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Flow bench Head Porting collected work by NOSIGMA

Performance mods and Advanced Stroker discussion.
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Flow bench Head Porting collected work by NOSIGMA

Post by 1bolt » May 24th, 2008, 5:49 pm

As far as I know the only 4.0 head porting that has been scientifically done with a flow bench (and written about on the net) are by John "NOSIGMA" Young, an Engineer who's an AMC car guy, an XJ owner and a member of my local wheeling club. Not to mention a great guy to talk shop with, as I recently had a chance to talk with him "in real life". while I was picking up a free cylinder head from him (and a whole lot more but I'll get to that in a sec).

Some will know his porting work from NAXJA, some from AMC forums old and new. I asked him if he minded if I repost all his net published writings on the subject here in a collected form, and of course he said go right ahead. While talking, John showed me his flow bench and related to me that he has been trying to sell it, with no serious takers willing to come get it and let him show them how to use it. He then offered to give it to me and show me how to use it (Yeah that's how cool this guy is, this was the first time we met or talked in person). But the bench is another story for a later post.

I have read this stuff over and over before touching the ports on my heads, and every time I pick up something that I missed the last time. Pay special attention to the velocity maps and understand how they are laid out, on a grid as a cross section of the port (or a slice of the port looking down the opening if you will). I'm editing this for format and to try and put things in a logical sequence. This stuff is from 3 different forums and multiple emails with the odd note in italics from me.


Advice
For a high rpm motor and a big cam the extensive porting is really worth while but for an off road motor bigger valves, and a lot of easy cleaning up of the bowl, throat and flashing will give you big benefits at lower lifts and lower rpms. I wouldn't suggest doing much to the runners so you can keep the velocities high for low rpm off road work. This is the sort of stuff you can do with a drill, a couple of cutters, a cheap abrasives kit and an Dremel with a flexible shaft.

Unless you are building a high rpm motor focus on cleaning up the bowls and throats, larger valves (shift the intake), notching the block and narrowing the valve guide bosses. A dual pattern cam make up for a lot of the problems with getting the exhaust to flow. Remember its a SYSTEM.

Notching the block gave large improvements, combined with shifting the intake valve more towards the exhaust. Shifting the valve over is easy to do when you put in oversize valved guides. This gave improvements in low lift flow and more area under the curve without having to make the runners larger which hurts you at low rpm. Its really not possible to flow effectively unless you wet flow and velocity map the ports as you cut on a junk head. Anyone can hack up a head and kill the low rpm performance.


He's talking about notching the top of the 258 cylinder bores, but the 4.0 may also benefit from this. This next picture I marked up should illustrate nicely- 1bolt

Image

the notch he put in his 258 block would look a lot like this notch he put in the cylinder head adaptor of his flow bench, this chamfer is only about 1.75" long but made a nice difference in flow, also don't mind the shape the bore adpator is in it has been banged around from moving and needs to be sealed back up
Image
Also it is well above the top compression ring so its harmless to do

Velocity Maps
the numbers are relative. whats important is knowing that where numbers are highest you can cut and improve CFM where they are lowest, cutting will likely only make pockets (like eddies in a river) and turbulence, which will kill air speeds, lower torque and make your engine feel gutless off idle

The yellow boxes are flow reversals (air moving towards the valve) the larger the red number the bigger the flow reversal.
Image

Here are the intake maps. The green areas are the areas of highest velocity. I only did .250 and .500 lift. It wasnt as interesting as the exhausts and its pretty obvious what to do.
Image

The intake flows were increased by widening the port floor and pulling the ramp into the bowl closer towards the manifold face by several millimeters. This did involve (shudder) lowering part of the port floor in the process of moving the ramp back toward the manifold face. I hit water on one head while widening the port floor. I cut a "trapezoidal shape" into the port with the ceiling being narrower than the floor. On another head I broke through into a bolt hole where the port necks down. This is all after cleaning up the chamber, bowl and cutting the valve guide and valve guide boss into a more aerodynamic shape.

The exhaust work involved cutting where the flow was fast and not touching the floor at all. I alway wish I had a "junk motor" to try some pyro putty in to build up the ramp coming out of the exhaust bowl. Another fix is to copy what is done on big block Ford and make some bronze port plates that bolt in behind the header and put a tongue into the port that raises up a hump in the floor.

