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Is port CSA the last word????

Posted: Sat Apr 09, 2005 6:27 pm
by ou812
Im running mopar W2 heads on my 360 and the min. csa is at the pushrod pinch. Going by the numbers I have enough csa to run 7200 rpm and thats it. I have more everywhere else in the port, so my question is this: will this csa be the deciding factor in my max power rpm no matter how much cam and compression I run? Currently I shift at 7000 rpm, so am i understanding correctly when i say that if i wanted to get more rpm, the pushrod pinch would be the place to look all things being equal?

Thanks guys...

Posted: Sat Apr 09, 2005 7:53 pm
by bill jones
-How close is the pushrod to the outside of the port wall?
-Is there any reason you can't cut thru the pushrod walls and epoxy a thin flattened tube in there so you widen the width to the absolute max?
-How do you go about getting that area as thin as possible the way the ports are now?
-Have you looked at shimming the rocker and the pushrod over on top of the valve tip another .030" or .060"?
-Offsetting the rocker may not LOOK exactly right but you usually can get do these sort of things and get rid of another .150 " to .200" worth of port wall.
-Even if you only got .100" x 2" tall that's .2 square inch area and that's worth another couple hundred rpm.
-What is the crossection square inch area now that you have?
-Then where is the next smallest area and what is it for square inch area?

Posted: Sat Apr 09, 2005 10:23 pm
by ou812
The cs of the pushrod pinch right now is 2.444. I could make it bigger, by maybe .080w x .040h. Next smallest cs is the short turn which is 2.584. Throat is 1.800 for cs of 2.832. My biggest question is if I installed a cam that was say 8 degrees more duration and changed nothing would the engine speed be increased and max rpm increase over the min. cs limited pushrod pinch. In other words is the min. cs THE last word in max power rpm? Another conscern is if I enlarge this area it will slow it down, right? I dont want to make the engine lazy by making the port larger but if it wont then Id like to increase the pushrod pinch to the size of the short turn cs. Most heads that I deal with all look like this one, having the throat largest, then the short turn then the pushrod pinch for cs. This port also goes over 400 fps right before the apex of the short turn, so Im assuming this could also limit rpm?? The short turns in these heads is really tall and the ports are oval, and from driving the car id say that it pulls very hard...runs 98mph in the 1/8 and best 60ft. of 1.46.
Thanks for any help...

Posted: Sat Apr 09, 2005 11:54 pm
by bill jones
-I really can't answer the questions for certain.
-Larry Meaux should know exactly what you need tho.
-If the engine was mine and I could get another .2 or .4 square inch area by reducing the pushrod bulge I would do it.
-An example is we had a 360 SBC, methanol injected in a sprint car and it was plenty strong from as low as about 3800 to around 7800 but the guy needed more power for a couple of long tracks and we felt we needed to be strong to at least 8300 and maybe even to 8700rpm.
-The only things I did was to change from 1.65 stud mounted rockers to a set of used 1.5 Jesels that had a small offset to the intake pushrod, something like .200".
-The heads were Brodix Track 1 that flowed 294 at .600" with the injectors installed.
-I machined the pushrod walls away on my mill to where I had huge gapping holes, then I epoxed in some "D" shaped pieces of thinwall brass tube so that the pushrods were running right along the flat side of the "D".
-I was really disappointed that I didn't get one more CFM after all this work and I thought that I'd ruined the heads.
-This change enlarged the ports about 6CC's and straightened out the path really nice.
-But when we got the car on the 3/4 mile track it was apparent that what I'd done was well worth the effort.
-The car won that race, and beat some serious other racers with supposedly a lot better engines than we had on a regular basis for about 3 years on short and long tracks.
-The neat thing was the engine didn't lose any of the bottom end so the short bull rings we still had the power we wanted.
-I had worked on that engine for several years prior to this to get the the engine to outrun all the hotdogs out of the corners without laying down on the top end, and the pushrod wall/offset rockers etc was all like an extra 500 to 800 more top end with NO loss of power anywhere else.
-We actually took some valve lift away because of the rocker ratio but we changed from steel to titanium valves and used the same valve springs.
-It proved to me that there are days when simple logic prevails over what the flowbench shows.

Posted: Sun Apr 10, 2005 1:44 am
by ou812
Thanks Bill! How did you get injectors into Track 1's??? Brodix says they cannot be installed in Track 1's. Maybe these are the new style?? I understand you about common sense, and I try really hard not to let the flow bench be the deciding factor in what I do so...I guess I should pull the heads and try it. I will have to match the intake to it as well so what the hell! Thanks again Bill!

Posted: Sun Apr 10, 2005 12:21 pm
by bill jones
-We used obsolete 2-3/16" Hilborn stack injectors where the rules allow larger newer style injectors but those have to have a 2-3/16" restrictor up in the stack.
-I don't know what you mean about getting injectors into the Track 1's unless you mean installation of down nozzles, which we didn't use.
-I don't even know if down nozzles are legal, I don't think they were legal when we first built the engine.
-I had a ton of time in getting the injectors and the heads to flow as a unit and really all I got there was about 12 cfm and I still was losing about 3 CFM between a radius inlet and the injectors, but I never find how to get those last 3 CFM.
-We also had a lightweight homemade air filter box attached to the injectors when doing the flowtests and it didn't hurt the airf low at all.
-The neat thing about it all was here we were beating the USAC and the west coast hotdogs nearly every time we raced with them for something like 5 years.

Posted: Sun Apr 10, 2005 11:20 pm
by ou812
I reverse flowed the head today, never done it before...what should I be looking for? And is it VERY important to try to get the short turn cs the same as the throat? Thanks again guys!!!!

Posted: Tue Apr 12, 2005 4:26 pm
by Cheapstreetduster
on the W2 head the pushrod moved over?
so there should be room to open it up..
a eggelson tool can work good to find the max wall clearence.
what is your intake valve diameter?

i am mapping on a set of W1's or what is called the transam head..
offset rocker arms and the pushrod hole is relocated (but the material in the intake window is still thereas cast)... but it has been machined/ported out.. these heads were done proffesionally and flow very good air.
i am trying to compare/duplicate this heads flow characteristics to a set of J heads .
these are basically the same casting but the push rod hole was drilled closer to the center line of the portwindow, (standard La head)
the issue with these similar intake ports are that;..
the intake manifold port is rather large, then there is the restriction at the pushrod pinch, than it opens up after the pinch , then it gets smaller like you stated near the short turn entry, then gets larger into the bowl.
i think this is its biggist problem as far as airspeed accelerating then decell. than speed up again..
this cant be good for holding a steady velocity and low interuptions..
to me it just seems like having slack in the rope in 2 or 3 different places,,,
seems that keeping the intake window more on an average with overall port will help..
the valve diameter will effect this .. and or not removing material from key areas... to help average the port archetecture.
but i have gotten to the conclusion/ data jsut yet..