I dont mind spending Bucks on some heads!!.
it will have full boltons. So what heads and cam.

Thanks, I forgot to say My 350 is a 1999 vortec roller cam motor.
I am missing the heads. But not sure what heads to buy. Im sure being a roller cam will help some also..

same car/same motor, with slightly larger TURBO cam, mildly touched up vortec 906s, vortec HSR and stock TB, just laid down 363rwhp with locked timing at 28* and afr of 13.8{still needs more tuning}

I respectfully disagree as there are way too many variables there to be meaningful. It's not a trade off that way.

So we have options. Buy a set of used 083 heads from an L98. rebuild them with a valve job/studs/springs setup for .550 lift etc. Get heads for 100-150 bucks, 100 in springs, 150-200 in machine work/valve job provided you reuse the stock valves, more if you get new valves, 70 for screw in studs.
On the worst end thats 520 for a set of heads.

Do the same for some vette L98s.... 250-350 bucks for heads used...100 for springs, 100-200 for valve job/machining/cleanup, etc. Probably looking near 720 complete now. OR you can skip machining and just do springs, your out 400 bucks. Oh, you may also want to deck them down abit to ensure good flat mating surface tothe block, especially for an old set of aluminums... 100-150 bucks more.

Vortecs similar situation. Buy them 550-600 a pair from SDPC already race ready. Junkyard maybe similar price as above heads, 150-350 depending, id ont know the going rates. Needs cleaned up to handle cam lift/screw in studs/springs, couple hundred there assuming no valve job. May be wise to just buy them already built from SDPC. THEN you need vortec base plate from SDPC which is 360 bucks or so I believe.

Those are your cheapest outs right now and vortec is not the cheapest option considering the price of a base. You may make 300whp on a stock base ported out abit. If you do buy all new TPI or whatever intake you run, then vortecs are not a bad idea.

Or spend 500 or so more and get a good set of aluminum heads that will really flow much better than the above heads, provide weight savings over iron stuff, no special intakes needed, more efficient chambers, better performance overall and room to grow if the need ever arises.

Since you dont mind spending money on heads, might as well get something you can enjoy later. Just my thoughts.

That seems like a very efficient combo and among the highest numbers from vortecs i've seen. What size cam? 13.8 air fuel and 28 deg timing on stock TB and those hp numbers seems optimistic unless the cam was a good size cam. That rivals numbers from AFR headed HSR cars with 268 type cams like XFI or even the larger CC503 224 duration cams.

There are alot of variables to look at, but assuming SAME intakes used, same bottom ends, same car/driveline, more head flow providing the intakes dont restrict it, the more power you can make. I dont see any motors making less power when you give them more air flow.

Better combustion efficiency with a modern head design compared to an older design makes for more power on less timing. Every car I've seen with a head swap to a head that flows more than baseline gains power unless the intake wasnt able to support it. IF it didnt why would we buy heads? I still think given a set motor and intake, I'd go with a better higher flowing head and less cam than a weaker flowing head and more cam. With the smaller cam duration, you will have more lower end power and better driveability.

Jon Kaase:


" I hate flowbenches. As you may know, most of our work is with 815" Pro Stock engines. On these heads the flow bench is almost totally worthless. I think it's misleading at best. We can port an older aluminum A-429 CJ head to flow 400 & 250. Then we can have a P-51 head that flows the same. The P-51 will dyno75HP better than the CJ. It's all about sizes, areas, shapes, and valve placement in the bore. I think you'll find that the more an engine builder uses the dyno, the less he trusts or even uses the flowbench. There are so many flowbenches out there in use that almost everybody thinks he's an expert.

One of our main goals when engineering these heads was to be able to deliver them with 400 cfm intake ports. We have reasonably well achieved that goal. In high flowing intake ports with the port opening positioned down close to the head gasket surface, the air often breaks away from the port floor and results in turbulence. This usually occurs above .600" valve lift when the air flow is high. With the P-51 head, some of the intake ports will be smooth and quiet all the way to .800" lift. Those ports will usually flow over 400 CFM. Some of the ports will go turbulent at .550"-.650" lift. When it happens, the sound changes and the airflow will drop off about 20CFM. The flow will be the same or better than the well behaved port right up to the lift where it goes turbulent. There are several ways to fix this, all of which are not a good idea. If we raised the port entry about 1" at the manifold, it would be a big help because the air would not have to make such a sharp turn. Of course none of the manifolds would fit. If we made the port a lot wider or taller at the short turn, that would fix the problem because the air speed would be much slower. But slow is not what you want in a good performance or race engine. When flowing one of these problem ports, sticking a butter knife or blade in the floor of the port will usually straighten it out to flow 400. We have dyno tested engines with heads that flowed 400 and then changed to heads where every port went turbulent to flow 375. They both made the same power. Now, if you ran a set of heads that flowed 375 because of improper porting or seat work, and then reworked them to flow 400, they would for sure make more power"

#70- Airflow Fallacies: Avoiding the Pitfalls of the Flow Bench

Category: Tech Talk —
Published in National Dragster

Written by David Reher

“What’s it flow?”