(Or maybe a 0331 head (2000+ XJ/TJ 99 and up ZJ)... the exhaust ports are dramatically higher (especially the floor) and better shaped, and may be just the ticket for porting, provided you can find a seasoned head that doesn't crack)

AMC article
(this is a comparison of 258 heads to the 4.0 HO and his ported HO head)

This is the text from an article I wrote several years ago. I will try to edit it and add the charts after posting.
Flow Tests of AMC 6 Cylinder Heads
There has been quite a bit of talk about what 6 cylinder head is the best over the years. Pretty much everyone agrees that the 4.0 HO head is the best but no one seems able to produce the flow data to back it up or show just how much better the 4.0 head is than the others. I set out a couple of years ago to not only get the head flow data but to also test intakes, carburetors and modification that would improve the performance of a friends �stock� class race car.


The Flow Bench

Rather than do it the easy way and pay someone to do these tests I built a flow bench. It took quite a while to get it built and calibrated but it has been well worth the effort. With a bench it is possible to check each modification in steps to see its benefits (or problems) and to insure the flow of each port is identical. The data presented is corrected for air temperature, pressure and humidity as well and is given at ISO Standard Atmosphere. All data is corrected to 25 inches of pressure drop. AMC 258 +.040 was used for the bore diameter. Swirl was evaluated using string inserted into the intake port.


The Cylinder Heads
Four cylinder heads were purchased and one was donated for the tests. Each was hot tanked and bead blasted . The valves were lapped but not ground. Seats were radiused into the bowls and chambers using a Dremel tool.

65 Closed Chamber
The 65 head has large ports but a poor port shape. The 65 head was expected to have poor flow since the closed chamber would greatly restrict flow around the valves at low lift to medium lift. The quality of the machine work and casting was quite good on this head.

69 Open Chamber
A 69 open chamber head has the same port shape as the 65 head. With less restriction around the valve due to the open chamber design it was expected to flow much better at low and medium lifts. This head is used by several drag racers in a modified form. Machine work and casting quality were good on this head as well.

83 Small Port Semi Closed Chamber
AMC spent quite a bit of time designing this head and it was the subject of a series of SAE journal articles. The ports while smaller have improved shape and are suppose to provide improved flow and across the RPM range. This may have been true on custom made test articles but the production head tested had horrible machine work and the casting quality was terrible. Lips, seams, shelves and misalignment of the bowls to the ports were commonly found throughout the head.

4.0 HO
WOW. Larger intake valves, beautiful intake ports that sloped down into the bowls, high port floors, high quality machine work and casting quality so good it takes a little time to find any areas that might need improvement. The chambers are semi closed and the ports are comparable in size to the 65 and 69 heads.

The Tests Results Intake
The 4.0 head is clearly the best head (220 CFM) and by a very significant margin. The 4.0 HO head is about 60 cfm better than the next best stock head at .500 lift. The 83 head is a disaster unless you make major modifications to it. With a lot of work this head flows quite well (179 CFM) but it still fall short of the stock 4.0 HO head. Stock the 69 intake was marginally better than the 65 head. The 65 head was able to achieve flows of 165 cfm stock, 175 cfm with minor bowl work and 195 cfm after extensive modifications to the bowl and valve guide boss (flow results not shown).

Image

Test Results Exhaust
As with the intake the 4.0 HO head has better exhaust flow. But the port design is not the best. There are strong flow reversals along the lower half of the port at nearly all lift values. Filling in the bottom third of the port actually increased flow by 10 CFM with the improvement starting at .200 lift. The 65 head is clearly better than the 69 across the board and as expected the 83 head is terrible. There were flow reversals at all lift values on the bottom half of the 83 head. By reshaping the short side and raising the roof and increasing port width the superior shape that AMC designed into the floor can be taken advantage of and the flow increases by 40 CFM or 50% almost surpassing the stock 4.0 HO with its larger valves.
Image

Conclusions
The 4.0 HO head is the way to go. No surprise here but the margin of difference between the 4.0 HO head and the others is much larger than I was expecting. Once I finish a set of customer heads I will start serious mods to the 4.0 HO and get back to you.

John Young
66 Rambler American Convertible.

