Small Port Small Valve Porting ??'s

[340king]

I am working on a set of small block Mopar heads for an IMCA modified engine. The tracks where this 360 engine will run are normally really dry slick and don't require a ton of HP. We are building another engine for the second car to run on heavy track nights anyway, so this engine is purely aimed at dry slick tracks.

The concept is to use a port on the smaller side and try to get decent flow out of it to allow a wider usable power range without making the engine too peaky. From past experience the larger port heads seem to have what might otherwise be known as turbo lag in them. When you step on the gas they react softly, then blow the tires off when the rest of the engine catches up with the throttle. We wanted to avoid that. To that end I started to copy my favorite heads for modified racing, ported 273 castings. I know they are tiny but that was the whole point in this exercise. I had some done by a guy back in about '98 that were pure magic on the track. The castings had been abused prior to the porting and the cracks surfaced allowing the water and air to combine.

I have been copying the port layout and the majority of the work the other porter did to my heads. I have a decent flow now, but am suffering from some turbulence near maximum lift. I have probed the port with the flow balls and have found that even the 1/16" ball will correct the issue and gain a substantial amount of flow. The location that seems to fix the issue is on the hot wall side of the port near the short turn about midway up the wall. Once there the port goes quiet and the flow jumps about 5 cfm.

My issue is that I can't seem to find what is causing the problem. Since the velocity is a little higher in the port I am thinking that there is a minor shape issue that needs attention. My current guess is that there is a little bend in the hot wall side of the port and I may have mine at a little tighter radius and that is causing some separation when it gets to the short turn area. Kind of a deflection issue causing the flow to separate from the wall.

I have worked the port with the strings and have very smooth flow over the short turn (the string lays dead flat on the port floor) until I get about 1/4" from the wall junction on both sides with the hot wall side being worse. If I push the rod a little further in the string goes straight down and doesn't waiver. I do get a little waiver up both sides along the walls above the seat.

The ports are about 180 cc's (I dunked the port mold into a beaker and got a ballpark size), use a 1.94" valve and are flowing in the 245 cfm range (@28" H2O) right now before going into turbulence at about 0.540" of lift. I think low 250's are possible if I can kill the turbulence.

As a newby head porter I would entertain any ideas on the possible cause(s) of my turbulence.

[cv67]

Subscribed. had a hard time getting 240-250 out of a 1.94 stock head (GM) depending on what it was without startin to really hack into it

[zums]

trying to isolate one area in a high velocity head is going to be extremely tough and once the manifold is on the complete flow pattern will change, but i can say this , i have a similar combo 1.94 valve 178cc 246cfm from.6-.65 sbc , in a 373cid with a single plane the throttle response is instant and explosive, if its short track, you will kill a large port head similar combo

[340king]

trying to isolate one area in a high velocity head is going to be extremely tough and once the manifold is on the complete flow pattern will change, but i can say this , i have a similar combo 1.94 valve 178cc 246cfm from.6-.65 sbc , in a 373cid with a single plane the throttle response is instant and explosive, if its short track, you will kill a large port head similar combo

That is the exact idea. These 4 link cars are pretty fussy about how the power is delivered and how quickly it comes on. The ability to hit it quick and yet not too hard is the key to better performance in my mind. I haven't tried flowing it with the manifold yet. That may help things out. Thanks!

[ap72]

do you have any photos of the short turn? Also, while it can get messy have you tried spraying a little dye ahead of the port when flowing it at that lift? I've done it a few times and it can show some problems, especially if its on the walls.

[wyrmrider]

Second 273 head thread in a month- it's been almost 40 years...

why not a magnum head with the floors filled in and the short side radius built up like Kay Sissell used to do with the Chevy 6?
He brazed them but you could use some epoxy
too large a valve for the port will also cause the turbo lag and come on all at once breaking loose the tires problem
I'm going to dig out my Red Ram's...

[340king]

The engine owner would rather do a self dentistry root canal than run stud mounted rockers. Just saying. He is not flexible on the idea either. I am a pretty strong believer in the shaft rockers myself and didn't fight his desire to stay with the shaft rocker family of heads.

As for the photos, I will have a new set of port castings later this week that I can show that will probably reveal much more than a poor quality photo of the short turn radius.

After sitting here and thinking about it some more I am kicking myself that I didn't have the shop owner come over and hold the small ball in the spot where it seemed to fix the flow issue and then probe the port with the string. That may have been very informational.

My biggest issue is that the flow bench is 170 miles from my front door and all this R&D time costs a lot in travel expenses. I have about 1/3 the price of a used bench into travel expenses on this and another pair of heads I am working on. I am looking into a bench for my own use, but that is another issue since I don't have 3 phase to the property. Since I run the electric system here, I know it never will have it. I am looking into the possibility of using a roto-phase converter or using a VFD to take my single phase and convert it to 3 ph.

I will post some photos of the port work when I get new castings made up.

[goldmember63]

If you want to tame the thing down spread the lobes. I think the head games could help but reducing and smoothing the torque curve to help traction could be attained by other methods.

