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  1. #1
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    Default Big CI motor small carb.

    Normally when we talk 500 2 Barrel Rules you see 355 and 383 that short of combo. I know you don't traditionally have a big runner like 200cc is the most before you don't perform as well. When you go to a bigger motor say a 427 ci like I have does that rule change? Edelbrock 2925 intake no spacer, roller cam, 200cc Dart Heads minimal work just blending from what I understand and a 500cfm with 1 3/4 Plates. Dynoing at 565HP at 6,000rpm and about same torque but 4500. 8" Mod Tire. We just got a repave so I might need more power. Just want to learn more about motors. Does the stuff for the small CI we see more common apply with this 2 barrell or does the bigger CI change the game?

  2. #2
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    from my experience , when running a 500 cfm 2brl on any cubic inch , the more compression the better , kinda like a restrictor plate engine , if your rules allow and you cant run domes , angle milling the heads helps tremendously ......

  3. #3
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    Only Rules we have are. Steel Head, Steel Block. 500 Holley with 1 3/4 Plates that's it! I think I'm around 14 or 14.5 to 1 motor from what I was told by the builder. He hasn't done as many 2 barrell so we went conservative in some areas on head work. The Heads are Angle Milled. Flat top Pistons. T and D Shaft Rockers, Roller Cam and Lifters I do have the Cam Card just not on me at the Moment

    Quote Originally Posted by fastford View Post
    from my experience , when running a 500 cfm 2brl on any cubic inch , the more compression the better , kinda like a restrictor plate engine , if your rules allow and you cant run domes , angle milling the heads helps tremendously ......

  4. #4
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    A big cube engine will run out of breath at the end of the straights with a 500... worse with a 350! Just my opinion... your mileage will vary.
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  5. #5
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    thats why you need all that compression , because you can not turn it very much....

  6. #6
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    Default

    All depends on the carb. Seen 500 cfm 2 barrels and seen 780 cfm 2 barrels......

  7. #7
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    Mines closer to the latter. Ran the car its been running quite well out the gate. Until it got taken out for the lead I'm in the process rebuilding it. I actually have WAY to much motor for this track they didn't do the repave like we thought. I'm actually trying to find ways to kill the power by as much as 80-100. I run an Edelbrock 2925 with a Super Sucker on it and a Holley 500 With no spacer. I can light the tires up anytime I want and while I have throttle control and know I can only use about 12 throttle for consistency reasons trying to find a way to restrict it without making the air flow turbulent. I've already knocked as much timing as I can safely knock out. Can I run a 4 barrel adjustable spacer to restrict it then put my super sucker adapter then carb on top? Or will having the 4 hole restriction be too turbulent
    Quote Originally Posted by hpontap View Post
    All depends on the carb. Seen 500 cfm 2 barrels and seen 780 cfm 2 barrels......

  8. #8
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    I guess you could put a 390 carb on it. People think that a carb will go lean when it gets maxed out but it doesn't. They go dead rich.

  9. #9
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    can't put a throttle stop on it?

  10. #10
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    We have to run a Holley 500, I have a throttle stop on it. I can hold it at half throttle and not spin tires i have good throttle control it’s just easier if you can kill it and use WOT much easier to be consistent would 4 barrel restrictor on top of the open plenum then my 4 to 2 HVH super sucker with carb on top be a bad idea?
    Quote Originally Posted by powerslide View Post
    can't put a throttle stop on it?

  11. #11
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    Don't know what stacking plates would do to the distribution. You could try it by hot-lapping a couple of laps and do a plug check to verify that no cylinders are running lean.

  12. #12
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    Default

    I ran 436 ci engines with a 350cfm carb and 500cfm at another sanctioning body. Worked great I had success in texas, minnesota, alabama, kansas, iowa and nebraska. The smaller the carb the bigger the cube was what we all did around here for years.

    If you have too much motor change the cam its not rocket science, go to a wider lobe separation to smooth out the power, oval track cams hit hard in a small area... others with wider lc dont.

  13. #13
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    That's what Im fighting it makes gobs of torque at 4500cfm. They won't let me run a 350cfm I tried. Its Nascar sanctioned and they said they rules say 500cfm 4412. It also has oversided throttle plates but the rules allow it. I want something I can knock down for the small track then when I go to the 1/2 mile high bank crank it back up. I'll post some cam specs see what you think I should go to I honestly didn't think of cam because what I have will work at the bigger track.
    Quote Originally Posted by stock car driver View Post
    I ran 436 ci engines with a 350cfm carb and 500cfm at another sanctioning body. Worked great I had success in texas, minnesota, alabama, kansas, iowa and nebraska. The smaller the carb the bigger the cube was what we all did around here for years.

    If you have too much motor change the cam its not rocket science, go to a wider lobe separation to smooth out the power, oval track cams hit hard in a small area... others with wider lc dont.

