Race Engine Forum UK

Hello Mr. Croft,
If you remember, I contacted you earlier regarding a blowthrough type of turbo system for my Scorpion. It would seem that that path is revealing more problems than it would be worth. However, my research has uncovered other ways to do this without resorting to fuel injection. I have enclosed two pictures with this post, they resemble early drawthrough Buick V6 installations incorporating alot of stock pieces. I'd appreciate it if you would have a look and give me your analysis. The guy had it done professionally as the work shows but knows nothing about how they mapped the air / fuel ratio etc. He expresses no problems whatsoever with reliability over the last two years at 8 psi boost as a daily driver. What do you think? Better than blowthrough? As usual, any help would be appreciated. I'm trying to get more pictures of the carb with the cover off to see more detail. Thanks again.

To my trained eye it's pretty crude, but the guy's been using it so you can't argue with that and I'm not going to criticise it as-such.

Purely from a professional standpoint, I don't like:
1. No intercooler
2. All those pipes, ex/inlet. Messy and inefficient.

That said, it's none of my business so if the owner is reading this, all I can say is 'well done'.

The only problem I'm aware of (ie: have seen) is one can encounter a tendency for the compressor to hold the throttle plate open. Strange but true. On a blow-thru you can use a dump valve to vent the excess pressure. I figure they have a very stiff throttle return spring?

Calibrating such-thru is no different to anything else, jet it up on idle, acceleration and full throttle with appropriate jets. I would want boost-retard, don't know if it has it - about 6 degrees ignition retard at full boost and rpm above that, wherever that falls.

GC

Guy has made a very good point here - if it works reliably then there can't be that much wrong with it, even if it is a little agricultural.

I do have one major problem with the way it has been installed and that is the positioning of the air filter relative to the turbocharger. I'm not 100% up on the quality of airflow through the engine bay of a scorpion/montecarlo but at stationary the induction system is going to be bathed in the waste heat from the turbo. Given my personal experience with comparable installations in X1/9s I would want to see a heat shield between the turbo and the carburettor for a start and preferably some ducting to allow the engine to breath cooler air.

Quite right Julian!

I myself should have remarked on that. The underhood heat will of course be prodigious.

Just shows how much I depend on others to keep GC Q&A 'up to speed'.

GC