Ported 4.0 HO Update
The dashed purple lines in the two charts to the right show the intake and exhaust flows of the ported 4.0 HO head. The flow of the intake at .500 lift is 233 cfm at 25 in H20. This is a 15 cfm improvement over the stock head at 218 cfm. Notice that the flow improved at all lift values. Almost all of this was gained by cleaning up the bowl and smoothing of the short side radius. Eventually this was raised to 246 cfm with added flow at all lift values by widening the port with most of it occurring at the roof and then tapering down to the floor. Thinning of the guide bosses and careful shaping of the ramp leading up to the guide boss increased flow at all lift values.


(Edit 1/9/08) Additional flow gains were made by widening the floor to a trapezoidal shape. The widening continued all the way into the throat. A peak of 264 CFM at .500 was achieved on the stock intake valve. I ruined one junk head (hit a bolt hole) and then hit water on the second head doing this. The port was biased towards the cylinder center side and the floor was lowered just a bit on the cylinder center side forming a very very slight trough along the wall. Biasing the valve guide boss to direct flow towards the exhaust valve side combined with the trough and port bias brought swirl way up, far more than any other head tested.
Image

The exhaust flow of the 4.0 HO head was improved by cleaning up the terrible shelf on the short side and then widening at the roof. 148 cfm was achieved. Narrowing the guide bosses and additional widening of the port raised this 157 cfm. It would probably jump another 10 cfm if the floor could be raised as was done with clay in the earlier charts.
Image

Larger valves were then installed on both the intake and exhaust with the exhaust valve move closer to the intake to clear the 258 blocks cylinder wall at .513 lift. 5/16 stems were retained. Unfortunately I ran out of time and had to get the engine assembled an in the car (I was moving to California) so I never measured the flow with the larger valves. One can only guess where it ended up.

John Young

Development Notes
To be continued
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Re: Flow bench Head Porting collected work by NOSIGMA

Post by SilverXJ » May 24th, 2008, 9:15 pm

Its too bad he didn't have a chance to measure the flow with the larger valves.

Why did he think the 5/16 stems being retained was bad?

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Re: Flow bench Head Porting collected work by NOSIGMA

Post by 1bolt » May 24th, 2008, 9:17 pm

Formatting mistake :) fixed it
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Re: Flow bench Head Porting collected work by NOSIGMA

Post by John » May 25th, 2008, 3:41 pm

Keep the info coming, Flash and I were chatting recently about this body of work. Thanks
John

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Re: Flow bench Head Porting collected work by NOSIGMA

Post by Flash » May 25th, 2008, 8:52 pm

I have not read thru this hole thing yet............but i believe that there should be copy in the fact section of it :)

What say you. :idea:

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Re: Flow bench Head Porting collected work by NOSIGMA

Post by John » May 26th, 2008, 3:31 am

I hope the info goes to FAQ as well!
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Re: Flow bench Head Porting collected work by NOSIGMA

Post by Flash » May 26th, 2008, 8:04 am

I'v read thru it now and some of it i have read several time ;)

the map with the boxes, I'm just not getting it. :?:
Maybe if you could shed some more light on that part.......thanks.

the consept of moving the valves inward. Grate example of that :cheers:

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Re: Flow bench Head Porting collected work by NOSIGMA

Post by John » May 27th, 2008, 3:36 pm

The head adapter notch picture made me smile. Do you recall the conversation we had about the cylinder notch on the Barney Navarro block? Things forgotten and rediscovered....
John

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Re: Flow bench Head Porting collected work by NOSIGMA

Post by Flash » May 27th, 2008, 4:05 pm

John wrote:The head adapter notch picture made me smile. Do you recall the conversation we had about the cylinder notch on the Barney Navarro block? Things forgotten and rediscovered....
John
I didn't thing it was necessary on a the bigger bore of the 4.0L...............Sound like it would help.....atleast on the exh side ;)


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Re: Flow bench Head Porting collected work by NOSIGMA

Post by John » May 27th, 2008, 5:03 pm

Couldn't agree more, but I have considered the exhaust side for the 7120 combo I use.
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Re: Flow bench Head Porting collected work by NOSIGMA

Post by 1bolt » May 29th, 2008, 10:48 pm

Yeah I think a bore notch will help the 4.0 as well as a .060 over bore stroker, but I intend to find out for sure using the flow bench and some new bore adaptors, with and without notches.

