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High comp SBC mystery motor and pump gas.
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disturbthepeace1
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Joined: 14 Jun 2003
Posts: 303
Location: Stanton, CA
10195.60 points


1965 Volkswagen Beetle

PostPosted: Fri Jan 04, 2013 2:56 pm    Post subject: High comp SBC mystery motor and pump gas. Reply with quote

Hey friends, its been more then awhile but I'm in the need of some tech advise.

I have in the shop a presumed 383 SBC that was installed in a car that was brought to me to plumb, wire and fire.. The owner does not have any specs on the motor that he had bought off his cousin that is nowvdeceased.

My problem is now that I got it running I can hear the comp ratio cackle and can only assume that it has 12+:1 compression and the cam sounds to be close 300@ .050. I know you can't hear specific cam specs but I've tuned allot of unknown combos and believe me it's a huge cam.

My problem is starting, I have a hard time getting it fired up when the timing is anything more the 10* at idle. It fights the starter trying to fire up. I can retard the timing by hand and get it to fire but its real difficult because it spits and backfire thru the carb.

I know a start retard box is needed but my question is about gas. It has plain old 91ump gas in it now. I have little experience with this high of compression and was wondering if any of you race guys had tried to start/break in your motors with pump gas and had similar issues.

I want to try to mix some 110 in the tank and see if that helps but I was wondering what your opinion was.

Here is some motor porn to give you an idea of the motor.



Good times

Joe

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squeeezer
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1991 Chevrolet Camaro

PostPosted: Fri Jan 04, 2013 4:42 pm    Post subject: Reply with quote

no way 10 degrees and kicking back at starter

id double check tdc first

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squeeezer
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1991 Chevrolet Camaro

PostPosted: Fri Jan 04, 2013 4:43 pm    Post subject: Reply with quote

too cold of plug/fouling/too much fuel??????
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squeeezer
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PostPosted: Fri Jan 04, 2013 4:44 pm    Post subject: Reply with quote

oem old starter??? non gear reduction
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disturbthepeace1
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1965 Volkswagen Beetle

PostPosted: Fri Jan 04, 2013 6:05 pm    Post subject: Reply with quote

I degreed TDC with a piston stop when I went over the valve adjustment. It does have a gear reduction starter. But it's wired with 2awg cable from the trunk. I have set up countless street cars with 2awg but not any with this much compression. I might swap it out for 1/0 cable but before I do I was hoping someone could let me know If they have used pump gas in a race motor and were able to get it to fire up normally.

I am using NGK yr5's for plugs

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af2
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1933 Willys Coupe

PostPosted: Fri Jan 04, 2013 6:48 pm    Post subject: Reply with quote

disturbthepeace1 wrote:
I degreed TDC with a piston stop when I went over the valve adjustment. It does have a gear reduction starter. But it's wired with 2awg cable from the trunk. I have set up countless street cars with 2awg but not any with this much compression. I might swap it out for 1/0 cable but before I do I was hoping someone could let me know If they have used pump gas in a race motor and were able to get it to fire up normally.

I am using NGK yr5's for plugs


2/0 would be my and what I run Hmmm. Could be that or could be the timing is not what you think.
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disturbthepeace1
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1965 Volkswagen Beetle

PostPosted: Fri Jan 04, 2013 8:54 pm    Post subject: Reply with quote

I have tried retarded to advance and can't find a sweet spot to get it to fire up consistently. I personally went thru the dominator and have tried diff primary jetting from 71-80 with no real luck.

Was thinkin if the compression was high enough that it would be like running pump gas in a diesel motor. But that could be an apples to orange comparison.

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Paul P
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1971 Chevrolet Chevelle

PostPosted: Sat Jan 05, 2013 8:55 am    Post subject: Reply with quote

If you played with the timing and can't get it to turn easily it is the starting system. Which gear reduction starter are you using? Some are not quite as good as others. Voltage is definitely a factor. I have some 1/0 or bigger welding cable for my relocation kit. Put a meter on the starter + and ground when cranking I'm sure it will tell you the story.
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1971 - Chevelle 408 SBC N/A
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10.78@122 MPH 1/4mi
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disturbthepeace1
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PostPosted: Sat Jan 05, 2013 10:48 am    Post subject: Reply with quote

Sounds logical, I'll put my meter on it. If that's the issue would you think 1/0 would be large enough?
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squeeezer
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PostPosted: Sat Jan 05, 2013 1:55 pm    Post subject: Reply with quote

1 ot or 2 ot is overkill imo but whatever 2 ga welding cable can handle 600 amps and no starter will need that
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Paul P
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PostPosted: Sat Jan 05, 2013 4:22 pm    Post subject: Reply with quote

squeeezer wrote:
1 ot or 2 ot is overkill imo but whatever 2 ga welding cable can handle 600 amps and no starter will need that


It's not the fact that the cable can handle 600 Amps. It is the voltage drop over distance the that matters in this case. 1/0 is perfect for this type of application.

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2001 Focus 2.0 Zetec
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15.63@87 MPH 1/4mi

1971 - Chevelle 408 SBC N/A
6.86@102.5 MPH 1/8mi
10.78@122 MPH 1/4mi
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af2
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PostPosted: Sat Jan 05, 2013 4:24 pm    Post subject: Reply with quote

Paul P wrote:
squeeezer wrote:
1 ot or 2 ot is overkill imo but whatever 2 ga welding cable can handle 600 amps and no starter will need that


It's not the fact that the cable can handle 600 Amps. It is the voltage drop over distance the that matters in this case. 1/0 is perfect for this type of application.


600 amps per foot???
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clay
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1972 Chevrolet Nova

PostPosted: Sat Jan 05, 2013 6:07 pm    Post subject: Reply with quote

I would say pump gas isn't your problem. At idle and cranking I would think that cylinder fill would be so low that it woudn't be problem. Have you checked cranking compression? That should give an idea of camshaft / compression compatibility. After that I would stick a degree wheel on and do a quick check of duration on intake and exhaust along with lobe seperation. I realize the owner might not be willing to pay for your time to do this but if you don't know anything you have to start somewhere. It would help him in the long run be having an idea what he has for tuning purposes. Clay
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squeeezer
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1991 Chevrolet Camaro

PostPosted: Sat Jan 05, 2013 6:40 pm    Post subject: Reply with quote

When i rewired my car i went to the welding supply company for some cable. He is also a a mod circle track racer and told me he and all his cronies use #2 welding cable.....so i said that will work for me too
that is a 10.5 to 1 motor
im swapping in a 13:1 motor so we will see

Measure cranking amps
measure voltage drop(cranking)
test the battery

Should find the problem there....if in cranking system

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disturbthepeace1
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1965 Volkswagen Beetle

PostPosted: Sat Jan 05, 2013 7:07 pm    Post subject: Reply with quote

clay wrote:
I would say pump gas isn't your problem. At idle and cranking I would think that cylinder fill would be so low that it woudn't be problem. Have you checked cranking compression? That should give an idea of camshaft / compression compatibility. After that I would stick a degree wheel on and do a quick check of duration on intake and exhaust along with lobe seperation. I realize the owner might not be willing to pay for your time to do this but if you don't know anything you have to start somewhere. It would help him in the long run be having an idea what he has for tuning purposes. Clay


Makes sense, honestly I might see about talking him into swapping it out unless he wants to run race gas all the time. Don't get me wrong, I love grumpy race motors for the street even more than than the next guy but this one seems to be just too much

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