Does anyone have a set of flow figures for a standard 128 head? (corvetteZ51 racer, scorp?) I remember them being published in either Hotrod or Carcraft sometime in the mid/late 80's, to compare them with the then soon to be released "113" heads. but I have been unable to find the article. :cheers:

 

I would have to dig pretty deep in my stuff to find the full flow numbers, but I do remember the peaks....

Intake - 199 cfm @ 0.500" @ 28" H2O
Exhaust - 110 cfm @ 0.500" @ 28" H2O

I didn't go any higher since stock valve lift is only ~0.408" or so on the intake...

 

Thanks Z51Racer, I thought that you might have them, I was just doing a bit of brain bending with my desk top dyno and wanted to compare them to a 113 head. I have a flow rating of 165 cfm @0.500" for a standard 113 exhaust. I know the intakes are virtually the same. ( I can interpolate for "near enough" mid range numbers)
I knew the exhaust was weak, but hadn't realised how weak, although I suppose knowing how small the port is in the throat area, it isn't much of a surprise. Its a good job theres plenty of material to open it up, as I believe you now know.
Out of interest, what were your final flow figures on your 128's? and would you share your learning lesson on the short side radius flow hick-up you encountered with some of us who port without the aid of a flowbench ?
:cheers: :steering:

 

Yes, the exhaust port on the 128's is disgusting. I became ill when I saw the stock ports.

Final peak flows (I don't have the whole flow chart handy) were:

Intake 245 cfm @ 0.500" @ 28" H2O
Exhaust 156 cfm @ 0.500" @ 28" H2O

Realize that since this was the only set of heads I had, I had not messed around with the 128's before, and didn't have the time to weld material back in if I messed up, I did not hog the heads out. There is plenty more there, especially on the exhaust side.

Well, as those of you who port heads know, if you're not paying attention, you can lose a LOT of flow VERY quickly by mis-porting the short side radius. At one point, I layed the angle from the peak of the hump to the inside of the valve seat a little too flat, and lost 25 cfm instantly. Fortunately, with about 30 seconds of massaging with a sanding roll on each port, I got it all back and about 7 cfm more. The main thing with the short side radius is to not remove much material from the peak, and simply massage the short side radius. I moved the peak back away from the throat a little bit, and made sure I has a smooth, gentle increasing radius as I came into the seat. I am currently talking with a forum member about doing a set of 113 heads for him, and if he decides to go with me for the porting, I will post pictures of the completed heads when I am done.

 

In 1988 the L98 aluminum heads were revised by GM to the 113 castings over the 128's.
What they did was:
Port roof was raised .100" and the floor was flattened to create the "D" shape you see on 88 and up heads.

Exhaust valves were treated to a 65 degree cut-back to enhance flow.

Basically,this is what GM did to create the famous 113 castings and it has become a good set of heads for power on sbc engines.Imagine,the ZZ4 crate engine with these 113 heads in stock form can create 355HP with the carb set up.

I do believe though,the 128's can be made to perform somewhat,but come in a little less than the D port's.This may be general tech for you but wanted to pass this along.Wondering if the 128's have the material left over/or enough material to do what GM did to make the 113's and port away.If so,they should be able to make similar power numbers.

The 128's can make about 330-340 HP in stock form if it was set up like the ZZ4 crate motor.Not great but not too shabby either.
:)

 

Thanks Z51, All tips and experiences are useful in my experience. I think my philosophy seems reasonable in that I believe (generally) air prefers to flow better around a larger radius than a smaller one. with the emphasis on a "gentle increasing radius" as you state. Keeping it rounded and smooth with a regard for overall port shape. I agree with your comments, thanks for your input.
On the 128 heads you might be porting, posting some pictures would be great, carry on the good work.
Bill, thanks for your input as well, I think we must all remember that some Forum members maybe don't have as much knowledge/experience as others and any relevent subject information makes the post a little more understandable for these members. :cheers: :steering:

 

I don't thnk 128's are listed, but there is a lot of SBC head info here: http://users.erols.com/srweiss/tablehdc.htm
Ben.

 

ive heard thats its pointless to port and fit 2.02's in the 128 castings which i have. just because the lack of flow on the exhaust side is so weak all the air would be almost trapped in the head without a good exiting. i take it since the intake and exhaust are so far from flow figures to each other its like being lop sided or something. :confused: :confused: :skep:

 

 

JoBy, I'm curious what source you have for those flow numbers. The flow numbers on the 128s are way off on the exhaust side, they are far too high for a stock head.

Dave, the heads I might be porting here soon are 113s, not 128s.

SuperNinjaBoy, it is true that it is pointless to put a 2.02" intake valve in a set of 128s for multiple reasons. The first is the one you stated, that the exhaust side is so weak that the intake/exhaust flow balance is too far out of whack. Now, I don't know if anyone has tried running a 2.00" intake and 1.60" exhaust valve in a 128 head in an attempt to allow more porting and a larger valve to help bring the exhaust side back up. The other major reason for not putting a 2.00" intake valve in a 128 head, is that installing anything larger than a 2.00" intake or a 1.56" exhaust valve requires the removal of the stock seats and the installation of oversized seats. The cost associated with this is very high for the flow gains you'll see. It is much more cost-beneficial to simply purchase aftermarket heads at that point.

