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What size exhaust for my 308

Started by _darrenmark1_ , Jan 24 2009 01:45 PM

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15 replies to this topic

#1 _darrenmark1_

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Posted 24 January 2009 - 01:45 PM

Well I've gota put a exhaust on my 4 speed manual 308 what size?

What I've got is :

308
Bored 20 thou
ACL flat top race pistons
Decked block
308 Pre pollution Heads
Ported and polished (A LOT)
New Oversize stainless valves (L34 Size)
Scorpion Rolla Rockers
Manley Chrome Molly Pushrods
Crane Anti Pump up Lifters
Crow Cam
(5761) HOLDEN Carby V8 1969-86 Hot Street Hydraulic Cam$272.8Add to Cart Part Number 5761 Lobe Separation 109 Valve Lift
Inlet Opens 38 B.T.D.C. Inlet Closes 74 A.B.D.C. 0.495
Exhaust Opens 76 B.B.D.C. Exhaust Closes 36 A.T.D.C. 0.495
Inlet Duration 292 at 0.050 292 Advertised
Exhaust Duration 292 at 0.050 292 Advertised
Redline single plane manifold
Holley 600
Pacemaker headers.
& evrything else new.

HP ... Got no Idea....
I would presume it needs to breath well but not to big

I'm thinking 2.5" with a crossover.

What do you think or what have you got?
Darren

Edited by darrenmark1, 24 January 2009 - 01:46 PM.

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#2 _ronaldoredsox_

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Posted 24 January 2009 - 02:05 PM

The cross over is important, as it stops the clapping. 2 1/4 sounds great on mine with a hot 308.

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#3 fatslr

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Posted 25 January 2009 - 08:32 AM

Bet you are hanging for them pipes :spoton:

Your engine specs are very similar to mine as above use the X pipe and choose quality mufflers with mandrel bends 2 1/2" and you will have a sweet note and optimum performance keep us posted

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#4 _Roadknight_

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Posted 25 January 2009 - 09:46 AM

Try a 2 inch twin system with balance pipe at the rear of the gbox. The balance pipe to be done at a right angle, H style not a X type.
It will be quiet rumble at idle but when you step on it people will know whats under the hood.

It has them guessing while your sitting at the lights.
Did the same for my bigblock.

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#5 _Herne_

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Posted 25 January 2009 - 10:06 AM

Twin 2" or 2 1/4" talk to an experienced exhaust man and he will probably tell you twin 2.5" is over exhausting to the point of loss of performance...X is best.

Herne

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#6 Redslur

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Posted 26 January 2009 - 08:54 AM

^^^^ Spot on Herne. My SLR was a comfortable 300 HP and only had dual 2" and went better than when it had the dual 2 1/2". Sounded better too. Too big is overkill.

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#7 royalplumss

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Posted 28 January 2009 - 12:54 PM

There are so many "experts" in the field but few with the dyno comparisons to back them up.
There was an article (somewhere) on DiFillipo's exhausts and his opinions.
Tuned length extractors with no interference construction and a SMALLER diameter H pattern crossover pipe were mandatory.
In addition, shiny stainless steel should be ruled out if you dont have deep pockets as it will thermal stress fracture quite quickly. Exhaust type stainless should be the type that actually rusts - it has the right expansion properties. Cant remember the number off hand (e.g 406)
General consensus was 2 - 2 1/4 inch

Chevy drops are still TOUGH also (not that I'm biased of course).
I think this must have been overlooked in the articles that I read though.

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#8 MRLXSS

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Posted 28 January 2009 - 01:25 PM

I would say maybe Twin 2.25", then if you want get some 2.5" tail pipes or something so it looks tuff out the back!

Maybe ask Tony from speedworks what his suggestion would be for the motor.

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#9 LS1LX

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Posted 30 January 2009 - 08:51 AM

FOR THAT MOTOR A TWIN 2" WOULD BE PLENTY, BUT IF YOU WANT IT LOUDER AND YOU PROBABLY WONT LOOSE ANY POWER, i WOULD GO FOR A TWIN 2 1/4".

Twin 2 1/2" shoulds shit on a mild motor and it starts getting tight getting the tail pipes over the diff.

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#10 fatslr

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Posted 13 February 2009 - 08:16 AM

So whats the verdict :blink:

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#11 Struggler

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Posted 13 February 2009 - 10:39 AM

I prefer single systems on mild 308's myself but each to their own.
The other guys are right, you don't need 2 1/2" duals and it would cost you torque.
It is far better to err on the small side with exhaust.
Having said that twin 2 1/4" will be fine (or single 2 1/2" !!)
A cross over pipe is a given, I like X's but an H is still effective.

JMHO

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#12 _chrome yella_

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Posted 13 February 2009 - 12:06 PM

I prefer single systems on mild 308's myself but each to their own.
The other guys are right, you don't need 2 1/2" duals and it would cost you torque.
It is far better to err on the small side with exhaust.
Having said that twin 2 1/4" will be fine (or single 2 1/2" !!)
A cross over pipe is a given, I like X's but an H is still effective.

JMHO

i agree with Struggler, i had twin 2 1/4 on my monaro with lukeys and 292/500 lift cam and it boomed, sounded fantastic but in the country you could sometimes get away with it, after i got busted for noise ihad to rethink how to make a top sound again. so we went for a 2 1/2 single thru the a lukey finished behind backwheel and cut to the angle of bottom of rear guard so you cant see it. anyway it sounded way crisper, in the high revs nothing sounds better but if you want pipes out the back like factory, put a 2" mandrel bent twin system on her.

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#13 _darrenmark1_

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Posted 13 February 2009 - 03:40 PM

So whats the verdict

Can't make my mind up!!
What i have to do is take the old headers off and fit new ones with new pipes and mufflers and tail pipes.

How much do you reckon? I have the new headers. so all i need is from the flange back. Quote $700.00 (bit rich i thought)

Went to a exhaust joint yesterday and asked his opinion.

He said

2.5 to the muffler with a crossover (worth 15HP His opinion) Then 2.5 tail pipes. No straight thru muffler to noisey. ( gota get a Roady )

I asked what sort of mufflers and all he said was there is a big choice. I want it to sound like the engine it is. Not like my SSV..

Now i wouldn't have a clue. I was thinking Magnaflow(expensive but good i thought)

What mufflers you guys got? Gota be below 95 dec, apparantley.

:banghead:

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#14 fatslr

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Posted 13 February 2009 - 04:19 PM

Can of worms :blink:

not game to comment :tease:

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#15 _Herne_

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Posted 13 February 2009 - 04:20 PM

Can of worms not game to comment

same lol

Herne

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#16 _darrenmark1_

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Posted 09 April 2009 - 04:00 PM

Well its all done!!
Pacemakers replaced with L34 Headers.

2.25 inch twin with a crossover

to redback mufflers straight thru.

Mandrel bend over the diff and out to some 2.5 inch chrome tail pipes!!

Its loud!

But hey he did the roadworthy, he just said when you take it to Vic Roads please take it on a trailer.

It sounds awsome.

Just gota tune it now.

Thanks for your help and advice.

Darren