Is my cam too big?

[NewZed]

BRAAP did a lot of studying on the NA engines.  He summarized his knowledge in the thread below.  The third post and more might be relevant to your problem.  I assume that your boost gauge is in the plenum.  "Boost" is caused by restriction to flow.   He also has quite a bit about port work.  If the runners and ports are restricting flow a different cam won't help much.   

 

Not an expert.

 

p.s. 270 HP from a 168 cubic inch engine is a lot.  1.6 HP per cubic inch.  At the rear wheels.  Have you thought about the bottom end, and durability?  Solving your problem might be the end of the engine.  Good luck.

 

 

Edited August 19, 2023 by NewZed

[72turboz]

Thanks for the thread link, I read through it awhile ago and I’ll read through it again. Might just be the nature of the beast with this engine. As far as the engine goes it’s a built/refreshed long block. Bottom end and top end have been gone through, replaced crank, balanced, bored over etc. only weak spots left are probably the pistons and if those go I’ll replace with forged flat tops. 

 

Im hungry for the 300whp number, although the car drives great and is a blast in its current state. Next time I’m on the dyno with the new intake, exhaust and cam I’ll bump the boost to 18psi to see if I can’t get anything more out of it.

[zboi]

People really need to stop with the whole build the bottom end up crap. We are talking about like 300hp people! No matter what you do you are never going to hurt the crank or rods. Were talking 50hp per piston/rod/crank journal. Don't throw money away!

That said your dyno results are interesting, your cam profile clearly seems to be aimed towards higher RPM yet your power falls off pretty quick. Do you have some more Dyno sheets with less boost? You should see power increasing pretty linearly across the board with each increase of boost. If power is increasing at the low end but not up top then there is a clear restriction. First try with exhaust off, if your lucky that will help. I think you may be running out of spark though.

[zboi]

But really need to see those other lower boost runs, if shape of graph is changing then that will make it much easier to diagnose.

[72turboz]

The only reason I rebuilt/refreshed the block was because it suffered a blown head gasket, and spun a crank bearing pretty much destroying the crank surface. Since I was having to replace it anyways I spent a little extra so I was happy with it. As far as the lower boost runs I don’t have pictures of those, but I do remember that the curve was slowly moving up as we turned up boost until roughly 13psi where it stopped making any power. 
 

As far as spark the car was not breaking up at all, and we were running one step colder plugs gapped at 30 and used non projected tips. Tuner didn’t seem to think it was spark related. 
I have no doubt that I’m running into some kind of restriction I just don’t know where it’s happening at.

[NewZed]

3 hours ago, zboi said:

People really need to stop with the whole build the bottom end up crap

 

Kind of extreme from a guy who has no apparent experience building engines.  I assume that you read something on the internet and absorbed it as your own.  You were asking how to install a turbo just a few days ago. 

 

Nothing wrong with questioning somebody's comment but if you're going to fake expertise try to do a better job.  Better yet, just don't.  And there's no need for the insulting tone.

 

 

[NewZed]

The basic subject of this thread was covered pretty well years ago.  The thread is kind of buried in the L series sub-section under Powertrain FAQ's.

 

 

[72turboz]

Thanks for the link. I’ve read that post extensively. I figure I’ll replace the cam so it’s where I’ll be doing most of my driving and get a 3 inch mandrel exhaust out the back. I’ll take care of some smaller items like adding an idle air control valve to the car for cold starts and when the electric fans kick on. Cars almost ready just is frustrating with the power figures.

[zboi]

10 hours ago, NewZed said:

 

Kind of extreme from a guy who has no apparent experience building engines.  I assume that you read something on the internet and absorbed it as your own.  You were asking how to install a turbo just a few days ago. 

 

Nothing wrong with questioning somebody's comment but if you're going to fake expertise try to do a better job.  Better yet, just don't.  And there's no need for the insulting tone.

