Technical Tips > Engines - Carbies - Exhausts - Dissys

What a decent exhaust can do for a 350!

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77CVT:
Dynoed my '77 on the weekend.  I changed the diff, trans and engine oils and indexed the spark plugs as best I could (at least they were all pointing up!).  The previous dyno run last year was done after I installed the stock heads with 2.02/1.6 valves, valve angle work, port matched Performer intake, XE256 cam, new lifter, double row timing chain, recurved dist and 9mm spiral leads. It improved the performance but not what I expected. I had already removed the cat converter and installed a twin exhaust (same mufflers). It ran 157.4 RWHP. :(:(  I was a little disappointed with that although the car had some go!

Since then all I have done is install a new exhaust (headers, H pipe and mufflers), removed the choke & tweaked the carb (QJet). (I changed from 73/42 jet/rod combo to a 75/46).

This time it dynoed at 226.1 RWHP. :bold:bold:bold   A gain of 68 HP at the wheels!  :D:D

The best thing was the shop owner stuck his head in the car after the 1st pull and asked if I had a 383. ;laugh  After the run he said “whatever you’re doing, you’re doing it right.” – I love that sort of comment!    :D:D

Considering it won’t spin the tyres off the line, I think a new torque converter (or TH700) is on the cards.

Judging by this, either the stock manifolds a total crap or my mufflers were a bin job (one was rattling), or both.

I’m pretty happy with the results, so now I can stop spending money on engine bits and concentrate on getting power to the ground. Just when the missus' thought it was over!  :P

rebel:
way to go !!!

In answer to your question re: manifold vs exhaust, I'd say the latter! The "Peformer" is a fine manifold but breathing via exhausts is where it's at! I've heard of a gain of 15 - 20 horses and a similar upgrade on an XR8 I used to own gave me 25 but 68 is awesome!!

Is removing the Cat legal though ..... ?

Anyway, I was going to get around to a dyno on mine but keep putting it off until I upgrade the rear with 3:55's.

You've just inspired me ..... ;-)

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