I'm am about to modify my Holley 4160 carb to install it on my 4-71 blown SBC. I understand how to "boost reference " the power valve on a Holley carb, but will vacuum secondaries still work with a blown motor?
You probably don't need to boost reference the power valve. Vacuum secondaries will probably work OK, most guys run a double pumper...because you can.... what size carb? what size engine? how much boost?
Its a 350 sbc with 9:1 compression and 4 to 6 pounds boost (estimated) and a 650 Holley single pumper, Comp cam (seat to seat duration 262 intake, 270 exhaust) in a '28 roadster.
Could probably use a bigger carb....650 is about right for the engine without a blower. 800 would be closer to what it needs.
Holley makes 780's with metering blocks specifically for blowers. Don't go more than 6# with that compression and you might want a timing retarder. As for the power valves just make sure they're half of your total vacuum at cruising speed. I run dual 780's no choke, with power valves. The newer carbs have byp***es to save your power valves but you can never be too safe. Lots of secondary jetting. Lean is awful with a blower. You would much rather be rich on the carb side. Best of luck to you. I believe it's the 3310-1 model I'm running, been beating the same carbs for 14 years. Do you know what LSA the cam is, plus I've seen a few comp cam failures in the last year or so. Maybe look in to a lunati voodoo with a LSA of 112-114.
Blowers also like a wide lsa. I would go minimum of 112*. Even at 6# you're talking 40% hp increase with a roots blower. I hope I'm not discouraging you, that's not my intention at all. I just don't want you to melt down your engine or chase a terrible idle situation that can't be fixed without the proper parts. Boost referenced power valves are quite simple also. Especially on a single carb set up.
[/ATTACH] View attachment 2677975 This blower installation is more about nostalgic appearance than it is performance. To me it is another high dollar fashion item like a Halibrand quick change. I'll probably never drive it like it was a race car so I don't care too much about the performance. I'd just like it to be reliable and not over heat. This engine has a couple thousand miles on it and I'm locked into it for now. I can change carbs now if it is necessary. If I change cams it will have to be when I replace the melted pistons.
Cant speak for the holley but I have an Edelbrock 750 on a 327 with 9to1 compression with a 471 that is street driven and reliable as can be. As a matter of fact my wife just drove it 200 miles each way to the Meltdown drags. I'm not a big fan of Holley carbs but I've used vacuum secondary Edelbrocks on 2 blown motors with no problems. As already mentioned a boost referenced timing retard box will make life much easier and probably save you from hurting the motor. I can and do run mine on 89 pump gas most of the time on the street.
If you don't buy a "blower" carburetor or at least the metering plates, be carefull, you may have to open the idle mixture and high speed p***ages some. The idle more thAn the high speed. I've known a couple of people that have had problems like this. It's why both Holley and Edelbrock offer blower versions of their carburetors. Mike
Just asking...Would a 4-71 be large enough to make much boost, at the ratio in the pic, I'd be supprised if it got to 5psi..yes/no?
Sorry for the late reply. You are right, probably about 5 pounds boost. It is intended to look early 60's and even though it is not apparent in the picture, it is slightly over driven. It is also a very snug fit.
Yes it do look ***e...In my opinion you have a proportionate package, nothing overwhelms..Wonder how long those belt labels will stay lined up..
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