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weiand 6-71 build
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87IrocTim
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PostPosted: Tue Feb 24, 2009 7:52 pm    Post subject: Reply with quote

sorry for such a late reply, but here is the latest. basically, my motor is coming out, im going to see what is has for a crank before i go buy one. ive decided to stick with my 350 that is in it now, mostly because of one, a decent aluminum radiator and electric fan will keep her cool, and two, there is still the cross hatches in the cylinders and they have no ridge at all. after i find out what crank i already have, i am honing the block, buying some keith black 22cc dish hypereutectics, putting my scat forged i-beams i bought in. no boost retard, just using my msd 6 al i already have. reusing my heads that have 161cc intake runners, but also have a mild port job, and crane rollers. using a solid flat tappet cam with a powerband of 2500-6000 and 112 LSA, sold my 400 head gaskets and getting a set of the thickest head gaskets i can find, a minimum of .050. the rev limiter will be at 6000 for now until i get comfortable enough to squeeze more.

using my speed demon 850 dp, and now im deciding whether to shoot for 8psi or 10psi.

my goals here are to get a minimum of 400 to the wheels through a th 375 automatic. the 142 at 5psi made 320hp and 340tq to the wheels with flat tops, so im hoping with the lightweight rods, kb pistons, and 8psi i can squeeze 400. the car will be dyno'd and tuned at SD concepts, where they will set a reasonable timing advance that will be safe with 93, no water or meth injection, but will eventually get meth injection, i jsut dont want it to need it.

i figured the only thing that will hurt this combo is high rpm's and preignition, so knowing it will see a max of 6000, and definitely wont be pre-igniting, even a stock crank should be fine with under a 12:1 total compression. if i can break 400 to the wheels and stick tire at the track, i should safely be below a 12.4 quarter.

i am also trying to be smarter about it too, i was going to go all out race, but i will only be at the track 1-3 times a month, and will be driving it almost every nice weekend, so the cam choice will get good mileage, still have a nice solid cam lumpy idle, and make better vacuum.

also, assuming my crank is aftermarket or will handle the abuse, (it is a 4 bolt motor) would it still be vital to get the motor balanced if the pistons and rods are changed. pistons are already hypereutectic aftermarkets, rods i have no idea. some of you may yell YES, but once again this motor will see a max of 6000, and only at the track. flywheel and balancer will remain the same. rods have already been weight matched, same with pistons.

and finally, from what ive heard, 5psi on a 6-71 will make much more power then 5psi on a 142, is this true? seemed possible considering a 6-71 flows a lot more, but 5psi is 5psi, weather its a person blowing into my carbuetor or a 14-71.

any guesses on what im looking at? my guess is between 400-430 through the auto...

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clay
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1972 Chevrolet Nova

PostPosted: Tue Feb 24, 2009 9:40 pm    Post subject: Reply with quote

I'm going to do some crude math just to get some ballpark numbers. If you are shooting for 400 at the wheels and assume a 25% loss through the automatic, that's 500 at the crank. A rough figure I have used for added power from boost is 18 h.p. / lb. of boost. At 10 lbs. boost you would have to be able to make 320 h.p. naturally aspirated which is a very reasonable number so I think your goals are very doable. As far as blower size of roots style blowers, this is how I look at it. A smaller blower that spins faster has higher mechanical effenciency because there is less time for leakage past the rotors to occur. However a larger blower that turns slower adds less heat to the air so there again, effenciency comes into play. From what I have read, smaller blowers on the street and the larger stuff for racing. As far as more power from it than what you currently have, I don't know. Clay
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SMOKEmUP
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1979 Chevrolet Camaro

PostPosted: Wed Feb 25, 2009 4:38 pm    Post subject: Reply with quote

Playing around with the turbo calc on the site and plugged in some numbers. I know this isn't a turbo but the same general rules apply.

Using a VE of 80%, boost 5psi, compressor eff 65%:
RPM Flywheel HP
1000 68.4
2000 136.8
3000 205.1
4000 273.5
5000 341.9
6000 410.3
7000 478.6

Changing Boost to 8psi
RPM Flywheel HP
1000 74.3
2000 148.6
3000 222.9
4000 297.2
5000 371.5
6000 445.8
7000 520.1

Lowering the compression ratio will lower the VE by reducing cylinder pressure. This will allow you to run more boost and raise the cylinder pressure backup.

I think you'll need to turn the boost up more than 8psi to reach your goal of 400 to the wheels.

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87IrocTim
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PostPosted: Wed Feb 25, 2009 6:56 pm    Post subject: Reply with quote

well, lets assume its a dead stock crank, forged rods, 7.5:1 CR. how much do you think i can safely squeeze on 93 gas? rev limiter will stay at 6000 for now. i would like 10 psi, but i will build around whatever is needed to get 400 to the wheels.
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af2
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Location: grassvalley, ca
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1933 Willys Coupe

PostPosted: Wed Feb 25, 2009 7:20 pm    Post subject: Reply with quote

87IrocTim wrote:
well, lets assume its a dead stock crank, forged rods, 7.5:1 CR. how much do you think i can safely squeeze on 93 gas? rev limiter will stay at 6000 for now. i would like 10 psi, but i will build around whatever is needed to get 400 to the wheels.


