There are blowoff valves and bypass valves. Most turbo cars come with bypass valves from the factory...also called overrun cutoff valves, as well as some other names, but they all do the same thing. They blow off the surge of air after the throttle closes. Theres a reason factories install these on turbo cars...I just dont know why they didnt do it on the TR's. It can save turbos if plumbed properly. A blowoff valve will cause a big rich spike after it vents, which can be a problem for a turbo car with a manual tranny, where they arent powershifting. They'll pop off the throttle between shifts, blow off all the boost, and then the turbo has to spool up again. The same goes for an auto car like ours, where you have little traction and have to feather the throttle. If you let off the throttle a little too fast or too much, the blowoff valve or bypass valve will vent all the boost and it has to spool back up. This is a case where having a good grainger valve comes in handy. The spoolup is so fast that its not a problem, even if you feather the gas a little too much and blow off all the boost. With my cobra, I ran a dual bypass setup. One before and one after the intercooler. It dumps the air back into the intake tube, so at no point is there any un-metered air being blown off causing a rich spike. Id heard nothing but stories about people being unable to make a bypass system work properly on the TR's. I set mine up the same way as my cobra (except Im running 1 valve now instead of 2) and the drivability is perfect. Theres no psh psh psh woop woop woop sound when I jump off the gas and the turbo spools right back up if I have to pop the throttle, in and out. Its totally drivable. Also, with a good bypass (you need a bypass valve, not a blowoff valve...get an overrun cutoff valve from Bosch. Preferably a 108 or 110 valve. It has a brass diaphragm instead of cheap plastic.) the bypass is open while cruising, since its open under vacuum. The whole time, the air is bypassing around the turbo, running straight from the MAF to the throttle body. Its basically an N/A motor under normal driving conditions. Then the moment you build boost, the valve closes and the turbo is back in business until you let off, it dumps the air into the intake tube (its like a muffled BOV sound) and its back to an N/A system. Its best to run dual bypasses and I intend to do this eventually. You want the vacuum source for the valve to come from the manifold, and the bypass valve itself plumbed up to the up-pipe (post IC) and the intake tube. That way you dont have a pre pressure drop (pre IC) vacuum source operating a valve which is controlling post IC pressure. And use a hard line for the vacuum source or the valve wont function properly. If the line expands and contracts (soft rubber), then the vaccum/pressure is doing more to expand/constrict the line than its doing to actuate the valve. It needs to have a solid, fast signal. Or you can just go buy a BOV and wave the rice flag.:biggrin:
Do a search on "boost bypass pics" with vadersv6 in the username part, and you'll find a thread with pics of my home-made setup.
do fender trim and handles eventually show metal underneath?
