let us know how you go and what the figures are!!!

don't worry, i will. this is what people want to see.

That looks very neat, i am very interested in seeing how it all goes, keep us informed.

Have a look at how short the rb26dett runners are

Sorry guys, i got it arsed backwards For N/A Engines, Higher revving motors (undersquare, shorter stroke compared to bore, such as GTR specs 86 bore x ~73.7 ? Stroke) will tend towards shorter runners (4AGE Twincam Quad throttle etc) whilst square or oversquare lower revving motors tend to benefit from a longer runner design, (Ford Straight 6, RB30 etc). For Turbo applications, longer runners are favorable as they give a good compromise between the above. The longer runners provide more off boost torque, thus a broader torque curve at low speeds, then at full boost there is enough air velocity to carry this all the way to redline, keeping the top end strong. The above is for general cases. The real deal depends on the cam shafts and valves. Having worked on Soarer Twin Turbo engines (1JZ GTE) i can assure you that the exhaust manifold is no more than 5cm long. Yet with a pair of highflows running 19psi, 440cc injectors and a piggy back/cooler/exahust etc, a car that ive been working on has made 240rwkw in manual form, 4th gear 1:1 ratio. I have seen many BIG single and custom twin turbo manifold applications fail because the exhaust manifold is tuned to the cam and the flow characteristics of the head. Having 300mm runners for a big single was a total failure, with fullboost at 5.5k (21psi) and 7.5k redline. It was so pathetic, a lightly modified soarer would have beaten it at the drags, even though it was making 340rwhp on the dyno. This was a car that i was looking at buying for a friend, but i quickly said not to buy it as it just didnt have the right package for a performance machine. High on wank factor, but low on performance. Peak power dyno figures mean NOTHING and this was a testiment to that. To add further to this debate, the GTR uses a 6 throttle application with 10cm runner lengths, whilst the RB25 uses a plenum chamber with long runners like the rb30 with a single throttle. SR20DET engines have a long runner and a log style plenum chamber. When Zoom magazine installed a GReddy GTR Style Plenum with short runners on the SR20, it was nothing but disappointing because it was not matched to the engine. Infact peak POWER was decreased and midrange torque was lower than the standard manifold. In short you need to find out what works for the engine package that you are designing for. What might apply for a V6 or a straight 4, will not apply to an RB30 specifically. There may be attributes to the design philosophy, but nothing is concrete unless you make a few plenums and find what exactly works for which stage of modification. Tapering plenum chambers reduce the flow to the rear cylidners to prevent leaning out. Even the standard GTR Plenum chamber has ~20% reduction in cross sectional flow area at cylinders 5-6. Air is fluid and as such will take the most direct path. In a log style plenum chamber, this is the rear cylinders. If your interested in plenum and turbo applications / design of turbo systems, then buy Maximum Boost by Corky Bell. Its an insight to what works and what doesnt work, and theres quite a few general cases that could assist you in finding the right design. If those that are designing and/or fabricating custom turbo performance parts, if you havent read this book then you shouldnt be making anything. I started my own turbo exhaust manifold then i read this book, now im starting again to get it right Cheers. Some original photos have not been recovered yet.

oooookkk then! thanks for the short story, i with just provide you will the figures. Then ppl can decide for them self. Thanks for the input darkstar you have given an easier understanding on runner lengths. But dyno and dyno papers are the main factor. Then take it from there. Thanks to everyone for their reply's

Exactly right davitt, the above is for general cases only, you need to tune to the engine your working on. If your manifold works better than the competitions, then your obviously doing something right. If you get the right design straight off the bat, then your very very lucky as it takes people a few goes to get the right design, then they have to tune it and get it 100% optimal. The engine/chassis dyno figures are whats going going to make a difference. Flowbenchs are nice, but they dont provide real world figures, only a running engine can show what works and what fails Some original photos have not been recovered yet.