Could you please recommend some header and exhaust specs based on the following with your software:

491" BBC, 4.25 stroke, 4.290 bore

Aftermarket Oval Port Heads - 2.19/1.88; 310/230 @.600, "D" shaped exhaust port
Cam - Lunati Solid Roller 256/264, .660/.660 110 LS, 106 ICL
Intake will be tunnel ram based MPFI, twin 700 CFM 4 bbl throttle bodies
10.5:1 compression

Street/STRIP car

Currently looking at starting with 1-7/8 primary, matched to port, with 3" exhaust, x pipe and dumps.

3650 lbs, 3.73 gear. Converter not decided, but likely flash to 3500-4000.

Shift point 6200-6500. Expecting 630-650 ft/lbs and similar HP.


Any criticisms of the parts?

Thanks for any help.

my personal oppinion is 2 inch pri with your X and dumps and i would assume your running drag muffs to, most cars will pic up time with them for sure also will you be sprayin it or no.what brand ram are you usin store type or custom made

Pipemax comes up with a race header design of:
Primaries - 1.976 x 38.8" to 41.3", including the port length in the head. Best wave from 4500 to 6300.
Collector - 3.689 x 20" to 25", tuned lengths are 5.6", 11.3", 22.5" and 45"
Crossover pipe locations at the tuned length.

For a street machine you might want to err on the small side, so the 1-7/8" primaries should work just fine.
www.headerdesign.com (http://www.headerdesign.com) comes up with:

1.78 x 33" primaries excluding the port length
2.90 x 14" collector
This is a street/strip header with the emphasis on street.

Originally posted by Doug F.:
Intake will be tunnel ram based MPFI, twin 700 CFM 4 bbl throttle bodies
10.5:1 compression

Street/STRIP car
Sounds like you'll have about the same setup as me! What throttle bodies are you going to use? I thought the Holleys were 1000cfm.

BTW, I've got the car back together with the new cam, 260/268 @.050 .748/.748 112LS. A couple of interesting things, first the car is by far more tame then the 245/253 hyd roller I had, pulls 1 inch more vacuum at idle (I miss the lope) but when I get on it look out, it's far more aggressive. The advertised duration on the new solid roller is lower then the hydraulic roller! This and the 112LS I guess is what tamed the idle down. I'll be at the track friday to see what the effects really are.

What heads did you go with?

FWIW, I'd go 2" headers if it were me.

Lee

a 1 7/8"-2" stepped would prolly be a hot setup...

I'm using a set of 1 5/8"-1 3/4" stepped on a 393 Ford motor I just did for my uncle.
Headers were $$$ but the combo works good.

I'm usually very conservative with sizes of cams, carbs and headers, but this surprises me. 10.5:1 491", big intake and 1400 CFM of carbs/FI, big solid roller cam, a little gear, some converter, I would have guessed 2" easy. 491 is still a big engine, we're not talking a 396-427 here.

Sounds like a great combination to me.

It's interesting to see this software or calculation coming up with such conservative numbers. I've been pushing smaller stuff for years, now a deal comes out that's even more conservative than me. Wasn't expecting that.

Tom

Thanks guys.

Lee, they are 700 CFM TBI units without the TBI injectors for air valves (read: cheap). I could use two 900's, but I have to think the 700's are more than enough. That's also what I like about solid rollers and EFI, really good vacuum even with a big stick compared to a hyd. roller.

I dynoed a pump gas 502 that made 650 HP with a dominator last year with 1-7/8's. Didn't go bigger but that engine ran well with those.

I will spray a bit someday, the short block will take a 300 shot. I don't care as much about effiency with nitrous, you just run more so I want it to run optimally on the motor. But I think I will have my hands full on the motor getting a 11.5-28 ET Street to hook. Just want a solid 10 sec. street car. I don't think that will be too boring for a while.

Doug - Another thing, when I was porting the heads I noticed that the D-Shape ports block a good portion of the lower tube and with 2" headers they were barely large enough to clear the upper edge of the ports. I had to clean up some of the welding slag with a grinder to get a good port match. I would think with smaller headers your flow on the top ports would run into the header flange/tube and not flow as well as it could. This is with the Edelbrock RPM/GM heads and with the flow numbers you gave it looks like this is the same head that your going to use?

Food for thought.....

Lee

One big point that is missed on header applications is the assumption that the exhaust flow out of the head is only due to positive pressure in the engine after the combustion when in fact there is a scavenging effect from the headers. A correctly sized/designed header will actually suck the exhaust out of the chamber. That is proven in the inherent design of overlap built into cams. If this were not the case, all the laws of engine tuning that we use would go out the door.

The best proof of this is the usage and design of expansion chambers in 2 stroke engines. Anyone who has raced a dirt bike will fully understand this principle.

Lee,
THey are Holley oval ports.

I have to look into a set of Flowtech 1-7/8 headers. Even though they are "cheapos" I think the first few inches are swedged out to a bigger diameter to better match the port. I'll have to look at some first and see what all of the transitions look like.

I had the same problem as 70_chevelle with the 2" Hooker Comps on my 315 AFR heads. I had to grind ALL the ports to eliminate any mismatch, especially at the top of the port. Two or three ports required a lot more grinding to get a smooth transition.

John