Making LS7 more reliable and faster ? I hope so

[acammer]

Originally Posted by void_kp

got the car back.
First of all... the car sounds MEAN. Like, really loud (despite stock exhaust) and absolutely menacing.

here's a cold start (the 1st cold start I heard of it)
https://youtube.com/shorts/BhsriMgaqxI?feature=share

phone doesn't fully capture the chop

speaking about more interesting stuff...we were all a bit disappointed by the result. It's good but we were expecting more given how extreme the cam is.

car drivability is VERY low below 2000 rpm, engine picks up revs much quicker and sound is definitely insane above 3000 rpm. very race-car like. I couldn't pull gears to the end so i can't speak for perceived performance, but overall it feels a bit quicker.

I was expecting at least 550 at wheel... we are close, but both me and tuner were expecting more, with much less extreme cams they saw over 560 at wheel.

my theory is that there are 2 factors at play here:
1/ in washington state we only have 91, so a bit is loss due to "bad" fuel
2/ everyone else that changed to a similar setup also changed intake and 103mm CF. I did not. Maybe airflow is a constraint at high revs?

lastly, it would well be that the heads don't flow better than the stock heads, but it's unlikely to be honest.

I will post more as I will drive it, today I could only suffer in heavy traffic while I was bring it back home. Seattle is as bad as Los Angeles in that regard (no joking)

Well - it's about what I would have guessed. I don't know that it's way off on power, it's just not a highly optimized combination. There are definitely a few factors at work here, but the camshaft is the major piece of the puzzle, and the intake manifold is a less important, but contributing factor. My first post in your thread read:

Originally Posted by me, earlier

The cam is a really interesting grind - it's got a pretty early IVC and late EVO, which is going to keep it from wanting to do big rpm in a 427, but it has ridiculous amounts of overlap (34.5*) that's going to make a pretty focused powerband in the 5800-7000 range. Reading the advertisement, the marketing matches - it seems primarily focused on sounding super aggressive. No doubt it will achieve that with the overlap, but it's gonna drive very aggressive in a manual car. I would not expect to enjoy just cruising around under 2600rpm anywhere.

When I said interesting, I was being polite - this is not a great camshaft. I think we're seeing that play out, it's not that strong through the mid-range, it makes a fairly narrow curve, and signs off early. Driveability sucks, and it sounds like a racecar. So, it lives up to its marketing to sound awesome, but it's hard to love that cam in any sort of performance application. A different camshaft could have produced stronger results with better driveability. By comparison, my 376CI NA pump gas motor matches it in torque from about 4500 on up, beats it by 20whp, and has a nice, fat power curve. It does that with 21* of overlap, and drives extremely well for the NA power it produces.

An aftermarket manifold and throttle body would no doubt add some additional power from 5500rpm on up, probably adding 15-20 at the peak to get you closer to that 550whp goal. It would also help stand the power after the peak up a little better. That would be my next move on this combination - assuming you're not ready to yank the cam out for something else.

I don't think the fuel octane is a major contributing factor here - 93 octane might pick up a small single digit HP gain, and E85 might pick it up 10-15whp, but this is not a high compression setup that should be extremely octane limited.

An engine is the sum of it's parts, and in this case the combination is not highly optimized. It's definitely up power over stock, but would take a little more sorting out in terms of parts selections to really deliver your goals. I think with the right camshaft, and a matched intake manifold with 103, you could stand to pick up another 40-50whp pretty easily, along with a broader power curve AND substantially improved driveability. That's not to say run out and make changes, it's already a big gain in power, so I'd go live with it for a while and revisit after the season if you're not happy with it. We're always here at GPI if you decide you want to talk cam options down the road.

As far as the lifter preload - it's not going to change the power output in any meaningful way. The lifter pretty well does it's job no matter where in it's preload window it is. Obviously, if it's bottomed out, it's gonna hold the valves open and the engine won't run, and if there is lash (zero preload) it's gonna make a LOT of noise. Outside of that, it's gonna do it's job whether it's at .030" of preload or .130" of preload. Taken a level deeper, the higher preload actually has the benefit of reducing the potential for squish in the lifter body - you can't give up travel that you don't have. That's the concept behind a short travel lifter, it may only have .030" of preload, but then it's only got another .025" of travel left in the body, not much room to squish that cushion of oil (which likely has at least a small degree of air mixed in it that can "squish").