 

 

Wow, I've built plenty of engines. I've built 1000 hp turbo LS motors. I've put out tuning guides even. Your the guy who posts a one word answer. I asked a simple question, are the injectors big enough and is the computer smart enough. Your the dude been insulting, and nothing is worse than a bunch of people throwing out a bunch of unfounded "buy this, upgrade that" crap. Show me an L series with a bent rod or broken crank.

[72turboz]

11 hours ago, zboi said:

Wow, I've built plenty of engines. I've built 1000 hp turbo LS motors. I've put out tuning guides even. Your the guy who posts a one word answer. I asked a simple question, are the injectors big enough and is the computer smart enough. Your the dude been insulting, and nothing is worse than a bunch of people throwing out a bunch of unfounded "buy this, upgrade that" crap. Show me an L series with a bent rod or broken crank.

To be fair I destroyed the first crank in my block.

[zboi]

7 minutes ago, 72turboz said:

To be fair I destroyed the first crank in my block.

We talking snapped or just beating up the journals?

[HowlerMonkey]

Spark plug gap or coil weakness

 

Did original poster ever mention what kind of dyno?

[72turboz]

32 minutes ago, HowlerMonkey said:

Spark plug gap or coil weakness

 

Did original poster ever mention what kind of dyno?

Gaps are good, and coil is strong, new msd. No break up in the higher rpm’s afrs not going rich with unburnt fuel.

[NewZed]

On 8/18/2023 at 7:40 AM, 72turboz said:

 

 

Looking back at your first post I see that you do have an aftermarket cam of some sort.  Is the cam timing adjustable?  Might be too advanced.  Of course, the Isky cam will probably be correct, but you might have possibilities already there.  

 

On 7/23/2023 at 3:33 PM, 72turboz said:

The cam specs are as follows; @015 TDC, Intake opens 33, Exhaust closes 33, Overlap 66. Intake Closes 77, Exhaust opens 77. Intake Duration 290, Exhaust Duration 290. Intake lift 540, exhaust lift 540. 112 LSA.

 

https://help.summitracing.com/app/answers/detail/a_id/4706/~/advancing-%2F-retarding-a-camshaft

 

 

 

[zboi]

Post another dyno sheet with lower boost!

[72turboz]

I don’t have access to any other dyno sheets, but I can assure you the curve was trending upwards as it should till around 13psi where it failed to make any gains. The cam was degreed correctly, I verified with a wheel, was my first thought initially as well. 

[zboi]

Was it identical in shape? Peak RPM and torque at same RPM each run? Trending up doesn't mean much. Like I said before your cam should not be falling off so soon, I'd expect peak power out another 1000 rpm. You have massive duration and overlap, which will amplify backpressure issues.

Edited August 30, 2023 by zboi

[72turboz]

Wasn’t identical as he was adjusting each pull. But power and torque were increasing with variations on where peak was until 13psi. I strongly think the cam specs are the main culprit coupled with the 2.5 exhaust from downpipe back.

[zboi]

Peak power RPM should not be bouncing around hardly at all. Fiddling with the tuning should either bring some gains in certain RPMs if its targeting AFR or spark, or move the whole curve up. Your tuner should have locked down pretty much everything at a lower boost, then started adding boost and seeing the result. Which should result in a nearly identical graph shifted up with each increase in boost, until a point where the turbo runs out.

[72turboz]

11 minutes ago, zboi said:

Peak power RPM should not be bouncing around hardly at all. Fiddling with the tuning should either bring some gains in certain RPMs if its targeting AFR or spark, or move the whole curve up. Your tuner should have locked down pretty much everything at a lower boost, then started adding boost and seeing the result. Which should result in a nearly identical graph shifted up with each increase in boost, until a point where the turbo runs out.

Yes and that’s what the lower psi runs showed. He found peak torque made adjustments and tuned around it. Like I said the graphs moved up from there till it hit a wall and any increase above 13psi did not net any gains.