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Posted: Aug 06, 2009 11:08:15 am
Davy-D



I am quite amazed how close the exhaust valve and throat is to the manifold face and none of the experts seem to consider it an issue ( dare I say that the last race engine I built was a 1400 pushrod with ports half that diameter and twice the length and with 20 inch primaries it gave well over 100bhp per ton and had a 3500 rev power band).

I note that some of our forum members have plans for SSI heat exchangers on a 3.2 engine .  Well I hate to poor cold water on their plans but having been that route before and tried them on both 3.0Sc and 3.2 I was made aware of the fact that SSI's do not respond well on 3.2 engines but perform well on the 3.0 and earlier this was emphasised by Geoff Everett (or who ever he was ) the tuning guru at AMD.

Having built many small race engines myself (Some quite successful) and being quite comfortable with the concept of equal length primaries etc. I was a bit flummoxed to be told this having lashed out on what appeared to me to be a superb piece of engineering with all the right credentials,to have this contradicted . so recently I returned to building another car to replace my old Targa 79 3.2SC . This time I being in a position to do most of the work my self I decided to retrace the route and understand the reasons, The current project a 79 3.0SC Coupe now has an 89 3.2 engine, 86 oil cooler 915 box and of course the SSI System,as the first system I bought was for a 3.0 I was curious to identify the difference and the problem . now I think I have it.

I have tried to make my findings known to various magazines who express great interest and it seems inertia.

The solution is obvious to me although it is a little previous to say so as my project is still a bit of final testing.

For those who are interested the solution lies in the fact that the 3.0 has 39 mm exhaust ports which are less then 50mm long,(which is shorter than almost any engine I know of) the SSI has 39mm dia. primaries which mate perfectly, and there fore carry the gas away with no problem, however the 3.2 has 42mm ports and a sleeve stub, so if you fit the 3.2 SSI to that with its tacked on stub spigot the gasses will run smack into it and in such close proximity to the valve this can only have a seriously detrimental effect negating all the benefit of the construction.

I have therefore devised a simple method of modifying the stub to create a venture and flow the gas from port to pipe and will be fascinated to see if this is the solution if it is it should go someway to restoring the missing power although the only real solution would seem to be for SSI to make the primaries out off 42 mm tube.

There is no doubt in my mind that the SSI is a superb piece of kit and having spent a very long time in engineering I feel can spot many benefits , weight, reliability, and design to name a few although to be fair the design was really Porsches 72 design so even it didn't increase performance it is still worth having . BUT IT SHOULD WORK and I look forward to reporting on my tests when I am in a position to do them.

I have progressed a great deal with my project and hope to fire it up next week ( I never did resolve the electrics so have called in an electrician), I have as they say done everything else myself  to date but may use a specialist for suspension geometry, and some paint, (as looks are not at the top of my priority).


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