[JoePapa]

I've recently ported my #62 cast iron heads and used the 1.75" sizing valve as a grinding template. I tried to follow the Jim Hand tips and McArthy video as much as possible.

Here are my results from the Superflow 600:

Head flow dropped off after 500 so they stopped recording intake there.
`
#62`heads
Head`1``````````.200````.300````.400````.500````.6 00````.700
Intake``````````154.96``205.62``250.32``274.16
Exhaust`````````102.96``149.76``177.84``187.20``21 2.16``230.88
`
Head`2``````````.200````.300````.400````.500````.6 00````.700
Intake``````````151.98``205.62``247.34``277.14
Exhaust`````````106.08``152.88``180.96``202.80```2 21.52``234




I was told the .550" lift value was decent and that these should run good as they are. If I feel the short turn very carefully, I can feel a very slight uneven ridge - almost like a little bump. The final grind has been done on the valve job so I'm not really eager to jump in there with a sanding roll and I'm tired of grinding but it's bugging me that these are dropping off at .500.

My question is - has anyone encountered this and what did you do to resolve it?


Thanks in advance!!


Joe

[Daniel Barton]

The heads need to be probed with a pitot tube on the flow bench but more than likely your air speed is way to high going over the short turn radius of the port, that area of the head needs to be enlarged to slow the air down so it can make the turn into the bowl... when air reaches about 350 feet per second it is in danger of "seperation" which means that it can no longer follow the shape of the port, I would recommend widening out the short turn on the side walls, proceed carefully and check your progress... grind a little and flow... keep going until you reach your goal. If you can probe the port with a pitot tube and find the area that is affected it will save you a lot of time and stop you from removing material from the wrong spot. Your profile on your valve and the profile of tha valve job can also have an affect on a port that stalls or backs up. I understand that this can be difficult and expensive if you dont own your own flow bench and pitot tubes but this is the best, correct and most convenient way to pinpoint the area of disturbance and rectify the issue. Hope some of this helps you, good luck! Dan

[Skip Fix]

McCarthy mentions that also -pretty common for the short turn on iron heads. Takes alot of work to get it out.

[brians]

Joe:
Something seems wrong with the intake numbers you posted.

It takes a very good port to get those numbers at .5” with a D-port head and
then they should not have stalled. (or did they reverse?)

Did you check the CC of the runners before and after?

Just a recommendation, I would not mess with the actual short turn rad. without a way of checking it. You really add high lift flow, but also really screw up a head plus odds are you will have to redo the valve job.

My opinion is to get the head rechecked before doing anything.

Brian

[John Bailey (GTOKID)]

if they go into reversion...you need some one to fix them who knows how to port heads. usally only hi flow heads have this...

[JoePapa]

Thanks for the replies guys. Here's a little more info...

When these were being flow tested I was told there wasn't anything abnormal about the air noise - no popping - no whistling - and so on.

I can't afford to have someone probe and fix each cylinder so thats not an option. I was told by two machinists that these would be fine to run as is if I don't go over .550 lift (since they fall off after that value). Up to that height, they seem to flow pretty good cfm.

I did find a little bump on the short turn that a sanding roll would fix. I can fix that pretty easily but we just did the final cut on the valve job so caution will be mandatory.

Would I get good performance out of these heads as long as I don't go over .550 lift?

The exhaust is fine - only the intakes had this symptom.

[65nss4spdGTO]

I've seen if the heads drop off before .600 lift, more work needs to be done. What about the flow numbers @ .200 and .300?

[Jim Robertson]

We did a set of 6X heads that went 280 at .550 lift; at about .570" lift they would lose 20 - 25 cfm. We dyno'd the 455 engine using a cam similar to the RAIV specs with .550 lift at valve and it made 512 HP and 565 lbft of torque with performer RPM, QJet, 1-7/8" headers and 9.7:1 compression.
Your engine should respond nicely with your porting efforts.
Go for it
Jim

[JoePapa]

Thanks for the info Jim, good to know. I found someone else who's air flow drops like this too and they're in the mid 11's on motor. I just watched the video one more time and feel better about what's going on. In the video, they mention the drop at higher lifts but also say I'll get good performance under that drop off point. In fact they say some of the drop is due to turbulence at high lift but that a slight turbulent effect helps mixture in the cylinder. I won't be running high lifts with this motor so I feel better about my situation now. I may reflow one cylinder after I smooth the ridge but don't think I'll do much reshaping now.

[screamingchief]

This info is purely for the sake of discussion here,as the valve-job is already done to these heads now.

If a fella were really concerned with the high lift flow dropping off with a head like this,IMO he may also wanna consider using a steeper intake valve/seat angle than the OE 30 degree angle the next time he went thru the heads.

Many folks will debate the benefits I'm sure,so take this post as just offering some "food for thought" here...

But consider that it can be real hard for a high velocity intake charge to make that sharp turn around the valve face,it's kinda like running into a brick wall in some cases.

You'll loose some low lift flow surely,so do consider the pros and cons.

HTH.

[Bob Eiler]

I haven't seen it posted here before, but 45 degree seats seal better than 30 degree seats, due to better wedging of the valve to seat.

When building for horesepower think;
1 sealing
2 friction
3 airflow

Too many people disregard nos 1 @ 2, and concentrate on no 3.

[JoePapa]

The McArthy video also talks about this and shows an improvement in airflow using the 45 degree angle. They said it was mostly high lift but it looked like a solid overall improvement to me.