482ci tunnel port horsepower numbers

[SFfiredog]

Hi Guys,
I just dynoed a 427 I built for a friend's Cobra.

Here are the specs:

483 ci tunnel port
block: center oiler 4.25" bore
crank: 391 truck forged steel, welded and offset ground 4.25"
rods: Oliver forged 6.700"
pistons: CP inverse dome 10.38 to 1 compression
cam: custom Comp Cams flat tappet "tight lash" 252/260 dur @.050 .616" lift int/exh
112 l/c installed at 108 i/c Schubeck flat tappet composite lifters
heads: factory iron tunnel port, ported by me
intake: factory 8V single plane
carbs: Demon 725 cfm vac secondaries 1" spacers
ignition: MSD billet dist with 6AL

2" primary, 4 inch colletor boat headers
HP 572 @ 6000 rpm TQ 533 @ 4800 rpm

1-3/4" primary, 3" colletor street headers
HP 565 @ 6000 rpm TQ 568 @ 4400 rpm

Superformance headers and sidepipe mufflers
(1-7/8" to 2" primary to sidepipe mufflers)
HP 548 @ 6000 rpm TQ 506 @ 4500 rpm

As you can see, the Superformance sidepipes didn't hurt HP as much as TQ (60 ft. lbs.)

All pulls were made on crappy California 91 octane unleaded pump gas

Timing was set a 37 degrees total

The engine idles at 850 rpm with 10" vacuum

The engine kept making more power on each pull because the rings were seating.

The dyno time was limited but I'm sure there is more power to be found with other minor changes.

It should be a fun, reliable street motor.

--Mike

[Steve R]

Mike,
Box it up and ship it over to me. I'll brake it in the rest of the way for ya.
Sounds like you had fun playing with that rare iron. Very cool
Steve
PS,
Do you have some pictures of the build up?

[mattr762]

Excuse my noobness, but why did you gain TQ with the 3" headers vs the 4"?

[SFfiredog]

Originally posted by mattr762


Excuse my noobness, but why did you gain TQ with the 3" headers vs the 4"?

The boat headers had relatively short primaries and big 4" collectors.
From the testing I did I came to the conclusion that to a certain extent, the primary pipe and collector size is more a factor of RPM than it is engine size or horsepower levels.
The smallish cam (for the size of the engine) made all of it's power by 6000 rpm, which is what I was shooting for, a good street engine. A 1-3/4 or 1-7/8 primary pipe size is all this engine needs to make good horespower and torque. If the engine were to turn 7500 rpm, the cam, and then the headers would need to be bigger.
In the same turn, this is why tri-y headers are so good for mild street cars and trucks.
It all depends on what you are asking of your combination.
--Mike

[Steve R]

Oh Yeahhhhh, THAT'S what I'm talk'n about!

[PatBuckley]

Mike -

I saw your letter in Car Craft - cool!

Pat