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Discussion Starter #1
Anyone have before and after numbers for 96-98 DOHC cylinder heads? I just flowed the cylinder heads that I'll be using on my Big Bore engine and am wondering how the gains stack-up against heads from the 'professionals'.

Here are the results for my home-ported heads with FRPP valves and valve job by VT Competition Engine Development (no work yet in combustion chambers to unshroud the valves):
Lift Intake Exhaust
0.1 103 88
0.2 178 146
0.3 241 183
0.4 267 195
0.5 283 202

For comparison, a stock 96-98 head with stock valves and valve job were flowed on the same flow bench under the same conditions.

96-98 stock
Lift Intake Exhaust
0.1 90 75
0.2 155 129
0.3 209 154
0.4 226 166
0.5 240 167

Comparing my heads to the stockers, shows gains of

CFM Gains Over Stock
Lift Intake Exhaust
0.1 13 13
0.2 23 17
0.3 32 29
0.4 41 29
0.5 43 35


% over stock
Lift Intake Exhaust
0.1 14% 17%
0.2 15% 13%
0.3 15% 19%
0.4 18% 17%
0.5 18% 21%


The conditions for both were:
SF-600 flow bench
3.53" flow sleeve
3.55" bore flow plate
no claying/header tubes/ intake tubes at the port entry/exit
measured at 28" of water

I've come across some flow numbers that are pretty high. However, they are at conditions that are somewhat suspect (e.g., a 4" flow plate) and the sources for them do not have flow numbers for stock heads undr the same conditions.. So, to make a relatively direct comparison, I'd like to find some before/after numbers on the same bench under the same conditions.

TIA
 

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Good post. Subscribing.
 

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Discussion Starter #4
LeadSled1 said:
These graphs are from Avengercylinderheads.com done on a 3.55 bore.







http://www.avengercylinderheads.com/product_info.php?cPath=30&products_id=64
Thanks for the info. What I found interesting is comparing Avenger's 96-98 flow numbers with their '99 flow numbers - the 96-98 heads flow considerably more than their ported '99 heads. I've read and been told that 96-98 heads can be ported to flow impressive numbers on the flow bench, but that it doesn't translate to power in a NA application due to lower velocity associated with the 96-98's larger runner volume.

Anyone have any thoughts or experience on this topic?

In any case, I'm happy with the intake side. For the minimal amount of material that I removed from the runners and bowls, I think the gains are respectable (at least for my expectations from the engine).

However, I'll have to spend some more time looking at the exhast side to see if I can achieve numbers closer to Avenger heads and otehr numbers I've come across. I did very little to the exhaust from a porting standpoint, other than matching them to BBK LT header ports.

I did the combustion chamber work today, and will be putting the heads on the flow bench tomorrow to determine any gains (or losses :) ) from the cc work. I'll post the results.
 

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I talked with TEA about doing a set of 96-98 Cobra heads and Brian (the owner) said that they normally see around 320CFM on the intake side and 250-255 on the exhaust side. This was with a CNC base/ hand finish Port and polish and a "Good" 5 angle valve job. Price on the labor at that time (last year) was $1200. I saw one 96-98 Cobra head that they had worked and the results looked AWESOME!!!! :eek: :eek: :eek:


Hope that helps. :cool:
 

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Discussion Starter #7
Well, these two pictures shed some light on increasing the flow on the exhaust side of the 4V heads.

Avenger Cylinder Heads (exhaust: 247 cfm @ .500) http://www.avengercylinderheads.com/popup_image1.php?pID=62'

NMRAPRO50 (exhaust: 255 cfm @ ???) http://www.modularfords.com/forums/showthread.php?threadid=3050&perpage=30&highlight=heads flow numbers&pagenumber=3 (third page about 1/2 way down - FWIW, there is some good tech in this thread for anyone contemplating 4V heads)

Both of these heads have the protruding portion of the guide's removed. I was being a bit cautious and hadn't done this.

Also, in the pic of the Avenger port, it seems apparent that they are not raising the roof too much between the guide and the manifold surface (notice the patch of as-cast surface that remains). This was something I considered doing to increase flow on the exhaust side.

In doing some testing on a set of 2V mod heads, my friend (owns the shop with the flow bench that I use) noticed a significant increase in flow on the exhaust side by removing the protruding portion of the guide. I want to say that it was around 10 cfm at .500".

It would seem to me that on a 4V head, removing the guides would provide considerably greater gains than on a 2V head as 1.) there are two guides per exhaust port, and 2.) the width of the guide is a much larger percentage of the width of the relatively narrow 4V runners (relative to a 2V head).

