Don Terrill’s Speed-Talk

I’m fooling around with building a mild 496 for a 72 K10. Not in a hurry and I enjoy the research. I’ve often read that a smaller port helps velocity in a low RPM application so was thinking maybe peanut ports instead of 781’s or 049’s. But then I read this article:

https://www.motortrend.com/how-to/ccrp- ... der-heads/

and I’m going man, those aftermarket heads are a lot bigger than the peanut port. Even with a very mild cam, the aftermarket heads walked all over those peanut ports even at low RPM.

So what’s the deal? Does a small port really help that much in a low RPM application or not? I could even see myself springing for the Edelbrock heads since they have the heat riser if they wouldn’t hurt my low end too much. Thinking something like a 750 vac secondary (or street avenger equivalent) on an RPM intake with a small hyd roller and exhaust manifolds. I do keep my heat riser functional.

I read, and read a lot. In general terms, if velocity is too high, particularly around the short turn, then flow, and wet flow quality, is sacrificed. Peanut port heads are a great head if you work within their limitations, or even work to reduce their limitations.

On mild performance builds using peanut port heads, whether 467 or 496, I see most using a 2.12” intake and a 1.80” exhaust. The logic that the smaller CSA on the peanut port heads need too much grinding to “almost” properly support a 2.19”/1.88” valve.

The cam in that test is not radical, I’d imagine slightly larger valves and minor porting could get the peanut ports into the 560-570 hp range, and do so with corresponding bump in average torque and horsepower. On smaller-cammed street builds, it really does blur the line for large oval and aftermarket heads. If the cam was much bigger though, larger heads become more desirable.

Stop looking at the port in terms of volume. Regardless of how the engine is built, it's going to require a certain port volume that's dictated by engine demand. RPM, camshaft, induction, etc. will determine what sizing the port needs to be. Also don't overlook valve sizing. In today's engines, you can't put a big enough valve into them to properly fill the cylinders, so it's a compromise with what you have. An engine will require a certain cross sectional area, and within that you need to maintain a certain velocity. Too big, you can lose velocity which will kill cylinder fill. Too small and it can go into sonic choke from too much airspeed, and kill it as well. It's not a one size fits all deal, and selecting a cylinder head can be a very difficult task.

That being said, I wouldn't put a peanut port head on anything. Small valves, small ports, and poor design. The 781's or 049's are much better heads if going that route, and with some work can perform very well. A 496, even a mild build, is going to want to move some air. My best advice to you is reach out to a few head porters and talk to them. Good ones will give you solid advice, others will just try to sell you what you may not need. Just do a little homework first. And the 781's and 049's are not aftermarket, they are OE passenger car heads.......There are many aftermarket heads that will walk all over the top of any of those as well, reasonably priced.....just remember it's about proper port sizing for the combo, air speed, and port shape....

Dragginwagon406 wrote: ↑Fri Nov 26, 2021 12:18 pm I read, and read a lot. In general terms, if velocity is too high, particularly around the short turn, then flow, and wet flow quality, is sacrificed. Peanut port heads are a great head if you work within their limitations, or even work to reduce their limitations.

On mild performance builds using peanut port heads, whether 467 or 496, I see most using a 2.12” intake and a 1.80” exhaust. The logic that the smaller CSA on the peanut port heads need too much grinding to “almost” properly support a 2.19”/1.88” valve.

The cam in that test is not radical, I’d imagine slightly larger valves and minor porting could get the peanut ports into the 560-570 hp range, and do so with corresponding bump in average torque and horsepower. On smaller-cammed street builds, it really does blur the line for large oval and aftermarket heads. If the cam was much bigger though, larger heads become more desirable.

I wouldn't run anything smaller than a 2.25" intake on a 496, and a 2.30 valve with the correct port would be better. A 2.19" isn't even enough for a decent small block these days.....

Coloradoracer wrote: ↑Fri Nov 26, 2021 12:21 pm

Dragginwagon406 wrote: ↑Fri Nov 26, 2021 12:18 pm I read, and read a lot. In general terms, if velocity is too high, particularly around the short turn, then flow, and wet flow quality, is sacrificed. Peanut port heads are a great head if you work within their limitations, or even work to reduce their limitations.

On mild performance builds using peanut port heads, whether 467 or 496, I see most using a 2.12” intake and a 1.80” exhaust. The logic that the smaller CSA on the peanut port heads need too much grinding to “almost” properly support a 2.19”/1.88” valve.

The cam in that test is not radical, I’d imagine slightly larger valves and minor porting could get the peanut ports into the 560-570 hp range, and do so with corresponding bump in average torque and horsepower. On smaller-cammed street builds, it really does blur the line for large oval and aftermarket heads. If the cam was much bigger though, larger heads become more desirable.

I wouldn't run anything smaller than a 2.25" intake on a 496, and a 2.30 valve with the correct port would be better. A 2.19" isn't even enough for a decent small block these days.....

You’re building for a different purpose. For a mild build destined for a 3/4-ton 4x4, 2.25” are hardly necessary.

