Just considering my options. They may be closing the local race track here so I may need to find a new use for my race motor. Thinking a polished 6-71 sure would look good on the street. Motor is a sbc .020 over, forged eagle crank and H beam 6"rods. Problem is my heads are the 49 cc darts. Intake runners are also 215 cc, not good for street. With dished pistons and 4.200" bore .80" thick head gaskets I think I can get the compression ratio down to 9. That is low enough isn't it? Are those 215 cc intake runners going to be a problem even with the blower?
Can I 6-71?
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wannarace, I say "yes" to the 671 blower. Go for it. But, I'm a little bias. LOL. If you're gonna spend the money on a blower, I'd put out some extra cash and go with a 7.5:1 or 8:1 blower piston. If you stay with the 9:1 it will work, but your gonna need to run the blower more conservative on ratio and boost. Kinda defeats the purpose IMO. I'm running mine with 7.5's. and I'm spinning it 12% overdriven. (Don't let anyone tell you that you can't run overdriven on the street.) Can't beat the instant boost of an overdriven blown engine. I ran my last car that way for more than 9 years without any issues at all. Blown motors for the really street don't require any exotic components. Just a strong lower end, and it sounds like you have that covered. As for the heads, I don't think you'd have a problem but if your worried, you could probably sell yours for good money and get a nice flowing street heads in their place. Being a sbc there are a lot of reasonably priced aftermarket choices out there. For a cam I'd go with something from one of the blower companies or a "blower" cam from one of the big cam companies. High performance, lopey, high lift (non-blower) cams aren't required and don't work well on blown street engines. The carbs and carb tuning are the key for street drive ability. Done right, your car will run, idle and drive better on the street than a radical (almost track) street motor would. I've never had a problem, fouled a plug or been left stranded with my last blown car. Well... there was that time I broke both rear axles... My current car isn't on the road yet, but is running and I've had it up and down the block a few times. (2 nice little burnouts) Once you have a blown car you will be hooked. Nothin like it.
Oh yea, one more thing... you'll have to get use to smoking the rears when you mash the gas at highway speeds. My 57 did it regularly with 18.5 wide M/T Sportsmans on the back. Scared the crap out of more than one "boy racer" who tested me.
Heres my current car:
Here's the blown 57 I owned and drove for about 10 years:
Oh yea, one more thing... you'll have to get use to smoking the rears when you mash the gas at highway speeds. My 57 did it regularly with 18.5 wide M/T Sportsmans on the back. Scared the crap out of more than one "boy racer" who tested me.
Heres my current car:
Here's the blown 57 I owned and drove for about 10 years:
YEA!!!! that is what I NEEEEED! Would like to get compression as low as I can but it is hard with those 49cc heads. I have looked at cam choices some. Would like to find a mechanical roller. That is what I have now and the lifters are good (Crower). Would like to keep them but I can't find a mechanical roller cam for a blown street motor. I have a spair 350 block and two sets of vortech heads that would make a nice 383 but they just aren't as shiny as the BIG BLOWER.
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10,475 Posts
You will really enjoy the blower. 9:1 is doable but, not the best way to go. anything between 7.5 and 8.5:1 is where you want to be. I would not be so dead set on a solid roller, you really don't need it with a blower. A solid flat tappet will make all the power you can imagine. You don't need to RPM the engine with a blower. The beauty of roots blowers is the low end torque they make. A head, cam, and piston swap and you will be in business. You don't want to lower the compression using a thick head gasket. You didn't mention how large your engine is but, with a blower 215cc heads will be just fine. You kind of have to change your thinking aboutport size and velocity when talking forced induction. My heads started life as 215cc (Darts as well) there has been some port work done so the port volume is now a little more than 215cc, my engine is a 388. I have an 8-71 on it and run it underdriven still makes 12lbs of boost and the torque is just stupid. As far as the cam goes I recommend calling Mark Engle at Engle Racing Cams, he took real good care of me and ground a cam that does EXACTLY what I asked for (it's a solid flat tappet). Tell him what you want and have your car details ready, hthey are good people to deal with and listen to you, they won't force anything on you. They will work with you to get you what you want.
Mark,
Nice looking project. When you get a chance hit the "pictures" link in my signature. We have similar taste it appears. My project is not back on the road yet, hopefully in a couple months.
Mark,
Nice looking project. When you get a chance hit the "pictures" link in my signature. We have similar taste it appears. My project is not back on the road yet, hopefully in a couple months.
If you don't own a blower yet you might want to check out the new Whipple twin-screw 6-71 blower. Its a direct replacement for a 6-71 but with an adiabatic efficiency of 75-76% its right there with most centrifugals and turbos, but with the low end boost of the roots. You can run 12 psi at 9:1 compression, just like a centrifugal. I'm sure they are proud of them but its worth a look. Just came out about a month ago.
http://www.whipplesuperchargers.com/pdf/W305pressrelease.pdf
http://www.whipplesuperchargers.com/pdf/W305pressrelease.pdf
Are there problems with thick head gaskets? I was thinking a solid roller cam would be nice be I already have the lifters. I'm sure flat tapet would be the way to go. My crank is stock stroke so the motor would be a 355. I guess I could buy some new bare heads and put my valves in them to save $.
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9,367 Posts
there can be as you mentioned an .080" gasket. Your quench is gone to heck at that point and you might have detonation issues even though the cr is lowered. The best option is to swap heads to a large chamber.
However, I've known guys who've stacked two gaskets on a blown deal and had them work fine.
Jody
Hey camaroman7d... You're right, it looks like we have the same disease! Awesome looking ride. I'm hoping to have mine done in the next few months also. Here's a video of it when I first got it running. I have to warn you.... the sound ain't great.
Click here to see Video
Click here to see Video1 - 9 of 9 Posts
