SM Head Modifications on a budget

[PRH]

I'd use a set of templates and guidelines if it got me in the 280+ range with a set of edelbrocks.

The only porting templates I’ve ever had my hands on were the DC ones for stock BB heads.
They only addressed what to do in the bowls.

On most aftermarket performance heads, the bowls aren’t in need of much work.
Many are already technically “too big”.
Additionally, the SSR is usually already a big improvement over the factory head it’s designed to replace.
There isn’t often a lot of easy “low hanging fruit” like there usually is with a stock head.

My experience has been that it takes a fair amount of whittling to get a SBM RPM head to 280+.

And based off the results so far on the head featured in this thread, I’d say the SM’s do as well.

The areas I was referring to tidying up on the SBM RPM were limited to the port openings, where to me…….what action to take there is pretty intuitive.

As PRB mentioned, if there is a big mismatch between the seat ring and the bowl casting, that can be cleaned up or diminished some fairly easily as well.
However, my experience has been that that’s often not much of a problem area if you’re starting out with an assembled RPM head.

 

[Earlie A]

The only porting templates I’ve ever had my hands on were the DC ones for stock BB heads.
They only addressed what to do in the bowls.

On most aftermarket performance heads, they bowls aren’t in need of much work.
Many are already technically “too big”.
Additionally, the SSR is usually already a big improvement over the factory head it’s designed to replace.
There isn’t often a lot of easy “low hanging fruit” like there usually is with a stock head.

My experience has been that it takes a fair amount of whittling to get a SBM RPM head to 280+.

And based off the results so far on the head featured in this thread, I’d say the SM’s do as well.

Totally agree with the bowls already too big thing. There are many threads and even videos that say something like ‘the bowl needs to be x percentage of the throat size’. Those blanket statements lead to a lot of problems.

 

[Earlie A]

I’m starting to see a trend with these SBM heads that if you measure the apex area and figure an average velocity of 300 fps through that area, you have the max cfm. In rough numbers that averages 400 fps on the floor, 300 fps through the middle and 200 fps on the roof. It’s crude, but it’s pretty accurate.

 

[pittsburghracer]

Haaaayup. My heads don’t match match because I was just making the ST a skosh wider and there it was. That little blister you see when you know you are screwed.

So I had to grab another casting and start over.

If it’s not a W2 head I don’t even consider porting on them.

Mine are still buried outside my shop. Now that I have the capabilities of using my seat machine to easily open up for bigger valves I should clean one up and open it up to a 2.08 valve size and apply some newer knowledge to my porting work and see what I can get out of a port. They were 300-305 with the (3/8) stem 2.02 valve. No never mind that’s a really stupid idea.

 

[PRH]

The question I can’t answer at this point in time is…….wrt the SBM RPM head is…….
If you did nothing to the head other than cleaned up the port openings and blended/radiused the pinch area……..is that worth any flow?
When I’ve done it to those heads it was part of a bigger job, and I never isolated that part of the job to see what/if it was worth anything on its own.

Basically, I’ve found that small changes made to performance aftermarket heads result in……. small changes in flow.

Conversely, I can spend 20 minutes on a stock BBM 440 346/902/452 intake port and pick up 30+ cfm.

 

[Newbomb Turk]

Mine are still buried outside my shop. Now that I have the capabilities of using my seat machine to easily open up for bigger valves I should clean one up and open it up to a 2.08 valve size and apply some newer knowledge to my porting work and see what I can get out of a port. They were 300-305 with the (3/8) stem 2.02 valve. No never mind that’s a really stupid idea.

No it’s not. I say go for it.

 

[PRH]

I should clean one up and open it up to a 2.08 valve size and apply some newer knowledge to my porting work and see what I can get out of a port. They were 300-305 with the (3/8) stem 2.02 valve. No never mind that’s a really stupid idea.

You’re worried you’re going to enjoy it too much aren’t you

 

[pittsburghracer]

You’re worried you’re going to enjoy it too much aren’t you

As a matter of fact yes I am. I don’t want to travel the cast iron road again. Lol

 

[Mean416]

My RPMs are actually pretty old. I think I originally purchased them back in 2010. I haven't run them for any appreciable time. They've been on the shelf in other words.

Maybe the newer castings are just awful? I've disassembled these heads and there weren't any bad ridges in the bowls at all. I was fairly impressed actually, with the overall quality of the port. Smooth transitions etc. same for the pushrod pinch area. It's all pretty nice actually.

I'm not entirely sure what if anything I'm going to do to these before I put them on the 418. I do know they're going to hold that engine back but I haven't the spare cash to get them ported to the required level. I've thought about tubing the head bolt holes and pushrod holes and opening up those areas. Also considered getting a set of 2.05 valves and having the valve job updated, as well as a deshrouding cut in the chamber.

Of course I'd blend the valve job into the bowls, and do some basic gasket matching of the intake. But beyond that I'd probably not mess with much out of fear of doing more harm than good.

 

[Earlie A]

Daughter's wedding is 6 weeks from today so still busy with the house renovation. Today is wedding shower day and I'm not invited so I get a little shop time this morning.

We last left off with all the easy(ish) modifications complete. The next step was to attack the SSR and apex area. There are 3 ports getting worked at the same time now. This infomation is from post #304 which was the last flow test:

Test 628 is port 3/6 with a 15/30/45/60/70 valve job and a 2.055 valve. This is the port used throughout this entire post.
Test 634 is port 2/7 with a 35/45/60/75 valve job and 2.055 valve.
Test 635 is port 1/8 with a 40/50/65/75/80 valve job and 2.02 valve. The intake valve on this port has been shifted 0.060" and the exhaust port has been shifted 0.080".

