[Craig Hendrickson]

Originally Posted by Joe37

Where would you dump the blow off to?

Usually the outlet of the wastegate is plumbed into the exhaust pipe from the turbo downpipe. Some guys route it down to open air like the old engine road draft tubes. That's noisier, but has less backpressure restriction of course.

A blow-off valve just dumps to open air since it is venting air.

[twov8sandat4]

Originally Posted by Joe37

Where would you dump the blow off to?

This is a small turbo and I suspect will spool very quickly. I don't think lag time will be any problem and with a four speed you will never feel it.

I will get some pictures of the waste gate.

Joe

I would think with a manual transmission, you would really need a blow-off valve. This will allow the compressed air an escape route when the throttle blades close between shifts. This is better than the air rushing back and hitting the compressor blades. You can either vent the blow-off valve to atmosphere, or plumb it back to the intake tract of the turbo (the compressor, not the turbine side,) which would give the turbo a slight help to recover between shifts. You can get a cheap and very effective BOV from 90-94 Mitsubishi Eclipse turbo cars. They are usually good for around 20-25 psi.

[Joe37]

Thats a good point about the throttle blade and shifting. We will look into a blow off valve. The kits didn't have one but must have worked with damage to the turbo, but I can see how it would help.

Joe

[Tom Vaught]

A Compressor By-pass Valve, as was mentioned, is very common on today's turbo cars.

It doesn't by-pass the compressor, it by-passes the air as was said in Post #42 vs having the closure of the throttle drive the Turbo into surge when the mass flow stacks up on the closed blade.

Tom Vaught

[KEN CROCIE]

Turbo Vacuum control : For standard dist. I used the 68 Firebird dual outlet control.believe it was a delco 1115411.Also 1115367 By digging deep in the parts book ,I found a dual port HEI control used on some Caddys about 1980-81.delco P/N 1973595

[Craig Hendrickson]

Originally Posted by KEN CROCIE

Turbo Vacuum control : For standard dist. I used the 68 Firebird dual outlet control.believe it was a delco 1115411.Also 1115367 By digging deep in the parts book ,I found a dual port HEI control used on some Caddys about 1980-81.delco P/N 1973595

For those who don't know, Ken Crocie is the ultimate encyclopedia of knowledge of about all parts Pontiac!

I'm privileged to have had him as General Manager of H-O Racing Specialties, Inc. and then later when he was the owner of same.

[twov8sandat4]

Originally Posted by Joe37

What this car has must be the waste gate, its mounted down under the engine on the exhaust system. I only looked at for a minute or two. It has a small hose running to it, right dead center of the top. I assume the boost pressure opens this at a set point. Is it adjustable? The whole top seemed to rotate but it could just be loose or defective.

So if I understand this right, the waste gate controls the exhaust going to the turbo. As boost comes up the waste gate opens at a pre set pressure thus dumping excess exhaust away from the turbo. This seems like a good choice as the turbo would not need to work any harder then needed.

A blow off valve is on the clean side of the turbo and acts like a pre set pop off valve. Once it opens, the turbo can still wind up due to the excess exhaust build up in the system thus over speeding the turbo shaft. Does the turbo know the blow off is open? or does it continue building boost only to have the blow off dumping the excess away? I can see how it would limit the amount to the engine, but it seems a funny way of doing it.

Thanks for the lessons,

Joe

From Tial's website:

Plumbing wastegates with manual boost controller to set boost:
http://www.tialmedia.com/documents/w..._wginstall.pdf

Plumbing Blowoff valves:
http://www.tialmedia.com/documents/w...bovinstall.pdf

Should give you some more ideas.

This is how my AWD Talon is setup, except I run a pair of wastegates instead of one.

[BruceWilkie]

Originally Posted by KEN CROCIE

Turbo Vacuum control : For standard dist. I used the 68 Firebird dual outlet control.believe it was a delco 1115411.Also 1115367 By digging deep in the parts book ,I found a dual port HEI control used on some Caddys about 1980-81.delco P/N 1973595

THANK YOU!!! I think that helps me a bunch. I used to have easy access to a bunch of old Motors Parts and Labor books...a gold mine for finding part numbers. But the old man that had them passed on and his family threw them away before they sold his shop!

I often found myself being the go to guy for hard to find or oddball parts...even when I was in the Air Force. Seems I have a knack for finding them one way or another.

Think I know someone not far from me who just may have one of those(more maybe?) cannisters now that I have some numbers...

Thanks again. I'll let you know what I turn up.

[CROCIE JR]

If you find a extra 2 port 68 vac. control, let me or Ken Crocie (Dad) know. This will help our latest project. Pure simplicity.

