CUIN HP Max for 2" headers

Recommendations for the maximum HP CU/IN combination for a BBF c/w NOS with a 2" header. Looking at changing out the 351C s/b in my street/strip car, it is a stock engine compartment 6-point deal, have mounts and 2" swap headers so a bigger header is not in the mix. 3200 lbs up to 55O HP 2-stage plate kit (likely 250+). I have a 466 and 473 here looking to go bigger how much can the 2" headers handle before they are costing power?

2" primary ?

gmsmkr wrote:2" primary ?

Yes 2" primary long tube multi-piece with crossovers under pan for Dove style oval ports, 429 Mustang swap headers.

They will support more than the heads for now

Don't forget on the hose get it out quick

Last time out I ran 9.72@138mph in the 1/4 3235# I had 2" long tube headers 552bbf with a429 heads. The truck had more left but had a tire mess up on the front and parked it for that night.

gmsmkr wrote:They will support more than the heads for now

Don't forget on the hose get it out quick

X2

9.40s and 6.01 through 2" primaries. A429 heads.

Primary tube diameter is BOTH engine size and RPM related; (primary tube length is strictly RPM related).

a 466 at 7,000 or a 521 at 6,200 would be right there at the peak.

gmsmkr wrote:They will support more than the heads for now

Don't forget on the hose get it out quick

69F100 wrote:Last time out I ran 9.72@138mph in the 1/4  3235# I had 2" long tube headers 552bbf with a429 heads. The truck had more left but had a tire mess up on the front and parked it for that night.

DanH wrote:

gmsmkr wrote:They will support more than the heads for now

Don't forget on the hose get it out quick

X2

70FB wrote:9.40s and 6.01 through 2" primaries. A429 heads.

Thanks Guys, good info... are you 9 sec guys using Mr Frosty ?

rmcomprandy wrote:Primary tube diameter is BOTH engine size and RPM related; (primary tube length is strictly RPM related).

a 466 at 7,000 or a 521 at 6,200 would be right there at the peak.

How quickly does it fall off after peak, the gear tire combination is going to need more RPM for the bigger inch combos. I have no problem getting custom headers built, however the front end will not accommodate it right now, it will be a shoehorn with the stock shock towers. Ideas?

I ran 5.70's @ 3200 lb 557 TFS Streets 860 hp 2 inch primarys 3.5 collector.

No spray on mine just a 1050 APD alky carb

IDT-572 wrote:I ran 5.70's @ 3200 lb 557 TFS Streets 860 hp  2 inch primarys 3.5 collector.

Holy F&*%, where is the bowing icon what max RPM not that it is relevant in my case? Do you think it would have worked as well with the 340 cnc's

69F100 wrote:No spray on mine just a 1050 APD alky carb

Wow, cool same question what max RPM

7000 rpm shifting at 6800

FalconEh wrote:

IDT-572 wrote:I ran 5.70's @ 3200 lb 557 TFS Streets 860 hp  2 inch primarys 3.5 collector.

Holy F&*%, where is the bowing icon  what max RPM not that it is relevant in my case?  Do you think it would have worked as well with the 340 cnc's  

69F100 wrote:No spray on mine just a 1050 APD alky carb

Wow, cool same question what max RPM

Shifting at 7000, peak tq at 4800, 760 ftlb, 5200 converter, peak hp I think was at 6700-6800 rpm. Head flow was around 380 @ ,800 lift int. and 255-260 @ .800 exhaust.

And yes I fee the new 325 cnc heads would be faster if combination was tuned and matched well.

Piston speed will swallow up primary size. A big bore short stroke engine will need less header tube at the same rpm as the equal CID engine having more stroke and less bore.

This leads me to believe that a 528" with a mid 9 CR on a Frosted street/strip car would be a viable build.
4.42   B
4.30   S 4340
6.605 R (alum)
1.45   CH
78     CC

Am I in the ballpark here?

rmcomprandy wrote:Primary tube diameter is BOTH engine size and RPM related; (primary tube length is strictly RPM related).

a 466 at 7,000 or a 521 at 6,200 would be right there at the peak.

FalconEh wrote:This leads me to believe that a 528" with a mid 9 CR on a Frosted street/strip car would be a viable build.
4.42   B
4.30   S 4340
6.605 R (alum)
1.45   CH
78     CC or 72 cc

Am I in the ballpark here?

Thinking custom NOS solid cam or Hyd roller with the above, not sure if the rod choice is correct, if they should be 4340 steel or longer. 28"x11.5 tire 4;11 35spline DL, braked C6, 1050+ dommi

rmcomprandy wrote:Primary tube diameter is BOTH engine size and RPM related; (primary tube length is strictly RPM related).

a 466 at 7,000 or a 521 at 6,200 would be right there at the peak.

__________________________

What would peak be for a 545? I'm currently spinning mine to almost 7K w/ 2" primaries. I am fully aware this is not the best scenario. It's just what I currently have. I think someone else asked, but what is the "drop off" rate after peak? little? lots?

So, How does someone (myself) determine the correct primary tube length for a given combination. I am wanting to upgrade my headers, but am a bit puzzled about which way to go. Currently, I have 2" into 3.5, then down to 3" x-pipe and mufflers on a 545 nitrous engine. Heads are uncut P51s with a cam of .786/.779 - 284/298 @.050. I have pushed my 3200lb car to a 5.48@128 with them, but know there is more there, especially with more nitrous. The consensus seems to be that I need 2 1/4 primaries to take advantage of the cubic inches. How important is the length? How can I determine it? Is there a formula somewhere?

Does anyone have any experience with this change? How much more can I expect to see if I go from the 2" to the 2 1/4" I'm trying to weigh out the costs vs return. Stainless headers seem to start about $2500 to have built. I would hope to see significant increases in power for that outlay.

Can a system be developed to take full advantage of a great race exhaust system and still be quiet enough for the street?

Peak has a lot to due with the avaliable inductions.

6700 is about where a typical single plane will peak with enough cam.

460Dave wrote:

rmcomprandy wrote:Primary tube diameter is BOTH engine size and RPM related; (primary tube length is strictly RPM related).

a 466 at 7,000 or a 521 at 6,200 would be right there at the peak.

__________________________

What would peak be for a 545?  I'm currently spinning mine to almost 7K w/ 2" primaries.  I am fully aware this is not the best scenario.  It's just what I currently have.   I think someone else asked, but what is the "drop off" rate after peak?  little?  lots?

So, How does someone (myself) determine the correct primary tube length for a given combination.  I am wanting to upgrade my headers, but am a bit puzzled about which way to go.  Currently, I have 2" into 3.5, then down to 3" x-pipe and mufflers on a 545 nitrous engine.  Heads are uncut P51s with a cam of .786/.779  - 284/298 @.050.  I have pushed my 3200lb car to a 5.48@128 with them, but know there is more there, especially with more nitrous.  The consensus seems to be that I need 2 1/4 primaries to take advantage of the cubic inches.  How important is the length?  How can I determine it?  Is there a formula somewhere?  

Does anyone have any experience with this change?  How much more can I expect to see if I go from the 2" to the 2 1/4"  I'm trying to weigh out the costs vs return.  Stainless headers seem to start about $2500 to have built.  I would hope to see significant increases in power for that outlay.

Can a system be developed to take full advantage of a great race exhaust system and still be quiet enough for the street?  

Just because a header system will PEAK at a certain RPM doesn't mean that it won't or can't run higher in the RPM range than where it PEAKS.
With ALL other things considered, the engine itself may PEAK higher than the header system does.