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Old 11-08-2019, 04:40 PM
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ErikW ErikW is offline
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Default Stroke choice for turbo motor

So, I am building a twin turbo motor for 2020 Drag Week. I have a 1970 400 block bored 30 over with Program center caps, arp studs. I have, on order from Dave at SD Performance, a set of 95cc 325cfm Edelbrock round ports with a few turbo tricks including T washers.
My issue is rotating assembly choice. I have a very nice Crower billet 4.25 stroke crank and 6.800 Oliver rods on hand but from what I've been reading, everyone is suggesting a shorter stroke.
So what would be the disadvantage to me using the 4.25 combo, and the advantages to selling it and going with say a 4.0 stroke? Thanks for any input.

Erik

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1964 GTO
501, Edelbrock Heads NA, 3460 lbs.
9.76 @ 137mph
1971 Trans Am Lucy Blue, 11.56 @ 115
1966 LeMans. 462, SD prepped Kaufman D ports. 11.90 @ 112
1976 Trans Am twin turbo 462, SD Edelbrock heads 8.50@159
2009 G8 GT
  #2  
Old 11-08-2019, 06:14 PM
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Tom Vaught Tom Vaught is offline
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I would run it with the parts you have....

Good parts are worth more from the durability side vs using a Scat Forged crank that is 4.00 inch stroke. Drag Week you want durability, especially with a Factory Block (even with splayed caps). You would want to spend your time getting every thing ready for the event vs worrying about the perfect combination the first year you run the event.

Tom V.

Kelvin Poe has run the event (as has Richard with the 65 GTO (from Canada)).
I would try to talk to BOTH of them before you get very far in your efforts.
Richard has run a boosted 65 GTO for several years now.

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Last edited by Tom Vaught; 11-08-2019 at 06:22 PM.
  #3  
Old 11-08-2019, 07:31 PM
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Isn't there also a member here with a turbo poncho equipped sunbeam tiger? I believe he runs in the 8.80's and does so reliably. Might be worth looking at his setup as well.

For the life of me I can't remember his username. I think 1320 on YouTube did a short video on the car from drag week a couple years back.

Edit. Here's the vid. https://www.youtube.com/watch?v=-GVw1ga0ZWU

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Old 11-09-2019, 08:41 AM
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The only downside I see to running the long stroke crank is the extra side thrust loading that it will put on a factory block, that may or may not be an issue over time. A shorter stroke crank could have a better R/S ratio/ better piston compression height etc. But you already have a nice quality Crower crank - certainly better than any Scat/Ohio forging.

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Old 11-09-2019, 11:20 AM
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Yup, that's my dilemma. I need to order a custom set of pistons and can't decide on stroke. Probably just going to use the Crower/Oliver combo.

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1964 GTO
501, Edelbrock Heads NA, 3460 lbs.
9.76 @ 137mph
1971 Trans Am Lucy Blue, 11.56 @ 115
1966 LeMans. 462, SD prepped Kaufman D ports. 11.90 @ 112
1976 Trans Am twin turbo 462, SD Edelbrock heads 8.50@159
2009 G8 GT
  #6  
Old 11-09-2019, 05:13 PM
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Depends on what level of power you're looking for...

Street driven car short stroke . Track car, either but i guess the long stroke in the end wins if you can get it all to the ground ..

Disadvantage would be extra torque. More of a challenge with traction .

Going from a 4.00 to 4.25 its not woth it because you have a real good crankshaft already ..

If you went to a 3.75 id say it would be worth it..

That would be my choice..

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  #7  
Old 11-09-2019, 05:16 PM
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Quote:
Originally Posted by JLMounce View Post
Isn't there also a member here with a turbo poncho equipped sunbeam tiger? I believe he runs in the 8.80's and does so reliably. Might be worth looking at his setup as well.

For the life of me I can't remember his username. I think 1320 on YouTube did a short video on the car from drag week a couple years back.

Edit. Here's the vid. https://www.youtube.com/watch?v=-GVw1ga0ZWU
I met him this summer at Norwalk . Very nice guy. Cool car...

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  #8  
Old 11-09-2019, 05:34 PM
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Run what you have. Traction may or may not be an issue depending on your rear suspension set-up. If you need traction help your converter and axle ratio become a very important choice. I have a 462 with a tight converter and a 3.08 gear. With drag radials this works well for me on the street.

  #9  
Old 11-09-2019, 05:45 PM
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RUDOLFSSON RUDOLFSSON is offline
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4.25 every single time.

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Old 11-09-2019, 08:35 PM
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Thanks guys. 4.25 for the win. Appreciate the responses. I'll post more as the build progresses.

Erik

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1964 GTO
501, Edelbrock Heads NA, 3460 lbs.
9.76 @ 137mph
1971 Trans Am Lucy Blue, 11.56 @ 115
1966 LeMans. 462, SD prepped Kaufman D ports. 11.90 @ 112
1976 Trans Am twin turbo 462, SD Edelbrock heads 8.50@159
2009 G8 GT
  #11  
Old 11-09-2019, 10:25 PM
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v869tr6 v869tr6 is offline
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My 4.5" stroke combo has been working well for over 10 years, my new combo will be a 4.25 stroke. I say run your 4.25" stroke.

  #12  
Old 11-11-2019, 12:47 AM
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JSPONT JSPONT is offline
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4.25 here, just had it apart, 3 years of street stuff, 8-9k miles, bearings looked new.

  #13  
Old 11-11-2019, 08:28 AM
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GTOGEORGE GTOGEORGE is offline
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I don't have a turbo BUT I've always liked the GRUNT of a 4.5" stroke engine!


GTO george

  #14  
Old 11-11-2019, 03:27 PM
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I've got one of them in my N/A 64 GTO. She'a a torque monster.

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1964 GTO
501, Edelbrock Heads NA, 3460 lbs.
9.76 @ 137mph
1971 Trans Am Lucy Blue, 11.56 @ 115
1966 LeMans. 462, SD prepped Kaufman D ports. 11.90 @ 112
1976 Trans Am twin turbo 462, SD Edelbrock heads 8.50@159
2009 G8 GT
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