Pipemax 101 - Pipemax Program discussion

[200cfm]

I was thinking "street header" was for OEM. What is the difference between a street header and a shorty header? Do you stay with the same recommended lengths if you can't satisfy the pipe OD recommends? It would seem they would both have to be matched to work properly. (tom)

[jfholm]

Tom,
I have not found a program yet that does well at calculating what the power would be with stock exhaust manifolds.

The shorty headers are usually built for tight fits in cars with little clearance and have very short primary tubes usually in the 8" to 14" length that go to a very small collector.

The street headers would be small tube headers, unequal length with small collectors.

Race headers would be headers that are fabricated with equal lengths on the primaries with the proper lengths and collectors for the engine in question.

That is why I feel if you calculate power using the shorty headers it would be closer to a stock exhaust manifold.

John

[200cfm]

Ok, I used the shorty menu header as possible OEM equivalent. My driver side downpipe measures 1 7/8 OD and is 34" long. Then I have this coupling that takes it to a 2 1/2 OD collector that is 13" long. Total length around 49.5". If I set the peak rpm hp @ 5500 Pipemax calls for 21.3" collector at 2.562" OD. My collector OD is standard 2.500" so the OD is close. So I assume I have to add around 6" length to the collector. But Pipemax calls for a very small OD on the primary of 1.517". I am at 1.875 OD so that is way off on design. Want have time to change the primary side but may be able to weld an extension to the 13" collector and test hopefully this evening and see if there is a gain. My passenger side is further off base with a 2" down pipe primary. Would it work better by going from a shorty header outlet of 2" to a 1.500" OD down pipe primary?

[Flash]

Tom, here is the Hill Billy solution :p

Make you collector/extension 20" long, spray paint the extension
Now make a 1/4 mile pass.

cut or shorten the pipe were the paint stopped burning. :;):

Not the best way to do it. but it will put you in the range

[coulterracn]

Using the shorty headers & muffler for pipemax will give you the primary tube size/length and collector tube size/length as you already understand.

The primary tube is the your cast manifold. The exhaust pipe bolted to the manifold is the collector.

Using your ET/MPH and several other inputs, pipemax will calculate your horsepower. Click on 'HP from ET Slip' and input data requested.

Ray

[jfholm]

Tom,
The sizing recommendations in Pipemax, I am pretty sure are for 4 tube headers. Go with what you have. I would make the collector area short with an adaptor flange so you could bolt on different lengths.

JMO
John

[200cfm]

Guys, just back from the track and tis late but got in three test runs before dark (6 to 8 pm frame). Tested two changes, one a carb change and the other a 10 inch extension by 2 1/2 added to the collector of each side. What I call the collector (my 2.500 piping is now set at 21.3" length). I welded 10 inch extension to what you see in the photo. Pipemax called for 21.3 collector by 2.562 OD and that is now the collector length. The smaller primary are around 34-35" long. (see photo for clarity)

Please to say the car ran faster on et and speed. All runs were above 114 and et was down .2

Run 1: 1.864 5.147 7.857@ 90.53 10.191 12.154 @ 114.89

Run 2: 1.849 5.119 7.807 @ 91.18 10.125 12.079 @ 115.36

Run 3: 1.861 5.131 7.814@ 91.3 10.132 12.084 @ 115.49

It increased the mph at the 1/8 and finish and leaves a little stronger. It hitting close to 6000 at the finish line now. I think with cool air and some race headers from PTS world headquarters she will break into the 11's.

[jfholm]

Way to go Tom! That is fast and quick.

From some of Larry Meaux's writings he has mentioned that the collector shows more importance than does primary tubes being equal length. If you build some 4 tube headers try to get the primaries to match what Pipemax suggests, but pay careful attention to your colletors.

We always take slip on extensions with us and play at the track.

John

[blaktopr]

So Tom, I am reading this as each change as you wrote it above, baseline to carb to pipe. Not alot of guys devote this kind of effort, so I applaud yours. I'm sure you will get into the 11's with a real header. Not that it's the same but with a street 408 sbc I built many years ago for a friend, he first ran with shortys and a single 3" exhaust. Consistent 13.0's. Then full lengths were installed and first ran open. First pass was 12.30. Mph from 101 to 110. Then dual 3" went first to the 12.60 range and eventually tuned to 11.90's. Just to give some possible preview of what you have in store for the future.

[200cfm]

Thanks. Here is the carb I tested. It is on loan with option to buy. I like it.

[jfholm]

Tom,
Is that the Pro-Form center in the carb. It looks good. Adjustable air bleeds and the works. Idle circuits front and rear. How many cfm is this one?

John

[bruce]

[200cfm]

Yes, that is a Pro-form center section. It is a 750 cfm. Front jet is a 74 (checked it). Haven't checked the rear yet. Front pump is a 30 cc but the rear is a 50 cc. It idled real high at first and has holes drilled in the butterflies. But I got the idle down by adjusting the secondary hold off screw. They were cracked open some. Front butterflies were closed off so I opened them some. Idles around 1000 in gear now. Haven't touched the 4 corner adjustments yet. Take a look at my third run video and tell me what you think about the A/F. It idles at around 13 A/F. Watch the launch. It goes rich when I step into it. I tracked the A/F in movie maker vista (where you can stop the tape and it A/F falls to 10.2 for the launch. Goes to 11 A/F by 3500 and 11.4 A/F by 4000. Around 11.5 at 4500, 12 A/F at 5000, and holds 12.5 from 5500 to 5900.

Should it be that rich on launch? I am thinking perhaps too much fuel on the start. Gives sort of a "hickup" engine sensation when I stepped into it. Might be from too much pump shot. Or it might be from the load traction grip or engine pull down. The engine does pull down some. To be expected I suspose because of the tire size and glide 1.76 low. And the converter is tight for carb only torque. So much to learn, so little time.

tom c

[Flash]

I'm going to assume that your foot braking it. and stalling it at part throttle?

With that assumption, i would agree that it's from excessive squirter in the rear,........could be front squirter as well.

I thing jetting may come into play as well.

I notice that your burn out was on the rich side.

I think the converter is adding to the low rpm problem.

Try a full throttle launch. hold for two sec, and then release the brake. If the stumble and rich are gone at launch, got to be pump squirter.

[jfholm]

Tom,
Here is an article I downloaded and saved as it had a very good discussion on tuning of a carb and has fuel ratios etc quoted. It is a little long but the links to the photos seem to still work. John