68birdls6

Hello, I'm looking for some ideas as to why my combo seems to be a little down on power. I have an aluminum 6.0 block with forged rods and pistons (10.5 to 1) with a set of 799 heads with 918 springs. I have an edelbrock performer RPM dual plane intake with fuel and air delivery being handled by an msd atomic efi tbi system. Spark is controlled by an msd 6012. I have a pretty mild comp cams 222/224 566 568 camshaft. Long tube 1 3/4" headers an dual 2.5" exhaust with borla mufflers.

So I just had the car dynoed and it put down 339hp @5450 and 361ft/lb @3850

I was expecting this combo to put down something a little closer to 400 at the wheels. I know that dynos vary but this still seems pretty low to me. The other concerning thing to me is where the peaks happened. I thought peak HP should be around 6000 and peak torque around 4500 rpms.

The car seems to run well without any issues, but is seems like these numbers are from a more bone stock LS2.

Anyone have any insight as to what I should look into?
If you need more details about the setup just ask.

68 Firebird with T56 Magnum 2005 GTO irs 3.46 rear

Thanks

68birdls6

A couple of things I forgot...

MSD has target air fuel set to 12.8 for WOT
340 Stealth in tank pump with return line set to 55psi

Here are the other two runs with timing settings for each

335.4hp @5250 365.6ft/lb @3550 28 degrees total timing
339.0hp @5450 361.5ft/lb @3850 30 degrees total timing
326.1hp @5300 357.3ft/lb @4050 32 degrees total timing

Tuskyz28

What type of dyno ?

HCI2000SS

iTrader: (2)

Ran it at the track yet?

68birdls6

I think it is a dynocom

No, I haven't had it a track yet.

68birdls6

So no suggestions of things I should check?

G Atsma

I think the general feeling here is to see what it can do at the track. Dynos are really only good for comparison of setups as then it's apples to apples as long as it's the same dyno. Dynos are all different.
You might think you have low numbers, but it might be the dyno reading low. The track does not lie. What you car does there is what it can actually do. So until you can run at the track, we REALLY don't know what it's capable of.

68birdls6

OK, thanks. I guess I will just take those numbers with a grain of salt. I was just posting on here in hopes that someone with a similar setup had the same experience and I would have a smoking gun for me to check and boom! there's my lost 50rwhp

Darth_V8r

iTrader: (4)

I'd like to know the LSA and ICL of the cam. Your peak torque RPM and HP RPM are a big clue that the cam is either installed on the wrong ICL or is just too small or too tight LSA for the duration.

As you noted in your OP, cathedral ported LS engine should peak torque at 4800 and HP at 6300 based on intake runner lengths, etc. It's actually quite a lot of effort to NOT peak there. Your peak torque is 1000 RPM low, which screams of a very early IVC. Carbureted intake changes things up some, but usually shifts the power band higher, not lower, due to runner lengths.

I think the peak torque at 360 is about right, but peak HP should be around 390 if the torque carries like it should. Cam with those durations should be something like a 116 LSA and 112 ICL. However, lots of times "Carbureted" cams end up with a 112 LSA and 108 ICL, which is fine if your durations are on the order of 230/240.

Short answer -- my guess is your cam or timing set is off by a tooth.

68birdls6

Thanks for the advice, do you suspect it is advanced or retarded by a tooth? Here are my cam specs

Darth_V8r

iTrader: (4)

Advanced. That cam should peak right at 6300. Advanced brings the peak down

Zac_Speed

iTrader: (4)

Switch out the dual plane intake. Go to a single plane or GM intake.

Jimbo1367

Zac_Speed

iTrader: (4)

It's the dual plane. There was an Engine Masters where they had this same problem with an LS running a dual plane.

68birdls6

Yeah, I saw that one. It was with a holley system and mine is running much better than that one did. Going to verify my cam timing this weekend.

68birdls6

Well after working on my car most of the day yesterday the verdict is in....the cam was advanced one tooth. Since the timing marks on the lower gear were not visible, I had to remove the oil pump and pump drive gear to see the lower timing mark. What a pain in the ***! I will follow up here when I get a chance to get it back on a dyno, but seat of the pants feels like the power curve has moved to where it should be. The car is still pulling hard now at 6500 rpm, Thanks for the advice!

Darth_V8r

iTrader: (4)

Excellent news!! Glad you got it fixed and thanks for reporting back

68birdls6

No problem, have an appointment to get it back on the same dyno this Saturday. So I should have a apples to apples comparison except for the change in weather conditions. I will definitely post an update with the results.

Darth_V8r

iTrader: (4)

I bet it will take a fair amount more timing now too. The tune will wake it up even better.

68birdls6

Well I got the car back on the dyno this morning and I did see a substantial increase in hp and torque, but they are still occurring at the same rpm. The torque curve is smoother and doesn't fall off the table like it did before. The average hp increased 14.4hp and average tq increased 29.1 lb/ft. So I am guessing the rpm peaks are being dictated by the properties of the dual plane intake. I am very pleased with how it runs now. It is making over 350 lb/ft from 3000 to 5500 rpm, and pulls hard all the way to 6500 rpm.

352 hp @ 5450 rpm 390 lb/ft @ 4050 rpm