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Old 05-23-2010, 01:20 PM
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383 Blower Motor

I'm putting together a 383 stroker motor with a 6/71 Mooneyham blower for my 1930 Ford roadster, which weighs about 2600#, turbo 350. 373 gears. I'm wondering what combustion chamber cc and runner length cc I should choose for good low end and mid range performance to 6500 rpm max. 64/190, 68.5/195 or 76/210 or any better combination? Also what cam specs are best for this configuration? I'm running 8:1 pistons.

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Old 05-23-2010, 01:28 PM
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Quote:
Originally Posted by eaglenook
64/190, 68.5/195 or 76/210 or any better combination? Also what cam specs are best for this configuration? I'm running 8:1 pistons.
"8:1" pistons are only 8:1 with a certain chamber size. Please describe the piston crown configuration, cc's of dish and the compression height. Also, mfg and part no. please.
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Old 05-23-2010, 02:42 PM
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Piston info

Thanks for the reply. I guess the pistons I have were designed to be 8:1 compression with the stock 2.02 cast iron camel bump heads the engine was originally being built with. I've now decided to install aluminum heads and wondered what the best port size and runner length combo would be, as well as cam specs. I believe the pistons are speed-pro dished blower pistons - model H8590P .030 over Part #04-329-05-A. The car is a 1930 Ford roadster about 2600# with turbo 350 - 3.73 corvette diff. I want to acheive good street performance in the 2500-6500 rpm range. Suggestions would be appreciated.
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Old 05-23-2010, 03:07 PM
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H8590P .030 is a bad number, but I suspect you meant H890CP-030. Does this look right?
http://www.summitracing.com/parts/STL-H890CP30/

If so, then here are resultant static compression ratios with these different size combustion chambers....
76, 7.80:1
74, 7.97:1
72, 8.11:1
70, 8.25:1

When you get this nailed down, then you can intelligently choose a cam and heads.

Last edited by techinspector1; 05-23-2010 at 03:15 PM.
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Old 05-23-2010, 03:26 PM
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Piston Part#

I guess I should have put my glasses on. The actual # stamped into the top of the piston is H859CP .030 and below that 04-329-05-A. I had someone suggest that 64cc chamber heads would work okay with these pistons, but I can see that might raise the compression ratio too high. Good thing I'm getting a second opinion. Better to get it right now than later. What about intake runner length and cam specs? Do you know of any good publications that provide information on building a sbc blower motor. Thanks
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Old 05-23-2010, 04:05 PM
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H859CP-.030 is a 12cc piston. The best you can do with them is to make an 8.50:1 motor with 76cc chambers. You're gonna need more dish if you want to get to 8.00:1 SCR.
http://www.summitracing.com/parts/STL-H859CP/
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Old 05-23-2010, 05:06 PM
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Blower Pistons

I suppose 8.5:1 is okay. When I got the car the 6/71 blower was mounted on a stock 350 with flat top pistons and I didn't have any problems running on pump gas with that set-up. Thank god I didn't buy the 64cc heads or I probably would of had a real detonation problem trying to run pump gas. I'll go ahead and look for some 76cc heads. What about the intake runners 190cc or 210cc for this application? Any cam suggestions? Thanks
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Old 05-23-2010, 07:31 PM
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Check over these recommendations from Blower Drive Service.
http://www.blowerdriveservice.com/recommend.php

The motor won't be under boost all the time, so I would choose a head that would still work naturally aspirated. That would, for me, be in the range of 210cc's on the intake runner. As far as a cam, I'd use the same timing as I would if the motor was naturally aspirated at the rpm's I wanted to make power to. For instance, if I wanted to make power to 6500 r's, I might choose a cam, no matter who grinds it, with the timing figures of the #4600 or maybe the #5300 cam on the BDS list.
Chevy 262, 350
4000 .465/.490 270/274 221/226 110
4100 .450/.465 264/270 214/226 110
4200 .465/.485 270/280 221/232 110
4600 .490/.485 274/280 226/232 110
5300 .484/.505 280/292 232/244 110
5400 .505/.525 292/304 244/256 110

Notice that BDS recommends 110 lobe separation angle with gasoline, while recommending wider angles with alcohol. Most everyone will tell you (mistakenly) to run a wide angle with a blower, period. I'm not sure how these wrong wive's tales get started, but if you are running gasoline, run 110. If you are running alcohol, run 112 or 114. That's what the engineers at BDS recommend and they've been doing it a long time.
But it has been years since I fiddled with a blower and that was a 4-71, not a 6-71, so don't use any of my info as gospel. Give the guys at BDS a call and yank their chain about some recommendations. Things have changed since I did this.

