Choke flow/ 2bbl engine

[mnmatt]

To whom it may concern, not many of you on here are into 2bbl motors but I did some bench testing tonight and this is what I found.

350cfm Holley carb with a Edelbrock 2701 dual plane manifold. This is the rule on the carb and manifold for IMCA stock cars.
The motor will see .555 lift and thats where most of the testing was done at.


Carb and manifold @.555 lift 28"H2O. Normal numbers with 1/2" radius plate W/O manifold and carb @.555 lift.
180cc Dart 2.02/1.60 .... 181cfm. 248cfm
200cc RHS 2.02/1.60.... 187cfm. 285cfm
235cc AFR CNC 2.125/1.60.... 202cfm. 348cfm
167cc IMCA EQ 1.94/1.50... 182cfm. 240cfm

All the numbers were within 5-10 cfm from .200-.600 lift

The AFR head was used to see the extreme, I can buy the IMCA EQ set for $300, would this be the best set for a stock car engine out of the 180 Dart or 200 RHS?

[FloydODB]

very ineresting. I ported a stock said of ford heads (220cfm) and my costumer wondered if a set of windsor sr's would help power. I simply told him I didnt believe we could find more HP with a bigger head when we were working with the 4412 carb aand stock manifold anyways. the engine ran with some of the bowtie/rhs headed chevys out there. won a few features and several heat races.

[Brian W]

I do a bunch of the 2bbl heads. Everything from the stock IMCA spec head, to "hidden" port work on the spec and other EQ and dart heads. However I have never had an engine on a dyno to do back to back testing to see what my work is really worth for power. They run really well on the track though. Most of the time the guys who run this stuff don't want to spend the extra $$ on dyno time....

I am going to have a IMCA hobby motor on the dyno here in a few weeks, that I will be trying a few sets of heads on to see what difference they make. The hobbys run a Rochester 2bbl that flows around 500 cfm and EX manifolds, if I can find a 350 holley I'll throw it on and a set of headers and compare. That won't give you apples to apples comparison because this engine is only 9 to 1 but might give you some idea.

[Old Grey]

very ineresting. I ported a stock said of ford heads (220cfm) and my costumer wondered if a set of windsor sr's would help power. I simply told him I didnt believe we could find more HP with a bigger head when we were working with the 4412 carb aand stock manifold anyways. the engine ran with some of the bowtie/rhs headed chevys out there. won a few features and several heat races.

Which head ran with some of the Bowtie/RHS headed Chevys, your ported stock heads, or his Windsor Sr's?

[FloydODB]

ported stock heads. D0OE? we didnt touch the intake so it was probably choking. and a real long runner that dives to the lifters and comes back up and then back down the runner I think my intake port ended up 170ishcc's. and I meant to say "bowtie manifold"... marine or whatever you want to call it.

[mnmatt]

Any thoughts?

[k-star]

I am at the front end of this 2bbl deal with a new customer, last year. I can tell you that the guys that have it figured out are not talking. I can see that it is going to be a long road to get a good handle on it.

I am not going to betray my customer and give away any data that we have found so far, but I can say the heads seam to play a big part in what power the engine makes, so don't discount the head because of the carb choke point....

If you think about the architecture of the Ford head compaired to the Chevy you will start to see some of what I am talking about and why a plane Jane Ford head will run with a better Chevy head.

Keith

[mnmatt]

Think a 200cc RHS with a 2701 edelbrock dual plane with a 350 carb and 3.340 stroke hurt alot of bottom end? The cam is 242 246 on a 106

[Matt Gruber]

whatever head, the key may be to stuff in a 2.125 intake valve.
2bbl has a lot of vacuum and is filling the cyl frantically right up until the valve closes.

[stockcar5]

Think a 200cc RHS with a 2701 edelbrock dual plane with a 350 carb and 3.340 stroke hurt alot of bottom end? The cam is 242 246 on a 106

pretty much everything you have will hurt bottom end. i'd go with a smaller runner head like a 180eq or even small port vortec bowties. also your cam is backwards. switch the durations around and install it on a 100 or 102. also add some stroke...that thing will be a dog on restarts and out of the corners.

[mnmatt]

How do you know? Have you tested all these combinations? or just going by what every other uneducated bench racer says?

[stockcar5]

tested on the dyno, flow bench and about 60 races per year of track testing. and you sally??? lol

[340king]

Regardless of what most people think, creating HP in a 2bbl class is usually not going to get you where you want to be. Typically all you do is lose torque in the effort and in the end that is really all you have or rather HP at a lower rpm. It is kind of like Scotty talking to Captain Kirk, "I can't change the laws of physics captain!"

So you have to concentrate on what you can get and get the most of it that you can. It is like baseball, keep your eye on the ball! The chassis performing well will make the engine look that much stronger. That is another ball that needs constant attention.

[stockcar5]

i agree. we go for best average hp and torque and a flat as a pancake torque curve if possible. these are the motors that do best on the track. another thing to look at is cylinder pressure..the more the merrier!

now we just gotta get kids like mnmatt to open his eyes and learn from the FREE advise that he is getting (and what he asked for is a previous post).

[mnmatt]

Ok, stockcar5 I know you don't agree with the combination i'm doing and that's fine we will see if it works or not. If it doesn't we will know what not to do. That's how people go faster by trying things maybe i'm wrong, I am not scared to throw shit at the barn, I'm not saying this motor is thrown together hoping and praying it does what I want to my knowledge which is limited, it is a very well thought out engine. Maybe every 20 year old kid works on motors to the extent I do, maybe not. I do know that I am open minded to everything but when all I see is "stroker" motors going on the dyno and seeing the power and tq curve look like a polygraph or straight up and straight down it raises question to my mind, what if I put my education to work rather than copy everyone else peaking power at 5000-5300rpm maybe if raise peak tq, the curve will be flatter and longer than anyone elses maybe not, its almost a direct overlay dyno graph of my mom's Yukon. All i'm saying is you don't have to be like every other close minded dirt track racer and point fingers with everyone else. Hey maybe someday we can work on a combination together to make it perfect maybe not.