Inliners International Forums General Discussion Hi Performance 2.5 liter Chevy L4 -- dual exhaust?

A friend of mine has an '88 Chevy S/10 pickup w/ the 2.5 liter engine. We're getting ready to rebuild the L4 engine. The question is: can a 2 piece header set be fabricated 2 -into -1 -twice to get dual exhaust? Since the firing order is 1-3-4-2, should the first collector siamese the output tubes of cylinders 1 + 2 and the next one 3 + 4? Would a crossover tube be of any benefit? He's also wondering what diameter of exhaust pipe to run with, and where to fit the catalytic converters.
Interesting engine -- it traces back to the old Chevy L4 153 CI "Iron Duke" that is very close to being 2/3rds of a 250 -- Also has TBI and flow thru head.

The only header i know of is a 4 into 1. I see now reason why you couldn't make your own and Yes How ever the stock is should be copied the same 1,2-3,4. As for the tube size stay with either 1-1/2 or No more then 1-5/8. Now as for a cross over tube?????? No real clue I never Used one.

I think if I were going to make headers for this application I would make tri-Ys, teeing 1 and 4 together with 20" primaries, likewise 2 and 3, and Y into 15" secondaries, then into a 2.5" single pipe all the way out. Might not look impressive but it would come out of the hole like an angry bear.

according to tom langdon, frenchtown flyer's correct about paring of the exhausts.

i have a mercruiser 4-banger in my model a and tom recommended 20" primaries, 24" secondaries into a single 2 1/2" pipe.

however, a 4-banger, with dual exhausts will have a definate and unique sound! (remember some english 4-bangers w/duals, exiting the rear with double-barrel-shotgun-like pipes?)

using the same 1 to 4 and 2 to 3 paring, you can run 2" duals and mufflers. fair warning! they can be loud and you may have to juggle mufflers until you get 'em quiet enough for the street. an equalizing tube might help reverberation, too.

I think 2.5" may be a bit big.... 2.25 may be better

On a 305 V 2.25 duals work well 2.5" kill low end torque - I fooled around with exhaust combos on the 305 for 2 years..... what worked best

ported stock mainifolds, with a 30" long 2" head pipe into a 2.25 duals with a cross over...

what didn't work - too big

hooker 1 5/8 headers and full 2.5 duals
headman 1 1/2" 3/4 length headers into 2.5 duals with crossover

Since the 2.5 litre 4 banger is 1/2 size of the 305 this guide should work

there oughta be a formula for determining the size/length of exhaust pipes.

a friend recently bought a set of shorter/larger pipes for his triumph T100R motorcycle. (hey, it's an inline TWO-banger)

it won't idle well and has less low-end torgue... acts like it's now running lean.....there's gotta be a connection between the different sizes of the pipes and the way it's running, now!