VDiddy

Need some ideas ya'll.... I recently installed an iron 408 in my CTS-V with L92 heads, L76 intake and 236/238 cam with ~.600 lift and 114 LSA. I use the 1.7ratio L92 rockers and CTS-VR lifters. It's not perfectly tuned but is right at 13.0:1 AFR at WOT according to Wideband and is running about 28 degrees Total advance. It's putting 435HP and 405 lbs./ft. of torque to the wheels. This seems WAY low to me according to what else I've seen out there. The motor makes pretty good oil pressure (around 30 lbs. at idle and 52 lbs. at 5000 rpm). It seems to run fine, nothing that would indicate compression or leak down issues... just not what I expected. Any ideas why it could be so off on power?

It does consume about a quart of oil every 1000 miles or so, but with no visible oil smoke out of the exhaust except at WOT high rpm...even then very little.

99blancoSS

iTrader: (115)

Is it an automatic? That would account for low dyno numbers.

allthrotle

iTrader: (2)

Cts-v should be a six speed, but I agree that with your setup you should be putting down alot more power.

RZRSEDGE

iTrader: (21)

I would still expect it to make more power even if it was an automatic. Oil pressure isn't the best in the world; but acceptable. Maybe a mismatch of the cam in combination with the heads and intake? Good luck!

TchargedLS1TA

iTrader: (9)

Could be in the tune, not enough/too much timing, bad VE, etc...
Where are you having it dyno'd at?

99blancoSS

iTrader: (115)

13.0:1 AFR at WOT according to Wideband and is running about 28 degrees Total advance.

Tune doesnt sound bad at all. Should be around at peak power 13.0 and 28*. Maybe a 408 is a whole different animal but that should almost be peak power in an ls1. Some run them at 12.5 and some at 13.5

VDiddy

It is a 6 speed. I've seen some other people finding out that their spark plugs were "skipping"...whatever this means. This winds up pulling about 75-100 HP out of the motor because the other pistons are having to freewheel the bad cylinder when it doesn't fire. The compression is 10.66:1 by my calculation...is that too low? Even so I'm not sure it would account for 65 horsepower, possibly more.

jed.only

iTrader: (9)

the oil has to go somewhere. are the pistons forged?

VDiddy

yes, pistons are forged... With moly rings.

95FbFormula

iTrader: (25)

First i would want to find out were that oil is going it is most likely the cause to why you oil pressure at WOT it also a little on the low side usually should be 65-70psi Also check to make sure you are getting spark in all eight cylinders If one isn't firing the is probably were the power loss is and low oil pressure and consumption.

beardWS6

iTrader: (1)

My A4 408 makes 520rwhp 500trq. Something isn`t right!

JRracing

iTrader: (35)

Thats a bad *** motor though!

SS101

iTrader: (2)

i agree...you may be down a cylinder for whatever reason.

VDitty spec'ed your compression at 10.66, if that's your SCR that's pretty low for a 408, don't get me wrong, there are deeper problems at work here, but you might be putting down closer to your full potential then you realize

mullenh

iTrader: (1)

if a cylinder was missing in my car "I" would know and i think most pepes would, especialy someone who knows that their afr is a 13 at 28 degrees of advance. Mine is closer to 12. Try the gen IV forum where they are familiar with your set up.

Jordan S.

iTrader: (17)

Just because someone can remember their tuner telling them, "your A/F is 13:! and you have 28 degrees max timing" doesnt mean they can tell if their car is missing or not, especially if they have never had a big cube cammed car before. Some missfires you can hardly tell they are even there.

2000Hawk

iTrader: (5)

Could there be a possibility that maybe the cam has something to do with the numbers being what they are? Are the heads ported in any way?
-Joel

RGKSR

iTrader: (9)

Try using a hand held infrared thermo device on each header tube. If they are all firing then the tempature should be the same. If one is low, that's the culprit.

Bob K.

mrr23

iTrader: (3)

just because the a/f ratio looks good, doesn't mean it's tuned correctly. here's a dyno from a friend's car. on the before, the a/f ratio 'look's fine. after tuning, he gained another 40 rwhp.

Disturbed Bird

iTrader: (9)

what bolt ons do you have? ie(headers, pulley, xpipe, catback) id it a irs rear? if so you would loose alot more power to the wheel.

i would get a better tune.

Asmodeus

I can tell you exactly why your car is down on at least some of it's power. Your cam is horrible. You're missing 20 degrees on the exhaust side, and you need to advance the ICL about 8 or 9 degrees. You have huge CC runners with crappy low flowing exhaust ports in the L92 heads. You need to open the intake valve a LOT sooner to compensate for the low velocity intake, and you either need more duration on the exhaust or more lift on the valve, either way, there's no way you can be clearing the entire combustion chamber through that exhaust port with a 2 degree split. The intake/exhaust ratio on those is only slightly above 60% iirc. Katech is running a 233/277 in their L92 headed budget 427. I would go at least with a 236/260 on yours and try to get the ICL around 105-106. (not the LSA, the ICL.) The heads are very different from cathedral port heads, you cannot use the same thinking as any old LS1-2-6 motor.