 

Thanks for the correction Z51, I did read and digest what you wrote, (you may be porting a set of 113's not 128's) unfortunately my typing fingers got mixed up. Thanks again. and to all who have chipped in. :cheers: :steering:

 

JoBy Thanks for posting that info. Where did you get the info from ? As Z51 said the 128's exhaust is very small in comparison to the 113. From what I remember about the HotRod or Carcraft article from the 80's (If you can believe them!) the inlet flows you have seem about right. I remember the 128 having a slightly 'better' inlet than the 113, but the exhaust being some-what behind. The other flow figures you posted, look about right from information commonly available. I would say though, there is a fair bit of material in the 128 exhaust port, and it should be able to be brought up to at least a standard D-port if not slightly higher. (If I had access to a flow bench, maybe I would be able to prove or disprove this) One other thing I will comment on was the variance in port dimensions between one inlet port and another in the 128 heads on my 87. For example the pushrod pinch on some ports was a good 1/16" different to others and the intrusion bulge from the head bolt on the adjacent (siamesed) inlet port was more pronounced on some ports than others. This may account for some of the differences in opinion as to how well the inlets flow on the 128's (good/bad). It is fairly easy to match them up and then give some further enhancement as well. IMO. :steering:


[Modified by Davemc1963-87conv, 1:10 AM 5/26/2003]

 

Sorry, but I don't remember where I found the #128 flow numbers.

Is the #128 exhaust port really that much worse than 1985 and 1988 heads?
The hp did increase when they changed from iron to the #128 heads ...

Exhaust - 110 cfm @ 0.500" @ 28" H2O seems way low.

If that is true then they would flow about the same at 0.500" lift as the older iron heads does at 0.250" lift. I have a hard time believing that.



[Modified by JoBy, 1:58 PM 5/26/2003]

 

I found source of the numbers.
http://www.chevyhiperformance.com/te...98/index4.html

It does not actually say if it is the #128 or the #113 aluminum heads.

 

JoBy, Yes the exhaust port throat in standard form is small on the 128. However, I have not seen it on a flow bench and yes I would have thought it would have been as good as an 85/86 iron head. However Z51 racer has had his on a flow bench, and the figures he posted are what he got. For comparison, the exhaust port throat on a 80's 305ci head I have appear larger, however this dosen't say that they will flow better. Like I have said though, there is plenty of material in there, so they should respond like any conventional pre D-Port head to modification.
:steering:

 

I had Lingenfelter "super mod" port work done on my 128 heads back in 1990. Valves are 2.00 and 1.56 and the port volumes measure 180cc and 68cc. Exhaust flow numbers with 2 inch pipe extension:

.1 57
.2 122
.3 158
.4 171
.5 177
.6 180

A few years later I asked them if upgrading to 113 heads was worth it and they told me that 128 and 113 heads make basically the same power after LPE porting.

 

Those are good numbers, though having the extension on the exhaust port will improve the flow numbers. The extension makes the flow out of the port more realistic. The flow numbers that I have for my 128s are without the extension on the exhaust side, but they do use a bellmouth on the intake side which is absolutely required when flowing the intake.

 

Thanks Torquejunky, Those are good exhaust port numbers, at least they prove that the 128's can be made to work as I thought.
180cc inlet ports have had a fair amount of material removed from the stock "163"cc, so I guess they should show good figures as well. I think a 180cc inlet port is a nice size for a Tpi.
I don't suppose you took any pictures you could share with us. :thumbs:
:cheers: :steering:

 

On the exhaust I also measured with Lingenfelter 1-3/4 headers bolted on and lost about 8 cfm at max lift compared to a 2inch pipe. You loose another 5-10 cfm measuring with no pipe. The stock exhaust manifolds really killed the flow- somthing like 130 cfm of flow at .6 " lift as I remember.

I have the heads off so I'll take some pics and post them. I agree 180cc is about right for a 350 TPI. The intake flowed (with bellmouth):

.1 60
.2 111
.3 160
.4 204
.5 229
.6 248

This was how I received them from Lingenfelter with larger valves and full porting but no chamber work. The larger valves were shrouded but it contributed to the best swirl I've seen. I opened up the chamber (was measured at 59 cc went to 65cc) to lower compression (for supercharger) and unshroud the valves. New flow numbers are:

.1 66
.2 129
.3 179
.4 224
.5 239
.6 249

 

Do you have a swirl meter? If not, how are you measuring swirl? From a flow standpoint, you want 0 swirl in the port, and rely on the piston crown and combustion chamber to generate the swirl. Simply speaking, swirl kills flow.