Choosing pressure relief, wastegate vs blowoff etc?? - Lateral-g Forums

Slick · #1 08-31-2006, 09:20 AM

Please exuse me if this has been discussed before, I couldn't find anything with a few searches. I've been going around in circles with a friend discussing the design of a TT system, neither of us are to sure of the pressure regulation methods (I guess that's a good way to word it). I see systems with wastegates on the hot side and blowoffs on the pressure side....some with just wastegates and some with just blowoffs. I guess my main question is what are the theories behind when to use which? I've built enough cars/stuff to know it's all about balancing tradeoffs so I'm more interested in the thoeries/ reasoning to using each type than having someone tell me "just use this"...if it doesn't make sense to me I can't get the check book out if you know what I mean

For some background...my friend is building a TT Camaro and is all about drag racing speed so his reasoning comes from that background, he's using wastegates and pressure side blowoff (alright it's a Banks system which varys a bit but basically pressure side blowoff). My take is that he's trying to get every last bit of power out so he wants to keep both pressure sides as even as possible which makes sense to me. My build is honestly more show than go (not that is won't be driven but I won't be trying to shave a .1 off my 1/4 mile time). My theory is forget the wastegates (yes I'm trying to be cheap

) and just use blowoffs, might not be perfect for drag racing but is there an issue?

Enough rambling, lets here the real reasons from people that know

Thanks!!

**camcojb** · #2 08-31-2006, 09:38 AM

Quote:

Originally Posted by Slick

Please exuse me if this has been discussed before, I couldn't find anything with a few searches. I've been going around in circles with a friend discussing the design of a TT system, neither of us are to sure of the pressure regulation methods (I guess that's a good way to word it). I see systems with wastegates on the hot side and blowoffs on the pressure side....some with just wastegates and some with just blowoffs. I guess my main question is what are the theories behind when to use which? I've built enough cars/stuff to know it's all about balancing tradeoffs so I'm more interested in the thoeries/ reasoning to using each type than having someone tell me "just use this"...if it doesn't make sense to me I can't get the check book out if you know what I mean

For some background...my friend is building a TT Camaro and is all about drag racing speed so his reasoning comes from that background, he's using wastegates and pressure side blowoff (alright it's a Banks system which varys a bit but basically pressure side blowoff). My take is that he's trying to get every last bit of power out so he wants to keep both pressure sides as even as possible which makes sense to me. My build is honestly more show than go (not that is won't be driven but I won't be trying to shave a .1 off my 1/4 mile time). My theory is forget the wastegates (yes I'm trying to be cheap

) and just use blowoffs, might not be perfect for drag racing but is there an issue?

Enough rambling, lets here the real reasons from people that know

Thanks!!

The wastegates control the exhaust pressure to regulate the boost made. They will open at a set pressure and vent excess exhaust flow (pressure) out the exhaust, bypassing the turbos. No wastegates, no boost control. A blowoff on the pressure (intake) side is for when being in boost and then snapping the throttle shut, it opens and lets the boost out to prevent damage to the turbo impellers and throttle blades. It is not used to control boost.

They each have a separate purpose and both should be run. A blowoff on the intake will not regulate boost so if you run that and no wastegates you have no way to control boost. It opens under vacuum, not boost. I guess there's something that could be plumbed into the intake to vent at a preset boost, but it better be pretty big if you're not regulating boost with a wastegate.

Do it right, run both.

Slick · #3 08-31-2006, 09:56 AM

Thanks, that was exactly as I had always thought, just seems I've seen some lately with no wastegates so it got me thinking how they were doing it. We were also wondering if your not using wastegates...there is going to be more pressure on the exhaust side than the intake side...how do you even get air in the cylinder?

How about sizing on wastegates...say 38mm vs 44mm etc? How do you size them? Blowoff..I haven't even began to look at yet so I don't know what to ask

Thanks

nitrorocket · #4 08-31-2006, 10:10 AM

Cam pretty much summed it up!

Also. You MUST run a Wategate, you do not have a choice here. Every turbo system has one, you just may have been hidden in the systems you have seen. some are built right into the turbo.
For your car, the BIGGER the wastegate, the LOWER you can turn the boost down. If the turbos are sized properly, and you have a large enough wastegate, you can just about turn the boost OFF.
The wastegate bypasses exhaust around the turbo. The more open the wastegate is, the less exhaust actually goes through the turbo to spin the turbo, the less max boost you have. You cannot go to large on the wastegates for a street car.

A BOV will drastically increase the life of your turbo. You will eventually tear the bearings out of the turbo without a BOV.

Good luck, Both Cam and I have good experience with turbos, so feel free to post away!

Slick · #5 08-31-2006, 10:34 AM

More good info,thanks. Like you said maybe I'm just missing the wastegates on some of these cars...one that had me thinking the other day and probably why I just posted to ask this stuff was Scott's (XcYZ) posting the other day of his georgeous set that Nelson just did for him, where are the wastegates in there? https://lateral-g.net/forums/showthread.php4?t=5696

Damn big wastegates....Tial 44mm the gates of choice nowdays? I'd rather jump on the 38mm...but you know how it goes...I'll probably just buck up and reach deeper...

**camcojb** · #6 08-31-2006, 11:03 AM

Quote:

Originally Posted by Slick

More good info,thanks. Like you said maybe I'm just missing the wastegates on some of these cars...one that had me thinking the other day and probably why I just posted to ask this stuff was Scott's (XcYZ) posting the other day of his georgeous set that Nelson just did for him, where are the wastegates in there? https://lateral-g.net/forums/showthread.php4?t=5696

Damn big wastegates....Tial 44mm the gates of choice nowdays? I'd rather jump on the 38mm...but you know how it goes...I'll probably just buck up and reach deeper...

There will be an adaptor between the header and the turbo where the wastegate will mount. He just doesn't have that yet.

Jody

nitrorocket · #7 08-31-2006, 11:05 AM

Scott does not have the wastegates or the piping installed yet. The 44 mm will allow you to run lower boost at WOT if you want to.

You can see where I installed mine. They must be between the motor and the turbo on hot side tubing.

https://lateral-g.net/members/tt71chevelle/

**XcYZ** · #8 08-31-2006, 11:18 AM

Like Jody noted, I haven't got that far yet. I have too many irons in the fire. lol

Slick · #9 08-31-2006, 11:22 AM

Thanks, that makes more sense now. So Scott, yours will be a bolt on adapter "block" between the turbo flange and header flange? That's actually how we were thinking of doing mine as I have some headers I don't want to hack into unless I have to.

So what's the theory on blowoff valve sizing?

Thanks again, I can never have enough informed info.

nitrorocket · #10 08-31-2006, 11:31 AM

BOV, Again, bigger is better. Some guys run 2! The bigger the turbos you have the bigger the bov you need. You would need to get rid of more air quickly. Alot of people like the Tial 50 mm. Seems a little on the small side for me, When I let off at full boost it takes about 2 seconds for all the air to escape. Ball bearing turbos keep the turbine spinning longer creating even more air. I did not notice this with my slightly smaller non BB turbos.