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Thread: 2bbl heads

  1. #1
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    Default 2bbl heads

    Building a new 434 for a 2bbl street stock class. Can run any 23 degree steel head. Kinda stumped on what size intake runner to start with?

  2. #2
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    With that many cubic inches, you can run larger cc intake runners and still have good port velocity at the lower RPM. 210cc to 230cc. But a 2 bbl limits the upper RPM of that motor. Dart Iron Eagle has a 215cc and a 230cc, I would choose based on 2bbl size rule and cam rule. Both are available in 72, 64,and 49 cc combustion chambers, depending on your piston or compression rules.

  3. #3
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    best sets of heads i have had on my 2bbl stuff were small port vortec bowties and eq 180 runner heads ported by harrys heads. No need for anything over 200cc.

  4. #4
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    Very good point about the flat torque curve. Everything I try to build is with that in mind. Sorry... His question left a lot of variables by not listing his piston, cam and carburetor size and fuel limitations. I was assuming this was some sort of Open/Outlaw street stock class running that many cubic inches. Possibly roller cams and large 2bbl carb. and possibly methanol. Next time I will ask before spouting information.Safe rule of thumb: If you can't decide between 2 different sized heads, go with the smaller of the 2 for better "all around" performance.Most everything in our region is 362 ci limit, 500 cfm, FT piston and flat tappet cam on gas. 200cc runners is the biggest I run turning in the 7600 rpm range. But I also am on top of the valvetrain and am willing to hang extra gear and turn it 7800-8000 when the track dictates it. My combination starts pulling 2500-2600 and never goes flat. Broad, flat curve. But there are many different ways to do things. Example: To try and compete with the torque of that many cubic inches, I would have multiply my torque output through the final gear ratio to equal the torque output applied, at the tire contact patch.

  5. #5
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    LOL Ok smarty pants. I sense your sarcasm. I am just saying that with the combination that I have been running. If I were to be at a high idle, say 1500 rpm, going around the track, and mash it to the floor, it has that low rpm lug till about 2600 then you feel it start pulling. That's when cam profile and the port velocities start to come in and it does not stop pulling till you let off the gas. Its a smaller but aggressive cam profile, with moderate sized heads, with a tall plenum (not a large plenum) intake to get the carb. as far away from the plenum floor as possible. Then you run light valves and valve train to be able to control the valves at high rpm so that it never stops pulling. It is a combination that works with our rule structure.

  6. #6
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    I run my gauge legal 4412 361ci motor right around 8100. Pulled real hard all the way. There is more than one way to get the coon.

  7. #7
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    Quote Originally Posted by ford396 View Post
    I run my gauge legal 4412 361ci motor right around 8100. Pulled real hard all the way. There is more than one way to get the coon.
    what head you got on that engine ? im with stockcardriver on this one, a 2brl engine with that wide of torque curve baffles me.

  8. #8
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    Wow.... I didn't come on here to be in a pissing match. I was just offering advice from my past experiences. If we could build large CI motors in our area we would. We have to resort to other ways of getting power to the tires. With large CI you don't need to turn the rpm to make the torque. With a larger CI motor it WILL go flat at 6800 because there is not enough air to supply that many cubic inches. There is enough air to supply smaller cubic inch engines into a higher rpm range. That is what we have to work with. That is why I mentioned being on top of the valve train. It is a very, VERY, important part of the combination. It's all in the combination. When I mentioned that it started pulling at 2600, I didn't mean that it had the torque that your motor would have at that rpm. Not EVEN close.... My smaller motor has to depend on the gear ratio to multiply the torque applied to the tire contact patch. Example: 525 lbs tq x 6.0 gear= 3150 lbs tq at the tire. vs. 475 lbs tq x 7.0 gear= 3325 lbs tq at the tire. Its all part of the combination. It seams to me that you are going a little over kill with the light weight valves and lifters, if you are only turning 6800. A good set of springs should be able to control standard weight parts at that rpm. But this is all just my humble opinion. If you are serious about trying a different engine combination, I don't mind helping. But in your situation being able to run large CI its easy torque and lower maintenance on the valve train.

  9. #9
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    what has lighter valves have to do with the torque curve of an engine? by the way, the pissing matches are for the gossip section.

