Stock head flow cfm?

[SquadX]

I had a pair of 00 GTS heads put on a flow bench and they flowed 198 cfm. Does that sound extremely low as I remember hearing the stock GEN 2 heads flowed around 225 cfm. Can anyone clear this up?

I had the heads port/polish and valve and they got 50 cfms out of them so there are now seating at 247 cfm. But if they truely 225 stock then Ill have a bone to pick with the shop.
The heads were on another car (GTS 00 with headers and side exhaust, T & rr) and made 475 rwhp.

 

[SquadX]

and yes, I know I should have gone with Greg good but had heard good thing about the shop from some road course guys.

 

[RTTTTed]

A flowbench is a tool, not really good for measuring hp, just airflow at certain settings. Different settings and setups means different numbers. Like a dyno it gives and indication of performance that may be available.

A 25% increase in flow is great. Of course that depnds on the rest of the chart. What lift? What pressure? etc.

The main purpose of a flow bench is for measuring and correcting flow differences between ports in the heads for YOUR engine. If all the ports have equal flow the engine will produce max power for what you've done. If one port is slow compared to all other ports, it will drag the power level of the engine down.

Ted

 

[TexasPettey]

247 sounds a bit low, but not too far out for a basic porting job. I believe that the ROE heads are ~270 cfm.

By way of comparison, Greg Good got my Gen1 heads to flow 305CFM! I think he get's Gen2 heads near 320, but I don't have direct experience.

 

[SquadX]

247 does sound low. Shop said the heads keeping flowing as they go up but I am waiting for the flow chart.
If anyone has cfm for stock GEN 2 heads, let me know.

 

[RTTTTed]

If you wnat bigger numbers you could just ask for a higher pressure for measuring the flow. Like a supercharger higher pressure means higher numbers. Like a dyno, different benches will show different numbers.

How fast is the car? You've put on a 1,000mi. Feel any difference?

Ted

 

[SquadX]

Let me correct myself. My concern is that if stock heads flow 225 cfm and they are claiming a they got 50 cfm out of the heads then osmething is off. They said my heads flowed 198 cfm so are my heads just bad or....
I understand what you mean about different flow benchs yield different results but I would think all stock heads would flow the same. I will post the flow chart when they send it. Thanks for all the advice/help.

 

[RTTTTed]

So if the numbers are that important to you you can send your heads to Greg Good and have hom flow them on his bench for HIS numbers, or take another set of stock heads to your porter and get them flowed to compare your OLD head numbers.

Maybe Greg's machine will show huge numbers? Probably another stock set of heads will flow the same numbers as yours (unless they told you that the heads you gave them had bad casting flaws all stock heads are close) at that machines settings.

My point is that they're just numbers. If you want to compare to GG's numbers you should have your heads measured on his machine, not compare someone else's numbers to Greg's.

If your heads were ported properly, you'll feel a difference. If you had OS valves and seats installed you'll feel a bigger difference, etc.

There's different types and levels of head porting. A street car (without supercharger) will lose mileage, power and torque if a set of race ported heads are installed. Sometimes the numbers lie.

Ted

 

[2001 GTS]

Stock numbers were 227, Roe was 267, and Greg's were anywhere from 300 to 320.

I have Roe Heads and now am having a set of stock heads ported by Greg.

 

[KenH]

Here is a flow chart from JMCylinderheads website which show stock numbers over different valve lifts for both intake and exhaust to give you an idea of typical numbers on a stock head and then in this case compared to their Stage 3 heads with porting and larger valves.

50CFM increase, especially if the valves stayed stock, seems pretty reasonable to me and I doubt the factory castings are fundamentally flawed. My guess is that it is just the way they have their flow bench setup. In this chart, the pressure is set at 28" H2O. Factory valve lift is about .541.

