Opening up FP exhaust manifold...

[BombThreat]

I have read and was told to open my factory pipe manifold to approx. 48mm to help with my engine mods. I have also read that the ealier manifolds were 42mm and the newer ones are 44mm stock from factory pipe. I just measured mine and both the manifold and headpipe are 39mm. What gives? Would that suggest this is a 650 pipe? Also is it still safe to open both up 9mm?

 

[SUPERTUNE]

Must be a real early FP, New ones now are bored at 46-46.5mm, so you need about that to start with for a stock 701.

 

[SUPERJET-113]

Yeah, the early ones are 44-44.50 mm..
I bought my 701 61X manifold w/ltd chamber B pipe new when they first came out and paid $525 for it like 13 years or so ago. I didnt throat bore/match my head pipe and manifold until last year and it was at 44mm. I went to 47.50mm.

Regards,

 

[BombThreat]

alright, so what do you guys think,,, could this possibly be a 650 pipe? also do you guys just trace a gasket and follow that to bore it?

 

[shawn_NJ]

Sounds like a 650 headpipe. Becareful when boring it... This is what happened to mine.