Exhaust manifold sizing for 4,6+ engines

minorv8 · Post by **minorv8** » Mon Sep 03, 2007 5:37 am

I´m curious about the manifold you are using on bigger engines, are they with 1,5" primaries or larger ? I would anticipate that 4,6 litre and larger engines around 300 hp mark would need bigger primaries, say 1 5/8" OD. Any thoughts ?

pitsnow · Post by **pitsnow** » Mon Sep 03, 2007 10:11 am

We made an exhaust group buy for several RV8 powered Dax Rush in the Rush-owner forum this year. The exhausts were made by Simpson Race Exhausts. Matt recommended 1 5/8 manifolds.
The quality and service done by Simpson was first class.
Maybe give Matt a call and see what he recommends for your car?
http://www.simpsonraceexhausts.com/

Peter

minorv8 · Post by **minorv8** » Mon Sep 03, 2007 11:17 am

Thanks Peter for the link. Will contact him.

I inspect welds for living and judging by the photos on the website first class quality is an understatement !

Eliot · Post by **Eliot** » Mon Sep 03, 2007 12:26 pm

Wow - never heard of them. Handy link.

Wotland · Post by **Wotland** » Mon Sep 03, 2007 1:04 pm

Hello,
I have an friend who has an 4.6 Twin plenum Hotwire (68mm Throttle disc, 45mm trumpets, Stage 3 RPI heads, Piper 285, Mallory Unilite, 20AM AFM, Mark Adams Remapped). He has an custom 4-2-1 exhaust manifold with 44mm primary pipes.
http://img139.imageshack.us/my.php?imag ... 006ss0.jpg
http://img293.imageshack.us/my.php?imag ... 014lf6.jpg

kokkolanpoika · Post by **kokkolanpoika** » Tue Sep 04, 2007 6:31 pm

I´m also think about the same question..
And i´m planning to use also this 41,5mm primary pipes from my stage 4, 4.6++?? engine..
I´m trying to use Ford Mustang 5.0gt 1991- shorty headers from my SD1..
http://store.summitracing.com/partdetai ... toview=sku

My friend has got those headers, and what i try on them to my heads, 2 primares and 2 port of the head is in identical place, but 2 primaries is about 1" too short/away from the port.. but that is not a proplem. also flanges must to be changed..
And price is not so expencive..??

I think 44mm primaries are too big for road going rover v8.. Think that those mammoth primaries are only suitable for racing or big block chevy or over 4-500bhp ablications..

5000SE · Post by **5000SE** » Tue Sep 18, 2007 2:17 pm

I ran 1.75" (44mm) primaries on my 4.6 litre.

With Stage 3 heads, 10.5:1 comp, twin flapper airflowmeters on a twin plenum top end, with 45mm trumpets and a relatively mild Hybrid 200 cam, it made 313 bhp at 5100rpm and 367lbft, with very smooth delivery.

The headers were V8 Developments' own product, which had been designed to suit a 4.5 litre race car, but they were excellent on the road.

1.75"/44mm is not too big for a 4.6. My next engine is 5.0 with Wildcat heads, and Wildcat insist that 1.75" is the minimum that will let those heads breath.

alex · Post by **alex** » Sun Sep 23, 2007 8:43 pm

My 5.0 wildcat is running with 2inch bore primaries all 28inch long as recommended.
Mild cam? 8:1 comp and procharger giving 470 hp@ 5000
Alex