I do not have any experience with blowers but really would like to set up a small 4-71 for a flathead for t-bucket project I got going. These is one listed on ebay that is remanufactured and ready to go for gas application but it is a 3-71. Starting bid is $1200, buy it now is $1600. I really seems like it would work for the flathead I'm interested in it for. Is this is the right ballpark for a unit like this? Any input will help. Thanks.
The 4-71 has been used often on hot rod stuff, so manifolds, carb adaptors, etc. are available. Not really apples to apples due to drive ratio differences, but the 4-71 engine was 284 CI vs. the 3-71 at 213 CI. I would check around on all the stuff needed to make it work, or be prepared to make it yourself before getting the 3-71 blower.
Call Dyers in Chicago. They've been building blowers for 60 years. Gary Dyers still puts in time .. but primarily it's his son's business now. 3-71, 4-71, 6-71, 8-71, 10-71 blowers .. .. they build them all. I used to send Gary pallets of used GMC rotors and cases for core purchase. Great guy. Gonna' spend that kind of money, I'd get one from THE guy that helped build the blower business. Not all "rebuilt" blowers are specifically for gas high performance applications. Dyers definitely is.
Exactly. Know what your getting. I have a 3-71 that I am thinking about sticking on a inline six . But that is down the road.
Yes! Call Dyers, Buying a blower off evilbay may not be a wise move. Gary and Bill Dyer are experts and great guys to deal with, always willing to help. Gary built my blower and Bill built the drive- perfect!
@mad mikey that's cool man. I love those guys. Always treated me right. Wish I kept my blower. Sold with a boat. Crinkle finish, polished ribs, & plates. I shipped 12 to 20 cases to him .. at a time. Paid me AFTER receiving. That should tell you about Gary's honesty, & how much I trusted him. He's legit, for sure.
I have a complete 3-71 GMC blower with an original Cragar manifold and drive components. I intend to use it on my 265" small block that is now in my roadster. I realize that the 3-71 is designed for 213 cubic inches, but, since it is all original Cragar equipment, it will be fine with me.
Don't get hung up on the CI displacement of the original engine. I posted it as a relative blower capacity to each other at typical auto drive ratios.
I have a 471 on a flathead currently. Got the pruned 471 nd blower intake/heads from HandH. It is starting to breakdown and I'll tell you, it runs baby!
Run a 3-71 that is overdriven to provide 5-8 psi of boost on my 286” flathead. Runs very well. 306 hp at 5200 rpm, 330 ft-lbs at 3800 rpm with 6 psi of boost. For the street, 5 to 6 psi of boost and a 7.2 to 8.2 compression ratio allows you to still use good premium pump gas and still safely get about a 40% increase in power over a naturally aspirated engine. A Roots type blower with a capacity of 1/2 to 2/3 of the engine displacement per revolution works well on the street, 5-6 psi of boost. A 4-71 on a small engine, under 300 cubic inches, needs to be under-driven, 12 to 14%, to get 5-6 psi of boost and prevent over-boosting at high rpm. This can restrict making power at lower rpms. The 3-71 would have to be slightly over-driven, 9-1o%, to get the 5-6 psi of boost. Better performance at lower rpm but may sap a few more horsepower to turn. The use of Gilmer drive pulleys makes it easy to adjust the final drive ratio depending on your needs. Additionally, boosting a street engine over 5-8 psi of boost normally requires expensive upgrades to the engine e.g, forged pistons, oversized/reinforced main caps, porting, etc.
Think of the blower as a heat pump. The faster you spin it, the hotter the air gets. So an over driven 3-71 vs an under driven 4-71 set up to deliver the same boost will generate more heat in the incoming air.
Another satisfied Dyers customer here. Determined the one I sent him for rebuild wasn't going to be enough for my engine. Bought it from me for what I paid. Glad to run a setup from the man who started it all.
That is quite true. But a 3-71 will have shorter rotors and less internal leakage than a 4-71, so a faster turning 3-71 will usually generate more low end boost, and a stronger mid range. So its not all bad for a daily driver.
Warpspeed, all good insight and no argument from me. Since the OP said he was new to blowers and doesn't seem to have a buddy with some experience with such things, I was in hope of pointing out there are a lot of variables that affect tuning and picking a blower and engine combo. It takes a bit more thought that buying a loaf of bread. I think some of the best advice given in this thread to the OP is to consult with one of the blower shops and work out a package before buying any parts. And Dyers is certainly on that list.
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