New Questions on 383 Retro

[fc3]

Hey Guys, I have some new questions from my engine builder. I have asked him lots and now he wants to hear some from ya'll. I will paste his e-mail on this posting. Thanks for everyones help. Fred.

Fred,
Well...I just spent some time comparing the Edel RPM heads to the AFR's.
Edel RPM:
170 cc in port
64 cc ex port
64 cc chambers

AFR 180:
181 cc in port
? cc ex port
68 cc chamber

AFR 190:
191 cc in port
? cc ex port
68 cc chamber

I compared the flow #'s of these heads, using the CHP mag test info, and here's where things get interesting:
At .400 in valve lift, the AFR 180 had +12 cfm in, and +36 cfm ex flow, over the Edel.
At .400 in valve lift, the AFR 190 had +26 cfm in, and +31 cfm ex flow, over the Edel.
The 64 cc chamber Edel head yields 10.8 compression with a .030 piston, and 0 deck height, and .039 gasket.
The 68 cc AFR head yields 10.3 compression with a .030 piston, and 0 deck height, and .039 gasket. (You will loose .5 point compression with the AFR's).
Now, the 190 AFR heads come highly recomemded, and their in ports are 21 cc bigger, so of course their flow #'s will be higher. Also, in this test, they used a 76 cc chamber AFR head, that further unshrouds the valves, so of course the flow #'s would be higher still. (Not a good comparison, in my opinion).
Low-mid rpm power making street engines often need smaller ports for higher airflow "velocity" to fill the cylinders, and high cylinder pressure, (more compression), at low and midrange rpm for torque. You could have them mill the AFR's down to 64 cc, but this would require a .024 flat mill. This, combined with the possible .015-.020 or so block mill, would probably require special length pushrods to reset the valvetrain geometry, and a possible extra intake side mill, to get everything to fit and line up right, and there must be enough piston valve relief for proper clearance also. (No big deal, but more time and $).
In my opinion, 170 cc would be enough to support 383 cubes at 5,500 rpm, and I really can't understand how 21 cc more volume intake runners would be higher velocity. The AFR's must have a really good ex port though, or, are they just bigger?
So, the big question is, will these AFR heads make more low and midrange power/torque to accelerate your 3.08 geared street friendly vette, from idle to 5,500 rpm faster than the RPM heads? I would really like to see some real life proof, to make the right decision!
Why don't you post this on the vette board, and see what their thoughts are. And tell them our intent is not to flame anybody, or prove them wrong, you just want some opinions on these points, and you value their imput. I would like to see what some experts have to say. This should be very good info for other people on that board, as well. Let's see some pros/cons.
Mike

 

[Stingray6974]

Having built more engines than I can remember I'm going by personal knowledge and experiences. One thing I have learned is 170 cc is too small for a performance engine, 200cc is too large for street engine. Afr heads have been around a lot longer than edelbrock's heads. Ever hear of Brownfield? If you're going to spend the money, buy the best. As for compresson you left out valve relief cc's, piston depth in the cylinder, and quench. 10.8 is way too much unless you go with a much larger cam to reduce cylinder pressure. There goes the low and mid torque. Now add a set of small runner heads and you've got nothing. What good is an engine that won't run clean below 3,000 rpm? With 3.08 gears you'll have to downshift to second to pass someone on the highway.
Here's a thought. Build an engine that starts making power at 1,600 rpm, power band to 5,000, realistic compression: 9.5 - 9.8,
the best flowing heads for the budget that don't choke at 4,000, will idle at 800 and let the power accessories work.
Since I spend most of my time actually working on Corvettes I'll let you post this on the Vettenet. And yes 170cc will feed a 383 at 5,000 rpm. So will a 350 cfm carb. Neither one will make any power above 3500 rpm.

