Well for spark I'm upgrading a msd box ran a very mild spark a thunder bolt stock .Ran 5 lbs boost plugs were pretty good looking ran 31 32 locked timing 4000 feet. Primary 73 jet and 81 secondary.Higher speeds Rpms just doesn't feel like it has much takes a lot of throttle and trim to get high speeds . Big rooster. Like 70 max

Not fast enough

With snowmobiles running at that altitude I'd run less jet in the carb days. With the air being less dense requiring less fuel is it possible larger carbs wouldn't be as much of a factor? I would think at that elevation they still would. Now if were boating at 30,000 ft on top of Mt Everest might be different story. But then we wouldn't be concerned with carb size as we would survival. Lol

only way we could get to work with them was about 10" from flange in # 5 primary, did work fine there..really need to see AFR's sound like its rich to from what you describe..also, we made 700+hp on a procharged blow they setup with a 750 on a 509

I hope I am saying this correctly, but wasn't it Articfriends who was testing carbs on this most recent/latest project with his one his dyno partner's modified Holley #4150 850's??? They tried several other sized carbs including a #4500 Dominator and according to Articfriends the modified Holley 850cfm carb always came out on top according to the dyno....but remember, this was a modified Holley 850cfm carb---modified by his friend who has been modifying carbs for many years.

Anyway, it might be worth some consideration....have fun.

I think its safe to say, that a "blow thru", and a N/A engine, share very little in carburetor results.

Blow thru, you can use a much smaller carb, and make big power. The compressor is BEFORE the carburetor. N/A, you need flow, but you also need fuel atomization. Roots, are totally different animals.

Either way, I am willing to bet, with proper tuning, the engine will wake up big time. 5lbs of boost at 4000 feet, isn't much at all.

What pulleys do you have on the blower setup? Are you running an intercooler? What is the static compression?

Yes I have a intercooler not for sure on pullies but I'm getting about 4-5 lbs boost

I only run about 70

I've heard that a sportcat is a caddy ride but hard to go fast . Do u think this new msd should help it. I've been trying for 3 yrs to run better.

Also Xr drive 1.50 gears 26 lab prop