What’s the best main sprocket size for drag racing ?

[flatheadDave]

In your opinion what would the best sprocket size be for a WL flathead? Considering I’m 220 lbs I’m not going to get off the line too fast I suppose. I assume the length of the track is considerable in considering. Is a 17 sprocket too small? Interested to hear your thoughts

[RooDog]

Check your RPM through the traps. You should just have passed your peak horsepower RPM at the finish line.
You do have a tachometer, now, don't ya'?
The point is not to run outta power before the end, nor to still be revving there either....
Now get a hand full of sprockets and dial that engine speed in...
....RooDog....

[kitabel]

What speed do you expect to make in the quarter?
What sprocket do you have now?
Completely stock WL with iron or aluminum heads?
Carburetor?

[Andygears]

Are you racing on a strip quarter mile, or eighth? Pavement, dirt or sand ( like TROG) ? Tire type?
Are you plannng to hook up the rear tire quickly (lower gear) or spin & go( taller gear) ?

Andygears

[RooDog]

Thank you, Andy.
So, this question is like "What's the best ice cream?"
More input is needed.....

[flatheadDave]

Ok here’s some more details

1/8 mile
My carb is an M88 linkert
Firestone AND tires
I’m using a magneto
Aluminum heads
I have a 32 sprocket on now
I’m not sure what time or speed
Stock WL but there’s hot cams and also race valve springs

[kitabel]

The 32 is much too big.
What cams, springs?

[flatheadDave]

I know that a 32 sprocket is too big, I’m using these race cams that this guy makes that I bought them on eBay, I’ve used them a few times and they’re great, I couldn’t give you the specs, but trust me they’re an improvement. Here are the options below from 45 Restoration, I’m just unsure of which number to try, thanks

[RooDog]

Drag racing, like all racing, is a business of cut & try. You ain't gonna get it right the first time. Just pick a number and hit the track. Then make the changes you think will make it better. If you get it right the first time, you were just plain lucky.
As I mentioned earlier, a tachometer will be your best friend.
PM sent.... RooDog....

[kitabel]

That cam isn't going to do much with a stock engine and that small carburetor.
Were the cams new, bought outright? Cost? Picture? Receipt?

If you don't mind testing more than once, I don't think you'll reach 60 mph.
4,500 RPM for 60 mph with 26" tire is 5.80:1.
25 tooth on the engine is 5.69:1. I'm not sure if your primary chain is the right size? The 17, etc. take 96 link, 30, etc. take 100.
The engine will be very noisy @ 4,500 (tappets) but that's about maximum power.
A stock M-88 has a .052" jet (marked "#1"), use a bigger size or drill it slightly, H-D #2 jet is .0531" (+4%), #54 drill is .055" (+12%).
Set spark to 5/16" BTDC.

[flatheadDave]

It’s an antique drag race here in SoCal in a few months. I have to use antique parts so the linkert 88 is the largest of the linkert selection. Nevermind the linkert M16. Now that carb is tiny! Thanks for the info about the jet. I know I defiantly won’t hit 60. I guess I want to get off the line quickly. I’m not sure if the 22 servicar sprocket is the way to go. Or if it’s just way too small. Anyone had experience using a 22 motor sprocket on a WL?

That cam isn't going to do much with a stock engine and that small carburetor.
Were the cams new, bought outright? Cost? Picture? Receipt?

If you don't mind testing more than once, I don't think you'll reach 60 mph.
4,500 RPM for 60 mph with 26" tire is 5.80:1.
25 tooth on the engine is 5.69:1. I'm not sure if your primary chain is the right size? The 17, etc. take 96 link, 30, etc. take 100.
The engine will be very noisy @ 4,500 (tappets) but that's about maximum power.
A stock M-88 has a .052" jet (marked "#1"), use a bigger size or drill it slightly, H-D #2 jet is .0531" (+4%), #54 drill is .055" (+12%).
Set spark to 5/16" BTDC.

[RUBONE]

A stock M88 uses a 15/16" Venturi, a stock M51 uses a 1-1/16. And a 1-1/8" venturi was an option and used on ULHs. They are the same size body and three bolt with the M51 being the standard WL carb. The M88 was a military version designed to help keep soldiers hands off of it and internally vented to function well with the big oil bath air cleaners. Not much performance wise.

[kitabel]

If 25 reaches 60 mph, a 22 will reach 52.8.
It's just arithmetic, not voodoo.

[flatheadDave]

Oh this is good to know. I have an M51 in my box here that I was saving for my UlH build. Maybe I’ll use that one with this 45 for the drag.

A stock M88 uses a 15/16" Venturi, a stock M51 uses a 1-1/16. And a 1-1/8" venturi was an option and used on ULHs. They are the same size body and three bolt with the M51 being the standard WL carb. The M88 was a military version designed to help keep soldiers hands off of it and internally vented to function well with the big oil bath air cleaners. Not much performance wise.

[Architect]

For TROG I have run 30 and 31 tooth motor sprockets on a stock and worked motor, same tires. 30 had me winding out the motor about 50 feet too early, a couple of close races required me shifting to third. Third as you know is very far away from second, if you can you want to finish in second. But the 31 tooth was too tall off the line, gave up too much at the start. If I was racing tomorrow I would stick with the 30 and decide if I had to shift into third based on where my competition was on the track. My experience is based on sand where you dump the clutch at full throttle and hold on, not sure how it would shake out with traction. I don't think a 45 can handle full full dump on the street, too many things to break, meaning you will be rolling out from the flag.

I think a super small sprocket is going to have you starting in second and forcing you into third. If your transmission is stock , the drop off from second to third is like falling off a cliff. Good luck and have fun.