AFR and horsepower on an LT1

[Craig 94 TA GT]

I had another disappointing day at the dyno, only putting down 340 RWHP. The good thing is that it put down 340 from 5500 all the way to 6600 RPM, so it was a huge "under the curve" area.

Here's the weird thing: the car wasn't that responsive to changes in the AFR when the tuner would load a new flash of LT1edit. On the first pull, it was running extremely rich at 10.0:1 AFR. He shut it down at 6k and it put down 324 RWHP. The next pull was 12.2:1 AFR and ran it to about 6600 and it put down 339 RWHP. The last pull was 12.4:1 and it gained 1 RWHP to 340. I've heard of stock LT1 AFR changes from 11.7 to 12.7 and gaining 15 RWHP. I don't understand why my setup only gained that amount going from 10.0:1 to 12.4:1. The heads flow 288 CFM @ .600 so I would have thought AFR is crucial to the #s. Does this change in AFR to hp sound right?

Also, I am at a loss trying to figure out why my previous tune went sour at 10.0:1 AFR. It was set to 12.4 previously, so I don't know what went wrong. I did clean up the filter and change the plugs (engine builder put in nitrous TR-6s for some reason), fuel filter, IAC, driver's side O2, and a few other minor fixes. I don't think that would cause it to drop to 10.0:1? Kinda scares me because what will prevent this from happening again?

[Trash man]

check ur fuel pressure regulator, mite have dumped on you. whats you whole set-up? i havent been following along

[Jeff_in_Atl]

I don't have any answers but 340 out of normally aspirated LT1 is pretty darn good. That's more than my LS1. I wouldn't be so dissapointed.

[Craig 94 TA GT]

Thanks, I never thought of the FPR. I'll check the fuel pressure to see what's going on. As far as the build, it's a forged pistons/rod 355 rebuild, decked block, AI 200cc heads (flow 290+ @.650), mid 220s cam, shorty headers with cat, Borla catback with a huge dent in the i-pipe, Moser 9", 3200 stalled auto.

Jeff, you're right - 340 isn't so bad, but considering Advanced Induction's customers see 400+ out of their "daily cams" (probably 230 degrees though with LTs and possibly 6 speeds though), I thought I would have seen at least 370. I know that the stalled auto sucks up power, the 9" can rob up to 20 hp, and the shorties + cat setup isn't the best, but I really thought I'd see more. The good thing is that I passed smog easily - no monkey business trying to get fake smog numbers.

One of the mechanics at the shop said that his 310 RWHP LT1 with a 2800 stall ran 12.2, and said my setup, if I work on suspension, can be good for mid 11s. The stalled autos with mid 300 RWHP are faster than the dyno says, according to him. I'm going to test it at the track real soon with the Nitto 555Rs, so hopefully I can at least hit 12.4 or so. I guess we'll see if I'll really be disappointed in this setup.

[Jeff_in_Atl]

340 hp, 12 second quarter, and street legal. I like it! Good job!

[Craig 94 TA GT]

Thanks, well we'll see this weekend how fast it really is.

I now have Jeff Creech helping with the tune because I know he will figure out any issues and bugs - and probably net be another 10-15 rwhp. But as of right now, I have no idea what ET it'll run.

I think I'm coming to accept the fact that shorty headers + cat + automatic + 9" rear is not going to be a dyno queen!

[Joe 1320]

I'm still a fan of a well set up automatic at the strip. And I do emphasize well set up. A big part of that depends on traction.

For a road course, it's the stick shift.

[ConElite]

310hp and a 12.2? with only a 2800 stall? Thats kinda questionable.


Granted LS1s pushing 315+whp (Stock) with 3000+ stall and dr's run 12's all day but not almost 11's.


You should be in the 12's easy though with some stickies.

Check the reg. Could be bad and dumping to much fuel.

[Craig 94 TA GT]

The guy who ran a 12.2 trapped at 109 and cut a low 1.6 short time. He had a few weight reductions but nothing major. He said the suspension was hooked up really well.

I have the exact same package that propelled a 4100 lb Caprice to a 11.9@113. That is why I was expecting more out of the dyno, but as everyone says, a dyno for stalled A4s are a tuning tool, not a definite answer to what you're going to run in the 1/4 mile. I've seen guys with supposed 400+ RWHP trap at 107, and others with only mid 300s trap at over 110. I guess my answer will come up soon - hoping for 12.5@110 because I know there's a lot more tweaking needed. I guess ultimately 11s would be the final goal without any power adders and a smog legal LT1.

Here's a video of the bad AFR dyno...it was shut down early at 6k.
http://www.youtube.com/watch?v=Z9-L3wnURqc

[ConElite]

I trap at 107 at 314hp and a 2.1 60' and thats a whole second slower ET. Granted im Stick so I trap a bit higher but 109traps with a 12.2? I dont know something seems fishy.


Just does not add up in my book. He must be cutting 1.5 60's.

[Craig 94 TA GT]

Your stick dynoing at the same power level as a stalled automatic does not mean they are putting the same power level down at the track. I have heard of stalled autos with gears vs stock stalls cutting .5 to .7 of their ET...yet they are not outputting anything different on the dyno. In fact, the dyno will probably read lower. He said he had weight reductions as well, and the fact he was cammed probably meant his power band went up to around 6200 RPM. Granted, he probably moved the whole curve one way, but he still improved the overall curve compared to a very mild stock cam. Area under the curve is what's important, not what power made at a spike or at a very specific RPM.

I recall seeing an MS4 cammed LS1 that put 20+ RWHP more down than an LE2 LT1. From a stop, roll, or any kind of dig, the LE2 LT1 pulled and pulled because it had so much more power under the whole curve, and not just a specific point. I'm not talking about a slight pull either - it was pretty much a walk.