. This can be fudged a little higher, with the big plenum runners, and creating a taper, to reduce the effective length of the port.

Best I've heard is a Jeal/Kirchhofer 415 which went 724 hp at the crank, at 7550 rpm. Impressive as that was, the BMEP (hp per cid, per k rpm) was lower than the best 385/415s from LPE, etc. That suggests to me that pumping losses and friction was significantly impacting power at that high RPM.

Todd

[Tyler Townsley]

Solid lifters on a LT-5 was tried by Lane Goldstein some years ago. He went back to hyd because adjusting them required removal of the cams which changed the adjustment as you put them back. Getting good chains was a real exercise in spending money. Since he went with 1 in deck plate the chaines had to be longer and he spent a lot of money because the supliers could not get it right. His 431 ci motor put out about 950+- HP. Best time was 8.9 or so. With the exception of maybe Rod no one else has taken the LT-5 to the real edge.

Tyler

[A26B]

When I said 8000 rpm, it wasn't my intent to infer that 8000 rpm was a viable, sustainable redline, but rather to illustrate that the hydraulics in the LT5 are pretty damned good! I have no false illusions about positive cam following. I have never incurred "float" like I have in other conventional, pushrod engines, back in the old days. Considering the much reduced mass in the valve train & lighter valves associated with the shorter stems/smaller dia heads used in the LT5 4 valve/cyl design, float is essentially a non-issue of any significant matter. I regularly hit the limiter (7500) with my 415 in 1st gear. With the fidanza, 3.73 gears and the torque of the SGC 415, it happens real quick.

Todd's comments about the chains is well taken. However, the Challenge cars were running at sustained high rpm, whereas most of us will never use our toys in that manner, so the chains will hopefully stay with us. The closest I have or will ever come to that would be in a standing mile or ORR event and I don't have the gonads to run fast enough in an ORR to be pushing the rev limiter.

Bottom line: my 8000 rpm comment was a slightly exaggerated statement meant to say, I would look for cutting edge performance in other areas than solid lifters. I would hate to think about having to remove the cams & lifters to set lash and then degreeing the cams back in. Can't imagine trying to do this with the engine in the car.

I think turbocharging is the answer for more power......and it comes with much better manners than radical, normally aspirated power at the same power output level. I guess my feelings about that are obvious, what with our current project to develop an affordable, rear-mount TT system for the ZR-1. With a purpose built engine, the LT5 should be North of 800 rwhp @ 16~18 psig boost. Aaron Scott's recent TT for Wayne Hale supports those numbers. Also, boost overcomes the LT5 design limits Todd aptly stated.

[Aurora40]

The higher compression and lighter rods is I believe what Callaway and Lingenfelter do on their 350 builds. Though I thought they raised compression via a piston change, not longer rods. But I'm no engine builder by a long shot.

I always think it's bizarre that there can't be improvements made with cams, but I guess even with stock cams, a little porting puts the power peak practically at 7,000 rpm anyway. So maybe the cams are already pretty aggressive. In my head it seems like if the primary lobes were the same as the secondary ones, you'd really make power then, but maybe there's some kind of symbiosis going on between them. What the hell do I know anyway...

Edit: Also, if you're gonna go all outside the box with solid lifters, etc, there might be more to be had going to a flat plane crank instead? It might also be a little easier to do in terms of supporting things that have to be done. But maybe not as the firing order would change.