You must be registered for see images

 

[plumcrazy]

i think mine stock were 260

 

[ruckdr]

The answer to your question is in the form of a question:
Are all flow benches the SAME? NO
One flow bench relative to another flow bench has very little meaning.
One flow bench relative to itself has significant meaning when making port/combustion chamber changes, valve size changes, valve grind angle changes, valve seat angle changes, and other considerations; not to mention atmospheric differences.

Later,

 

[SquadX]

Well to clarify more on why I am so on numbers. I just want to make sure the shop is not just telling me they got the heads to flow 50 additional cfm. I know alot goes into port/valve job on a head and vary for different applications.

I should have the heads back late next week and will swap them out with my current heads on my car.

 

[plumcrazy]

talk to GG. he will tell you its NOT all about flow, its not the size of the chamber,its not the size of the valves. its a combo and the way the chamber is shaped has something to do it with it too im pretty sure.

 

[Russ M]

Well to clarify more on why I am so on numbers. I just want to make sure the shop is not just telling me they got the heads to flow 50 additional cfm. I know alot goes into port/valve job on a head and vary for different applications.

I should have the heads back late next week and will swap them out with my current heads on my car.

The only way to know the answer to your question is to have witnessed the air flow first hand. Problem is all it takes is a knob adjustment on the flow bench and the numbers can look completely different.

The other thing you can do is send your heads to someone you trust, and have them flow benched after you receive them. That way you will know for sure if they are what you paid for.

 

[PowerKraus]

Another check is compare the flow at lift; then compare the flow at a certain lift, to the lift of your cam. For example, do not compare the intake flow of the head at .600 lift, when your cam only opens the intake valve to a max of .550.....If .550 is your max cam lift, any flow above this lift is irrelevant, as the valve never opens 'that far'. So get your cam specs out and have them available when you get your heads checked.

And as stated, the 'style' of the port job is most important; a reason to go to a 'head porter' that knows the desirable charateristics of the Viper motor.

Good luck.

 

[Greg Good Cylinder Heads]

I had a pair of 00 GTS heads put on a flow bench and they flowed 198 cfm. Does that sound extremely low as I remember hearing the stock GEN 2 heads flowed around 225 cfm. Can anyone clear this up?

I had the heads port/polish and valve and they got 50 cfms out of them so there are now seating at 247 cfm. But if they truely 225 stock then Ill have a bone to pick with the shop.
The heads were on another car (GTS 00 with headers and side exhaust, T & rr) and made 475 rwhp.

198 cfm on a stock Gen 2 head is low. On my calibrated Superflow 600 a stock Gen 2 head flows in the 240 range on the intake ports and 175 on the exhaust.

BUT, a flow bench is a comparator. As long as the before/after numbers are measured on the same bench, and you gained 50 cfm, that should give you a substantial gain in power. What you need to do now is run them and see how much the car picks up. There is a lot more to wringing extra power out of a set of heads than the airflow numbers. There is the wetflow, the quality of the valve job, the spring package, etc. Everything counts.



Good luck.

 

[RTTTTed]

If a set of heads are ported, it's obvious. The grinding work cand be seen from the outside. However, if the floor was ground the heads are junk. Smoothing and polishing the port floors is OK, any visible lowering of the port floor turns the heads to junk. Otherthings, like valve unshrouding and valve backcutting aren't so obvious.

If you look into the heads and the ports are smoothed you can be assured that a lot of work went into them. If you know that a flowbench was used ... you can figure that almost half the time spent on the heads was attaching them to the machine and testing them. Less time if the heads were only flowed once.

Ted

 

[SquadX]

Got the flow chart back (well excel file until chart is available):

Here’s the flow results, when our network is back up I will email the report out of our Superflow 1020

Valve Lift
Exhaust Flow
Intake Flow

.100
50.6
59.0

.200
113.4
109.4

.300
149.4
153.8

.400
174.6
191.6

.500
182.2
220.0

.600
187.2
237.3

.650
188.2
240.1

.700
190.1
242.6

.750
190.9
245.7

.800
191.8
251.1

.850
192.2
256.3

AVERAGE
166.9
205.4

 

[SquadX]

Going by the numbers I would need one hell of a Cam (.850) to get any additional power. This just looks odds to me, but could just be me.
I got these heads from a 00'GTS, so these are not my orginal heads. I will be swapping these out for mine when they arrive if I even put them on now as it seems like they are worse then stock heads.