There are a couple of fellows on this forum who run 6-71's daily. Maybe they'll chime in with words of wisdom.
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Old 05-23-2010, 08:49 PM
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yep 110 ls for gas . get you parts book out and look at all there blower cam grinds write it down then go to the regular grinds and you can get real close and save a little by not having the word blower in front of it.
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Old 05-24-2010, 08:16 AM
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I ran my motor originally as a NA motor with a single 750 vac sec at first. It ran very well however it was a bit hard to live with in heavy traffic. Even with a 3000 converter it didn't like to idle less than 900 in gear and that was shakey.

I installed the 6-71 on the same motor in less than 36 hours. It runs perfect now. It idles at 700-750 anytime in heavy traffic. It is very responsive and easy to drive.

My car weighs 2780 with a full tank. T-350, 3.50 gears, 355 sbc, alum heads, 8.75 CR and cam roughly equal to the 5300 above. I do have 112 LC but frankly I don't thnk you can tell the difference.

If you are going to drive a lot on the street don't get too carried away with the cam. Since you are working on low compression stay with that and use the blower boost for power. All you have to do is change pulleys and watch the AFR gage and change jets as required.

If you plan on lots of racing, well you are going to have to make some compromises. You are not likely to run heads up except for grudge racing so if you can run 11.20 or what ever who cares. Consistancy counts so work on getting the car to hookup.

It's hard to beat a blown big block for a tire distruction machine, but the blown sbc that hooks will get there first consistantly. Mine hooks real hard and barely spins the tires on good pavement. Believe me, mine gets 0-60 very quickly.

I drive my car a lot, nearly every day in fact. I've been to 21 events and 2000 miles in a little over 2 months so far.

Don't spend all your money on fancy parts. You will need plenty for gas as the blower motor is pretty thirsty. I fill up twice a day sometimes.
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Old 05-24-2010, 09:43 AM
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Good advice

I really appreciate the time you've taken to give me your advice and recommendations. I want to get this right the first time and I know enough to know I don't know much about all the technical aspects of hot rodding and engine building. I think your suggestions have pointed me in the right direction. Thanks
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Old 05-24-2010, 02:39 PM
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Those pistons you are using are not forged they are Hypereutectic, you need to avoid detonation at all costs or you will be rebuilding it again. It sounds like you have it apart, you may want to consider some forged pistons while you have it apart. I blew apart a set of Hypereutectic pistons when my dist hold down slipped and the timing wandered a little.
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Old 05-24-2010, 03:01 PM
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Pistons

Good point. It won't pay to cheap out on critical parts like that.
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Old 05-24-2010, 10:02 PM
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Another little goodie to check into is a water/methanol injector. I'm looking at these myself now mainly for self preservation when my kids take the car out. I know they thrash the heck out of it as there is rubber and tar dust in the rear wheel wells when I get it back.

Snow performance makes one that is popular with the diesel truck guys. There a couple others that are pretty good too.

The nice thing about these is that you don't have to mess with retarding the timing. In fact you can run more lead and let the water/methanol injector take care of the detonation. With more lead 4-6 deg the motor runs better at part throttle which is very similar to NA conditions.

I'll find out more soon.
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Old 05-24-2010, 10:28 PM
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Comp cams XE284H-10 pn 12-250-3 needs a 10" 3500 stall.

AFR 195 Eliminator w 75cc combustion chamber Cylinder heads
KB forged -18cc dished pistons 5.7" rods.

Last edited by F-BIRD'88; 05-24-2010 at 10:36 PM.
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