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:mrgreen:

[A26B]

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?

[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.

[Jagdpanzer]

I would think twice about solid lifters if you plan to run this engine much. Setting the valve lash with shims as a real bitch on a DOHC engine with plane bucket style cam followers like the LT5 has. For the those who have been around engines for awhile high rpm hydraulic lifters are a gift from the engine gods.

[FU]

Use the KISS theory. Just go with a good top end port and cam timing. They are THE package for the ZR1. Don't try to reinvent the wheel here, It's been tried and true.

[QB93Z]

When I was talking with Marc Haibeck last weekend at Carlisle, he pointed out that the ZR-1 is essentially an engine with two different cams. In normal power, there is a civilized, smooth performing, "low-end" cam. When the secondaries kick in, the engine characteristics are dominated by a hotter cam. He said that it is one of the ways the designers got such a broad useful power band out of the LT5.

This might explain why there is not much improvement seen by swapping out cams.

Jim

[Aurora40]

When the secondaries kick in, the engine characteristics are dominated by a hotter cam.
But it's only controlling one of two sets of valves. That's why I'd think if both cams had that profile, the max power would be improved, though I'd think low throttle driveability would suffer. But I guess that's not the case as people don't seem to gain much with cams on a 350.

[QB93Z]

Not exactly related to the cam discussion, but interesting, Marc also said that the combustion chamber flow was a swirl in normal power operation with only one valve flowing. The swirl was very effective for low power operation and emissions. But at full power operation, the combustion chamber flow was different with two valves flowing and was better for high power. Once again showing the genius of the LT5.

Jim

[cward]

I believe that Fastlane's drag car had solids but that engine had tons of R&D in it. His cam profiles were developed to make power at very high (for LT5) rpm. That engine also had 16:1 compression. Used leaded race gas. Lane did stuff to the LT5 that no one else has done and probably never will. He spent mega bucks on both his 368 engine and the 431 engine. I have a great deal of respect for Lane. He really pushed the envelope with that car. And he took the car for us to see perform many times from California to Bowling Green. No short trip. Thank you, Lane.

Curtis

[32valve]

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

[cuisinartvette]

Not that Im interested in more rpms, just the way it makes power to there in comparison to hydraulic. The LT5 has no problem revving but if youve taken (for instance) a Gen 1 with a hydraulic and put in a comparible sized solid you know what Im talking about, seems like the motor "works" less at higher rpm
. Not that I wwould have funds to do this, but it intrigues me...That would be awesome to have a solid LT5.

I built a motor for a freinds stripped out stepside a few years ago...Long rods, great heads, etc etc. Used a typical 246 @ .050hydraulic...Moto[/email]r ran pretty hard. I swapped in a comparable solid cam with damn near the same specs and could not believe the difference in how it grabbed rpm and how effortless it did upstairs. Sure it was a 2v head, but still...

I havent really checked out these lifters yet but if they operate anything like a typical Gen1 on principle I would think a large stroker that use a lot of cam could really pick up some power with this done. Trying to learn here.

Only thing I know about chains is the few that are flotaing around still...Supposedly they are prestretches/stressed as without doing that GM was having problems with them snapping from having a lot of rpm thrown at them. Maybe someone can elaborate more on that.

Doesnt the tesioner take up any kind of slack so if say you milled the heads there wouldnt be a tension issue?

Good discussion, keep the input coming

[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.

[cuisinartvette]

I agree forced induction is the quick way to big power..If I didnt have 2 projects going I could probably swing it but I still like old school musclecars so Im always car poor and scraping to get that next piece...

Im guessing the reason why these dont have float problems is due to light spring pressures on these cars, they just dont run into it with a small lift cam.

Different lash ramps and timing events would need to be ground into the cam also and Im not familiar enough with these to fool with it and get it right. All Ive heard is basic specs, but theres more to it than lift and duration at .050

[A26B]

I agree forced induction is the quick way to big power..If I didnt have 2 projects going I could probably swing it but I still like old school musclecars so Im always car poor and scraping to get that next piece...

Yeah, me too. When I went to pick up my Zee after Aaron finished the 415, we went to the shop and he started it up. I stood behind the car and was just mesmerized with the sound. You know, the lopity-lope sound of good cams! After several minutes Aaron had to just shut it off. No telling how long I would have stood listening to it.

I've have no interest in NO2 and never owned a boosted car until now. Turbocharging is just so efficient and still leaves great manners. The pull of even more power than the 415 finally moved me to the dark side. Driving the prototype 95 LT1 with single turbo was so much fun. Can't wait to finish the remaining C4 systems and build my own. I think the 415 will be on a stand in the shop one of these days and a 372 low compression LT5 will take its place in the LPE Aerobody. The car just kinda has that turbo look about it.

