Stock head flow cfm?

[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]

Originally Posted by 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.

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]

Originally Posted by 2001 GTS

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,