[CROCIE JR]

Not sure if I understood a previous post. Instaling a BOV will keep the turbo speed in check, not increase it. If air is moving the turbo is doing "work." With no BOV the turbo can overspeed when airflow stops, like throttle shut. Put your hand over a running shop vac inlet and listen to the motor speed up. Correct me if I'm wrong here.

[meanone]

Originally Posted by CROCIE JR

Not sure if I understood a previous post. Instaling a BOV will keep the turbo speed in check, not increase it. If air is moving the turbo is doing "work." With no BOV the turbo can overspeed when airflow stops, like throttle shut. Put your hand over a running shop vac inlet and listen to the motor speed up. Correct me if I'm wrong here.

The wastegate is used to control turbo speed, not the bov. A portion of the exhaust mass and pressure is bypassed around the turbine so that only enough mass and pressure enters the turbine to spin the turbo to a speed wich produces a desired boost level. If a wastegate wasn't used, and 100% of the exhaust mass was allowed to enter the turbine, the turbo would overspin and there would be no control over the boost level.
If there wasn't a bov in the system the turbo could be damaged when the throttle closes. When the throttle closes the air stacks up and pressure is sent back toward the compressor wheel. The wheel could be stopped and started again very rapidly by this, and could damage the wheel or even break the shaft. The turbo does not speed up when the throttle is closed and there is no bov installed. The reason that the the turbo could possibly speed up when the bov is opened is because of pressure on each side of the turbo. Pressure and mass is driving the turbine wheel wich is driving the compressor wheel. The compressor wheel is pushing air into the engine when the throttle blade is open. When you shut the throttle blade and the bov opens there is no more pressure in the charge pipe, but there could be some pressure in the turbine side. Think of it as a tug-a-war. Two guys are pulling on the rope and one guy lets go letting the other guy go flying. If everything is sized correctly and a w/g is used the turbo shouldn't overspeed when the bov opens because as the throttle closes exhaust mass decreases putting little pressure on the turbine wheel. This is how I understand it. I hope this helps. Ronnie

[CROCIE JR]

My BOV post was a throttle shut scenario, just after WOT.

[Joe37]

Moving forward with the project, I tore into the engine for a quick check. Turns out water had gotten to the cylinders when the car was being wet sanded during its paint job. The block and pistons were damaged, heads ok. The block is .030" over now with a TRW forged piston. I suspect it will have to .060" to clean up, it might at .040" but unlikely. We will need new pistons and are wondering if we should lower the compression. Summit sells Icon forged pistons that are dished +14 cc, the TRW / Sealed Power are a +6cc piston. Will that make much difference? Remember, this is a restoration project, 6-8 psi boost only and no racing. I know Ross makes great pistons but may be out of the budget, we are still in the planning / recovery mode.

It also has the exhaust crossovers in the head filled. I believe this should come out to help cold starts and atomize the fuel better, but being a turbo engine, will it matter?

One more thing, the engine has a solid harmonic balancer install. When I say solid, I mean solid, no moving parts! I can not see any point in this, who was selling them back in the late '90s when this engine was built and why?

Joe

[Tom Vaught]

Originally Posted by meanone

The wastegate is used to control turbo speed, not the bov. A portion of the exhaust mass and pressure is bypassed around the turbine so that only enough mass and pressure enters the turbine to spin the turbo to a speed wich produces a desired boost level. If a wastegate wasn't used, and 100% of the exhaust mass was allowed to enter the turbine, the turbo would overspin and there would be no control over the boost level.
If there wasn't a bov in the system the turbo could be damaged when the throttle closes. When the throttle closes the air stacks up and pressure is sent back toward the compressor wheel. The wheel could be stopped and started again very rapidly by this, and could damage the wheel or even break the shaft. The turbo does not speed up when the throttle is closed and there is no bov installed. The reason that the the turbo could possibly speed up when the bov is opened is because of pressure on each side of the turbo. Pressure and mass is driving the turbine wheel wich is driving the compressor wheel. The compressor wheel is pushing air into the engine when the throttle blade is open. When you shut the throttle blade and the bov opens there is no more pressure in the charge pipe, but there could be some pressure in the turbine side. Think of it as a tug-a-war. Two guys are pulling on the rope and one guy lets go letting the other guy go flying. If everything is sized correctly and a w/g is used the turbo shouldn't overspeed when the bov opens because as the throttle closes exhaust mass decreases putting little pressure on the turbine wheel. This is how I understand it. I hope this helps. Ronnie

When the throttle slams shut, I agree with Ronnie, that the interrupted flow sends the compressor into massive surge without a CBV (compressor BY-PASS valve), a BOV (Blow-off valve), or a CRV (Compressor Recirculation Valve). CRVs are used on EFI systems with Mass Air Meters.