[8upZR1]

If someone has the desire for higher revs and has sorted out solid lifters, stronger chains, cams heads and intake, what is the next limiting factor? Piston speed with stock stroke doesn't seem too crazy for 10K+
I have seen on the web CNC'd heads that flow 400cfm+ for LT5. I believe that would not limit rpm's to below 10K.

Turbos are definetily easier, but they have their own problems to deal with. Too bad LT5 is dead in terms of engine development.

Titanium valves have very little fat and will give some extra float protection. I was personally looking at an incomplete set on Ebay a while back. Also, beehive springs from compcams look like they will fit with no problems. Zomething to think about.

[tpepmeie]

In my opinion, valve size becomes the limiting factor (and with valve size goes port size, per my previous post). Using a stock stroke length, with the biggest valves known to fit in the LT5 chamber, the mean velocity at the valve head approaches 80 m/s at 8000 rpm. That is pretty inefficient, as even F1, etc. are typically 73-75 m/s.

To achieve the real big rpms, you would need a more oversquare engine (shorter stroke:bigger bore) and intake valves around 34% of bore area. And ports to match, of course. That would allow more reasonable air velocity as revs increase.

Then, finally, I am told that the ladder-frame sump allows the crank to "walk" in its journals at higher RPMs. Perhaps that is solved with studding the bottom end, though.

Todd

[A26B]

Todd,

I'm going to school here & havve a couple of questions.

In my opinion, valve size becomes the limiting factor (and with valve size goes port size, per my previous post). Using a stock stroke length, with the biggest valves known to fit in the LT5 chamber, the mean velocity at the valve head approaches 80 m/s at 8000 rpm. That is pretty inefficient, as even F1, etc. are typically 73-75 m/s.

If the LT5 has higher port velocity than the typical F1, then should cylinder fill be more efficient from the inertial ram effect.....or....is the velocity higher but total flow volume lower because of port restriction?



To achieve the real big rpms, you would need a more oversquare engine (shorter stroke:bigger bore) and intake valves around 34% of bore area. And ports to match, of course. That would allow more reasonable air velocity as revs increase.

I've read a number of articles regarding port size and it's a generally respected opinion that larger port size is not necessarily always a good thing. More Hp can be realized with higher port velocity in many cases, as a result of more efficient cylinder fill and a/f mixture. I'm assuming your comments are directed to the full-out, purpose built race engine which will operate nearly continuously in the top 20% of the rpm range.


Then, finally, I am told that the ladder-frame sump allows the crank to "walk" in its journals at higher RPMs. Perhaps that is solved with studding the bottom end, though.

Wasn't this an issue with the 375 Hp engine design that precipitated the 405 Hp bottom end design?

Jerry

[tpepmeie]

Jerry, heck I don't have a PhD in engine design that's for sure. Just a self-educated enthusiast, who has absorbed a lot of the theory from various sources.


If the LT5 has higher port velocity than the typical F1, then should cylinder fill be more efficient from the inertial ram effect.....or....is the velocity higher but total flow volume lower because of port restriction?

Beyond a certain point, too much velocity can kill power big style. Once the flow is "choked", then inlet density is reduced despite higher velocity. Additionally, so-called pumping losses skyrocket, as the effort to draw in the mixture at super high velocity is too great. It is not a good thing to have higher inlet velocity than F1 or other race engines. You will find that most of the optimized unrestricted engines operate at around the same factor (called Lovell factor, to be precise).



I've read a number of articles regarding port size and it's a generally respected opinion that larger port size is not necessarily always a good thing. More Hp can be realized with higher port velocity in many cases, as a result of more efficient cylinder fill and a/f mixture. I'm assuming your comments are directed to the full-out, purpose built race engine which will operate nearly continuously in the top 20% of the rpm range.

Oh, for sure. Too much port volume can be detrimental absolutely. Again, you are right that higher port velocity, & smaller ports are a good thing *up to a point*. The key here is that there are nearly universal laws around something called the Mean Inlet Mach Index (refer to textbooks by Charles Taylor for additional info). Above about .55 Mach average inlet velocity, power suffers.

You are right, for good low-rpm driveability you want smaller rather than larger ports, provided you can still get the needed airflow at peak power speed.

It's a lot of textbook, and theory. But I have researched several many successful 4-valve race engines, and the theory does hold in practice.


Wasn't this an issue with the 375 Hp engine design that precipitated the 405 Hp bottom end design?


Probably right on that account, perhaps the 4-bolt mains solved the problems.

Todd

[A26B]

Thanks Todd, always a pleasure to discuss such things with you!