Danger of intake manifold leak in blow through turbo setup??

I'm building a blow through turbo system using a GM TBI on a home-made log manifold, with the goal of running somewhere between 7-14 psi boost. This is my first attempt at making a log manifold and I'm reasonably sure it seals flat against the head and doesn't leak, but a thought occurred to me: Since it's a "wet" manifold under pressure, would any leak between the TBI and the intake valves result in pressurized, vaporized gas spewing into the engine compartment?

Anybody been there, done that? Any way to diagnose a problem before my project goes out with a bang? (he says, only half in jest.)

You could pressure test the manifold... a lot of older supercharger systems have safety valves on the incase of a backfure. That might be something you look into. 

Imho, the risk is pretty minimal, I would use RTV at all the mating surfaces, just as cheap insurance.  

Also, make sure any vacuum lines are pre TBI injection. I know this is a no s*^t statement, but some would overlook it. 

akamcfly said:

Watch out! the diamond plate floor boards might fall out!!!!!

Thanks NordicSaab. I pressure tested the intake track up to the TBI to insure no leaks, but I'm not sure how I would go about pressure testing the manifold on the engine. I saw a video on y-tube where a guy used soapy water and revved his engine to generate a small amount of boost, which caused bubbles to form wherever there was a leaky joint. I might try that. I did use two intake manifold gaskets to help compensate for any small imperfections in my intake flange.

Just one of those little worries that come to you in the middle of the night...

Actually pressure testing any turbo system is a great idea. Generally you find leaks and sealing them will make a noticeable increase in boost (and power).

The best way IMO is if you can make sure all valves are closed (cam/lifters out). But I rarely have time for that so I just put the engine where most valves are closed. The engine also needs to be blocked from spinning, with a manual gearbox I use something like 4th gear, handbrake on and wheels blocked.

Then I like to make a plug for the turbo inlet, (instead of the air filter), fitted with a tyre valve stem. Set the regulator on your compressor to something like the boost you will run plus a little extra. The plug needs to be securely fastened to the turbo - not just hose clamps, I use one or two straps around the turbo to keep it from flying off. Be careful, the pressure forces are big!

Then you can pressurize the system and check for leaks with the engine off.

Gustaf

I was thinking pressurizing the entire system would be tough because air would escape through an open valve. However, it occurs to me that you could also plug the exhaust system just down from the turbo -- install plugs at both the turbo air inlet and turbo exhaust outlet and pressurize everything in between. Then you could find leaks in the intake and exhaust. Hmmm, may give that a try.

Its not available to everyone but check if any of your friendly local auto parts stores rent smoke machines for evap diagnostics. I’ve used them a few times on turbo cars . I usually grab the boost pipe right off the turbo and pressurize the system to 2-4psi. Then watch for smoke to come streaming out of the pinholes left from my piss poor welds in the ic piping or places where gaskets have been pushed out by excessive boost.

jamesl said:

I was thinking pressurizing the entire system would be tough because air would escape through an open valve. However, it occurs to me that you could also plug the exhaust system just down from the turbo -- install plugs at both the turbo air inlet and turbo exhaust outlet and pressurize everything in between. Then you could find leaks in the intake and exhaust. Hmmm, may give that a try.

This will probably pressurize the crankcase through the ring gaps, which is not good for the oil seals.  You also need to be careful pressurizing spaces connected to the turbo, because if the pressure releases quickly the flowing air will spin the turbo, which isn't good for the bearings if there's no oil pressure because the engine is off.