Input on header design? Ferrari F355/Pipemax

[INTMD8]

Hello,

I was hoping to get some feedback on this project as I would like to just do it once

The car in question is a 95 Ferrari F355. The car is stock (stock headers) with catalysts deleted and a Capristo muffler.

It currently makes 340rwhp/250rwtq and ran 12.4 @116.8 in the 1/4 at 3,140lbs.

I started with Pipemax.. My dilemma lies in the fact that the original headers seem to be metric tube OD as it doesn't align with what is readily available. That and it's kind of a weird design after the collector.

The end of the stock headers Y's off and one outlet goes (originally) to the primary catalytic converters. The other outlet goes to a Y pipe (which was also catalyst originally) with a bypass valve that opens at about 3600+ rpm for additional flow. The current muffler keeps those two paths separate. Y-pipe bypass path is essentially wide open.

The original headers measure as follows-

Exhaust flange (oval) 1.57x1.35

First y-segment 1.55 OD 20in long

Second y-segment 1.9 OD 6in long

Collector 2.39 OD 10in long


With pipemax I am coming up with the following for a 3 step tri-y

First y-segment 1.434 OD (low/mid) 1.559 OD (high rpm) 11.5-12.8 long

First y-segment 2nd step 1.559 (low/mid) 1.684 (high rpm) 5.7-6.4 long

2nd y-segment 1.684 (low/mid) 1.809 (high rpm) 5.7-6.4 long

Collector 1.816 taper to 2.816 13.5 long (TQ) 2.066 taper to 3.066 13.5 long (HP)


So I'm thinking 18ga 321 for everything.

First y-segment 1.5 OD 11.5-12.8 long

First y-segment 2nd step 1.63 OD 5.7-6.4 long

2nd y-segment 1.75 5.7-6.4 long (a good bit smaller than original?)

Overall length 23-25.5in long (pretty close to original)

Collector- Not sure. Can't really be a megaphone as it's a curved pipe and has 2 outlets. Do straight 2.5 and be close to original? The length of the collector before branching is 5.5in. Dont think I have the room for a 13.5in long megaphone -before- branching to the outlets. (and if I did it would still be on a bend).

I'm leaning towards optimizing high rpm as the tach doesn't drop much below 7k during a WOT run. (8700 shift point)

Based on the above and the following, anyone have input on the design of these? Any thoughts appreciated! Thank you.

-Jim

[mk e]

Ha! I'm not the only Ferrari guy here!

My thought is I'd be petty surprised if it helped much up top and expect it will hurt at normal driving rpm. My experience has been the stock stuff is pretty good and what pipe max is spitting out is pretty close to what you already have....unless you're doing other work i suspect there is very little to gain from new headers.

[INTMD8]

Hi Mark,

Looking through your build thread now. Phenomenal amount of work! Very cool

Agreed that the headers will likely not gain much.

Do you think I should go with 1.5 primaries off the head? Only slightly smaller than original and I think going to 1.63 might be too much for this.

And on the first y segment. Pipemax is recommending quite a bit smaller than original. Trust that or copy the originals? Thanks.

[mk e]

It turns out there are a lot of ways to build tri-y headers.....

The factory first collect/segment could be sized to allow it to be a formed not welded piece? Or it's sized to make it plus the 2nd collector plus the muffler act as a long collector at some rpm.....hard to say for sure without modeling it all and playing with it in dynomation.

I don't think I would go smaller on the primaries if top end improvement is your goal, maybe.... but it just doesn't seem right......do you know the wall thickness for the one tubing? If they are 16g you could go to 1.5OD 18g as you propose and be about the same, I think PM assumes 16g?