Different strokes for different folks.

i understand that 781 and 049 castings are factory. i'm trying to reconcile the following apparent inconsistency:

(1) i frequently read about smaller ports being advantageous for lower RPM applications.
(2) I found the linked dyno test where an Edelbrock head with a 290 cc intake port was 9 hp ahead of a peanut port head with a 208 cc port at only 3200 rpm.
(3) i can't see how a peanut port head could possibly have any advantage at all over an oval port factory head with a 250~ish cc intake port if a 290 cc edelbrock head is making more power than peanut port at only 3200 rpm.

i understand there is a lot more to it than intake port size - compression, combustion chamber, material, etc. but if a peanut port had any advantage at all over an 041 or 049 head, shouldn't it at least be able to beat a 290 cc aftermarket head at only 3200 RPM with a mild cam?

i82much wrote: ↑Fri Nov 26, 2021 12:45 pm i understand that 781 and 049 castings are factory. i'm trying to reconcile the following apparent inconsistency:

(1) i frequently read about smaller ports being advantageous for lower RPM applications.
(2) I found the linked dyno test where an Edelbrock head with a 290 cc intake port was 9 hp ahead of a peanut port head with a 208 cc port at only 3200 rpm.
(3) i can't see how a peanut port head could possibly have any advantage at all over an oval port factory head with a 250~ish cc intake port if a 290 cc edelbrock head is making more power than peanut port at only 3200 rpm.

i understand there is a lot more to it than intake port size - compression, combustion chamber, material, etc. but if a peanut port had any advantage at all over an 041 or 049 head, shouldn't it at least be able to beat a 290 cc aftermarket head at only 3200 RPM with a mild cam?

This was a production head with stock valve sizes, right? Did it even have a 5-angle valve job, 30° Back cut on the valves? Take care of that short turn and other details, and it’s probably much closer down there in the rpm range.

Keep in mind, the flow window is much larger on a 2.19, let alone a 2.25, so low lift flow can be much less restricted than a 2.06.

The peanut port heads were used in the 366 and 427 truck motor applications. Even in those the performance was marginal. They offer no advantage to any other head, and are a poor choice in any application, in my opinion.

i think i hear ya. you're saying if i took a pair of peanut port heads to a competent builder, i'd probably do better than the peanut ports in the test.

that goes a long way to helping me see what is really going on here. but let's flip the question on its head, so to speak, and ask it this way. i do not own any heads at all other than the 702 heads on my current 396. if i can find a set of 781 or 049 cores for 300 bucks, is there any reason at all that i should look for a set of 236 peanut port heads instead? my impression is no - i would not give up any discernable amount of power anywhere in the RPM range on a 496 by using a set of open chamber factory oval ports instead of a set of peanut ports. in other words, other than the 300 bucks for the cores and the fact that i can might scrounge some peanut ports for free, there is no advantage to the peanut port for my intended use.

You will lose measurable power with the peanut port heads over either the 049 or 781, if you are staying with a stock head. Even at low rpm, a 496 is going to have substantially more demand on the head than a smaller engine. You need to size it accordingly. I'd do a little shopping around and make the calls I mentioned to you already, BEFORE you spend any money, regardless of amount. You'll be money ahead in the long run with a little more research and information.....

i82much wrote: ↑Fri Nov 26, 2021 1:01 pm … in other words, other than the 300 bucks for the cores and the fact that i can might scrounge some peanut ports for free, there is no advantage to the peanut port for my intended use.

That’s perfect.

There were 427 large oval port closed chamber heads used on some tall deck 427 motors that make great truck heads with larger valves. A welcome bolt-on to my 93 454 TB pickup, no other changes.

And about this:
(1) i frequently read about smaller ports being advantageous for lower RPM applications.

I put a Edlebrock sp2p manifold on a stock 350 in a truck and it idled great and had more torque up until 3500 then it felt like the motor had a governor, it did, same thing happens with heads that have too much air speed and not enough CSA to support the demand.

ok. this is simple. if i wake up tomorrow and there is a set of peanut port heads magically laying on my driveway, i'll spend the $300 bucks on beer and go a little slower. otherwise, i'll look for a good set of open chamber oval ports and go from there.

The bigger valve will only help you with low torque and power. Think area. Up to a certain point, probably around .550, your working off the valve and throat size. You need to get past .25 L/D to work off the port.

SpeierRacingHeads wrote: ↑Fri Nov 26, 2021 1:15 pm The bigger valve will only help you with low torque and power. Think area. Up to a certain point, probably around .550, your working off the valve and throat size. You need to get past .25 L/D to work off the port.

So:
2.06 x 0.25 = 0.515”
2.125 x 0.25 = 0.531”
2.19 x 0.25 = 0.548”
2.25” x 0.25 = 0.563”

I have no idea, so I’m asking questions.

I’m assuming that:

• 11/32” vs. 3/8”

• necked down vs. not necked down stems

• flatter valve head shapes vs. steeper and thicker head shapes

Also play a role as to when the port becomes the limiting factor, presumably, at a lower lift, since they’d allow more flow at a similar lift.

But, putting a 2.25” valve in a peanut port head doesn’t make sense since it would cause an undesirable drop in velocity as the port struggles to keep up with the valve. I’m assuming that’s why a 2.125” valve is popular in the PP head.

Sound about right?