Help me analyze this torque curve.

The dyno owner feels the plateau in the torque curve is due to a change in the timing tables. I feel it is because of the camshaft, but I'm not sure why.

The plateau has always existed with this camshaft and his split camshaft has a similar plateau.

What will it take to remove it?

Here are the specs . . .
LS2-402

Duration 250/246
Lift .631/.631
LSA 114 +6 advance

TEA tested heads flow
327 cfm @ .600 intake
318 cfm @ .600 exhaust with a 1.875" pipe
250 cc intake runners
86 cc exhaust runners
1.875" Kooks with cats & Corsa exhaust

12.4:1 static compression
8.67:1 dynamic compression
93 octane
32 degrees advance

FAST 90/90 unported
Lingenfelter cold air intake
Factory 85mm MAF descreened

A dyno sheet picture is attached below.
Also attached is a Dyno Simulator chart that also shows a similar lower speed plateau.

 

That is definitely a funky camshaft and probably not matched well with the heads at all. Who spec'd that combo for you ?

Looks like you've got a pretty good flow of intake CFM already so a crutch with a big reverse split like that shouldn't be necessary.

 

AFR 225's | COMP 244/248 .612/.615 112LSA !!!!



Not being a smart *** but there is a guy on here with this setup ( above ) with your compression and cubes and his trq is amazing and he making 534 hp and 496 trq I will see if i can track it down for ya !
Your heads.... what are the vavles size ?
But I with him its the cam!

 

I agree,

Think a smaller cam and a 1 3/4" headers will up that lower to mid range torque, plus smooth the torque curve out.

If I understand this correctly you loosing low and mid range torque with too much duration and too high a lift. Do one or the other, not both.

 

Okay guys, enough guessing.



SLP camshaft. I've talked to several people who spec camshafts and none have said they can improve what I have. I'm not looking for a change, unless its guaranteed to help, just a concrete analysis.



I have 2.1" intake and 1.575" exhaust valves as listed in the signature. That's not the issue though.



Nope, I had 1.750" headers and I lost power. Header size did not effect the torque curve. See the old dyno sheet attached. Both the torque and horsepower increased evenly across both curves.

My only change is a point increase in static and dynamic compression and .125" increase in header size.

 

You have a mismatched combo, period. So if you want the power to change/improve, you're probably going to have to swap some things out. Beginning with that cam

 

Power at and below 3k looks very weak (should be at least equal to your CID in rwtq @ 3k), but after that, you're actually in pretty good shape.

The rest of the graphs looks fine to me, but it certainly didn't look right at first glance, due to the scaling of the HP and torque. But that low end bog is not good.

The rest seems right, because all LS1s make a huge gain in the 4000-4500 realm as you are doing here and peak at 4800 (due to the manifold - not the cam). It looks exaggerated by the different scales for torque and HP for the axis. It's around a 40ft-lbs increase in the 4000-4500 range with an additional 15ft-lbs coming by 4800 for the peak at ~490ft-lbs. So, that means that the combo is making good midrange and top-end power.

It may be that the heads don't have enough velocity for lower air speeds at say 2800RPM on the 402 (250cc are large, but not so large).

 

I see what you're saying. Your combo looks good, even the cam, given the compression you're running; if you're on pump gas? The only things I would see a problem with is the Livernois heads, velocity being low with those large runners on a 402 in the lower rpms. I would put money down that if you were to get some TFS 235 heads, and port your 90 combo, and get rid of the descreened MAF, you would like what you see, DRAMATICALLY.

Where is the AFR curve from the dyno? How is driveability in the lower rpms? AFR will help us see whats going on in the motor.

Edit: I see you're on pump, sorry about that.

 

Thanks for the feedback guys.

If I remember correctly the air/fuel ratio was a solid 12.9:1. I will try to get a better graph without the offset numbers on the torque side and post it.
Otherwise, I am virtually at 400 lbtq at 3000 RPM. I understand about the velocity of the 250cc heads. The heads are marketed as 240cc, but I measured them twice with a burette and got 250cc. I was surprised.

I increased the compression because the camshaft bleeds off so much of it and the increased compression should help with the 250cc runner.

As mentioned about the FAST . . . yes, I have a ported FAST 92 with a 95mm throttle body and a larger MAF just about ready for installation. Trying to find 4.250" ductwork is a challenge.