You can also (as Ken C jr mentioned) set up your system to where you can run a oversized Turbo and keep it out of surge by having the BOV open (adding mass flow to the system but wasting it) until the engine goes into WOT and then BOV closes and the turbo supplies the larger air flow to the engine.

Tom Vaught

[meanone]

Originally Posted by Tom Vaught

When the throttle slams shut, I agree with Ronnie, that the interrupted flow sends the compressor into massive surge without a CBV (compressor BY-PASS valve), a BOV (Blow-off valve), or a CRV (Compressor Recirculation Valve). CRVs are used on EFI systems with Mass Air Meters.

You can also (as Ken C jr mentioned) set up your system to where you can run a oversized Turbo and keep it out of surge by having the BOV open (adding mass flow to the system but wasting it) until the engine goes into WOT and then BOV closes and the turbo supplies the larger air flow to the engine.

Tom Vaught

I 100% agree with you Tom. My buddie had his car set up like that.It was a stickshift and he wanted to keep the turbo speed up to prevent lag between shifts. I was trying to help Ken Jr. understand what happens to the turbo when the throttle closes, and why the bov is used. He was stating that the turbo would overspeed from shutting the throttle without a bov, and used the hand over a shop vac as an example. That would make the engine the shop vac and the turbo it's motor in his example. Ronnie

[Craig Hendrickson]

Originally Posted by Joe37

Moving forward with the project, I tore into the engine for a quick check. Turns out water had gotten to the cylinders when the car was being wet sanded during its paint job. The block and pistons were damaged, heads ok. The block is .030" over now with a TRW forged piston. I suspect it will have to .060" to clean up, it might at .040" but unlikely. We will need new pistons and are wondering if we should lower the compression. Summit sells Icon forged pistons that are dished +14 cc, the TRW / Sealed Power are a +6cc piston. Will that make much difference? Remember, this is a restoration project, 6-8 psi boost only and no racing. I know Ross makes great pistons but may be out of the budget, we are still in the planning / recovery mode.

The W72 engine has a CR of 8.1:1, so that will be fine with the TurboForce. I used TRW flat tops in my 1976 Firebird T-F Revival with a 73 400 engine.

It also has the exhaust crossovers in the head filled. I believe this should come out to help cold starts and atomize the fuel better, but being a turbo engine, will it matter?

If not too much trouble, remove the exhaust crossover fill.

One more thing, the engine has a solid harmonic balancer install. When I say solid, I mean solid, no moving parts! I can not see any point in this, who was selling them back in the late '90s when this engine was built and why?

I never saw one much less used one. As your dad, Jim says, "throw it as far as you can!" LOL

[Tom Vaught]

Originally Posted by Craig Hendrickson

I never saw one much less used one. As your dad, Jim says, "throw it as far as you can!" LOL

Joe37, when you throw the solid balancer away, throw it in a box and send it to me.
I can use it, in another project I am working on, as a register for a degree wheel.

Send me a PM and I will send you an address! LOL!

Tom Vaught

ps I would never use one of those things on a RUNNING ENGINE!

[KEN CROCIE]

TV & CH : you old guys are sure forgetful! Remember Pontiac used solid,no damper, hubs in '76-'77.Those engines used a bolt on timing tab as well. Maybe this is what joe has. I wouldn't use it either. The '67 and earlier engines used a solid hub with a bolt on dampener. maybe one of those found it's way to joes engine.

[Joe37]

The balancer appears to be aftermarket. It was black at one time but now rusted. I don't believe its a Pontiac hub as it matches the originals in size and diameter. My local machine shop had never seen one either and also said to toss it. I can send you a picture if you wish to post it or see it.

TRW pistons it is and some digging on the heads. I believe they used Hard Block in the cross over's, it sure reminds me of concrete and flakes out like concrete.

The camshaft is not marked so I need to degree it and see what it is. A reproduction 068 cam should work, shouldn't it? Can we get a original cam for this engine? or how about the HCO1 cam from SD Performance, I have used it with really good results. The Summit 2801 cam is also a decent street cam.

Joe

[Craig Hendrickson]

Originally Posted by Joe37

The camshaft is not marked so I need to degree it and see what it is. A reproduction 068 cam should work, shouldn't it? Can we get a original cam for this engine? or how about the HCO1 cam from SD Performance, I have used it with really good results. The Summit 2801 cam is also a decent street cam.

FWIW, I used a real H-O Racing HC-01D I got from Ken Crocie in my 1973 400 in my 1976 Firebird T-F Revival. It sounds great out the exhaust, idles good, has good vacuum and runs awesome behind a TH350 and 2200 stall converter. The Summit K2801 is slightly smaller than the HC-01D, so it should work nearly as well. I had one in my 1979 W72 Trans Am (4-speed) and it fit my criteria. The repo 068 is an older profile and would not be my choice.