Header size

[Eric Justus]

I keep scratchin my noggin on the appropriate size header to run on this motor... 1, 3/4" vs 1,7/8". I know it seems basic, but I always like to get some insight from everyone.

84x94
13.1 cr
44x37.5 heads
48 idas
1.4 rockers
MSD ignition

[John Rayburn]

That's a dyno session question.

[Paul Bate]

Hello John,

You haven't stated what cam you are using but even if you were using an FK89 with the 1.4's I would still recomend a 1 3/4 big is not always better.


Kind regards Paul

[Jason Foster]

I agree 1 3/4 or you may be better off stepping it. But as John said you'd need a dyno session to try your options. I believe too big is bad you want to keep it somewhat tight to keep exhaust speed up.

 Daniel Kurtzmans S/G car runs much the same combo you mention:
84x94
44x37.5
only 10.1 to 1 though
1.4's with FK87
MSD
 We run 1 3/4 header.

[John Rayburn]

Hi Paul! Eric was wondering. So, how are you? I wouldn't discount the larger system without dyno time. Greg Brinton uses 1 7/8. His dyno sessions gave him that answer. 1 3/4 didn't cut it with his combination. Again, ask the dyno.

[Gary Justus]

It's an FK89.

[richie]

Eric/Gary, surely head flow would affect the size required more than anything?conservative ports wouldnt require as a big a header as some huge race port job? John is proberly correct,only the dyno can really answer this,my old n/a 2332 worked perfectly with 1 3/4 phoenix merged header but it was only 10.2/1

cheers richie,uk

[Gary Justus]

Hey Richie! Good points. 1 3/4 was the direction I was headed, but diving into new waters just brought up options. As well, the dyno can tell the "tune".

[Dominick Luppino]

1 3/4 is what I would recomend.

[Gary Justus]

Seems like the "votes are in". Thanks, Dom (and everybody else).

[danny gabbard]

Maybe a silly question but the air you draw into the combustion, bore and stroke, would that have anything to do with size tube you use when building your header and collector length? Shit, Stuff I do not under stand

[Speed-Randy]

compression ratio also affects size of tube. lower compression, smaller tube, high compression11.5:1 or higher and thats when you start looking for the 1 7/8. the dyno will prove this everytime