John Scott Posted December 21, 2000 Share Posted December 21, 2000 Since my last bout of carburetor woes, I've had a lot of time to ponder the good and bad side of a blow through system. As I stated in another post, it seems the carburetor can only handle two sides of the supercharged curve. Cruise speeds with no or little boost and overly rich secondaries that finally come into their element at max boost. Everything in between is probably going to be running too rich. I've been hashing this over with other members, a Nascar carb guru, ATI, Holley and even posted the problem on other performance oriented boards. No one seems to have a good solution for a blow through carburetor...until now! I finally found a carb shop that not only understands a blow through system, but will pit their carburetors against any fuel injection for hp, and still provide excellent drivability. One of their personal commuters is a 383 producing in excess of 700hp! The Carb Shop www.customcarbs.com will completely re-do your Holley to very specific engine specs. They claim to drastically change the flow for a dedicated blow through carb. The end result is a carb that produces big hp with a balanced delivery throughout the rpm/boost range. As usual, this comes at a high cost. I was quoted roughly $500 for the upgrade to my 600. I don't want to start a FI vs carb issue here and agree that FI is the best solution for precise metering in most conditions. This is just the first time I've encountered a carb shop that really addresses the blow through system with excellent results. JS Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted December 21, 2000 Share Posted December 21, 2000 I've heard fo those guys, I believe they're supposed to be pretty good. I've spoken to other guys having troubles with blow-throughs, it's a pain! I'm a BIG fan of EFI but the carb route certainly seems easier on th esurface. But by the time you add up the sealed bonnet over the carb, the custom carb, and the troubles with keeping it and it's air bleeds clean I really have to wonder. Are you going to go this route? If so please keep us posted as if there's a carb that can do this "right" I might be interested down the road. It has some definate possible upsides over machining an intake, buying a throttle body, having rails made, pumps, programming and on and on if it works well (sigh). We'll see... Quote Link to comment Share on other sites More sharing options...
John Scott Posted December 21, 2000 Author Share Posted December 21, 2000 The Holley with minimal mods works pretty well for a blow through. The bonnet, or hat came with the supercharger. Only need plastic floats, air horn milled and the choke linkage hole plugged with jb weld. Simple! I've been running mine for a few years now with few complaints. I think the higher you go in boost, the bigger the spread in primary/secondary jetting become, the more desirable the carb shop's units become. I don't have any problems as far as drivability, but It sounds like the Carb shop takes care of some inherent problems with the blow through. Its not anything I can afford right now, but would give them a go if I had the spare $$. I encourage anyone interested to give them a call. They are very willing to give information. JS [This message has been edited by John Scott (edited December 20, 2000).] Quote Link to comment Share on other sites More sharing options...
Ray Posted December 21, 2000 Share Posted December 21, 2000 John have you looked into using a nitrous plate with fuel solenoids on both sides. they can be activated by Hobbs switches. This would give you a cheep adjustable way to keep the carb and run more boost. I have seen a few very simple systems like this on carbed turbo apps but never with a blower but the principle is the same. Good luck with what ever you do. Ps: you don't have to use the expensive solenoids that the nitrous guys use you just need a 12v solenoid with a brass valve. Quote Link to comment Share on other sites More sharing options...
John Scott Posted December 21, 2000 Author Share Posted December 21, 2000 ATI's tech Mark, will defend the Holley for blowthrough. He is running a 351 in his daily driver mustang pulling over 700hp. He claims the flow through the Holley, as modified above) will flow linearly and not experience the overly rich conditions below max boost. His jetting on the seconday side is 30(!) steps above the stock jetting. So maybe my 89 jet I'm trying next will get some good results. Of utmost importance is the fuel pressure 7+ psi above boost. He recommends the Aeromotive pump and regulator for high boost applications. "The Mallory 140 is an excellent performance pump for naturally aspirated engines". The carbshop offers a big step above, but I'm going to work on what I already have to see what can be done.I need a different pump!! JS Quote Link to comment Share on other sites More sharing options...
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