The 258's stock bore is 3.75" the 4.0 is what 3.87? at thirty over 3.905 and at sixty over 3.935

In terms of displacement and bore to stroke the 4.0 has a significantly larger bore, but in terms of the valve location and shrouding I think it's a tiny difference... That notch on the bore adaptor is close to a quarter of an inch. Which would mean it starts just about a 16th of an inch outside a sixty over 4.0 bore.

One thing I've learned very quickly already, sharp edges and steps flow like shit, radiused edges anywhere in the intake path help flow and you can clearly see that the intake side of the combustion chamber is poorly matched with the bore, there's a shelf created by the chamber being slightly too wide. Thats bad for flow, but it also probably wastes some combustion energy trying to push down on the edge of head gasket and block deck.

Flash: each map is a slide or cross section of the port first one is 1" in from the port opening. If you were looking at a head staring straight down the port and cut a piece of graph paper to fit perfectly across the port 1" inside. The first box would be that little piece of paper. the next one DOWN is an inch and a half inside the port. Now if you look to the right of the first box those three other boxes are the same location but measuring with the valve more open. So at the bottom is 2.5 inches into the port (near the bowl) the next box to the right is at .2" of valve lift, .3" and so on.

The intake one is simpler (he didn't probe at muliple valve lifts only .25 and .5) but is the same concept Box 1 is the first cross section. the one on the left is at .25 lift and the one on the right is at half an inch. The next box down is half way into the port, measured as .25" of lift.

The numbers inside the boxes are relative, a velocity probe that spits out a feet per second number is nice and expensive but unnecessary you only need relative numbers to guide you in porting the same heads.
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Re: Flow bench Head Porting collected work by NOSIGMA

Post by John » May 30th, 2008, 5:10 am

"The 258's stock bore is 3.75" the 4.0 is what 3.87? at thirty over 3.905 and at sixty over 3.935"

After reading this, I just finished measuring a awfully good 7120 head that has been untouched from the factory, the combustion chamber widths miked, on average 3.932, that turbulence inducing ledge is sharp and large enough to be significant.
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Re: Flow bench Head Porting collected work by NOSIGMA

Post by Flash » May 30th, 2008, 6:01 am

John wrote:"The 258's stock bore is 3.75" the 4.0 is what 3.87? at thirty over 3.905 and at sixty over 3.935"

After reading this, I just finished measuring a awfully good 7120 head that has been untouched from the factory, the combustion chamber widths miked, on average 3.932, that turbulence inducing ledge is sharp and large enough to be significant.
John
Let me see if i got this straight...........the head creates a shelf (on the intake or exh side?) which is bad for flow and................
Wouldn't this piece of head gasket, that is exposed, Glow???? Is this why we can't make as much compression as other engs with out ping????????????

Wait!, the head gasket is 4" right! Has any one measure that spec for sure.

Vary interesting.

And thanks for discripion of whats going on in then boxes. ;)


Flash
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"I've also never completed a motor, yet. My mouth (fingers) is also writing checks my ass can't cash."

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Re: Flow bench Head Porting collected work by NOSIGMA

Post by 1bolt » May 30th, 2008, 10:03 am

Hmmmm very interesting thought Flash, it does seem strange that our strokers don't like even moderate low 9's compression (mine is 9.2:1 and pings on hot days and at part throttle lugging when the AW4 shifts to OD at low cruise speed like around town). Obviously some of that is Quench, and factory set timing curve, but a hot spot... that's an interesting possibility.

Most of us have 4.6 strokers thirty over, that shelf is still there on a 30 over bore. The edge of the block could easily be a hot spot, especially considering hot combustion gasses have to hammer on the unmovable shelf and turbulently roll over to follow the piston down into the bore.

Even if it doesn't make a hot spot, it is certainly wasting energy. Which means its robbing some horse power.

You can see the chamber is outside the bore in that photo I marked up. its on the intake side. The combustion chamber is outside of the bore, meaning the block deck and possibly part of the gasket are exposed there. Its like that with 0630 and 0331 heads as well (I haven't miked an 0331 to be sure but I can see the head gasket impression on the head and its the same as every other head.
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Re: Flow bench Head Porting collected work by NOSIGMA

Post by Alex22 » June 6th, 2008, 6:10 pm

I didn't have time to read the entire thread, but I will post up the flow numbers I have now.
This was done on a SF-600 and a 4.000 bore.

http://naxja.org/forum/showpost.php?p=2 ... stcount=20
From this thread http://naxja.org/forum/showthread.php?t=929773

~Alex
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