 

[RTTTTed]

Those are the stock flow #s or the after porting #s?

As stated before, you need a baseline from where the numbers started before you can decide if the after porting numbers are better than the stock numbers.

The flowbench is mainly a tool to equalize port flow. Where are the individual port flow #s? An indication of quality of workmanship would be a low percentage difference between ports. Bad job the numbers would show a large difference between port flows.

Just writing a set of numbers is useless as you haven't posted pressure drop, hg merc. etc.

Ted

 

[SquadX]

Sad to say these are the after porting numbers. The shop will send the flow chart with all info. once there network is back up as I can compare the before and after.

I am not sure of all I need to ask for, will the flow chart so pressure drop, hg merc. etc.?

These numbers just look like stock to me. As stated my only concern is "did this shop really gain 50 cfm on the port/valve job" as these numbers look like stock and its just odd that 'after' you port my heads they resemble stock cfm numbers. I just doubt that my heads would be the only ones made that flowed 40-50 cfms lower then all others.

I know must shops use a superflow 600 and this shop used a 1020, not sure how much of a difference that made.

One reason I keep digging at this is when I asked the shop if they had a chance to get before flow numbers, they said no they just started the work but after the heads were finished magically they said they flowed 198 cfm before any work was done to them.

I understand what everyone is saying but what I am stating is is the shop lying and this is suppose to be a respectable shop. Just seems from the looks of things that my I might as well keep my stock heads on. Not many people run Cams with over .600 lift on the street (which is what my car would be used for) and to get any kind of additional flow I would need to run at least a .700 lift Cam.

Again these are not my heads, they are a spare pair I am having head work done to.

 

[plumcrazy]

do you have pics of the porting ?

 

[SquadX]

I should have the heads back next week. I will take pics and post them. Apparently when they were assembling the heads, they found two guides broken/cracked so they are replacing them.

Thanks againt o Greg Good for speaking with me on this earlier, great guy.

 

[RTTTTed]

Porting heads is extremely labor intensive. Figure that the shop charges about $75/hr. Figure that 40% of the time you pay for is to flow all the ports in the heads. You can also add a 3 angle valve grind to the cost and a valve backcut as well.

It should be obvious why headporting is very expensive.

Ted

 

[ruckdr]

SquadX,
You said:

Not many people run Cams with over .600 lift on the street (which is what my car would be used for) and to get any kind of additional flow I would need to run at least a .700 lift Cam.

Remember the rocker arms are ratioed, such that the cam lift is multiplied by the ratio of the rocker to give valve lift.
Simple example:
Cam Lift = .500"
Rocker arm ratio = 1.5
Valve lift = .500 x 1.5 = .750"
or with 1.7 ratio rockers
Valve lift = .500 x 1.7 = .850"

Later,

 

[2001 GTS]

But usually when a cam says .500" lift that already has factored in the 1.6 standard ratio.

 

[RTTTTed]

Ditto. Cam lift specs are measured at the valve and usually include the rocker ratio in the specs.

Ted

 

[ViperTony]

So is it a bad thing if 1.7RR's are installed when the Cam has been measured to include 1.6 RR's?

 

[ruckdr]

But usually when a cam says .500" lift that already has factored in the 1.6 standard ratio.

YES, my example starting with .500 CAM lift was a poor choice and should have been in the .350 +/- range for 1.6 ratio rocker arms. Was merely trying to show that the actual cam ground lift times the rocker arm ratio gives the valve lift.

And measuring flow at valve lifts way past the cam/rocker arm lift is of little value.

Later,