Exhaust Manifold design

[lowtechguy]

Who can make me one?

I have been told supersprint manifolds are actually a 1.5mm mild steel manifold hence the rusting and cracking etc.

The manifold at the collector is red from the heat going though so I am thinking something other than supersprint is needed.

Q1 How do you work out the exhaust system, The cam is now 290 degree not 244 so something different is needed anyway...

Q2 Do you think I should copy the supersprint design and just change the bore if calculations say something larger bore is needed or do you think I should just repair/replace etc etc.

[hudsonhenry]

Lowtechguy

Got your PM but I thought it best to post info up here for anybody else who is interested. I am having a 4into1 manifold and system made for me by a company called Simpsons – www.simpsonraceexhausts.com

They are expensive at £850.00 plus vat for a stainless system but the quality is first class and seems to be the going rate, I was quoted between £600 and £1600 by other companies. The prices are a reflection of the time it takes to fabricate this knd of thing to a high standard.

They will not design a system for you, but will built one to fit the space available to your or your engine builders spec.

I did some calculations base on using a 290 cam which are as follows

Primary length (P) 25 inches from valve head
primary id 1.321
Collector length (CL) 5.22 inches
Tail pipe length (TL) 23.171 inches

4 into 1 equal lengths
Merged collector
Lambda boss
Re-packable silencer
Gas purge welded

Simpsons minimum tube ID is 4.8 inches so I have had to compromise the design slightly. By calculating the volume of the 25 inch 1.321 tube and then working out the length of 1.48 tube that gives me the same volume I came up with:

Primary length (P) 20 inches from valve head
primary id 1.48

The primary length for a 421 would be the same overall but split into two parts, I can work out the length of each if you like.

I looked at building my own system but by the time I bought all the bends, a merged collector, a proper re-packable silencer, had it gas purged welded I was only going to save about £350, it would have taken weeks to work out and would not have been anywhere near as good as theirs.

With a bit of luck it will work OK, anyway it should look the nuts....



Nigel

[babaracus]

Seems quite good for a custom job, although when your young and on a tight budget think i'll be sticking to supersprint!

[hudsonhenry]

Yeh I did not think it was too bad, especialywhen you compare it to the £5000.00 I've just been quoted by Colotti inn Italy for a straight cut 4 speed gear kit for the 500 box!! mind you, rated to take a max of 130CV

[lowtechguy]

Hi HH,

Many thanks for working out the calculations! 1 question though, the 4-1 manifold design is good for promoting a wider band I know but what revs is it designed to? Ideally I should be making peak torque at 4.5-5.5k so i would want it tuned to that, would the calculations still be correct?

Secondly, how do you work it out?

Thanks again and can't wait to see your exhaust on thursday!

[oldschool]

lowtechguy said:

Hi HH,

1 question though, the 4-1 manifold design is good for promoting a wider band I know but what revs is it designed to?

This goes for the 4-2-1 system. The 4-1 is more for peak power delivery.