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Hello to all you Acura experts! I hope you can help me with some header specs please
I recently bought a J32A (JDM) engine (apparently the exact same as a J32A2) read to instal into my mk1 Miata.
I need to know the ideal dimensions to fabricate the headers. In particular the ideal length of the primaries from the engine ports to where they merge into the single exhaust section. Obviously the factory headers are very short and cast. I've seen lots of after market stainless steel items which look longer. But I cannot get any dimensions at all. A tuner mentioned he made some 17" long headers, based on physical limitations rather than the optimal length. But I do not know the IDEAL length as this must be critical for tuning surely? I know it will be hard to measure due to the curves. I guess using a length of tape or string would work.
If anyone has some headers they could measure I'd REALLY APPRECIATE your time and effort! Happy to buy you some beers for your time!
If you look at Comptech headers, the primaries are not very long. The primaries I'm pretty sure are 1.5" that merge into 2.5". One or two custom long-tube headers have been made. I believe they were put on cars that were stroked (3.6L or used the J35A3 so 3.5L). Since you're using a 3.2, you might want to do something a little smaller like 1.6" with a nice merge collector into 3". The J engine love to breath, so big intake, big throttle body, porting the manifold and runners will help. Also I believe P2R sells the flanges, so you can fab off those.
Here's a mock up of a set. They were 1.8" primaries, 2.5 downpipe to a 3" merge.
Could you let me know the rough LENGTH of the ideal header pipes please? Looking at the photos I would guess somewhere between 13" and 16" long? Is this critical? I am guessing it must be. If anyone has a set they can measure the length of the header section I'd really appreciate it! I know it will be a bit tricky as the pipers are curved!
I'm not sure there's an ideal. Longer primaries will probably yeild more torque down low. I'd say make the primaries as long as possible before you have to merge and bring the pipes under the car to merge. I'd guess the comptech primaries are closer to 10" if you measured with a string. So 13-16 would be great if you can pull it off.
P2R really know their J series stuff. If they suggest 17" primaries then do it! They apparently broke 300whp on their J32 tuned Accord and I'm pretty sure they had custom long tube headers. So I'd go 17". Also post some pics!
P2R said it worked out very well, although we’re honest enough to say they only tried that one size due to instal limitations.
I really appreciate all your input. I will leave the final dimensions down to my talented installer / fabricator. Clearly we will have to work around the fixed Miata limitations.
I need to have the plenum modified so the throttle air intake angles down lower under the Miata hood. So a bit more custom fabrication to do. So before that is done...
Does fitting a larger throttle body make much different to power? If so which make and model do you suggest using? Or is this a waste of money for sensible power instals?
01-29-2018, 04:03 PM