So, if removing the protruding portion of the guides picks up 15 cfm per guide, that would gain me another 30 cfm - putting me at about 232 on the exhaust.


Hmmmm...something to sleep on....
 

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David,


FYI - I have another set of Cobra heads for sale if you'd like to have another set to work with. These heads have only 5,000 miles since a 3 angle job. I took these heads off because I thought they may have been the cause of my detonation problem, but apparently that wasn't the case.

I promise to pack it up good this time, LOL :idunno:
 

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Heres mine

Not sure on the conditions, I remember them being a little different than usual but can't seem to remember why.

Ported
LIFT INT EXH
100 91.5 67.5
200 146.4 105.75
300 207.4 155.25
400 237.9 191.25
500 305 225

Stock
LIFT INT EXH
100 92.5 66.6
200 130 86.95
300 170 127.65
400 195 157.25
200 250 185
 

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Discussion Starter #10
Re: Heres mine

Steve Dohoney said:
Not sure on the conditions, I remember them being a little different than usual but can't seem to remember why.

Ported
LIFT INT EXH
100 91.5 67.5
200 146.4 105.75
300 207.4 155.25
400 237.9 191.25
500 305 225

Stock
LIFT INT EXH
100 92.5 66.6
200 130 86.95
300 170 127.65
400 195 157.25
200 250 185
Steve - Thanks for the info. Another data point is always welcomed.
 

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Discussion Starter #11 (Edited)
I had another productive – and educational - day on the flow bench. First, the numbers and then what I learned.

I entered an incorrect number in the initial data that I presented. My .100” lift was initially stated as 103 when it should have been 95. I superimposed some numbers when putting together my spreadsheet.

So, my initial numbers from above are:

Lift Intake Exhaust
0.1 95 88
0.2 178 146
0.3 241 183
0.4 267 195
0.5 283 202

After cleaning up the combustion chambers and removing the protruding portion exhaust guides, the following numbers resulted during today’s trip to the flow bench.

Lift Intake Exhaust
0.1 102 94
0.2 182 165
0.3 243 196
0.4 272 210
0.5 289 215

Now for the learning part: Unfortunately, the two sets of numbers don’t correlate directly as I learned, quite by chance, that the flow bench (Super Flow 600) looses accuracy at high flow %’s for its lower flow ranges. I was measuring the .100 lift value for the intake at a particular flow range. To make a measurement, you start the machine, set the vacuum to the desired setting (i.e., 28” of water) and then read the percentage of flow 0-100% from a different gauge. As this particular flow point was near 100% of the flow for the flow range I was on, I happed to look over at the measurement gauge to see if I was going to have to switch to the next higher flow range (i.e., if I was exceeding 100% on the gauge).

As I continued to increase vacuum toward 28” of water, the measurement gauge hit 100% and then started dropping to about 96 % when the vacuum hit 28”. In the past, I had just set all the points and then taken the measurement. I just casually watched to make sure I wasn’t exceeding 100%. A majority of my initial numbers corresponded to readings above 94% on the measurement gauge.

So, I set he flow bench to the next range and took the measurement again. With this flow range, the reading was down at 61.5%. Voila – when I entered the two numbers into the spreadsheet, the two measurements produced different flow numbers (the flow corresponding to a reading of 96% was lower by about 8 cfm). So, I set the bench to the next flow range and it provided nearly the exact reading for a reading of about 41%. Specifically, 61.5% reading on flow range 4 resulted in the same calculated flow as 41% reading on flow range 5 (both measurements taken at 28” of water).

Based on this new information, I re-ran all of the lift points for intake and exhaust making sure that at least two flow ranges provided the same resulting flow number. Proceeding with this approach, all of the flow measurements were between 40% and 70%. I guess this is the sweet spot (or within the sweet spot) of the flow bench.

Probably more information than you wanted to know about my flow bench operating technique. But, I thought it was important to present as it reflects the accuracy/consistency of my measurements. If nothing else, I feel confident that all of my readings from hear out will be consistent and accurate relative to each other.

So, the intake side is done. I’d like to see the exhaust side flow about 85% of the intake side, which means that I need about 240 CFM at .500. As the only material I’ve removed from the runner walls on the intake or exhaust side is that to provide smooth surfaces/transitions and to port match to my headers, I suspect that removing some materials from the walls and ceiling of the runners is my next step.

I’ll post the next changes and the resulting flow numbers once I finish opening up the exhaust runners a bit.
 

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Re: Re: Heres mine

Blown46Cobra said:
Steve - Thanks for the info. Another data point is always welcomed.
Mine seem to jump alot from 400-500 lift as compared to yours. the numbers where scribbled on a recipet so I hope they are right!
 
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