SV Header Primary and Tail Pipe Length

[HayesCages]

We have a Lola SV (air-cooled) in the shop for new headers:

Any one have any idea how long to make the primaries and tail pipe on a 2L FSV type 4 engine?
Using 1-5/8" tube, 2-1/2" tail pipe material.

(I know that it depends somewhat on the engine build, looking for basics here.)

As it was the old primaries had varying lengths from about 26 to 28-1/2". Seems short to me.

I've built many FV systems but not air cooled FSV.

Any thoughts are appreciated.

[S Lathrop]

I has been a very long time since I built a FSV system. Here are a couple tricks that helped me a lot. First, I turned the car upside down. Next I baized the copper port gasket to the end of my header pipes.

I split the primaries and the collector about half way between the head and the collector. This made the part of the header that was likely to contact the ground a part of the collector. Hitting the ground can be an issue.

Making the headers on the long side is not an issue. The problem with these engines was low end power. The engines had a tendency to not run below 4000 rpm and you hit that number a lot. Out of slow corners it was common to slip the clutch to keep the rpm up.

1 5/8 primaries is right and 26 to 28 seems about right for length. You might do the tail pipe in 2 steps, say 2 1/8 for about 6" and then 2 1/4 after that.

These engines had a some what narrow power band, from 4200 to 6500. It came on very strong at low rpm once the rpm were above 4000 maybe 4200. It was very easy to tag valves at anything much above 6500.

[HayesCages]

Steve, That's exactly what I needed to know, thanks!
Lawrence