  10. #10
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    Well... Its not the valves, its the airflow. Example. 500 cfm dictates the air that can be pulled into the engine. This limits the rpm potential of a given engine. A larger engine would starve for air at a much lower rpm than a smaller engine. It can create a lot of torque in this lower rpm because of it consumption of air, but Its torque curve is "shortened" by the 500 cfm limit of air. Now the smaller engine can not consume the same amount of air at the lower rpm, so its torque starts to increase at slower rate. This increase in torque occurs over a larger/broader rpm range, due to the smaller engines rpm limit is much higher with a 500 cfm carburetor. The valve train has to be under control to take full advantage of the added rpm that the smaller engine can produce.
    Last edited by turtle1hp; 11-25-2015 at 11:02 AM.

  11. #11
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    you've about lost me, but I will say, I have a titanium valve that has the exact same dimensions as one of my solid stainless valves, as far as one changing the torque over the other by doing nothing but swapping the valves, I cant see it. Now, as far as reliability, at higher rpms, 7000 plus, then the light valves will aid in longevity , but for engines like being discussed here, I don't see how they could make difference. For the record, to the original poster, I would go with the small port vortec myself.......

  12. #12
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    You are right. The lighter valve does not make more power. The light valve creates reliability at higher rpm. I must be missing something here. What is your rule structure? We are limited to 362 ci. This combination is based off of 355 ci, stock bore/stroke combination (4.030/3.48), Flat top piston, any cast iron head, flat tappet cam, any intake, 1" spacer, gauge legal 4412 on gas, and headers no mufflers. Oh shoot... Is this considered jacking a thread?? Should I stop?
    Last edited by turtle1hp; 11-25-2015 at 01:29 PM.

  13. #13
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    14 degree RHS heads w/240cc runners. Best of the best. Big bore, short stroke. about 535hp. 485hp making it to the rear tires. This was out of a flat tappet, 361ci, 12.5:1 engine. Twisted the snot out of it. Won many features and invitational races. Since it is not the way you guys would do it, it must be wrong and wont work.

  14. #14
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    Quote Originally Posted by stock car driver View Post
    Im not sure who your talking to? Why so defensive? You just posted your specs and nobody has said anything about them, lol..
    Quote Originally Posted by stock car driver View Post
    I think these guys are measuring pulling to xxx rpm by making noise to xxxx rpm.. All my motors Ive built would do that until they went BANG also. But looking at the tq and hp curves they were dropping hard with a 4412 above 6800
    umm... you kinda called us out and said we cant make a motor to pull past 6800.... just sayin....

  15. #15
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    Quote Originally Posted by ford396 View Post
    14 degree RHS heads w/240cc runners. Best of the best. Big bore, short stroke. about 535hp. 485hp making it to the rear tires. This was out of a flat tappet, 361ci, 12.5:1 engine. Twisted the snot out of it. Won many features and invitational races. Since it is not the way you guys would do it, it must be wrong and wont work.
    man, that's a big head for a 2brl 361, how did you get a good useable torque curve to 8100rpm,s ? also I assumed you were blue oval powered by your screen name.

  16. #16
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    well.... ummm.... you see what happened was.... the dog ate my dyno sheets.... Stop laughing. It's not funny... It's true!! LOL Guys. I have enjoyed the conversation and the abuse, but I gotta go. I hope everyone has a Happy Thanksgiving!

  17. #17
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    Actually that is not that large of a head. Very long runner allows for more cfm in the runner. Cross section still small enough to promote excellent velocity under the two barrel carb.

    Actually it was a gm engine.

    I also tap out. Enjoy your conversation stock car.

  18. #18
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    these conversations are about the only reason I come to 4m any more , you would be amazed how much an old dog like me can still learn on here, sure we call BS sometimes, and sometimes were right and some times were proved wrong, that's how you gain knowledge if you want it, any way happy thanks giving all.

  19. #19
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    You can only pull so much air through a 2V carb so how would increasing the runner size help?
    I can't imagine a bigger pipe moving the same amount of water any faster....

    Compression plays a big role in the power produced when the supply of of air is less dense.

  20. #20
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    The 2bbl is rated at 3" HG flowing 500cfm. What happens when you pull 9 or 10"?

    Pulling vacuum at WOT under a 2bbl carb is where it's at. You can do that with a big port or a small one.

    A port must maintain proper shape for the valve size. Running a 2.15 valve is going to require a certain CSA/CC the same as a 2.02 is going to require a certain CSA and shape. The intake runner is just an extension of this.

    The vortec bowties run so well because of the efficient chamber. Couple that with the right other stuff and you're good to go.
    BUCKLE UP NOW, YA HEAR?

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