Took my car for a couple of runs on a chassis dyno yesterday and got some disappointing results. The peak horse power is not what I expected, but the torque curve and peak was the severe let down.

Motor specs:

• 512 low deck stroker
• 10.5:1 compression
• OOTB Eddie 84cc heads
• Comp XR280 roller cam - .541/.537 lift - 230/236 duration @ 0.050
• Holley Sniper EFI

Gary at Jake's suspects the torque converter for the lack of a broad flat torque curve. It's a Turbo Action 17809ST tight converter. I reused it from the build before swapping to the big block stroker.

You guys got any ideas? The results are with the exhaust dumps open on the car flowing though 1 7/8" primary mid length headers.

Thanks.

Heck, not a big block guy, but before drivetrain loss that looks like about 500 horsepower with stock eddies and a tiny camshaft on pump gas.
Sheesh, not so terrible..... lol

Not a big fan of chassis dynos or any for that matter other than for getting a fuel and timing map cos I put down 458+ tq and hp and go mid 9's at 3000+ lbs.........

Out of the box Edelbrock heads aren’t the best head to go with on a Stroker engine

Any AFR readings to go with the runs?
What was the timing and its advance curve set at?

I'm no expert at this, but I would willing to guess the Sniper EFI hasn't 'learned' enough yet, or the ignition curve is way too slow.

Take it to the track, see what it runs. That's the number that doesn't lie and can't be fudged by the operator.

I know I'm leaving power on the table with them, but their flow rate at my max cam lift should be capable of supporting more than 500HP. Besides, the peek number could just be a tuning issue. I wasn't happy about not producing more than 1 HP per cubic inch, but not having that broad torque curve is really what bums me out and what I'm trying to answer.

Timing was 24 degrees initial with 34 total. I forget what the curve is set at. I'll go back over my notes and come back.

AFR during the pull was 12.5 as reported by the Holley ECU.

I've got the data logs off of the sniper for that dyno run if anyone wants more specifics.

Post up what your air fuel ration looked like, what was your target set at?

Sorry, just edited my previous post to include it. Target and actual were 12.5 during the pull.

I only used a chassis dyno once and it was a 4-speed car. I've seen weird data from chassis dyno tests of auto-trans cars w/ any significant stall speed and don't put much faith in those tests as a result.

that's 500+ hp & torque at the crankshaft. with everything hooked up (mufflers, alternator, water pump, etc) and in the chassis I don't think that's terrible. go back and look at fuel delivery, mufflers, etc. that's not much cam for 500+cuin.

On a Dyno Jet, they read on the high side,about 10% less than crank,, 400 hp / .90 = 444 net hp @ crank, most all other Chassis dyno read about 17 % less than crank HP.

Chassis dyno numbers can be really weird with an automatic. I don't think I'd worry about it just yet. How does it drive? How is the Sniper working so far? Are you controlling the timing with the Sniper?

Did you record data logs for each dyno pull? If so you can open up the config file on your computer and then play back the data log. That will allow you watch what all of the sensors are saying during the dyno pull. I'd pay attention to the AFR and MAP to see what they say. Do you have fuel pressure hooked up to the Sniper so you can data log it too?

I think you'll have a great combo once you get it all dialed in. If you want to make more power down the road you can get the heads ported and go up one size on the cam and you'll be around 600 hp at the flywheel.

That’s a really small cam in a 505.

I would be looking at 600ft/lbs and somewhere around 500-525hp on the engine dyno.

My guess is you’re just driving through the converter, giving you that low tq reading at the wheels.

It would be interesting to see what it would ET at a drag strip.
I've never raced a dyno.

Hi Andy, it drives great. Plugs are burning good, throttle response crisp. I don't do many full throttle blasts on the street though. Timing is still controlled by the distributor.

I've got data logs for the last two runs. Second before last was through the mufflers and only netted 370 peak horse power. The car has 2.5" exhaust and I kind of knew it would be a restriction. The last run is the sheet I attached to the first post in this thread - it was with the exhaust dumps opened up.

AFR during the pull was 12.5 and the MAP was 95 kPa. Fuel flow stays within a few lbs of 294 lb/hr.

My Dad had his car run on the same dyno last year. It's a 408 roller with similar cam specs. His peak numbers were less than mine, but it made gobs of torque through the range - noticeably higher than mine. This is really what I'm trying to figure out. I can attach the data log if it helps.

I really appreciate you guys helping me out with this.

-Mark

This is what the shop owner theorized. It is a tight converter.

I get what you guys are saying about getting it to the track. I got a friend who is going to bum me a set of Mickey ET Street tires for a trip to Ubly sometime in August.

You have way too small cam......for sure !

I would have gone in the 255* at .050 area minimum....75 lbs of tq lost there.....JMO...

Dan

Go to the track and have some FUN with it.

I helped a guy with a 505 build last fall.
Not a great overall combo, but some of it was a situation of reusing parts on hand.

Rpm’s with a bowl blend and valve job, original Torker, 850vs carb, 1-7/8” headers, .480 hyd cam.
I told him 600tq/500hp.

Made like 615/510.

You’ve got a better cam, his had better heads.

I’m sure with a more substantial cam and an rpm intake the one here would have been at least 50-75hp better.