… I know most of these built back in the day were 12:1 high RPM engines. but would anyone have built a 9:1 4-71 blown 301? I’ve had that combo in my head for years… and it’s time to order pistons. I have a 4-71 intake and blower.. (going to need to machine the rest.) thanks for the input Levi
You have a couple of questions in there, and didn't state for what purpose. Is it a good combo? It's certainly not a bad one. Back "in the day",I probably saw more blown 301s in dragsters on gas or alcohol than on the street. Back then the drag cl***es were pounds / cubic inch so such a combo could be compe***ive. Would have someone built a mild blown 301 for the street? There were a few. But I would not let any of that influence you. If you have always wanted one, get building. With the gas today 9:1 static may/ may not be the correct number depending on your drive ratio. But work it out and start wrenching.
Hell yeah! Why not?! Custom pistons are likely in-order. Forged pistons are a must im my book. I would shoot more for 8:1 or 8.5:1. Better to make it up on boost, that to end up with too much compression to use any boost you make. How is the hot rodding scene up there? I have family in Kenai, by the municipal airport.
Its not quite as simple as just getting it bolted on and driven by some belts. You will need to look into what it takes to rebuild the blower and maybe new end plates. Drive set ups are available for 6-71s so they may bolt to the 4-71. Snout length may be a problem though. It might be better to get a 6-71 and sell the 4-71 rather than try to adapt it. I'm saying that because the blower needs to sit near the middle of the engine (front to back) and that would make for a long snout. A 6-71 might be easier and cheaper.....not sure, but worth thinking about. You also need to check the 4-71 lobes and case to see that they are usable before you start spending money. Might want to get a copy of the book by Pat Ganahl on Street Supercharging as it will walk you thru the checking and rebuilding process.
Sounds like a great idea ! I'm thinking about putting my 6-71 setup on a stock 307 that came in a project.
I have 6 cars with blowers. 3 of which are small blocks with 4/71 blowers.In my opinion, a blown 301 is a great idea. Remember a 4/71 was made to boost a 4 cylinder engine with 71 cubic inches per cylinder. This adds up to 284 cubic inches, which is right there for a 301.
How much boost are you getting with the 4-71s ? Are you overdriving them any? Do you have any pictures or info on the drive set ups and snouts that you use? All of that shold be very helpful for anyone wanting to go that route.
8.0:1 is a better setup if you are going to huff it. Run about 6-8 pounds of boost. 4/71s were more common blowers on street and or street/strip motors. They make more heat on the intake charge than the larger blowers, but they are what I remember seeing most often on street cars in the '60s and '70s. If you are buying pistons and shooting for 8:1 compression do not get pistons with an adjusted deck height. But dished pistons. I prefer forged pistons personally but that is your decision.
Hello, When we had built the first 283 SBC motor for our B/Gas Cl*** 1940 Willys Coupe, it was set up with Jahns Pistons, but at a high ratio for the street, using an Isky Cam and Kit. When completed with 6 Strombergs, it ran fine and was a healthy motor for the street usage. But, when we ran it at the drags, the results were in the middle of the cl*** with our learning curve. We lost more than winning, which was disappointing. It was a healthy motor, sounded great, had tons of power, instant acceleration threw both of us back in our seats and started instantly. We were proud of our first 283 complete build. Our friends were impressed with our first attempt at building a hot rod for the street and drags. It was nice to hear great comments and when we started the motor with the hood open. That was the first time with the carburetor powered SBC 283 c.i. motor. Then, after running the Stromberg powered 283 SBC motor, lightweight, 1940 Willys Coupe in the B/Gas Cl***, the results were not as good as we wanted, so we were in a dilemma. The advice from Reath Automotive was that if we were going to build a larger motor and use a supercharger, a lower compression piston set was necessary. So, we sold the high compression pistons from the 283 to a friend (along with the Isky Cam) and purchased a set of 8.5 to one for the blower spec 292 c.i. block. This included a new Howard 5 cycle labeled cam and accessories. After months of rebuilding and having a larger motor, (from SBC 283 to 292 c.i. with blower spec parts) The sound of the 671 supercharged 292 SBC motor and 6 Stromberg carbs made the “wow” sound on the street. When we chugged into the parking lots of the two drive-in restaurants, it made an instant impression… mainly it was… what the #$@#^. No one else had made such a supercharged motor set up. Sure, there were a couple of Paxton Centrifugal Superchargers on different hot rods, but since the 671 Isky Gilmer Blower Belt Kit just came out, we were the first to show up with a great sounding motor, our 40 Willys Coupe and the new 671 SBC power. Everything was all new since the parts had to be blower motor build specific. The Reath Automotive guys had several SBC motors already in place and they all had lower compression pistons around 8 to 1 or 8.5 to 1. Our friend with his dual 4 barrel carb 56 Chevy Bel Air Sedan had a 301 SBC motor with ported and polished heads, along with a Duntov Cam plus a set of 10 to 1 pistons. It was fast and a daily driver. Jnaki When everyone saw the 1940 Willys Coupe roll into the drive-in restaurant parking lot, we could only see amazement on their faces. Then when we rolled out of the parking lot and my brother gave it a little gas.. We drove around the block, came down the dark alley and pulled into one of the coveted rear row parking spots. A friend mentioned that he could hear the motor coming down the normally quiet alley. This was part of the reaction we were expecting from our original Stromberg powered 283 SBC and months later, 671 292 ci SBC Willys Coupe build. similar in build and looks We parked, raised the hood and stood back to talk to some of our friends. It was a good thing it was only red primer as the teens all gathered around the 1940 Willys Coupe to get a look at how it was built. The nods and approval comments were more than enough for us to be satisfied we did a good job with our first hot rod build. YRMV
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