Hilborn O pump with 4bbl carb on methanol-- Need bypass baseline help

[alkyal]

Have a hilborn O pump that is cam driven [1/2 engine speed] This will feed 100% methanol to a 4bbl 750 cfm Willies carb. We know this will require some type of a bypass system or device to keep the fuel pressure @ idle thru 6000 rpm [max engine speed as dictated by MSD rev limiter] to a max of 7.5 psi. These are crate 604 GM engines that produce a max of 325 hp on Methanol.My question is what system or device to use? If a Main  jet can type device is suggested-What size pill to use [@ least to start with] and what spring to use ? If other than std spring. If a regulator-by pass style is suggested, What style/brand do you suggest. Thanks in advance for your help. Al

[Spud Miller]

 You can't use a pill in a check valve...the pressure will back up against the pill and you'll have troubles. Your pressure will be higher than what the check-valve is set to. Without a pill, a check valve is just a pressure regulator...until it reaches its flow capacity, then pressure will climb and cause trouble.

 You could use a nice, bypassing style regulator and that would do the trick. There are a bunch of brands...just get a bypassing style. It'll have a return line.

 I've seen folks use a large check valve (or multiple valves) set to offload fuel after the pump and return it to the tank. Using a -1 style pump (way too big), a friend used 2 ea. -8 check valves (in parallel, not series) both set to 5 PSI and he say his pressure is always 5 PSI.

 Spud

 

[dreracecar]

I would think that a top brand electric alcohol pump would be a better choice because of its consistancy in flow and regulation no matter what the engine RPMS are. You are just feeding a sump thru a small orface needle and seat and your only demand is to keep it at the right level. If you really have to run that pump, I would be looking into running it at 1/4 speed and check valving from there. The pressures and volume from 1/2 speed will overcome the needle and seat throughout the engines rpm range unless mutiple checks and regs are used which equals cost. If the reason you are doing this is because the supply cannot keep up with demand and the carbs empty, there are other options, one of them being float bowl extentions to get more volume and hopfully allow the needle and seat to keep up with demand or you can"Dry Sump" the carb by removing the N-S and float (volume) and push the fuel in with one pump and remove at a running level with another pump. Did this quite often on Webber IDA's because the N-S could only stand 1 1/2# of fuel presure and the float bowl volume was not enough to let the pump catch up