cybernco

I'm looking for help. My engine is out of air at 6100 RPM, but it should make power to at least 6500 RPM. My current guesses for bottlenecks are my SLP Headers W/Cats & my stock LS2 fuel pump. My injectors were at 85% at WOT, so the pump may not be it. I can e-mail my HPTuners scan of my dyno pull if you PM me with your e-mail.

My Dyno is as follows; 480 RWHP @ 6100 RPM and 468 RWTQ at 4500 RPM.

SideStep

Have those heads had any work done to them???

WKMCD

iTrader: (2)

tlaselva

400+ci motors seem to run out of steam at 6K.
My 447ci had a very similar HP curve.

I'd wager it's the LSx style intake and 90mm t/b that's restricting the air your cubes need at that rpm. Drop a sheet metal intake, and your power would keep on increasing past 6K, but at the sacrifice of substantial low end torque. I've heard from a tuner that a comparison showed an increase of 15rwhp at the top rpm, but at the sacrifice of 30rwtq in the midrange.
IMO, unless your willing to spin your motor over 7K, and a drag only car, the sacrifice of mid torque you'd likely experience won't make up for the mid range torque loss of a sheet metal intake. And remember, torque is ET, HP is mph.

So to sum it all up, your making great power. But with today's technology, the LSx style intakes create great bottom end power, but do tend to choke a big cube motor. The alternative changes the power of a motor to a very specific and focused requirement.

If you want more, go with a small shot of NOS.

V6 Bird

iTrader: (15)

Modfy the runners on the LSX intake....Make them shorter and give them a larger plenum to pull from.

99Fbody99

Its funny,

All this arm chair quarter backing and no one is looking at the data he has.

MAP data from the dyno run will reveal a lot and end some speculation.

If you find your Map (vacuum) is increasing at RPMs then the is infact an TB/intake issue. If not, maybe you camshaft selection is not optimized to run to that RPM.

Dave

Louis

iTrader: (7)

My MAP on the L92/L76 is a consistent 97-99, never falling off. It pulls clean to 6600, and never falls off. Cam selection is a large part.

Louis

iTrader: (7)

BTW- are you using LS2 injectors, or the L76 units that came with the intake?

71CamaroLS1

Cam is where I would look as well. Comparing your combo to others with more high RPM extension, it looks to me like your IVC (intake valve close) is probably too early for high RPM power. Choosing a cam with more intake duration, wider LSA, and later ICL, will move your IVC later and extend the high RPM power, at the expense of some lower/midrange torque.

I'm sure you've thought of it, but testing for exhaust restriction is as simple as dropping out the cats for one pull, and the wideband O2 data will tell you if your fuel pump is leaning you out, assuming the dynojet operator uses a wideband O2.

ArcticZ28

iTrader: (14)

I'm gonna have to say the intake isn't your restriction at this point. My graph looks sorta the same as it starts dropping off after 6k, but I have a LS6 intake so that's my excuse. Your combo won't restrict you that much at your hp level. It's gotta be a cam issue. Your tq commits suicide at 5k.

Boosted LS1

I trhought cam as well but would be inclined to close the intake earlier and reduce pumping losses, maybe freeing up some extra rpm's? Could be wrong though

Boosted.

71CamaroLS1

To really understand how intake, exhaust, and cam work together in a high-performance engine, download the user's manual for Dynomation:

http://www.proracingsim.com/download...sersManual.pdf

and read the section called Wave-Dynamics Analysis, beginning on page 231. It sums up much of the important information from my Internal Combustion Engine theory course 25 years ago, but in a much more accessible form.

Unfortunately, it's a 44MB download, so beware.

And if you or your engine guru are particularly ambitious, buy the Dynomation program itself and model your engine. You can experiment much more quickly and cheaply in software than by testing a dozen new cams ...

chipabba

Any follow up CYBERNCO? Was the problem with your tune? Did you take the car back for a second run? If you don't mind me asking about the price on your engine (SDPC, right?). Thanks!

Ragtop 99

iTrader: (7)

Just how much are you down at 6500? It looks like maybe 10 HP from your peak at 6100, which isn't a huge drop.

What ICL is your cam?

wavrdr

iTrader: (1)

Off topic:

Louis, how does the curve on the G5X4 cam look on a 402+engine?

nitrousc5

What 99 said. Study your scans closely, if MAP numbers getting smaller (increasing vac) then air is folding/getting turbulent/bottlenecked, etc. Give your LSx intake to a porter that knows what he's doing; the LS2 intakes respond very well to proper porting, but it is easy to **** it up, too. Also port the 90mm TB by a professional. The idea is to increase flow and maintain decent velocities. This will gain the best power increase at both ends of the power curve. Also, go with a cam somewhere 234/246 .650 114 +0. Dont have any advance cut into the cam, this will help with intake close events without going too massive on the intake lobe duration. If you have a 2-piece timing cover and a Crane adjustable timing set where the cam sprocket can be adjusted to put retard/advance in, you can easily experiment with degreeing the cam between dyno pulls, just pop the water pump off and the top timing cover, retard the cam 2 degrees, put it back together, do another few pulls. Its a bit of work but you end up with a completely optimized cam phasing, then its just some road work to fine tune your AFRs with a wide band.

SideStep

Any updates on this???

SideStep

last BUMP for an update???

Ryne @ CMS

iTrader: (10)

i was the prototype car for GHL exhaust, and if you still have that trick looking x-pipe on your car ditch it, i had it on mine and got rid of it, and the car rev clear to 7k, with 418 l92 based stroker. the xpipe is messed because where it merges the cross section is only 2.5" across

cybernco

Wow, I'm sorry I let this go so long without a reply.

I have Stock L92 heads with the 40Lb injectors that came with the L92 416 from SDPC.

I'm not sure how to post the HPTuners scan file from my Dyno run on this forum.

Like several of you, I too think my cam is a very likely culprit of the upper RPM limitation. I think that the L92/L76 setup was just too new, when I ordered the engine in November last year. Not enough was known (Publicly) of what kind of cam the L92/L76 setup would really respond to.

Here are the specs on my cam:



I wish someone would design a better intake with shorter runners for the L92. F.A.S.T. are you listening???

GHL Crossover... Hmmm, I looked at the Borla and it has a small crossover section too. I'm curious about this one. Did you go to straight pipe on your car and eliminate your crossover completely?


I do plan on a 75 HP shot of NOS after I’ve installed in a better fuel pump and am confident of my tune.

You know, from 3000-5500 RPM's the car is a rocket ready to rip out the drive train. You gotta love torque!!!