62/71/13ss vs. 66/71/13ss, why is there a difference in lag

BgBlDodge

BgBlDodge

Hates hippies
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I'm getting ready to swap my 62 wheel and housing for a 66 wheel and housing. I know the 66 will be laggier but I'm hoping that between a ported manifold, turbo/manifold blankets, and the cam, that it won't be to bad. My question is is why is it laggier being the exhaust side is still the same? I know the weight of the 66 wheel has some to do with it, is the other part because it takes longer for the 66 wheel to move the same amount of air as the 62 thus it takes longer for the engine to get the air it needs to burn the fuel?
 
Don't you have to machine the back plate of the compressor section?
Doesn't the 66mm have a larger OD?
 
fnschlaud4620 said:
Its a mass thing, object at rest wants to stay at rest. More mass, longer to get it spinning.
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so theoretically if the 2 wheels wieghed the same, would the spoolup time be the same. Or is there still extra resistance due to the size of the wheel and the air it is moving?
 
Willy91 said:
so theoretically if the 2 wheels wieghed the same, would the spoolup time be the same. Or is there still extra resistance due to the size of the wheel and the air it is moving?
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You could say that if there is more resistance, the resistance is because it is pushing more air, which would help the truck spoolup better. It is pretty much because of the mass, and the location of the mass.
 
Not sure. I would think the diameter acts somewhat like a moment arm around the shaft axis. So with the turbine side being equal and the driving force being the same there would be there should be less force avaliable to bush air with. once again I could be wrong.
 
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Zstroken you do have to machine the backing plate. I'm taking it to a turbo shop to have them machine it and swap the wheel.

I figured the weight was part of the equation but wasn't sure if there was another part I was missing.
 
Moment.

A little over simplified, but think of the exhaust wheel as a lever on the compressor wheel.

You're moving the point outward with a wider wheel.

I'd be very interested to hear how it spools. I'm going to be turbo shopping soon.
 
I'll let ya know. I'd like to try and do one thing at a time (turbo/stock mani, turbo/ported mani, turbo/ported mani/mani blanket, turbo/ported/mani blanket/turbo blanket) to see how the spool improves but I doubt that will happen due to time and money constraints. Probably gonna do the manifold and turbo at the same time and then the blankets at the same time. I think with all of that stuff the spool shouldn't be to bad.
 
I've always wondering about this too and thought about making a thread on it as well. Please let me know what you find out! It's crazy to think that 4mm can make such a drastic change in spool up time
 
Will do. I remember you and I were discussing something similar a while back. I'm hoping to have it all on by next wednesday or thursday.
 
BgBlDodge said:
I'm getting ready to swap my 62 wheel and housing for a 66 wheel and housing. I know the 66 will be laggier but I'm hoping that between a ported manifold, turbo/manifold blankets, and the cam, that it won't be to bad. My question is is why is it laggier being the exhaust side is still the same? I know the weight of the 66 wheel has some to do with it, is the other part because it takes longer for the 66 wheel to move the same amount of air as the 62 thus it takes longer for the engine to get the air it needs to burn the fuel?
Click to expand...

High Tech 71 Series
Pro Street 66

For 2nd Gen ('94-'02)

HP range 575-675 w/reasonable EGT's
1350 ft. lbs. torque 66mm Compressor, 71mm Turbine
14 Wastegated Turbine Housing
4" Downpipe required
Part Number: 2466257
I don't think that turbo is gonna work to well for you Tyler.:hehe::kick:
 
MD-LUCKY said:
Moment.

A little over simplified, but think of the exhaust wheel as a lever on the compressor wheel.
Click to expand...

We're off to a good start. The turbine turns the compressor so a 62/71 has lots of leverage. Now we use the same turbine with a bigger compressor that not only weighs more, but will be biting more air each go around. The turbine now has more work to do with less comparative leverage.
 
yoshi470 said:
I've always wondering about this too and thought about making a thread on it as well. Please let me know what you find out! It's crazy to think that 4mm can make such a drastic change in spool up time
Click to expand...

Well, even though the inducer radius is only 2mm larger - the exducer is also larger - since the extra area & mass is shifted towards the compressor's major diameter, both moment & inertia increase accordingly (closer to the point of diminishing return).
 
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