I took my car to the chassis dyno last week to do some tuning and came out a bit lower than I expected. Let me give you guys the break down and maybe someone can shed some light on what might be going on.

355, 9:1 compression, AFR 190cc heads, CompCams 218/230 .495/.515 114 LSA cam, stock intake, plugs gapped at .35, ATI D1 @ 15#'s of boost @ roughly 6000 RPMs. MSD Digital 6, HVC II Coil, stock Opti. TH400, Moser 9" 35 Spline Detroit Locker.

I have DFI Gen7 in the car and started the tune very rich. It is still pretty rich, running 11:1 Air/Fuel throughout the entire RPM range. We started with 15 degrees of timing once we got the air/fuel straight. First pull at 15 degrees, we made somewhere around 400, moved it uip to 18 degrees and made over 450, moved it up to 20 and saw no change, moved it to 22 degrees and made 503RWHP, moved it to 24 and saw no change, moed it to 26 and lost 1 HP. This is all on pump gas (92 octane). The graph got real erratic up top over 22 degrees. Almost like it was misfiring or floating the valves. I can't see me floating the valves, the springs that came with the AFRs should be able to handle this boost level w/o a problem.

I can't understand why adding timing didn't make any bit of difference. There was an engine tuner there that suggested adding like 28-30 degrees in but I think that's crazy on pump gas and 15#'s of boost. I realize I am losing like 22-25% through the drivetrain, so I am still making over 600 HP, but I was expected numbers closer to 600 at the rear wheels.

 

just a quick comment on the valve springs... At 15psi manifold pressure, there's 48lbs pushing on a 2.02" intake valve.

 

What transmission/converter?

 

It's a TH400, converter is a B&M Converter, stalls around 3600 RPMs.

 

Be careful when comparing your hp numbers to 6-speed equiped cars. In high hp applications, the T56 will make drastically higher rwhp numbers than a auto/loose converter.

For instance, my last combo was similar to yours. I had an 8.3/1 383, AFR 210 heads, 224/236-114 cam, Hooker LT's, Vortech T-trim at 13 psi, and an Aftercooler. Through a TH350 and Vigilante 3200 (more like 4000), it made 550 rwhp. I, too, had hoped for 600+. I went to the track and it ran 10.40 at 133 mph at full street weight. Do the math and that equates to about 690 fwhp. Also, I've seen several 700+ rwhp T56 cars that ran the same mph at a slower et.

Some guys over on turbomustangs.com have gained upwards of 200 rwhp just by switching converters. Another board member over there dropped from 730 rwhp to 508 rwhp by switching from a 6-speed to a Powerglide.

Comparing my old combo to yours, I had a bigger engine, bigger cam, and bigger heads and made about 45 more rwhp than you. Sounds about right to me.

BTW, what exhaust are you running?

Mike

 

Good points Mike and I appreciate them. I haven't taken the car to the track yet. Well, with this Tranny. I took it with the T56 a while back and the tranny just wouldn't go into 3rd gear. I ended up going 1st, 2nd, 4th and netted a 11.6 @ 128 MPH, totally skipped 3rd gear. I switched to the TH400 after that.

I am thinking about lowering the gap on the plugs like I said and adding more timing to see if it cleans up the graph. Maybe I was blowing the spark out... I can't figure out why changing the timing did not raise the HP #'s.

As far as exhaust, I am running Hooker LTs to a Mufflex Y-pipe to a wide-open Borla.. No cat ..

--Sean

 

What are your IAT's like? I noticed you did not list an intercooler.

 

I have the ATI Twin Intercooler setup, IATS were running around 150 degrees at the top of the pull.

 

For some reasome I missed the part where you made 503, I thought you made 450. That sounds about right, my friend made 475 with a P600B at 15 psi and a FMIC. He had ported stock heads, small cam and a TH400 with a 10 bolt. Your better heads and head unit have you ahead of him. I've read some where that the 9 inch's offset pinion gives an F-body about a 1.5% power loss over the 10 bolt.

I would not worry about it, at the track with an auto and loose converter you'll be beating us M6 guys like you had 100 more hp than us.

 

Was it on a mustang dyno or dynojet? That seems about the right power to me, I run a th400 with a 4000 stall so I know about the power loss. Do you have any dyno nummbers with the six speed? My assumption is with a th400 and with a good suspension setup, you should run somewhere in the neighborhood of 10.4-10.7. I have the AFR 190's as well. Those heads do not flow very well at all. Lloyd Elliots LE1 package for stock heads flow pretty similar on the intake. The exhaust side on the other flows quite a bit better on the AFR's. Go to www.airflowresearch.com to check the numbers out. Also, where is it making peak power?

 

An erratic graph can mean you're getting into detonation and that would explain why timing advance doesn't help past where you are. The other thing is that the engine will tell you where max timing should be, and the dyno might be different than the track. Try to go into tuning mode with an open mind. If the engine doesn't want advance, so be it. Don't worry about what other engines need or have used. You have a fairly small cam and I can see where you might run into detonation problems under boost with pump gas. 15# is quite a bit. Are you using a fan for each intercooler?

 

exactly what i was thinking, also, are you using a locked timing flat across the rpm range? the guys over on turbomustangs swear by doing this on FI cars

 

I was on a dynojet dyno.

I got the AFR heads for the thick head deck more than the flow numbers. I can always have them ported more.

I've been talking about going to a slightly larger cam, but I always said I was building this car to run pump gas, so it needs to be streetable as well.

I doubt we were detonating, there are no signs of it, plugs looked great, still pig rich, etc. I have to get the knock sensor hookd up, of course, with the car so loud, it reads false a lot too.

Will, we did have the timing set flat across the RPM range for a while, we tried a lot of different things. I am still leaning towards taking the plug gap down and running it again.

I realize what everyone is saying about the TH400 and 9" sucking out the HP. I am yet to bring it to the track, nor did I run it on the dyno w/ the 6 speed, so I have no comparisons.