Small Block VS Big Block Gearing?

[SquidBonez]

If I wanted to swap from a small block to a big block (assuming identical kart with the same tire size), should I increase the gearing? Small blocks have less power/torque than big blocks but rev way higher, while vice versa for big blocks. If I swapped over a big block and kept the same gearing I had when it was a small block, it would accelerate faster but have a lower top speed due to less RPMs. That being said, can big blocks be geared higher since they are more powerful/torquey but rev lower?

 

[Denny]

I want you to explain why the big blocks can’t rev as high. That is the kind of misinformation that starts wars.

 

[madprofessor]

I think of a Predator 420 as a big block, a 212 as a small block. The 420 makes about 20 ft. lbs. of torque, while the 212 is only about 8 ft. lbs.
Those numbers tell me a change should indeed be made, but not a ratio change. The change should be from #35 chain and sprockets to something like #40/#41 etc. New sprockets yes, but not necessarily with different ratios.

 

[SquidBonez]

I want you to explain why the big blocks can’t rev as high. That is the kind of misinformation that starts wars.

If you throw enough money at an engine sure, but typically they don't. More rotating mass.

 

[SquidBonez]

I think of a Predator 420 as a big block, a 212 as a small block. The 420 makes about 20 ft. lbs. of torque, while the 212 is only about 8 ft. lbs.
Those numbers tell me a change should indeed be made, but not a ratio change. The change should be from #35 chain and sprockets to something like #40/#41 etc. New sprockets yes, but not necessarily with different ratios.

I already run #420 chain on my 212. Even then I get a decent bit of chain stretch that I have to tighten out. I'm talking about different ratios.

 

[Denny]

There is a big difference between reving to make power and having it already on hand. With a smaller engine you need to increase rpm to make the power a larger engine makes naturally. Gearing should be used to optimize the power band of the engine.

 

[SquidBonez]

There is a big difference between reving to make power and having it already on hand. With a smaller engine you need to increase rpm to make the power a larger engine makes naturally. Gearing should be used to optimize the power band of the engine.

Well I would argue gearing is more about the tradeoff of top speed vs torque. If I were swapping to a big block I'd want more of the former, and get the latter as a bonus of using a larger engine.

 

[landuse]

Done they all rev to 3600rpm stock out the box? No matter the size

 

[karl]

Max rated speed listed on hazard fraught's site says 3600rpm.

Does not matter if a big single or twin, most industrial motors are rated for 3600rpm continous.

If the governer is set low, only a throttle stop screw limits the travel of the throttle lever, easy to adjust.

I would look into going another tooth on the driven/ jackshaft sprocket.

 

[SquidBonez]

Done they all rev to 3600rpm stock out the box? No matter the size

Yeah, if you keep it with the governor in it. I'm well past the point of stock engines lol

 

[madprofessor]

What's needed if doing your ratio change? If just a split sprocket on the axle, I'd jump right away for $15 or less. Unless shipping is another $15.
I wouldn't be able to poop a diamond in 3 days after sticking a lump of coal up the dump chute, but pretty tight with the wad anyway. I'd wait to see how it goes, doing some good testing, before getting off the wallet for any other way to make the change, spending only afterward if necessary or desirable.

 

[ThunderKart79]

The big difference in gearing is a small block driven clutches are typically 6” while big blocks are 7” up to 8.5” the TC,s work just like gears the larger the back one is the lower the gear ratio will be. On my mannco express magnum the original Subaru ex17 would push my two son’s and I to 35 mph same set up with a tilly 212ee 40 mph but it would top out a lot faster. Now I have a 460 that will turn 7500 with champion 1:1 rockers and I am giving the monster gage 1:3 rollers larger valves and going from a 38mm flat slide to a 44 super BN carb. I promise it is an illness if I own it I have to modify it.

 

[ThunderKart79]

The big difference in gearing is a small block driven clutches are typically 6” while big blocks are 7” up to 8.5” the TC,s work just like gears the larger the back one is the lower the gear ratio will be. On my mannco express magnum the original Subaru ex17 would push my two son’s and I to 35 mph same set up with a tilly 212ee 40 mph but it would top out a lot faster. Now I have a 460 that will turn 7500 with champion 1:1 rockers and I am giving the monster gage 1:3 rollers larger valves and going from a 38mm flat slide to a 44 super BN carb. I promise it is an illness if I own it I have to modify it.

