Chassis Dyno- eye opening!

[2VNTG68S]

445 stroker built by Barry R. 495 Hp / 545 ft-lbs on Barry’s engine dyno

Best we could do on the chassis dyno was 365 Hp / 442 ft-lbs

I was shocked but the chassis tuner was not the least bit surprised.

Do those numbers indicate a breathing problem? Wondering if 2.5” exhaust was a huge compromise

Other factors:
Vintage Air
Power Steering
FPA headers
TKO 600
9” 3.70 Tru-Trac
Aluminum driveshaft.

[CaptCobrajet]

Not surprising considering all of the accessories and through the exhaust and driveline.  Engine dyno measured at the flywheel.  If you had the air cleaner on it, that is usually an easy 25hp hit.

[blykins]

Doesn't surprise me.   As Blair said, you're turning a lot of accessories, probably running an air cleaner, and turning a 9" rearend. 

[2VNTG68S]

Thanks guys - that’s helpful context.

I was considering going to 67 Shelby short nose hood (it’s a 68 Mustang vert) with a custom fiberglass air cleaner seal. Worth it to give it a straighter shot at the outside air?

[scott foxwell]

20% is what we usually allow so 23% is well within reason.

[2VNTG68S]

20% is what we usually allow so 23% is well within reason.

I was hoping to be on the low end of that scale, lol

[chilly460]

I feel your pain, can be pretty humbling to put them on the rollers!!  I think a lot is in the headers and exhaust that actually have to fit in the car, and of course the air filter can really be a bottleneck if hood clearance is an issue. 

[KMcCullah]

Dyno headers vs real world headers for the vehicle can be a big factor. The density altitude in Barry's dyno room vs the chassis dyno room can account for a few percent either way too.

[plovett]

I was considering going to 67 Shelby short nose hood (it’s a 68 Mustang vert) with a custom fiberglass air cleaner seal. Worth it to give it a straighter shot at the outside air?

I think a sealed outside air induction system is almost always a good idea and will help power.  It might not help much on a chassis dyno though.   The car isn't moving which defeats part of it's purpose.  Was your hood open or closed when you were on the dyno?

paulie

[2VNTG68S]

Was your hood open or closed when you were on the dyno?

It was closed but he had a huge floorstanding fan blowing at the Rad

I was thinking that since the HP impact was higher than the Torque impact it indicates a breathing restriction. My guess was the 2.5” exhaust.

[plovett]

I was thinking that since the HP impact was higher than the Torque impact it indicates a breathing restriction. My guess was the 2.5” exhaust.

Considering you made 495 hp on the engine dyno, 3" exhaust can only help.  It's entirely do-able in your Mustang chassis.

JMO,

paulie

[plovett]

I was thinking that since the HP impact was higher than the Torque impact it indicates a breathing restriction. My guess was the 2.5” exhaust.

I see what you're saying, that at low rpm (torque peak) there was less difference,  My feeling is  that chassis dynos are so freakin' wonky in how they get their numbers, that I wouldn't put too much significance in the hp losing more percent than the torque, compared to the engine dyno.  Engine dynos are usually much more accurate in what they are measuring.  Still, if you can make some changes and improve your chassis dyno numbers, that's valuable.

[NIsaacs]

My 1975 F-250 4x4 with a 428/440 only has 295/327 on the rollers. It has a C6, 203 transfercase and 14 bolt rear. For some reason a n/a gasser looses more than a turbo diesel. My '01 Dodge 4x4 with a modified Cummins has 400/900. I used to tow with the FE but not anymore, lol.

Nick

[Heo]

I bet the heat in the cramped mustang engine compartment steal a few horses to

[2VNTG68S]

I bet the heat in the cramped mustang engine compartment steal a few horses to

this is the other reason I like the 67 Shelby hood - heat extractors.