In practice, for a road race application like you have, I would want to minimize preload to somewhere around the minimum piston to valve clearance you have. The idea being that if you do get the valve-train unloaded in an over-rev and the lifter pumps up, you don't have more preload than you do PTVC as to avoid contact. I don't know if you've got a PTVC measurement, but I'd assume it's probably tight with that much overlap, and so a minimized preload would be appropriate on a stick car that does road course work.

Just some stuff to think on. Here's some driveability on my setup for comparison. Moderate power NA setups don't have to be miserable to live with when cruising around.

https://youtu.be/YLuDiMwtx4E?si=LMhZziHhc69fOutg

[void_kp]

first of all: thank you for the post. I really appreciate your comment and I know you already told me in advance, and to be fair I am glad you were right. It demonstrates your competence in the subject.

Driveability sucks, and it sounds like a racecar. So, it lives up to its marketing to sound awesome, but it's hard to love that cam in any sort of performance application

100% correct.

I'd go live with it for a while and revisit after the season if you're not happy with it. We're always here at GPI if you decide you want to talk cam options down the road.

this is exactly what I plan to do.

As far as the lifter preload - it's not going to change the power output in any meaningful way. The lifter pretty well does it's job no matter where in it's preload window it is. Obviously, if it's bottomed out, it's gonna hold the valves open and the engine won't run, and if there is lash (zero preload) it's gonna make a LOT of noise. Outside of that, it's gonna do it's job whether it's at .030" of preload or .130" of preload. Taken a level deeper, the higher preload actually has the benefit of reducing the potential for squish in the lifter body - you can't give up travel that you don't have. That's the concept behind a short travel lifter, it may only have .030" of preload, but then it's only got another .025" of travel left in the body, not much room to squish that cushion of oil (which likely has at least a small degree of air mixed in it that can "squish").

I am just worried that too much preload will add too much wear to the components with track usage.
I am ignorant so I might be completely wrong here.

a minimized preload would be appropriate on a stick car that does road course work.

yes.

[acammer]

Originally Posted by void_kp

first of all: thank you for the post. I really appreciate your comment and I know you already told me in advance, and to be fair I am glad you were right. It demonstrates your competence in the subject.

...


I am just worried that too much preload will add too much wear to the components with track usage.
I am ignorant so I might be completely wrong here.

I'm happy to help where I can - and I'll always try to be polite even when I don't agree with another approach.

IMO, too much preload would be if you're using more than 75% of the lifters total travel. An OEM lifter has right about .200" of travel, so it sounds like your on the "high, but ok" side of that. I wouldn't expect any additional wear as a result. I do think you have an excellent case for working towards a minimized preload for the safety factor on over-rev. Keep us updated - I'm sure the extra power is going to be a blast on the track.

[BamaGearSlama]

Posting because I also have a Texas Speed cam in my car, put in by previous owner. It's smaller than yours at 234/246, .635 X .635 and 115LSA +3 lift, LS7 rockers, TSP .660 dual spring kit and Comp LS Rocker Trunion upgrade kit. Mine has the MSD Atomic Air Force 103mm intake and Nick Williams 102mm throttle body, Bosch 52lb fuel injector set and MSD spark plug wires. It also has Dynatech 2" headers with straight pipes and full 3" exhaust with a Dynatech cat back. BTW, my car still has the stock LS7 heads and just flipped over 10K miles

I just had it dyno tuned on Monday since the mods were done 8+ years ago in Wisconsin and I live in Alabama. I could tell the car was running rich on the original Wisconsin dyno tune, and was hard to drive as it wanted to quit when taking off in first gear, making it a real safety hazard when pulling into oncoming traffic.

Anyway, that got resolved by leaning it out some and increasing the idle a little. I'd post a video of the last dynotune run but the file's too big to save from my phone to my desktop. I'll try and open facebook on my phone and see if it will let me post that way. Anyway, I'll post the dynosheet if I can figure out how, but max power was 574 & max torque was 529...

[BamaGearSlama]

https://www.facebook.com/10000007504...1050863611843/

[BamaGearSlama]

https://www.facebook.com/photo.php?f...9251229&type=3


The baseline pull was the original Wisconsin tune, not the stock tune. I gained 23 rwhp and 22 rwt over the Wisconsin tune and gained a lot of drivability.

And by the way, my tuner said the LS7's get a little better dyno numbers in a Z06 vs Z28 because of the Z28's taller rear gear (3.91 vs 3.42)...