This morning I spent 30 minutes total working the SSR on all 3 ports. They were lowered a little (around 0.015"-0.020") at the apex and the SSR was layed back a little to create a larger radius that terminated at the 60 degree bottom cut. Although I did not measure, I would guess that 0.030"-0.040" was removed from the middle of the short turn. No area was intentionally added to the apex area other than that added by working the floor. No cartridge rolls used - this was all done with a double cut 1/2" oval carbide burr.

Results are shown. Now back to the renovation work.

 

[pittsburghracer]

I’ll have to reread this after my brain wakes up. 3 ports with different mods gets confusing.

 

[PRH]

So far, in my mind, the 2.055 valve with the more “plain Jane” valve job looks the best.

The number two test in the last pic of post 335.

 

[Earlie A]

So far, in my mind, the 2.055 valve with the more “plain Jane” valve job looks the best.

The number two test in the last pic of post 335.

At this point I agree, and there may be an explanation for that. Of the 3 ports, port 3/6 (plain Jane) is the only one that does not have the valve sunk to achieve the steep top cut. The wide, steep top cut is shrouding some of the flow at low and mid lifts on the other 2 ports.

I sure am intrigued by the 2.02 with relocated valves.

 

[pittsburghracer]

At this point I agree, and there may be an explanation for that. Of the 3 ports, port 3/6 (plain Jane) is the only one that does not have the valve sunk to achieve the steep top cut. The wide, steep top cut is shrouding some of the flow at low and mid lifts on the other 2 ports.

I sure am intrigued by the 2.02 with relocated valves.

Let me be the first to say the 15 degree cut does not have to be wide. Just a break point.

 

[PRH]

Something I find that can happen when you’re chasing the high lift flow by messing with the SSR is………you can reach a point where getting the floor shaped better for high lift flow, ends up costing you some flow in the low/mid-lift area of the curve.
Then you have to decide which way to lean for the particular application the heads will be used for.

I would agree with your assessment of the valve sinking as being a big player in the lesser low/mid-lift numbers on the two ports..

 

[Earlie A]

Something I find that can happen when you’re chasing the high lift flow by messing with the SSR is………you can reach a point where getting the floor shaped better for high lift flow, ends up costing you some flow in the low/mid-lift area of the curve.
Then you have to decide which way to lean for the particular application the heads will be used for.

I would agree with your assessment of the valve sinking as being a big player in the lesser low/mid-lift numbers on the two ports..

I saw that on the cast iron smog heads a couple of weeks ago. The peak gets pushed father to the right on the flow curve and drags the whole curve with it.

 

[pittsburghracer]

Something I find that can happen when you’re chasing the high lift flow by messing with the SSR is………you can reach a point where getting the floor shaped better for high lift flow, ends up costing you some flow in the low/mid-lift area of the curve.
Then you have to decide which way to lean for the particular application the heads will be used for.

I would agree with your assessment of the valve sinking as being a big player in the lesser low/mid-lift numbers on the two ports..

As much as I hate to disagree with you on this I have to on this subject. I Dont think I gave up any thing high, mid, or low on this port. Sometimes I feel guilty telling guys not to aggressively lower the shortside on these heads because you have to. BUT and this is way I say it. You can mess up a port real bad if you Dont know the needed steps. I take caliper readings off my deck across the top of the shortside and have measurement’s for a 290cfm port, a 311-315 cfm port, and a 320 plus cfm port. You would be amazed at the shaping necessary.

 

[Earlie A]

As much as I hate to disagree with you on this I have to on this subject. I Dont think I gave up any thing high, mid, or low on this port. Sometimes I feel guilty telling guys not to aggressively lower the shortside on these heads because you have to. BUT and this is way I say it. You can mess up a port real bad if you Dont know the needed steps. I take caliper readings off my deck across the top of the shortside and have measurement’s for a 290cfm port, a 311-315 cfm port, and a 320 plus cfm port. You would be amazed at the shaping necessary.

View attachment 1716294079

Fantastic numbers for sure. I’ve told you before that you’ve really mastered the shape of the curve as well.

With a sharper short turn, one that backs up or noses over at 0.500 lift, would you see higher flow at 0.500 than the 294 in your chart?

 

[pittsburghracer]

Fantastic numbers for sure. I’ve told you before that you’ve really mastered the shape of the curve as well.

With a sharper short turn, one that backs up or noses over at 0.500 lift, would you see higher flow at 0.500 than the 294 in your chart?

You would probably crash the port because the air isn’t slow enough to handle it. The air would skip the bowl and disrupt the good air in The back of the bowl. That you will hear from 30 feet away.

 

[pittsburghracer]

And my hearing going.

 

[Newbomb Turk]

At this point I agree, and there may be an explanation for that. Of the 3 ports, port 3/6 (plain Jane) is the only one that does not have the valve sunk to achieve the steep top cut. The wide, steep top cut is shrouding some of the flow at low and mid lifts on the other 2 ports.

I sure am intrigued by the 2.02 with relocated valves.

And that head with the top cut WILL make more power every time.

 

[Earlie A]

And that head with the top cut WILL make more power every time.

I know you are a fan of the wide top cut and the steeper seat angles. Do you like the top angle to be straight or somewhat convex? A gentle convex top cut should allow for a little less shrouding and a little more flow (at least on the bench).