Outer Limits 4x4 Board

Does anyone know where that thread dissapeared to that was dedicated to exhaust tech, and mainly answered by some exhaust expert? Search doesnt work so i cant find it that way. I have some questions about sierra zorst.

PJ.zook wrote:Does anyone know where that thread dissapeared to that was dedicated to exhaust tech, and mainly answered by some exhaust expert? Search doesnt work so i cant find it that way. I have some questions about sierra zorst.

he went the way of the doe-doe...
Ive been waiting over 18mths for an answer.

Thanks for link. Well he hasnt posted for a year, so methinks he isnt around anymore, no point gravedigging the post.

He was probably just exhausted from all of the questions thrown at him.

Post your question up here anyway. You never know who knows what.

Jas.

want33s wrote:Post your question up here anyway. You never know who knows what.

Jas.

Exactly. You'll get so many opinions that one of them is certain to be right.

OK well basically im installing a baleno G16B into my sierra using Redback headers. Im ditching the old exhaust system as it was suspect to begin with (the cat was imploding). Anyway, im just wondering what pipe size i should use throughout (im thinking of same diameter as header flange, havent bothered to measure yet though, looks 2"+), what cat converter i should use and what i should use in the way of silencing exhaust while still having it free flowing and sounding good, ie should i use a full on muffler or would a hotdog do? Also where can i get the cat and muffler/hotdog nice and cheap?

According to car design books IE from Bosch etc.

You'd work out the full area of the intake (full length)

then work out the full area of the exhaust (full length)

then make the exhaust area slightly smaller than the intake area.

working it out fully:
you'd also like to work out the pulse of the pistons based around a bank, so you can work out the exact amount of back pressure you really require.

A bank is 2x3 pistons 1x6 pistons (V6), 4 pistons (V4), 2x4 pistons (V8)

The exhaust will start from these banks no mater whether it' a single exhaust setup or a twin setup, having different banks will change the back pressure requirements.

The pulse is a wave that travels from the engine.

when the exhaust port opens a pulse is produced from the combustion in the cylinder and exiting gases.

The pulse travels down the exhaust and exits the exhaust but part of it travels back to the engine.

you want the returning pulse to come back when the exhaust port is close to closing and the intake port is starting to open.

The pulse sucks out exhaust gases from the cylinder plus sucks in new air, so a pulse is basically called back pressure.

You want a pulse to end just outside the exit on the exhaust.

on a petrol engine you require back pressure, other wise it won't start or splutter all the time if the intake and exhaust lengths are wrong.

on a diesel you don't need a large amount of back pressure as air is always free flowing so opening up both ends will help it rather than hinder it.

anyway, probably not much help but something to think about I guess.

Thanks for the reply Zagan. I only require a basic setup, im not after every last horsepower by tuned length exhaust, scavenging, etc... just need a basic exhaust that will work nicely.
Main points i need are where to get good deals on parts, and what to use to keep exhaust at a non-boys-in-blue-attracting noise level.

I've done alot of research into exhausts in the past regarding high horsepower applications etc. What is your main concern? How quiet is quiet?

For all out power 2 inch mandrel bent system with high flow cat and on straight through muffler will do the trick but will be bloody loud.

If you want it quieter and cheaper I suggest running twin mufflers in a twin pipe system, so 2 inch high flow cat with a Y piece into 1.75 or 1.5 inch straight through mufflers all press bent. This will not restrict your flow but dull the noise alot over the system above however you may find it hard to get 1.75 or 1.5 inch straight through mufflers, therefore a 2.25 press bent system with 2X 2.25 or 2.5 inch mufflers inline will do the same job.

I have 2 inch straight through with high flow cat and muffler on my SWB GTi and it is bloody loud but I don't mind.

If space is a problem you can step down the pipe diameter as you go further back somewhat. As the gas cools it contracts and looses velocity so going down 0.25 of and inch at the rear before the last muffler wouldn't hurt. It can be hard getting twin 3 inch over the rear axle of early commodores and in back to back dyno testing twin 3 stepped down to twin 2.75 then 2.5 inch lost no HP and actually gained a poofteenth of torque.

Yeh space is an issue in sierras. The muffler on it at the moment is gargantuan, want to try and avoid that.