Edelbrock heads Vs. Stock 291-c's the unequivocal truth

[82Waggy]

Got to play around on the flow bench last night at my machinest place.

We put on a freshly built monster aluminum Pontiac race head.

Intake flowed well over 400cfm at 28hg and .800 lift - holy smokes!
Exhaust flowed well over 300cfm at 25hg and .800 lift - used a 2.5"d x 4"l stub tube.

Interesting to see that at above .750 lift the flow did not change much and that an exhaust stub tube made all the difference in the world. Used modeling clay to fair the inlet of the intake port.

I'm going to put my AMC 090 castings on in both stock form and after port clean up this coming week. Will let you all know what happens.

[jeepsr4ever]

Good to know, yes please post up all data you can.

More on the Edelbrocks

[Dusty]

out of the box and bolted on in a little gremlin with a 401 that a friend of mine races here in sonoma county he has always run amc cast iron but for the price the edelbrocks were hard to beat. his motor is .030 with speed pro pistons built 8 years ago with the PAW equivilent of the summit
8601 so pretty mild setup with a torquer. he noticed a definate increase in off the line hp and its about flat on the higher rpm performance

[Mudrat]

Couple things:
1) MC couldn't you have at least CLEANED the AMC heads before taking pic's
2) I'm ignorant - what the hell does this chart tell me??

Intake:
291 090 502
.100 71 74 70
.200 127 156 143
.300 179 201 192
.400 209 219 213
.500 217 226 220
.600 222 232 228
.700 228 238 236
Exhaust:
.100 55 56 59
.200 107 112 113
.300 135 141 146
.400 142 145 150
.500 145 149 152
.600 145 150 153
.700 145 151 153


Those are stock numbers for 3 different heads (via Ken Parkmans test). Edelbrocks walk all over the stock heads...ported you can get a set of heads to flow well but we are talking over port, brass shims and epoxy.

[FuzzFace2]

It shows flow rate for valve lift on the 291, 090, 502 heads. Move the head cast numbers over to line up with the flow numbers is all you got to do.
When you line them up right then post, the format goes to heck!
Dave ----

[Mudrat]

Ahhhhh OK gotcha. Is the flow rate in CC's or CF??

[jeepsr4ever]

UPDATE

Intake:
291 090 502 Edel (true numbers)
.100 71 74 70
.200 127 156 143 125
.300 179 201 192 212
.400 209 219 213 235
.500 217 226 220 266
.600 222 232 228 243 (bad turbulence
.700 228 238 236
Exhaust:
.100 55 56 59
.200 107 112 113 98
.300 135 141 146 130
.400 142 145 150 156
.500 145 149 152 174
.600 145 150 153 184
.700 145 151 153 (Edel @ .650 lift .187)

[82Waggy]

What are you comparing here? Looks like the stock AMC numbers that were tested without a stub or intake fairing.

Did you flow the Edelbrocks? If so, did you fair the intake port and use a stub on the exhaust?

[jeepsr4ever]

The post shows the stock edelbrocks compared to the stock heads.

[82Waggy]

Here are the flow numbers for a set of Stock AMC 291 castings. These numbers were obtained by Ken P., as were the above numbers you posted. Note the exhaust numbers obtained by using a stub to simulate a header. Ken noted that the above numbers were incorrect as he did not use the stub and determined that using an open port resulted in invalid data.

Lift Int,Exh,Exhw/stub
.100 69,53,53
.200 142,95,101
.300 192,130,143
.400 218,143,161
.500 221,144,167
.600 224,145,169

Note how much better the dogleg exhaust flows with a stub tube to simulate a header.

Here is a quote from Ken regarding this test:

[These heads had extremely badly pitted seats, and for the exhaust I was using a 1.68 valve. Both of those things will not make a big difference for flow. The intake shows the slightly poorer flow [of the 291 castings] compared to the later heads, but is typical. Notice how much difference the exhaust stub makes. The dog leg really comes to life with the stub, and of course that is the way it is on the engine with headers. I have now learned most of the exhaust flow numbers are done incorrectly (including my own from earlier testing). This is much more representative, and the AMC dog leg really is good.]

Ken then did some minor porting, a good valve job, and sized the throats appropriately for the valves.

Here are the results:

From Ken: [Next test with the basic work on the mill. I sized the throats correctly for the new valves, did the most minor unshrouding, but that got rid of the machined lip in the combustion chamber a 291 has. Also used the mill to square the port opening and size the pushrod pinch. Just a little bigger, trying to target velocity for about a 6500 rpm max 360. Then I did basic blending of this machine work. On the exhaust I did basic hand porting of the throat.]

Here are the results with your Edelbrock data added for comparison:

Lift 291Int,Edl Int,291Exhw/stub,Edel Exh
.200 137.8,125,107.9,98
.300 192.7,212,153.1,130
.400 236.5,235,177.9,156
.500 256.8,266,220.0,174
.600 248.0,243,227.5,184

[Now we're getting somewhere! I got most of the low lift intake flow back, and the upper lift flow is taking off. The drop above .500 lift tells me I have some more work to do yet, but the improvement are huge. The exhaust is amazing. That was not much work, and fantastic results. The dog leg really is that good, and way ahead of the ported rectangular SS heads with a 1.74 valve. Awesomely good design that dog leg! ]

---

Note that neither the AMC or Edelbrock heads appear to benefit from intake valve lift in excess of .500 as they both show a drop in flow - and that in bone stock form AMC heads show little appreciable gain in flow above .400 valve lift. With basic port work the AMC 291 heads were able to rival if not exceed the out of the box performance of the Edelbrock heads (at least within a margin of error) - Later AMC heads such as 090 or 502 castings theoretically flow a little better than the heavily shrouded 291 castings used in this test. Ken also determined that a 30 degree intake valve seat yielded even better intake flow numbers than the 45 degree intake seat used here.

My point is that a proper inlet fairing on the intake port and the use of an exhaust stub when bench flowing heads is necessary to get readings close to actual conditions as leaving the ports open ended is not the same as having an intake and exhaust manifold installed that helps straighten out the flow. The design of the dogleg exhaust port is heavily dependent upon the exhaust manifold/header for proper flow. It would be interesting therefore to know if you flowed the Edelbrock heads in this way for proper comparison.