Exhaust Question

[fry61]

Steady there lad, the nights are still long & cold.

[Guest lotusPaul]

I use a simpler set of equations. You need to know cam timings. And rpm to tune exhaust too. Finding the number of degrees the exhaust valve OPENS BEFORE BDC.

 

So lets say a 2.0ltr (any)

 

Tuning for 7500rpm Timing of 74'

 

Gives primary length of 25.8 inches

 

a different equation can now give you 1.75in internal diameter

Using a 4-2-1 system gives the secondaries as 2.4 inches

 

how does different lengths affect things?

Longer primaries=high rpm power gains

Longer secondaries=mid rpm power gains

 

Space and cost of a one off will generally be a contributing factor to manifold design and system after. Dont forget to balance against intake length tuning for combined results.

[Guest Ian & Carole]

We wanted quiet so stuffed it out the back, hasn't made a jot of difference to the performance, was built to tour with though and not race.

 

The mount has been changed sinse the pic was taken ,before you all start with the "that will break" posts.

[Snapperpaul]

I would think that the calculations work better if you use peak torque/rpm or even peak bhp/rpm than max revs unless you calcs are just for gas flow and you want big enough system to flow the gasses without restriction

 

I just wanted to

a. Know the exhaust system was good enough

b. Try and get some free torque

In the end the manifold was pretty good out of the box and I remember Gingerfix said that the manifold was built to some known good figures, I just had the collected modified and the placing of the silencer and total length made to the calculations.

[Guest 2b cruising]

I know exactly what you mean Florin. They should be grateful Im compromising the BHP / Tonne by taking them at all

 

As an aside, are you aware of the new Camera that's just out? Apparently the shutter speed is so fast that you can take a picture of a woman with her mouth shut!!

 

But would it catchTazzman in his supercharged car?

[Guest lotusPaul]

The figures I used were for tuning to 7500k rpm and the equation will give you a good base to work from.

 

There are many different ways to develop an engine depending on your thought pattern but essentialy lets assume you have your car rolling road print out. It shows a dip or flat spot at say 4000rpm. You can use the figures to "fill" at 4000 instead of 7500k. You will get different lengths and bore sizes. The point on exhaust pulse tuning, as it was an exhaust

Question is you are generally limited to what you can buy off the shelf. Therefore id always suggest going to the closest size downwards unless your prepared to accept a marginal loss of torque. Having said that it may be easier to fill the gap using intake pulse tuning techniques which may create a need for the exhaust to be developed for a different rpm range. You could go chasing torque all day on a dyno but it will soon hurt your wallet for possibly very little gains.