Art
quote:Originally posted by Daniel_Jones:
> David Berman had his motor dyno tested with an Edelbrock Performer adapted to
> work with his Blue Thunder heads, that motor made a tad more than 500 bhp, at
> around 6000 rpm, feeding a 408 cubic inches.
He'd gain a bunch by moving to a Yates intake.
> Your motor is making about 407 bhp at the flywheel, which is about all you're
> going to make using the cast iron 4V heads without porting & a good valve job
> (multi angle).
Dan Haynes made right at 500 HP on unported 4V heads on a high compression
351C. He'd have made more with porting but the heads are not the limiting
factor here.
> The primaries (header tubes) are 2" OD which I guess makes them 1-7/8's.
> The exhaust pipe from the headers to the four glass packs is about 2-1/4" OD
> so I guess you would call it 2-1/8". exhaust pipes running into four glass
> packs.
The primary diameter is too large, the collector too short and the exhaust
pipe too small. If your mufflers are too restricitive (and glass packs are
often among the worst), you won't see much benefit from header tuning.
Some exhaust system rules of thumb:
OID = SQRT (Ex_CFM * 1.27/FD)
CD = 1.75 * OID
where:
OID = optimal internal diamter (inches)
Ex_CFM = exhaust port flow (CFM) at 28" H20
FD = flow density (around 80 CFM/square inch @ 28" H20)
CD = collector diameter (inches)
Primary lengths between 24 to 36 inches (for bank separated 4-into-1
on V8's with dual plane crankshafts)
collector length between 12 and 20 inches good for 8000 RPM
Mufflers should flow 2.2+ CFM per HP (the point at which there is a 1%
difference between mufflers and open pipes), 500 HP requires two 550 CFM
mufflers
A friend tested his unported 351C-4V heads (Super Flow at 28" water, in CFM,
stock single-angle valve job and 5/16" Manley valves with an MPG port plate)
and at your peak lift, they were around 180 CFM without a pipe. Plug in the
numbers:
OID = SQRT (180 *1.27/80) = 1.69 inches
CD = 1.75 * 1.69 = 2.958
Most Pantera headers have collectors way too short (5 or 6 inches) with
too small ID collectors and exhaust pipes and way too restrictive mufflers.
> I am using Isky #8005-A valve springs. Lifters were part of Comp Cams K-kit
> for this cam.
Comps K-Kit includes the springs and lifters. For some reason you're engine
builder chose not to use the K-kit springs. Comps standard hydraulic roller
lifters don't rev well. The Crane link-bar lifters have proven to rev much
better and Comp has recently introduced their version of a link bar lifter
but I've not seen any test data on those. Much care must be exercise in
picking the springs and lifters when trying to get a hydraulic roller cam
to rev well with heavy 4V valves and 1.73:1 rocker ratios.
> Your motor is making about 407 bhp at the flywheel,
> I have a Holley 750 double pumper with mechanical secondaries.
In addition to the Performer intake being a wrong choice for your set-up, your
carb is a limiting factor. 100 HP requires 140 CFM based upon a reasonable
assumption for Brake Specific Fuel Consumption (BSFC). The BFSC assumption
keeps us from having to guess at volumetric efficiency. A 407 hp engine uses
an actual 569.8 CFM. 4 barrel carbs are rated at 1.5" Hg but that is way too
restricitive on a tuned engine. 0.7" Hg is a more reasonable pressure drop
(too keep the carb from being a limiting factor). Converting to rated carb
CFM:
Flow @ 0.7 In Hg = (CFM Rating @ 1.5 In Hg)/SQRT(1.5/0.7)
569.8 = X / 1.46385
X = 834 CFM flow rating required
> I'd let you borrow my Holley Strip Dominator. Surely one of the OC guys has a
> torker you can borrow.
I offered up a Strip Dominator, Blue
Thunder, Boss 351, and Torker for a dyno test but I don't think he's interested.