It is worth noting that even with all that timing and compression I just get one degree pulled about 4400 RPM. That is both on the dyno and on the road. But, I believe some fine tuning can help.

A few people have said the short plateau in the torque is due to the camshaft, but nobody has knowing said exactly how to fix it. C' mon experts!?

The dyno owner has a positive split camshaft with 248/256 durations in his 402 and his torque curve is stepped just like mine in the same spot. He has trick flow 225 heads. He makes more torque, but I make more horsepower.

So, the plateau must be due to the split camshaft, but why? What happens in the flows to cause the plateau around 4000 RPM?

The dyno owner's car is "2001 Chevy Camaro SS - Road Warrior" recently featured in GM High Tech Performance.

 

i'm really confused right now... what is the int/exh duration of your cam? Is it 250/246, or 246/250?

 

FAST Intake manifold causes this. The headers contribute to it. But it has nothing to do with the camshaft. The manifold is tuned for what it's tuned for and since it direct airflow into the engine, the engine can only do so much with what it has.

The TFS 225 heads are going to make more torque because they have better midlift flow numbers with a lot more velocity (due to the smaller port).

 

Please see post one.

Duration 250/246
Lift .631/.631
LSA 114 +6 advance

 

listen to this guy..IMO,he hit the nail on the head...

 

It's cool and easy to say "it's the camshaft," or "it's the FAST intake," but can anyone explain why? So far nobody has, it is all just speculation. Heck, it is easy to suggest things for other people to spend money on, but establishing proof is where the rubber meets the road. Just because three out of four people agree on something does not make it fact.

 

Did you read my first reply?

You've got a ton of air flowing through the intake with your setup. Reverse splits are generally used in engines to crutch the lack of flow on the intake, and depend on a good exhaust flow. You're pumping a ton of duration into the intake when it doesn't need it.

Roughly translated = Mismatched combo

 

The theory sounds good, but you haven't explained why the torque slows and then continues. Prove your theory.

 

It's an unanswerable question for me. I didn't build or tune your car. I haven't seen any of your tuning files.

All I can tell you is from what I see, you have a mismatched combo that needs to be changed around a bit. If anything you're a cam swap away from some much better HP/TQ #s.

 

I say prove it because . . .

1.) The guy who dynoed the car (Post #9) has a positive split camshaft and he also has a dip in his torque curve just like mine.
2.) With the dyno simulator I can smooth out or remove the dip by inserting flow numbers for a better flowing L92 head.
3.) I also wonder why a touch more timing in the 3900-4300 range couldn't adjust things. I have one degree on timing knock at 4400 RPM.
4.) Then again, maybe a bit more fuel in the dip area.

I just like to explore all non-invasive possibilities before tearing things apart. Especially when there is no guarantee.

 

Huh???????
Too much lift? Since when did that affect torque?
On to the subject. The lull, not the plateau, because it really doesn't plateau, is caused by too much cam. I can post graph after graph. Why does it do that? Well the simpleton answer is it doesn't come into it's own until about 4500 give or take a few rpm. Looking for the scientific answer? Probably won't find it here.
I can tell you that with the proper cam, and less compression, you can tune that dip, lull, whatever, right out of there.
As stated earlier, it's not the best combo. Too much cam, too much compression, and too much timing. What do I have for proof? Tons of dyno graphs that are similar, and many combos that have like power with less of everything.
The BIGGEST problem with running that much compression, is the lack of tune-ability. I don't care how much timing you have in it now, it ain't gonna have the tune "window" it would have with less compression.
The cam is just plain funky. Reverse splits are over rated. That much duration, on a 114+6 just sounds like someone was trying to make **** happen. It's probably a great cam for a single plane big cube engine that's going to be drag raced, and never see anything below 5000 except to idle around the pits. Nah, come to think of it, it's even funky for that.
BTW, no cam expert here, just a guy that knows what works, and what doesn't.

 

That's part of the problem. The LS motors tend to want to pull timing out through the same rpm range you have the dip in.
To tune that out, you have to have low enough static and dynamic to be able to put timing in in that range. The way your motor is set up now, you cannot. You'll actually have to pull timing in that same region to keep out the KR. It's inherent to the LS. L92s are somewhat forgiving. But not with that amount of compression.
Screw the dyno sim, that ain't real world. If you could build the perfect engine in a dyno sim, we'd all be racing software.