Even though I chopped my small collectors out to 2.5". I still had back pressure issue when running the 200 shot. (long story, but I know it was a problem)
So I've now cut the mutha's up again and stuck 3" tails on. Now when I look up the collector pipe I can see all four primaries with just a tad of the outside edges obscured by the collector tail. The 2.5" tails blocked off nearly half of the primary pipes.
I've also removed as much metal as I can from the exhaust ports with my limited tooling. I've nibbled metal away to make sure the the free area in the ex ports is bigger than the free area of the ex valve seat opening in the chamber and it gets progressively bigger up to the port flanges. That's about all I can do with these stock Range Rover EFI heads without forking out for bigger valves to be fitted in the ex side.
I've also got another 80 thou of valve lift from the cam as I had the guides trimmed down a touch.
So the stock engine is now tweaked as far as I reckon it can be with just a slightly wilder cam and stock sized forged pistons.
I know she is breathing better now because she needed and extra 3/4 turn on each idle screw on the Weber 500 to get her to settle at a smooth idle.
I do hope that 10.99 is on the horizon......I've been slowly chipping away for years now. 12.4 seconds PB back in late 2006. 11.26 last year with this setup + a 200 shot of gas. But then the stock pistons broke after 40 passes.
Bear in mind that this is a 90,000 mile Range Rover 4.6 that has not yet been rebored. I've broken and melted 4 pistons since May 2007 and just scraped the ally out of the bores with a stanley blade.
I'm also still using my stock MGB V8 diff and shafts. The engine still has its original crank and rods too.
So here a pic of my latest lash up.