[wyrmrider]

why have just one when he could have two?
It will be interesting to see what you come up with
Rocker Arm rebuilders is fairly reasonable for hard chromed shafts and bushed rockers
I used to run AMC lifters (for flat tappet) and hollow pushrods to keep from burning up the tiny rocker balls
what are you going to use for springs? step up retainers and keepers? or can you run longer/ chevy valves?
recall that tulip valves may work better
if high lift cam you may need to relocate the shafts- all well known LA procedures

[340king]

The current plan is to use a moderate cam in it, 254° at .050 with 0.554" lift intake tight lash split pattern cam. I have the Comp Pro Magnum steel roller rockers for it. It has a good rotating assembly, nothing fancy, just pretty decent stuff. Shooting for 480 HP. No monster here.

[Amilcar]

How much HP and what RPM(low and hight rpm) you`re seeing with your currently combo.
Which intake .... CR...

I`m not saying it can`t be done but, not having the flowbench & dyno near to you and a quite amount of time to spent on it, makes it harder yet.

You may find the 240-250cfm on these small heads but, chances are great to you not see the expected result on the dyno.
Theory says you need way higher than .560 lift using 1.94 valve, at least .600 if using 2.02 valve( without counting with any intake restriction per rules)
Too much speed ruins the mixture air-fuel, as you`re already having issues with it passing air only , after some short turn shape experiences, you may find it`s just a matter of CS there and then water jackets starts to appear.

Just taking a look around and you find a bunch of SBM making that HP level "480". A lot of them are bigger cubes, better heads and yet some with more cam than you`re willing to use.

Don`t know if it helps but, what about epoxy filling the 360 heads, not sure if you`re using them, those chambers are horrible, but yet better to start with than ending into water jackets on smaller heads.

Better yet, the extinct RHS-LA heads, now avaliable from indy, these have all you`re looking for, 8mm stems, high speed ports, shaft rockers, modern chambers, LA intake & valve cover bolt pattern.
They flow around 230-240cfm out of the box with 1.92 valve ( at least the ones I had in hands, from RHS)and can easily be upgraded to 2.02 valve, some short turn reshaped, VJ and reach 270-275cfm with minimal metal removed.
I can`t think in a better ticket than this for you reach your goals

[wyrmrider]

Recent engine dyno comparison used those RHS style heads with amazing results
I'd rather convert Magnums to Shafts than weld up the combustion chambers in 360 LA heads

[340king]

Amilcar, I have a set of the RHS LAX heads that I am working on also. The only issue is that the ones I got only flowed 208 cfm out of the box. I had them around the 280 cfm mark and zigged when I should have zagged somewhere and they went into turbulence. I never wanted to get into porting, but those heads ended all of that. It has been a long downward spiral since then! I blame it all on the LAXitive heads. LOL's

It isn't about making power per se in circle track, at least not in the IMCA modified class. Even a smaller lower HP engine can spin the tires at will at any point on the track when it is dry. The key thing is to have the correct feel to the power. Until you have driven a car with the proper feel to the power it is hard to understand. It is even harder to get the driver to understand what they want. That is until you educate them. The 4 link rear suspension has created this mentality that every driver thinks they are hooked up hard, when all they are doing is spinning the tires. Very few drivers can feel when they are spinning the tires. I see it all the time.

Wyrmrider, we have played with the shaft adapters in the past (1999-2003) and they work really well. In fact we were looking for the drawings the other day. I don't think I have the photos on this computer, but I can ship them up from the work computer. The prototypes were made from H11 tool steel and were really nice. Aside from an issue of having too smooth of threads to hold the bolts in, they were flawless. So I agree that converting the newer style heads to shafts is an option, however, we don't know what IMCA might say about that. We tried it in Wissota and had an issue with amnesia when we got the engine working properly. Wissota forgot that they had agreed to let us do it. So after some costly R&D, they made it illegal. I don't want to repeat history with IMCA. I will have to send the photos to them to see if they will agree to allow it. I rather doubt they will, although they appear to be more receptive to things like that than Wissota.

[wyrmrider]

I've heard that shafts had been done but I've never seen them
Don Bass at TMS Propane Performance and Speed-O-Motive were welding up the LA heads, special Cams by Bill Jenks at Moon
(Don still does consulting on burning highly pouted gas for environmental clean up- he starts motor off on propane then bleeds in the bad stuff, sometimes cutting the propane completely off)
All the rest of the development team are retired as I am or deceased)
Don has developed combinations for severe environment motors, chambers, rings, valves, guides, seats not only propane but gas motors for towing, trucks, buses, motorhomes)
later they came up with the pop up into the head piston design
I pioneered the tight closed chamber on the 440 using 67 915 heads or the earlier heads which actually work quite well with larger valves and some mild porting
I used TRW "6 Pack" pistons with a "D" Cup milled in, about 115 cc to create a cup similar to what became/ was the TRW "Turbo SBC piston- now days you can get pistons off the shelf with lot's less work, and those slugs were HEAVY
I went to chief engineer John Erb at Silvolyte and they put the pistons designs into the KB line for both the Big block and small block (we wanted to do Chevy 6 and AMC Jeep also))
The KB do work well but I would have made the compression height a little taller
Do do it right takes a trial assembly (or experience) and some milling/ decking or piston dome cutting to get a tight quench
The pancake combustion chamber only works at the very top end on race gas (same with BBC open vs closed chamber) where they do make some additional HP
anything else the quench chamber (or closed chamber) works best (IMHO)
Bottom line is that the combination of shorter overlap cam and quench (even with more compression) reduced exhaust gas temperature by 800 degrees on a 440

[340king]

Here are some photos of the shaft adapters. They were very easy to work with and looked every bit the part of some high tech deal, but were really simple. I think the tool steel made them look bad ass.