DOHC Stock Head Flow Numbers

[Q]

We flowed an "early" ('91-'95) head yesterday - just to see how well it flows. This fully stock head came from a junkyard. It's one of several sets that we have for analysis and future conversion to the Primatech DOHC-6 head.

Here's the data. (Taken at 67*F using a PMI9000 flow bench, 28" of water. We used a short molded entry to the itake and no pipe on the exhaust):

[Sorry if the columns don't line up perfectly.]

Lift intake Exhaust
.050 49.0 28.6
.100 96.3 74.2
.150 139.6 98.6
.200 177.3 125.7
.250 206.9 139.7
.300 232.5 148.7
.350 252.5 154.8
.400 263.5 155.95
.450 267.5 157.1
.500 268.7 157.2

Looks pretty good. If we had a later head ('96-'97) we could tell you about the improvement in the stock exhaust ports. Wider IS better!

For those of you who have flowed heads already, let us know how your numbers compare.
Q

[Guest]

RE: DOHC Stock Head Flow Numbers

sure would like to know what a early style ported head would do. I have a head with one port complete here.

Good numbers and thanks for sharing.

I have seen 3400 heads flow that much peak cfm but not at those low lifts like the dohc heads do. Whast the lift on the dohc cams? like .350?

[dohcfiend]

RE: DOHC Stock Head Flow Numbers

stock max lift i believe is .370. there is a thread on here somewhere by dmotorsports or something like that and it also shows a 91-95 head flow chart.

[your_I.D.]

Look like there maxed out around .430 lift. The last to mesurements are really close together.

[Q]

All that means is that the stock port is the restriction in the intake system. (Or exhaust). It also means you can run a longer duration cam and/or a split pattern cam at factory lift and boost the top end tremendously. The right header design will take care of the low end.

Q

[quantum110]

Seriously, Wow...
Just to give you an Idea, a couple of equations can help you figure the mathmatical potential of a head that flows that much...

Peak potential Hp= Airflow at 28" of water x 0.257 x number of cylinders

Lets estimate that the head does an even 255 @ .370 that would be a peak of 393.21hp

Peak HP rpm= (flow in cfm / 1.68 * 2000) / (204 ci / 6 cylinders)

and would produce that at ~8900rpm

Of course whats resricting that? Intake, well part of that was answered years ago w/ that breadbox intake that fiero guy made. But most aren't willing to sacrifice the lower-midrange this motor already has. Exhaust, has a good set of headers been dyno'd yet? Or a large part in the way the air and fuel is actually being mixed and entering the combustion chamber...something that I think we're all waiting to be answered w/ Kevwoods setup.

BTW..Here are flow numbers from an Aurora and a Northstar...

[Mike W]

Just thought I'd offer my thoughts. TheZR1 Corvette 32 valve has the following flow:

Intake .100 97.2
.200 181
.300 241
.400 267.1
.500 277.8
.600 284.5

Ex. .100 80.7
.200 165.
.300 195.
.400 214
.500 225.4
.600 234

relatively speaking, the dohc head flows pretty well on the intake and if any peak flow numbers were increased, I believe that valve shrouding could be a concern on the relatively small bore v6. I assume that the 96/97 head offers a worthwhile improvement on the exhaust side and would be interested in seeing if the flow numbers get nearer the ideal 80% flow of the intake. I'm not an expert and don't own a flow bench but have played with some port work and have done some dyno testing and flow testing. I found that experimenting with valve angles and back cuts on the valves proved very worthwhile. I picked up 15 cfm on the intake side of some AFR small block heads that AFR custom ported. I gained 15 cfm at .200, 6 at 300 and 6 at 400 with nothing other than the cuts on the backside. Even the exhaust picked up 8 cfm. If anyone knows someone with a bench, I'd suggest getting some spare valves and trying some back cuts to see what this head would like. Of course cleaning up the seats and the area in the throat below is necessary. Keep in mind that the engine spends much more time in the low lift range than at max lift. I think just some minor contouring could do a lot for the time and money.

[dohcfiend]

i haven't gotten the whole chart but here is an excert from another one of my threads. the heads are a 97 set.

"well talked to the machinist today be4 work. he is done with the flowbenching al i have to do is arrange pickup.

i did however get him to tell me the important numbers over the phone.

I E
200 170 124
300 196 160
400 252 185 "

edit: not sure of all the specs like the temp/water but the guy was using a superflow 600 flowbench. i will re-post when i pick up the sheet.

[Scott205]

hmm, i remember seeing a picture of that shoebox intake. I wonder if this is why all the IMSA and off road people stuck to carbs. I remember that super duty 4 in the Fiero used two 4 barrel hollys. I wonder what would happen with a high intake and a couple of 4 barrels on a 3.4L DOHC? wont really work in a FWD unless you like to have a big stack through the hood. But i do have my old 92 DOHC and a Fiero with a bad engine.. hmmmm

[Kohburn]

that was just one iteration - the superduty imsa racer fieros had one throat per cylinder can't remember if they were carbed or injected.

[Guest]

Those were available for the v6's too in both the iron and al head setup. Will has one for the aluminum head setup and I know where there is another one sitting. For the aluminum head 60 degree motors there were only 6 of the indi tb intakes ever made from what I am told. Thats all I am going to say about that

[SappySE107]

Can't tell us any more on the aluminum head 6 ITB setup? Pricing, where to get one if 1 is available? I remember someone saying RFRE still had some for sale though I think that was the iron head version. Probably both though huh.

[Guest]

I dont' know much more right now. I talked to a guy that used one when racing. Dumped tons of money into the engines and kept spinning the cam bearings.

THe ITB intake for the al heads he said is there were only 6 made. He told me by whom but I have forgotten. I will try to find out. But for you to find one would be super rare. You cant' buy them new anymoer I am sure. Cost new was $1500 I was told I do remember that. But that was like 1980s prcing as well.

And yes RFRE has the ones for the iron heads I actually have a pic of like 5 on their shelf, but maybe they sold a few since the pics were taken. I dont' think RFRE ever stocked the al head intake since only 6 were ever made.