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Thread: Big Bore small stroke big block chevy

  1. #1

    Big Bore small stroke big block chevy

    I am looking at building a new chevrolet engine for my pulling tractor. Before I get into it and get told "oh no for pulling you need lots of torque" let me explain. With the clutch and driveline setup we have we can leave the line at 6000+ rpm with no problem and probably will never drop below 5000 rpm in a run. Now my idea is to start with a dart big M block and bore it out to 4.6" then run a 3.76" stroke crank. (499 cubes when limited to 502) The only issue would be the heads. We are limited to OEM heads which would mean rectangular port GM cast iron heads. Would I be able to get enough airflow through them to make power at 9-9500rpm? What do you guys think? Would this engine combo run better than an exact match 496 (4.310X4.250) or would i be wasting a lot of money to do it?

  2. #2
    Senior Member RACING JUNKIE
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    Re: Big Bore small stroke big block chevy

    [quote="showdown496"]I am looking at building a new chevrolet engine for my pulling tractor. Before I get into it and get told "oh no for pulling you need lots of torque" let me explain. With the clutch and driveline setup we have we can leave the line at 6000+ rpm with no problem and probably will never drop below 5000 rpm in a run. Now my idea is to start with a dart big M block and bore it out to 4.6" then run a 3.76" stroke crank. (499 cubes when limited to 502) The only issue would be the heads. We are limited to OEM heads which would mean rectangular port GM cast iron heads. Would I be able to get enough airflow through them to make power at 9-9500rpm? What do you guys think? Would this engine combo run better than an exact match 496 (4.310X4.250) or would i be wasting a lot of money to do it?[/quote
    I have been Kicking ALMOST that same Combo around for AWHILE?And when the Next Motor is Built it will be somewhere in those Lines,EXCEPT for the Heads.
    A 990 GM Head sure worked GREAT on Several 427 Blown Alcohol Motors I ran.As high as 10 Grand and 26lbs of Boost,427 T/D Blk.427 Steel Crank,990 or 188 Heads.This was 30 + Years back!
    Later
    G 8)

  3. #3
    Senior Member RACING JUNKIE
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    Showdown: I am no expert on truck pulling, but it seems like the higher RPM & smaller stroke would actually make your truck pull harder while under load than a longer stoke engine would. I like the engine concept....
    "I would walk through hell on Sunday before I fear the enemy"

  4. #4
    Senior Member RACING JUNKIE
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    Does oem mean they had to come factory on a care,or does it just mean they must be GM HEADS? I ask because there are those older bowtie heads around that had huge ports...can't remember the casting number.

  5. #5
    Senior Member EXPERT BUILDER
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    I ask because there are those older bowtie heads around that had huge ports...can't remember the casting number.[/quote]

    Tod,
    That would be the 990 casting, Have a set on the shelf I would sell, if your interested showdown496
    Blowninjected 540 - when is going fast, Fast enough ?????

    http://www.racingjunk.com/profile/182079

  6. #6
    Senior Member SENIOR BUILDER
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    bbc combination

    can those 990's be ported, opened up? to run 9000 rpm, my numbers say you need about 380 cc intake runner :lol:

    what kind of fuel and fuel system?

    wouldn't you be better off with the longer stroke at say 8000 rpm if you are limited on the size of head? :wink:

  7. #7
    Senior Member MASTER BUILDER
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    Re: Big Bore small stroke big block chevy

    Quote Originally Posted by showdown496
    I am looking at building a new chevrolet engine for my pulling tractor. Before I get into it and get told "oh no for pulling you need lots of torque" let me explain. With the clutch and driveline setup we have we can leave the line at 6000+ rpm with no problem and probably will never drop below 5000 rpm in a run. Now my idea is to start with a dart big M block and bore it out to 4.6" then run a 3.76" stroke crank. (499 cubes when limited to 502) The only issue would be the heads. We are limited to OEM heads which would mean rectangular port GM cast iron heads. Would I be able to get enough airflow through them to make power at 9-9500rpm? What do you guys think? Would this engine combo run better than an exact match 496 (4.310X4.250) or would i be wasting a lot of money to do it?
    I am a truck puller and have to deal with the OEM headed motors for a while. There is a friend of mine who is running a motor like your trying to build except his bore is 4.5 X 3.76 stroke and making 850 + hp on Q16 fuel. The intake runners are pretty good on the 990 or 188 casting heads, but the exhaust really suck because the exhaust almost does a 90 degree turn. I know he paid quite a bit of $$ because the guy ported a Brodix intake to go with the heads.

    Does your rules allow you to raise the exhaust ports? Recently I ran into a builder and he told me that they take a 990 head, heat the head, and then weld to the top side of the exaust port. This way they are relocating the exaust port and the air does not have to make such a sharp turn. There is more to it than that, but that is the short version.

  8. #8
    Well...I guess i was wondering about the definition of OEM just last night. Technically if I was running a Dart block wouldnt Dart heads be oem for the engine?? That would probably be legal for one year if I did do that, but we also are not allowed to externally modify the cylinder head. So the 990 heads are what I would be stuck with. Would I be able to make power at 9500 with those heads (I'm already planning on having a set ported to the max of course) I really dont want to build the longer stroke engine because that is what everyone else has, How can you be better than someone else by doing the same things they do right?

  9. #9
    Senior Member SENIOR BUILDER
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    so how far can the 990's be opened up? how many cc's?

    i know nothing about pulling engines. but my math is not too bad. 8)

    do the other guys really spin their engines to 9500 RPM? do they need to? are they actually making power reving them that high?

    and i can understand wanting to take a different approach, but maybe there is a reason they all opt for the longer stroke :idea:

  10. #10
    Really 8000 is about all anybody is running with a 4.25 stroke. We have had some running a 4.00 stroke and running 8500. But the idea of 9000 just sounds very interesting, plus with a lower gear and more rpm there should be more torque available at the wheels, but if there isnt enough air available it will fall on its face!


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