Flat Plane V8 Race Engine - Single Exit Exhaust Question

[hoffman900]

1000cc Superbikes making ~240bhp+ are using right around a 2.25" outlet... If you look at them closely, you'll see choke be almost the same diameter as the secondaries before tapering up in diameter from there (think a long slow expansion.. maybe 2" to 2.25 or so).

[exhausted]

1000cc Superbikes making ~240bhp+ are using right around a 2.25" outlet... If you look at them closely, you'll see choke be almost the same diameter as the secondaries before tapering up in diameter from there (think a long slow expansion.. maybe 2" to 2.25 or so).

I hear you Bob but the RPM band is so high they are in another world from most of us V-8 2 valve Americans...still I have never seen a exhaust port that was too small...

[oneaves2005]

Exhausted,

Just to clarify, are your suggested lengths from the valve or the flange face?

The exhaust port length is 2.8"

Ollie

[exhausted]

Exhausted,

Just to clarify, are your suggested lengths from the valve or the flange face?

The exhaust port length is 2.8"

Ollie

Flange.

[oneaves2005]

Nice one, thanks.

I might be pestering everyone for some advice on Siamese port exhausts next....

[oneaves2005]

Hi all,

Just an update on this, the system was made as per Calvin’s recommendations. The halt on racing has stopped me being able to test against the completion however the dyno (although messing about) showed big improvements in low down torque and pickup is phenomenal from as low as 2,500rpm. Power peaks at around 7,000 rpm which is a bit lower than expected but that could be a number of things.

I will get back to a better suited dyno soon so I can share a graph.

Thanks again to Calvin for his fantastic advice.

Ollie

[hoffman900]

Looks good to me!

Calvin did an exhaust for a Triumph TR8 here in the States recently. It is built to a limited prep rule set (no porting, valve shape / jobs free, .030 overbore, 12:1 compression, .425" valve lift limit). Picked up 5% power over the mid range with the same peak power. However, he is going to do another round of cam development next (I linked him up with Billy Godbold) which should unlock more on the top end while the exhaust protects the bottom end. Currently at 243whp feeding through a single 2.25" od pipe, but I think with a bit more cam development it should be knocking on 260whp.

The British "experts" for these cars told him he would at best get 220-230hp at the crank with the stock heads... so far he's about 50hp up on that.