Exhaust / Intake Ratio

[nd55]

[ *** warning : armchair engine builder in the area *** ]

Exhaust:

exhaust valve curtain area + 10% for the primary, then use David Vizard's "no hp loss exhaust system" guide to select the secondary diameter.

David seems quite happy to plug Lukey 'Superturbo' style mufflers.

I've been told the trick to removing the exhaust raspiness is to use a straight-through mid-muffler whose major dimensions (width, height, length) are different to the final muffler to remove any common resonances.

The hard part is tuning the lengths for exhaust wave scavenging timing during the exhaust-intake cam overlap.

Intake pipe area size tends to depend on the 'throat' area just ahead of the intake valve.
The throat area, of course depends on the size of the valve and is very close to 89% (form memory).

This is the critical area, and any more than (i think) 7 degrees pipe wall divergence angle from this point will cause non-laminar flow which will kill overall flow and drop the flow speed too much and kill torque.
Even keeping the area constant seems to give fairly good results, as long as there a smooth transition at the opening (like a bell mouth)

There are computer programs like "Pipemax" which help a lot in this area.

Those are my notes on the issue, glad to hear others.

> Anyways you CANNOT calculate everything,

No but we can get very, very close.

Do a search for "Engine Analyzer Pro" software. There's others too.

Nick.

[wozzah1975]

[ *** warning : armchair engine builder in the area *** ]

Exhaust:

exhaust valve curtain area + 10% for the primary, then use David Vizard's "no hp loss exhaust system" guide to select the secondary diameter.

David seems quite happy to plug Lukey 'Superturbo' style mufflers.

I've been told the trick to removing the exhaust raspiness is to use a straight-through mid-muffler whose major dimensions (width, height, length) are different to the final muffler to remove any common resonances.

The hard part is tuning the lengths for exhaust wave scavenging timing during the exhaust-intake cam overlap.

Intake pipe area size tends to depend on the 'throat' area just ahead of the intake valve.
The throat area, of course depends on the size of the valve and is very close to 89% (form memory).

This is the critical area, and any more than (i think) 7 degrees pipe wall divergence angle from this point will cause non-laminar flow which will kill overall flow and drop the flow speed too much and kill torque.
Even keeping the area constant seems to give fairly good results, as long as there a smooth transition at the opening (like a bell mouth)

There are computer programs like "Pipemax" which help a lot in this area.

Those are my notes on the issue, glad to hear others.

> Anyways you CANNOT calculate everything,

No but we can get very, very close.

Do a search for "Engine Analyzer Pro" software. There's others too.

Nick.

There are just too many variables that change things.

The computer software calculators are very good, but alot of times not completely accurate and don't complete the overall picture.

Vizards work and dedication is unbelievable, and his results speak for themselves, however, if you apply some of his theory to components that aren't his designs they get different results. It doesn't mean his developement work is wrong, it just means that other developers have a different way of achieving a similar result.

An engine is, and always has been a system. When I state "engine" i mean a complete unit, from the area the air enters, to the area the air exits and everything in between.

Getting all the components and modifications to match is the key.

Cheers
Woz