2.5" or 3" ??

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rivmasta

rivmasta

New Member
Hey all, will be building the exhaust for the buggy over xmas (hopefully!) engine will stay stock, system will be:

800mm 1.5" primaries into 1000mm secondaries into a set of supertrapp ends. Question is should I go 2.5 for the secondaries or 3"? bear in mind - its a short system!
 
A combination of buggering around on EAP, reading through old threads here, whats available at the right price and, most importantly, whats practical for the car.

1.5" as its what comes stock and I want tq not hp so wanted velocity, 800mm as its convenient for the car (rear engined car with exhaust exiting over the gearbox), secondary size governed by the size of the supertrapp (2.5 or 3") length by vehicle practicality.
 
rivmasta said:
Hey all, will be building the exhaust for the buggy over xmas (hopefully!) engine will stay stock, system will be:

800mm 1.5" primaries into 1000mm secondaries into a set of supertrapp ends. Question is should I go 2.5 for the secondaries or 3"? bear in mind - its a short system!
Click to expand...

Primary's too small and a bit short, secondary too long. Velocity won't gain torque at low rpm and small primary's will kill top end. Try 1.75"/1.875" primary, 2.5" secondary.

http://www.v-eight.com/tech_forum/viewtopic.php?t=209
 
EAP ? Garbage in/garbage out. Never seen an EAP output backed up by fact. Any one else got engine dyno figures to back up their opinion/theory's.

If we are dyno daisies I will butt-out.
 
rivmasta said:
hmm... Re size of primaries, I was actually going off JBrady's comments here: http://lextreme.com///forums/showthread.php?t=5892

Secondary may be shorter, depends on how much gearbox clearance weve got! Bear in mind its not peak hp we're after - we're not dyno daisies!
Click to expand...

Riv, if you recall from the post you list above... I suggested that larger primaries for YOUR application would be resonable. My suggestion of 1.5" pipes was for stock RPM range engines looking to keep good low speed torque.
 
rms said:
Primary's too small and a bit short, secondary too long. Velocity won't gain torque at low rpm and small primary's will kill top end. Try 1.75"/1.875" primary, 2.5" secondary.

http://www.v-eight.com/tech_forum/viewtopic.php?t=209
Click to expand...

Erol,

Is your suggestion based on high RPM and aggressive cam profiles? Most testing suggests that small primaries are effective for response in the low to mid RPM range on a stock type engine. Do you agree or dissagree? If agree to what do you credit this condition to?
 
JBrady said:
Erol,

Is your suggestion based on high RPM and aggressive cam profiles? Most testing suggests that small primaries are effective for response in the low to mid RPM range on a stock type engine. Do you agree or dissagree? If agree to what do you credit this condition to?
Click to expand...

Attached engine dyno figures - Engine is UNOPENED 1uz, STD cams, with 50mm slide inlet, dry sump and exhaust.
System is (tri-y ?) 2 - 2 - 1

On ALL N/A engines I have dyno'd an exhaust system with primary pipes that are on the small side kills the AVERAGE torque/bhp over the effective range.
 
JBrady said:
Riv, if you recall from the post you list above... I suggested that larger primaries for YOUR application would be resonable. My suggestion of 1.5" pipes was for stock RPM range engines looking to keep good low speed torque.
Click to expand...

Stock is exactly how we're keeping this motor now - change cam belt, add oil and go racing basically. The only mod is the twin TB (done for prev engine config, but we're keeping it, even though its not much good without cams) and the exhaust with a 7,500rpm limit, and we need mid throttle response for offroad, hence the 1.5" choice. can also reuse the existing MLS flange gasket.

Re EAP - yep, familiar with gigo concept - i dont use EAP as a bible, but as a tool for rough calculations... I put more stock on the comments received here actually.

Re Dyno Daisies - I know there are none here, its why Im here instead of some other forums...
 
if youre going to rev it, open up your primares

if youre not, well, i wouldve said keep them smaller, but erols numbers dont lie. bear in mind the addition of his manifold should shift peak power 1000 odd rpm also
 
Enough advice for me! Im going to go up to 1 5/8" and 3" secondaries.

Exhause will basically be this arrangement:
5.jpg
 
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