Renault 807 header design

[jbcollier]

[MRN I J]

John, are the manifold bores the same size as the exhaust ports in the head & are the header primaries all the same length ?

[jbcollier]

Beats me.  Just found the plans on the net.

[MRN I J]

for correct exhaust header design see Four-Stroke Performance Tuning : 4th Edition by A. Graham Bell https://www.amazon.co.uk/Four-stroke-Performance-Tuning-Graham-2012-05-03/dp/B0184WRSBE/ref=sr_1_1?dchild=1&keywords=Four-Stroke+Performance+Tuning+%3A+4th+Edition&qid=1610314490&sr=8-1
flange should be 1/8th inch bigger than port & there should be approx 4 / 4.5" variation in primary length, this is from British Touring Car Championship 2ltr engines of the 80s & 90s.
Our own dyno tests on 2.6ltr & 2.9ltr 6 cyl engines backs up the misalignment of the ports, at the moment we are stuck at 93 bhp per ltr on engines designed in approx 1940.

[dakazman]

   Thanks for posting JB , 
I’ll compare it to my 843 Head. My head for the 843 came back from the machinist and the threadsert inserts came in . They do not work in the Renault Block .  Some of the photos look blurry on my phone , but very interesting.
Dakazman
 
 

[RoddyMac]

there should be approx 4 / 4.5" variation in primary length

That much variation?  I would have though much less than that (within an inch or so), but if that works then my header build for my new project will be much simpler to build. 

[Richard48Y]

Fellow who hand fabricated the headers for my TS headed car went to great effort to keep each tube exactly the same length.
He was very proud of his result and found it greatly improved over stock exhaust.

[GavinT]

there should be approx 4 / 4.5" variation in primary length

That much variation?  I would have though much less than that (within an inch or so), but if that works then my header build for my new project will be much simpler to build.

That's what I'd have thought, too.
I'd be interested to see the theory & practice around this.

I can see how one might arrange a 4 / 4.5" variation between two primaries, but four? . . or six?
How does that work logically?

[MRN I J]

Fellow who hand fabricated the headers for my TS headed car went to great effort to keep each tube exactly the same length.
He was very proud of his result and found it greatly improved over stock exhaust.

very old school & right at one rpm, get Bell's book & read it, the variation brings torque up over a broader rpm range, torque wins races, hp wins the bar talk.
UK BTCC engines of the Supertourer (& ETC) era were the most technologically advanced 2 ltr race engnes ever built

[MRN I J]

there should be approx 4 / 4.5" variation in primary length

That much variation?  I would have though much less than that (within an inch or so), but if that works then my header build for my new project will be much simpler to build.

That's what I'd have thought, too.
I'd be interested to see the theory & practice around this.

I can see how one might arrange a 4 / 4.5" variation between two primaries, but four? . . or six?
How does that work logically?

I took the flange off my 807 / 843 manilfold & had a new flange laser cut with larger bores to give a mismatch as per Dave Vizards findings on A series engines 30 years ago, and made sure I slightly modified the lengths to comply with Bells BTCC ideas who also specifies the mismatch. We had just had a 6 cyl Aston Martin head with an old school matched port by David Martin, ex Swaymar and Motorman, no matter what cam we used we never the hp over 213 on that head engine combo, we then had a head ported with a port left about 3 mm smaller (largely as cast) by John Middleton, ex Cosworth, same spec engine, 245bhp, never looked back until John retired.
Never tried the mismatch in length on one of our 6es, FIA regulations dont allow it, so stuck at 92.5 bhp per ltr until our new spec head is machined & the engine built, however we are sure we can get over 295 bhp from 2.922 cc on an engine designed in 1940.