  14. #14
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    This is what I’m working with and it was installed 3 degrees retarded


    Quote Originally Posted by stock car driver View Post
    I ran 436 ci engines with a 350cfm carb and 500cfm at another sanctioning body. Worked great I had success in texas, minnesota, alabama, kansas, iowa and nebraska. The smaller the carb the bigger the cube was what we all did around here for years.

    If you have too much motor change the cam its not rocket science, go to a wider lobe separation to smooth out the power, oval track cams hit hard in a small area... others with wider lc dont.
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  15. #15
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    Could not open the attachment for some reason. but Honestly, I have never heard of rules saying that you have to run more carb. Its usually how much restriction they put on the induction system to even the field. That's just crazy.
    Regardless, you can put an out of the box 500cfm 4412 on it or a more restrictive intake. If you have a nice carb you are running now, you could lose about 20ftlbs and 15-20hp by going that route alone and the intake might take away another 10hp and 15ftlbs of torque if you have a " good one " on it now.
    All else being said, having too much power is one of the best problems you can have unless the power is like a light switch ( either on or off ).

  16. #16
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    Roller Cam
    Gross Valve Lift - Intake 705 - Exhauat 667

    Duration at .020 Tappet Lift - Intake 287 - Exhaust 291

    Valve Timing @.050 - Open Int 22BTDC - Exh 58BBDC
    Close Int 56 ABDC - EXH 24 ATDC

    Lobe Sep. 107 Intake CL 107 installed 3* Retarded

    Duration @50 258 Intake - 262 Exhaust




    Quote Originally Posted by hpontap View Post
    Could not open the attachment for some reason. but Honestly, I have never heard of rules saying that you have to run more carb. Its usually how much restriction they put on the induction system to even the field. That's just crazy.
    Regardless, you can put an out of the box 500cfm 4412 on it or a more restrictive intake. If you have a nice carb you are running now, you could lose about 20ftlbs and 15-20hp by going that route alone and the intake might take away another 10hp and 15ftlbs of torque if you have a " good one " on it now.
    All else being said, having too much power is one of the best problems you can have unless the power is like a light switch ( either on or off ).

  17. #17
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    427 cubic inches and a 14.5:1 compression ratio with that camshaft. That combination with the big 4" stroke crank and the compression is going to make a lot of torque. It is screaming cylinder pressure. You could widen the lobe center out to a 110 or 112 as suggested earlier and more duration would also help raise the rpm that the camshaft makes power at. Should take away some of the abruptness. Good luck with it.

  18. #18
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    Thanks for the good advice! One question though why do I want to raise the RPM it’s makes power at? Wouldn’t that make my problem worse being I operate in the 5700 to 7200 range? It makes peak TQ at 4500 now. It got better or more manageable adding gear so I was farther on the backside of the curve?

    Quote Originally Posted by hpontap View Post
    427 cubic inches and a 14.5:1 compression ratio with that camshaft. That combination with the big 4" stroke crank and the compression is going to make a lot of torque. It is screaming cylinder pressure. You could widen the lobe center out to a 110 or 112 as suggested earlier and more duration would also help raise the rpm that the camshaft makes power at. Should take away some of the abruptness. Good luck with it.

  19. #19
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    Typically, adding duration will raise the effective rpm range is all that I meant by that. The camshaft you are running looks small to me for such a large cubic inch engine and the compression ratio along with that is going to make a lot of cylinder pressure which makes it harder to control. Changing the timing events with the camshaft, you can lower the dynamic cylinder pressures at given rpms.
    You are correct about turning engines past the curve, we used to turn one of our dry slick motors 9,200 so it was easier to drive when the tracks slicked off. Talk to a good cam grinder and give him all of your information. He can put you on a cam that will calm it down.

  20. #20
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    Ah ok I follow you now it will move the whole band to wider ends and spread it out. My builder is very good but has not built many of the mod motors to these rules and he did exactly what I told him but I should have been more specific I told him I wanted to kill power until certain rpm but didn’t know the track wouldn’t handle it later period so I should have done what you said and stretched it out through the whole band. This was a custom Comp I usually use Schneider out west but went with what the builder wanted to put in per my Info we knew we might have to change it we knew we were getting a repave but they didn’t do what we thought so we can’t use the power like we thought! Thanks this gives me a good idea what I need to look at.
    Quote Originally Posted by hpontap View Post
    Typically, adding duration will raise the effective rpm range is all that I meant by that. The camshaft you are running looks small to me for such a large cubic inch engine and the compression ratio along with that is going to make a lot of cylinder pressure which makes it harder to control. Changing the timing events with the camshaft, you can lower the dynamic cylinder pressures at given rpms.
    You are correct about turning engines past the curve, we used to turn one of our dry slick motors 9,200 so it was easier to drive when the tracks slicked off. Talk to a good cam grinder and give him all of your information. He can put you on a cam that will calm it down.

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