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valve springs in a turbo build
https://slantsix.org/forum/viewtopic.php?t=47927		 Page 1 of 1
Author:  Valleyant [ Thu Feb 16, 2012 8:30 pm ]
Post subject:  valve springs in a turbo build
I see the 340 springs are popular for this but I am curious......can I compare the valve springs open and closed pressures from brand x turbo engines or even the 2.2 chrysler turbo to see if the stock slant six springs are adequate? so far I have compared to the 2.2 chrysler turbo, mustang svo 2.3 turbo, and GN 3.8 turbo and the stock slants specs are better than all of these with exception to the Buick and those numbers are really close. I am not building a high boost slant, maybe 15psi max with intercooler about the max these comparison cars ever saw stock, with the Buick and Ford seeing about this much at the pinnacle of their runs. Any info appreciated and thanks....Cylinder head is at the machine shop now and rebuild is in progress.
Author:  1974duster kev [ Thu Feb 16, 2012 9:09 pm ]
Post subject: 
I use the erson springs with the erson cam kit

Kev
Author:  Valleyant [ Thu Feb 16, 2012 9:38 pm ]
Post subject: 
Quote:
I use the erson springs with the erson cam kit

Kev
Nice, whats the specs on the springs you have?
Author:  billdedman [ Fri Feb 17, 2012 4:39 pm ]
Post subject: 
This is our first turbo build, so we're not very knowledgeable about the necessary spring pressures. We are starting out with 340 outters and some fairly weak inner springs that will yield abour 115 pounds on the seat and 310 pounds open (.500".)

Hopefully, that will be enough to prevent valve float up to our red line of 5,500, with 20 pounds of boost.

Any ideas or advice?
Author:  Dart270 [ Fri Feb 17, 2012 10:12 pm ]
Post subject: 
Sounds like those should work for float resistance, Bill, but make sure they don't coil bind at that lift, or that the keepers hit the valve seals or guide tops.

I don't see why a turbo should need significantly different spring pressures than a NA motor. 20 psi on a 1.5 sq in intake valve area is 30 lbs at most.

Lou
Author:  Valleyant [ Sat Feb 18, 2012 2:30 am ]
Post subject: 
I think I am going to stick with some new stock valve springs and see how they work....can always change them out if problems are encountered. Like I said its gonna be a 15psi max turbo system since the engine is all stock inside. Later with a dedicated turbo engine build I will add all the good bits to handle higher boost.
Author:  billdedman [ Sat Feb 18, 2012 5:41 am ]
Post subject: 
Lou, our intake valves are 1.75"-diameter.

1.75" X .5 = .875"
.875" X .875" = .7656"

.7656 X 3.1416 = 2.40 square inches (area)

2.40 X 20 (boost) = 48.10 pounds

Is there something wrong with my math? pi X R squaared times 3.1416 = area????

Maybe I need to subtract the valve stem area from this figure????

Help! LOL!
Author:  Dart270 [ Sat Feb 18, 2012 8:41 am ]
Post subject: 
I would say you need to subtract the stem area, and only use the area inside the inner edge of the seat, since that's what the pressure is acting on. So, a 1.75" valve is around 1.5" diameter around the inner edge of the seat.

Lou
Author:  Shaker223 [ Sat Feb 18, 2012 10:41 am ]
Post subject: 
Quote:
Sounds like those should work for float resistance, Bill, but make sure they don't coil bind at that lift, or that the keepers hit the valve seals or guide tops.

I don't see why a turbo should need significantly different spring pressures than a NA motor. 20 psi on a 1.5 sq in intake valve area is 30 lbs at most.

Lou
Exhaust back pressure is usually the issue. It can be 2 or three times intake pressures.
Author:  Dart270 [ Sat Feb 18, 2012 2:53 pm ]
Post subject: 
Interesting. I was not thinking about that. So you are looking at maybe 50-60 lbs on the exh valve (smaller area, but higher pressures). With the usually mild turbo cams, I still don't think a big spring is needed, but I could be wrong.

Lou
Author:  MJF [ Sat Feb 18, 2012 3:03 pm ]
Post subject: 
You have really tiny turbo if exhaust manifold pressure is that high :shock:
Author:  billdedman [ Sat Feb 18, 2012 3:30 pm ]
Post subject: 
Okay, here are some revised figures for intake valve area:
Valve stem @ .307" -diameter = .107 square inches.

Intake valve diameter at the inner face of the seat: 1.5"-diameter = 1.767 square inches, minus .107 square inches for the stem area = 1.66 square inches.

20 pounds of boost X 1.66 = 33.2 pounds of valve spring pressure needed to overcome the boost pressure.

Looks like you were VERY close on your estimate, Lou!!!

Some of these guys actually run boost pressures in the high twenties, though, and we plan on taking ours over 30 pounds, if it doesn't blow itself into a pile of scrap metal before then...

We'll see....talk's cheap... LOL!
Author:  Shaker223 [ Sat Feb 18, 2012 4:37 pm ]
Post subject: 
Quote:
You have really tiny turbo if exhaust manifold pressure is that high :shock:
Not necessarily, it could be an inefficient exhaust system. Efficient systems can be close to a 1:1 ratio but most are not.
Author:  Dart270 [ Sat Feb 18, 2012 8:23 pm ]
Post subject: 
This is cool. I am learning some things. Thanks, guys.

Lou
Author:  Shaker223 [ Sun Feb 19, 2012 6:21 am ]
Post subject: 
Weld in a bung and use an oil pressure gauge with copper tubing to measure the back pressure.
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