I have not checked the speed with the BB yet I am also installing rack n pinion steering because the cart does a nasty lil speed wobble when you let out of it. Yes the 460 is faster but it pushes out more than 3x the ponies and I would lay a pretty penny down it cranks out at least 40ft/lbs of tourqe from a dead stop it almost pulls the front wheels up I am switching from a 40 series to a 44 magnum which has a lot more tuning potential. Cheaply out Pauls Karts if you want to learn how to make power. Paul has the world record with a 476 or so 470 something that pushed 65 horsepower naturally aspirated no nitrous no boost he turned that BB over 9000. Get a notebook ready because there is not much that he keeps top secret he explains how to design your build with a calculator I would have paid good money for the info he put out on YouTube.

 

[madprofessor]

Speaking of calculating, 1:3 rollers? Do you mean changing 1:1 ratio rockers to 1.3:1 ratio roller rockers?
On the calculating, when someone is making that kind of change, how do you go about figuring for a different length of the pushrods?

 

[SquidBonez]

I have not checked the speed with the BB yet I am also installing rack n pinion steering because the cart does a nasty lil speed wobble when you let out of it. Yes the 460 is faster but it pushes out more than 3x the ponies and I would lay a pretty penny down it cranks out at least 40ft/lbs of tourqe from a dead stop it almost pulls the front wheels up I am switching from a 40 series to a 44 magnum which has a lot more tuning potential. Cheaply out Pauls Karts if you want to learn how to make power. Paul has the world record with a 476 or so 470 something that pushed 65 horsepower naturally aspirated no nitrous no boost he turned that BB over 9000. Get a notebook ready because there is not much that he keeps top secret he explains how to design your build with a calculator I would have paid good money for the info he put out on YouTube.

Yeah I don't think I'd ever be going quite that far with a big block lol. Probably stage 2 at most. Paul has a lot of good info.

 

[ThunderKart79]

Speaking of calculating, 1:3 rollers? Do you mean changing 1:1 ratio rockers to 1.3:1 ratio roller rockers?
On the calculating, when someone is making that kind of change, how do you go about figuring for a different length of the pushrods?

Yes 1:3:1 I have pushrod length checkers they are adjustable pushrods. When I get my rockers I will buy a set of cut to length pushrods by using the adjustable pushrods length checker you can make sure your geometry is correct if you are going to turn any engine up you want to make sure your angles are correct. A gx390 head tends to run hot especially when it is on top of a 92.75mm bore with 68mm of stroke.

 

[ThunderKart79]

Yeah I don't think I'd ever be going quite that far with a big block lol. Probably stage 2 at most. Paul has a lot of good info.

I bought my BB from Vegas carts it was a diy 460 I got it with shipping for like $490 I paid extra for champion rockers and and a bored out carburetor. It has a 10 bolt block. Now I bought a Honda crankshaft that NR cut and welded to 68 mm which is also has been balanced and a Honda head with small ports which they milled .0050 off. Then from bullfrog I bought a billet 92.75 piston a one of there 4.62 billet rods. Then from Pauls I bought an ARC billet sidecover and a billet intake manifold. From NR I also bought there 280 race cam if I remember right it was the 2 nd option anyway I got the one that pulls hard from 2000 to 7200 RPMs. Now all I need is another block some gaskets and I will have enough parts to build another one. And my son has a Coleman mini bike with the 212 tilly race block with a flat top piston billet rod .265 cam with a tilly hemi head I told my son e very good dad needs to give there sons a hemi.

 

[madprofessor]

Not able to see it so well in my head just by the numbers, but enough to tell that's a motor anxious to run.
And any cam that pulls hard across that broad a range is what I'd hope for myself.
So, the adjustable pushrod checkers, do they just screw in/out to your happiness and then you measure them to get a set cut?

 

[ThunderKart79]

Yes that is exactly how they work also i have been told that a 1.3.1 ratio rocker adds 30percent lift and the 1.2.1 rockers add 20 percent lift so when I get mine I am going see if those numbers are accurate once I get the adjustable pushrods to the right length I am going to measure and see if it is 30 percent shorter

 

[ThunderKart79]

Also I buy the cut to length pushrods they come with one end pressed on and once you cut them to your desired length if you don’t have a press you can take a lifter and hammer the other end on you just need to make sure you have the end straight when you start to tap it down