Whenever a conversation about cylinder heads begins with that question, I cringe. I know where this discussion is going, and it’s not good. When a racer wants to distill the performance of a highly developed cylinder head down to a single number, I know I’m dealing with someone who is fixated on the flow bench.


I can speak from hard-earned experience, because there was a time when the flow bench was the center of my universe. When my partners Buddy Morrison and Lee Shepherd constructed our first flow bench in the ’70s, it was a revelation – or so we believed. We were addicted to airflow, and like three flow bench junkies, we convinced ourselves that big flow numbers translated to quicker elapsed times. But that was more than 30 years ago, and since then I’ve learned to avoid the pitfalls of flow bench testing.


Unfortunately many racers coming into the sport haven’t been taught the lessons that Buddy, Lee and I learned the hard way. Cylinder head manufacturers, porting shops, and engine builders constantly advertise flow numbers – and I confess that I’m sometimes guilty as well. In this environment, it’s understandable that some racers think it’s all about maximum airflow. They shop for the biggest cfm number at the lowest price, like finding a screaming bargain on a 52-inch TV at WalMart.


The strategy to win the “Biggest CFM Contest” is simple: Grind the largest port that will physically fit in the head, use the biggest valves that will fit the combustion chambers, and test it on the biggest fixture you can find. That head might win the prize for airflow, but it won’t win on the dyno or on the race track.


The factors that determine the performance of a cylinder head are complex. A head that is ported without considering air speed, the size of the engine, the rpm range, the location of the valves, and a dozen other parameters isn’t going to be the best head, regardless of its peak airflow. And yet I see racers who are seduced by big cfm numbers bolt a pair of 10,000 rpm cylinder heads on a 7,000 rpm short block and then wonder why the engine won’t run.


The most critical area in a competition cylinder head is the valve seat, and the order of importance works its way out from there. There are many questions that are much more important than airflow: How far are the valve heads off the cylinder wall? What’s the ratio of valve size to bore diameter? What’s the ratio of the airflow to the size of the valve? What’s the size of the port, what’s its taper, how high is the short-side radius? The answers to these aren’t as simple as comparing a flow number, but they are what really make a difference in an engine.


Airflow is simply one measurement among many that influence engine performance. With the availability of affordable flow benches and computer simulation programs, it’s easy to fall into the airflow trap. A builder works on a cylinder head, sees some bigger cfm numbers, and keeps working for more flow. But if he doesn’t stop and test the engine on a dyno and on the drag strip, it’s very likely he’s gone down a blind alley. What the manometer on a flow bench sees at a steady 28 inches of depression is not at all what the engine sees in the real world. The pursuit of a big cfm rating has ruined countless cylinder heads in terms of what will actually run on an engine.


I put more faith in dyno pulls and time slips than I do in flow benches. I’ll cite an example from back in the day when Buddy, Lee and I were winning Pro Stock championships. Lee came up with an idea for a tuliped exhaust valve. He filled in the back of the valve with Bondo, and tested the new design on our flow bench. It was killer. We instantly saw a tremendous improvement in airflow with a small exhaust port, a nice tight radius below the seat, and much more stable flow. So we had some titanium tulip exhaust valves made and tested them on the dyno – and the engine didn’t run well at all. We had great airflow on the bench, but the engine didn’t care.


We were working late one night, and Buddy decided to yank the heads off the block and have Lee open up the exhaust throats. Well, Lee kept grinding and Buddy kept taking the heads on and off, and eventually we picked up 30 horsepower that night. We were porting from the dyno and not from the flow bench. When Lee finally flow tested the heads the next day, they were down 30 or 40 cfm, but that’s not what that engine saw.


The final test of a cylinder head is on the track. Frank Iaconio was our chief Pro Stock rival, and he was a smart racer. Frankie used to change valves at the track — he’d make a run, come back to the pits and switch from valves with a 30-degree back angle to a 20-degree back angle. We did similar tests on the dyno, but he did it at the track. I was impressed.


I’m not dismissing flow benches. In fact, we use them daily at Reher-Morrison Racing Engines. But a flow bench is a tool, and it’s really not much different than a micrometer. A micrometer can measure the diameter of a piston, but you have to run the engine to learn the correct piston clearance. Knowing the sizes of the piston and cylinder bore doesn’t tell you if the piston is going to gall or collapse a skirt until you run it. And knowing the airflow of a cylinder head doesn’t tell you whether it will make good power on a given engine until you race it.


Experience is the most important tool in cylinder head development. A person with extensive dyno and track experience has been through it all before, and knows how to avoid the flow bench fallacies.