Best gear size?

[Brian F]

What is the best way to determine gear size?I was told I need around a 4.86.S-10,29.5" M/T slicks,4,000 TCI stall,engine made peak HP around 6,500.No gas (well maybe a 150 at best in future).I have 3.89 right now just to get me on the track and its killin me.

[Mike Bradley]

A few variables to consider.

We don't know for sure the MPH we're dealing with. If I was to venture a guess I would say once the bugs are worked out and a good base line is established I'd say the truck will be around 85-90 MPH. This is just a wild guess in my opinion.:helmet: So play along for a moment. A rough calculation is 90-mph, 4.88 gear, 29.5 tire, 4000 stall should equal roughly 6000 at the finish line. Change the gear ratio to say a 5.13 and you're looking at roughly 6300 out the back door. Brian be sure to factor in the power assist as well. Your combination may love being bottle fed and really pick up in mph which could lead to over RPM-ing the engine. Did you dyno the engine? If so, maybe post up the numbers to give us a better understanding of where the engine works best. I know we're comparing apples to oranges but when Jeff ran his car we always tried to run the engine a 1000 rpm above peak H/P and on the 1-2 shift not pull the engine below 500 above peak torque. Good luck and I'm sure some of the more experienced racers will post their acquired knowledge.

[Brian F]

My fastest run friday was 7.63 @ 89 mph with 1.7 60ft.Then had problems so the et went down from theer.Engine torque starts at 4,000 then carries to 5800 where it begins to drop.HP starts roughly around 6100 and carries to 6400 where it starts to drop(but would pull till 6800)only drops 8 hp from 6400 to 6800.The thing is my engine isnt really a nitrous engine.Not built for it really so nitrous would be a every once in a while thing in this engine.More of a learning engine so to speak.I mean its good rods and forged pistons,but wasnt built mainly for the gas.

[Mike Bradley]

5.13 and let it eat!

[Rick Rafferty]

I feel like your right on target, Mike, with his RPM max towards 6800.
If you wanted to keep it more towards the 6400 range then the 4.88
would be dead on. Good luck with getting the most out of your ride, Brian.

[Mike Bradley]

I think it's close. A little more data would help really pin point the "Best" ratio but I think the 4.88 or 5.13 will get him in the hunt. Brian you might talk to Aaron "Hot Rod" Brock. He campaigns a red s-10 that's close to your numbers. He's a little faster and I think he has a 4.56 gear. Don't quote me on the gear.

[Joe McCoy]

Brian, That 400 block may not like alot of spray. The walls can be a little thin on a stock block when you bore it. If I recall you used a non steel crank also so don't get too crazy turning a ton of RPMs with it. Like Mike said get a 5.13 and let that sucker eat.......LOL. Work on the set up and after you got that all maxed out if you want to spray it you'll get better results. JMO, JM

[Mike Bradley]

Joe/Brian what is the bore/stroke on this deal. If it's a 3.750 stroke like a stock 400 sbc would have been it must have a nice set of cylinder heads, intake manifold and cam package to make peak power up top. I assumed it was a 4" bore platform yielding a 350 family.

Great advice Joe on the siamese cylinder bore short comings. Stay on the conservative side Brian. We want you there all season, not sitting out due to parts breakages if we can help.:biggrin2:

[Joe McCoy]

Brian will have to give you that info Mike. A guy I know did the machine work and dynoed the motor for Brian. I think it's a 406 but don't know what rods or anything he used. Brian supplied all his parts I think so he knows what he has. RM

[Brian F]

The engine is a 406.The crank is a scat 9000 series profiled crank,manley sportsmaster profiled rods and weisco pistons,balanced.Heads are dart 215's with 2.055 intakes.Intake is holley strip dominator with 800 dbl pumper.Again the engine isnt a nitrous engine as you can see.The rods are rated at 550hp@ 8,000 rpm and the crank is close to that as well.The comp ratio is around 11.3-1 as I calculated on the keith black site with the 64 chambers.Over the winter I think Im gonna see bout slappin on a set of 49cc pro 1's to up the ratio a lil.Im gonna go for the 5.14 gear(9") and as yall say lettit eat!!!!!!!!!! I think Im gonna get another chunk with maybe 4.11's so I can play around with sum gas next year if not the end of this year just to get some experiance with it.

[Mike Bradley]

Good looking combo Brian. Your doing your homework and making good choices. With a little fine tuning here and there you should be a high 6, low 7 ride on motor. Hope to see ya at the track real soon!