Eddy RPM heads and cam lift

-
1

1969Fish

Well-Known Member
Joined
Feb 11, 2012
Messages
180
Reaction score
1
Location
Springfield, MO
My question is....

Out of the box what is the optimum lift that the heads can flow before becoming saturated and start going backwards in performance.

Have a drag race only 440 in my dart with more suspension and tire than motor. Eddy heads trw pop up Pistons. .030 over, 11.7:1 compression, 850 Holley, eddy Rpms, m1 intake 1:5:1 rockers, 10" tci with 3000 stall, and good rods. Had a 294/525 solid flat tappet. Looking to put more cam in it this year as I tore it down for refresh. Looking at the purple shaft that is .590 and 265 @ .050. Anyone use this cam or suggest anything different??

Car weighs 2900 race weight with me in it.
 

My question is....

Out of the box what is the optimum lift that the heads can flow before becoming saturated and start going backwards in performance.
Click to expand...
I never heard of this. Going backwards in performance due to being saturated.
Edelbrocks head specs should provide a clue to that between the cross sectional area of the ports and there flow rates suggest a ceiling of performance though a lot depends on how far your willing to push the as fast head and in what kind of performance your looking to try and pull off.

Another limitation is spring pressures as delivered though I suspect they will be changed out for a properly matched set to raise the performance ceiling as delivered.

The last limitation I can think of would be the head on top of a mountain motor. Or just more simply stated as, not enough head for the large sized engine. An extreme would be a stock 361 B engine head on top of a 540 engine, with all the race goods.

With the as cast ports and valve spring limitations covered, the performance level is at one I'd call very good for a tough street engine and/or a light drag engine performance. It is listed and sold as a replacement high performance head.

Just how fast it is possible to go with a as cast head is a good question and a clue maybe available in the thread about how quick can you go with a unported head.
"Unported head quickness" is the title found in the racers forum.
 
And now that I see more info, the MP cam may be a Stone Age cam but it still works well. Are there better cams out there? Sure. Opinions will vary and probably vary greatly which will also include a few cam company names from the well known to the obscure.

I think the base route to take on cam selection is the ultimate goal your seeking and how well of a balanced engine package it will be with the cam your looking at. Then combine the engine package with the rest of the drive train package and then the cars suspension and the car itself.

Sounds like your about ready to have some fun.

I'm a bit old school and I would think hard about it & then just get the cam and experiment with it while having some fun.

Good luck, enjoy!
 
What I mean by being saturated is when you get too much lift and the head can't flow that much. If the head has the port the size of a straw, if you will, you don't want to have a cam lift that opens the valve enough to flow enough air to support a port the size of a baseball.

Make sense at all? To me this is how you can over cam a motor. You wanna match the head flow to the lift of your cam to create optimum flow into the cylinders.

Also I do have good dual springs on the heads that are good to 600 lift.
 
Edelbrock has specs listed on there site for flow @ various lifts. You can have your local machinist double check the state of the head and the flow rates. From there, based on there info, you can find where the head flow stalls and the flow area under curve.

If your interested in racing more than street duty, exceeding the max flow point past stall or where it falls off is a route some take in racing. Just equip the head with the right spring.

On street engines, I do not exceed max lift of the head. Be it spring or port limitations. It's just a lot of work for minimal gain on a car that doesn't exploit the gains much if rarely at all. Excellent power can be had without going to extremes.
 
The port goes into stall. That's a combination of the port shape (overall and locally within areas of the port) and the overall port volume (including the intake and plenum all the way to the carb butterfly). Things like the valve job will affect that too. Basically you can figure on it stalling around .550 at the valve, depending on casting and machining quality. Some might go more, some less. That being said - that's only lift - not airspeed, and it's airspeed IMO that really determines choke points. If your heads are bone stock, you are probably pretty close to the limits. Having the factory Edelbrock valve job addressed and some basic clean up done will really wake them up. IMO more cam is a crutch for a poor flowing head. Your money is much better spent cleaning up the heads than opening the valves further.
 
1969Fish said:
What I mean by being saturated is when you get too much lift and the head can't flow that much. If the head has the port the size of a straw, if you will, you don't want to have a cam lift that opens the valve enough to flow enough air to support a port the size of a baseball.

Make sense at all? To me this is how you can over cam a motor. You wanna match the head flow to the lift of your cam to create optimum flow into the cylinders.

Also I do have good dual springs on the heads that are good to 600 lift.
Click to expand...


Actually I like to pass peak flow on the way up and on the way down and I also "over cam" according to many. I went 9.98 at 3200+ lbs w/slightly ported rpm`s and a .680-.660 Isky solid roller then fully ported em along w/the Victor intake and went 9.79 at 135+ at the same weight. Now I`m at about 3000 lbs and will see what it runs when I install the new 3rd member and axles. They have good potential out of the box but why stop there..........
 
In my experience an OOTB RPM head will not stall to .700" lift. I have not bothered to test the OOTB head beyond that because why go beyond .700" with an OOTB head that is only flowing, at best, 290cfm? In theory you could run a .700" lift roller cam with the OOTB heads and see an increase in performance. I have used RPM heads to .800" lift but they were fully ported, not stalling and flowed near 350cfm at that lift.
 
Exactly what I was pointing to Thumper! Exactly! What was the cams duration?

Thanks IQ52, again, exactly what I was saying. Good show!
 
I would say if anyone is seeing 290cfm with an OOTB intake port they are already in fantasy land. The port stalls - meaning no additional flow available - at around .550 lift and 250-260cfm on every one I've had tested out of the box. Inner port, outer port, whatever. Granted that's only 4 sets over the years since I think 2001 with the last one being 2010 I think. I have yet to see any other figures beyond that posted anywhere - except here.
Now if they've been ported and polished even mildly, expect a little more but not very much. Maybe another 10cfm depending on what was done. One can open the valve as far as they want past the .550-.600 range - but it's not going to flow any more than 250-260 plus a little at 28". That's where the RPM port stalls. That doesn't mean the engine won't go faster with a larger cam - but it's not the lift but the accompanying duration that makes the steam. Because the only way to get more air in once the valve is open .550+, is to leave that valve open longer. Even a professionally done hand Stage II port would get you more power than a cam change at this point.
 
When I was 5 and he was 6 we road on horses made of sticks.........
 
You must log in or register to reply here.
-
Back
Top Bottom