Dead stock forged crank and rods?? 500 + at 7500 rpm. I don't understand the rev limiter? I am open to suggestions! Laughing
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87IrocTim
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PostPosted: Wed Feb 25, 2009 7:32 pm    Post subject: Reply with quote

ok let me write this clearly.


my name is Tim. I have a chevy 350 4 bolt

i want to put an 8-71 on it and my goal is 400 RWHP

i have scat forged rods, will be using KB 22cc dish hypers

i am wondering if a stock crank will handle the abuse?

Tim doesnt know if the crank is cast iron yet, but Tim will find out when he takes the motor apart, but for now Tim is assuming its cast.

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af2
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1933 Willys Coupe

PostPosted: Wed Feb 25, 2009 7:55 pm    Post subject: Reply with quote

87IrocTim wrote:
ok let me write this clearly.


my name is Tim. I have a chevy 350 4 bolt

i want to put an 8-71 on it and my goal is 400 RWHP

i have scat forged rods, will be using KB 22cc dish hypers

i am wondering if a stock crank will handle the abuse?

Tim doesnt know if the crank is cast iron yet, but Tim will find out when he takes the motor apart, but for now Tim is assuming its cast.



So what do you want to do??? I know what you're name is ,I just have a hard time with you're thought!

By the way a stock crank is way better than a scat 9000.. Stock is nodular, Scat is cast steel with very little iron in it.
Tim, I don't understand the BS that you're post has givin me. If you want I will let you learn on you're own. I have 2 sons I can give more time on learning what don't work and money well spent! Good luck!! We have all been there and scwewed that up. How are you different! Laughing Laughing
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87IrocTim
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PostPosted: Wed Feb 25, 2009 8:16 pm    Post subject: Reply with quote

uuugh jesus come and rip me from this chair where i sit.....


i jsut spent $2800 on miscellaneos everythings for the nova, $500 on weld wheels, $850 to get my camaro fixed and back on the road because a tranny with 40,000 rebuilt miles blew, still owe $100 to the guy i bought a tranny off of to put in the camaro, i still owe my buddy george $400, just spent $160 on new front tires for the camaro, am going to need new back tires next month, i got an insurance bill coming for $365, $225 of forged rods, $100 on a gasket kit, $65 on a timing chain kit and what am i left with???

a chevy nova that needs $240 dollar pistons, $160 dollar cam and lifter set, and a $2500 supercharger to get it back on the road.

i am cutting corners. i dont want to buy a new crank, with good reason. im broke. i can even afford to scratch my ass with a piece of sandpaper. i want to throw the pistons cam and rods in, not get it balanced, reuse everything i can, stick a blower on it, get it running and go.

am i teaching my self magic of how to turn an engine into a pile of useless garbage, or will it handle 10psi of boost with a max RPM of 6000???

sorry to get annoyed but it seems almost every time i ask something i get some wierd answer that has nothing to do with anything. been a long long week to say the least.

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87IrocTim
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PostPosted: Wed Feb 25, 2009 8:27 pm    Post subject: Reply with quote

and smokemup, seeing that chart, 10psi should put me somewhat close, but i will have to squeeze some rpm's out of it, not a big deal.

and clay, i am going to do my research to make sure my combo will hold itself together, but reguardless i will be sure to tell you the dyno results. i mean if it ends up being a little less then 400, i will find a way to milk it. my quarter mile goals are less then a 12.4, but 400 to the wheels will most likely be less then that with my gearing, tires, and suspension.

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clay
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1972 Chevrolet Nova

PostPosted: Wed Feb 25, 2009 11:09 pm    Post subject: Reply with quote

I agree with af2 on the power / rpm levels you are looking at - I'd run stock stuff and not bat an eye. On the balancing thing - I'm no auto machinst so what I'd do is weigh the piston / rod combo in the motor now vs. the new stuff you are going to put in. Then go to your machinist and ask him his opinion. I'm sure there is some room for difference but I just don't know how much difference there can be. My gut feeling tells me with as low a compression ratio as you have, 10 lbs. should be o.k. even without water / meth. injection (I don't mean to keep bringing that up) and 93 octane. On the rpm levels, I think your peak power will probably come a little lower in the rpm range than the turbo setup shown on the calculator just because of the different design compressor so 6000 should be fine. Clay
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87IrocTim
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PostPosted: Wed Feb 25, 2009 11:29 pm    Post subject: Reply with quote

alright, i am eventually getting a meth injection kit once i recover from the blower hit, but one of my biggest things was not needing it, just having it as a bonus. ok then that is exactly what i will do. im going to take the motor out, take it apart, ill identify what crank i have now, keeping my fingers crossed. after i get the wristpins and rods together ill put them and the old ones on a scale and see where i stand. ill ask them what leverage i have with weight differences.

ill get the blower sent to me with 9-11 psi pulleys. it will be an 8-71 rather then a 6-71.

final specs will be.......

-7.5:1 with scat forged i beams and KB 22cc dish.
-solid flat tappet cam, forgot exact specs but 112 LSA and 2500-6000 powerband.
-mild ported gm heads, factory they have 161cc intake, with 1.94/1.5 valves.
-crane 1.6 rollers.
-th-375 tranny, ten bolt rear end with limited slip, 3.73
-et streets 325 50 15 on weld racing lights.
-traction bars, leafs lifted n teh right side.

hoping for a low 12 high 11 time, and 400 to the wheels. time will tell, time to file for them early tax returns Laughing

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