 

[sscam69]

CHP flow numbers for
Edl Perf. RPM
Lift intake/exhaust w/pipe
.05 31/23
.1 64/51
.2 29/104
.3 181/132
.4 218/157
.5 237/173
In vs Exhaust ratio remains at ~72%

Air flow 180
64cc exhaust port
.05 35/25
.1 66/55
.2 137/115
.3 193/164
.4 230/193
.5 250/208
In vs Exhaust ratio remains at ~84%

AFR 190
64cc exhaust port
.05 40/31
.1 71/67
.2 144/121
.3 208/157
.4 244/188
.5 262/202

In vs Exhaust ratio remains at ~77%

I compared CHP's independent flow numbers to that of AFR's catalog and AFR quotes them more conservatively.

The exhaust ports are the same volume and look at the difference in flow for both of AFR's heads to Edel's

ok now for this guys email

further unshrouds the valves, so of course the flow #'s would be higher still. (Not a good comparison, in my opinion).

Sounds like he is biased towards edelbrocks. You want to pay attention to the net effect of the heads. If it unshrouds the valves that improves alot of other things other than just flow. Swirling, tumble mixing etc.. Its a fair comparison IMO because both heads fall in the same class and it seems one has been designed better than the other. Hence putting bigger valves in a head that would other wise use small valves.

The AFR's must have a really good ex port though, or, are they just bigger?

nope just a really damn good exhaust port. Its the same volume and flows a heck of a lot more!! Could that be an indicator of how well the intake port/runner has been designed? I would think so. You have to actually get dimension of the heads to fairly measure both of them but then we are getting unrealistic for an engine that is only putting out 400hp. That goal is easily achievable with the RPM heads but you can do it with a smaller cam with the AFR's.

I would like to see what some experts have to say

I don't know, I am not interpreting this in a good way.

I'm with Stingray on this, your gonna have great low end with AFR's and if you decide to go bigger the flow is going to be there to support it. Unlike edels that you are going to have to get ported and in the end pay the same or more for something that you could of have bought the first time. Your gonna get a great set of heads with AFR. The numbers are there and I have heard of nothing but good things about these heads, I can't say the same for edelbrocks.

Another thing the AFR's come already CNC ported, unlike edels heads. Its going to cost you around another $1K (give or take) to get the edels CNC ported like that down the road. You can throw in an extra $300 and get the heads already CNC ported. I told you I did my research!!

I also agree about going with the best. I have learned not to shortchange anything. I always buy proven high quality items because it takes more time ,and sometimes money, to do it twice.

Look your gonna get a REALLY good set of heads if you go with AFR.


And another thing I don't like the tude of this guy.

 

[AKRAY4PLAY]

Fred,
the combination of the AFR 195's with 68cc chambers yielding 10.3 compression ratio is the perfect combination for what you want to build. the compression is low enough to run a carb and poor (88-90 octane) and not worry about detonation. it has enough to keep all the high performance you want and not sacrifice durability. when you start getting into flow numbers vs. stroke length, the larger heads work better. remember the flow starts and stops every other crank revolution, so you need a little bigger intake port to "suck up" the flow pulses. the trick is not to go too big, which is what Mike your motor man is trying to do. 383's are tried and proven to run super sweet with 195 intake runners. the 170cc Edelbrocks are designed for mild to moderate 350's and hot 305's. STROKERS LOVE CFM!!! i am so confident that you will like the AFR's, that i will buy them from you if not totally satisfied! i love mine, and think i could go even bigger than 210cc on a my 406. right now the thing you need to look at is the cam. this will be the limiting factor in your equation, as it should be. you never want your heads to be the limiting factor. flat top pistons and .039 quench with 68cc chambers will give a great burn pattern resulting in higher volumetric eff and scavenging. a lot of guys are running 210cc heads with a 383, but they are turning higher rpm as well. the motor will take the AFR's with a smile.
as for the other things. the pushrods need to gauged and ordered after the motor is assembled. DO NOT make the mistake of ordering the pushrods before assembly. every block and head combination has different tolerances, even same make and model. your p/r length is very dependant on the heads, gaskets and block. they are cheap to get good ones that are exactly the right length, and your valve guides will thank you in the future.
you have all the right ideas and a great parts list for a super motor configuration. just get the right cam after you decide which parts to go with. the cam is the key to making you happy. brian