question for the exhaust experts

[Martin_172]

dont know too much about exhausts on the actual design side of things so to start with i need to know what size of pipework im looking to use for an engine roughly to this spec for a project im working on...

supercharged 16v engine with around 130bhp at a guess

and secondly i need to know some info about exhaust manifold designs, all i know is 4-2-1 for mid range and 4-1 for top end power, but what else is involved as ive heard people talking about equal length and unequal length.

basically im looking at getting a full custom system designed to my specification inc manifold

no details on what car or engine it is yet

cheers in advance for the help

 

[Fred@BTM]

what engine? what capacity? how much boost?

 

[BenR]

if your boosting upto 130bhp then you wont have to worry much about exhaust design. Sufficient bore size is 2.25".

A quick calc for primary bore size is Area of Primary Pipe = RPM × Cylinder Size ÷ 88,200, where RPM is point of peak torque. Cylinder size has to be given in cubic inches and area will be given in square inches. A 4-1 design is fine for boosted apps as tuned lengths dont respond in the same manner. But you'll most likely be limited to the stock available size for exhausts tubing, and 1.25" OD might be the smallest size easily available, and for a peak usable rpm point of 7000rpm, then a 21" length will be circa the length you want to start.

 

[Gray]

if your boosting upto 130bhp then you wont have to worry much about exhaust design. Sufficient bore size is 2.25".

A quick calc for primary bore size is Area of Primary Pipe = RPM × Cylinder Size ÷ 88,200, where RPM is point of peak torque. Cylinder size has to be given in cubic inches and area will be given in square inches. A 4-1 design is fine for boosted apps as tuned lengths dont respond in the same manner. But you'll most likely be limited to the stock available size for exhausts tubing, and 1.25" OD might be the smallest size easily available, and for a peak usable rpm point of 7000rpm, then a 21" length will be circa the length you want to start.

Just what i was going to say...

 

[BenR]

Its a rough starting point, people can get hung up on 'custom' exhaust design, but fact is that it'll only be optimal for a very very narrow area once you've crunched a million numbers.

 

[Martin_172]

thanks a million mate, i did think the fine technical details wernt that important as long as its roughly the right spec. but just thought id double check