Dyno Results (above)

Disclaimer: Let's keep this thread on topic and relavent. I'm over the previous disagreement and I expect others to be as well. Mike made the best of the situation and turned a disputed subject into an excellent writeup (above). A lot of good technical information there, let's talk about it.

Tech Section:

A.) I am extremely iterested in the 35 hp delta in performance between ported and manifold vacuum. There are two reason this makes no sense to me, and I'm not sure what that means.

1.) Ported and Manifold vacuum should be equal at WOT.
2.) Vacuum advance should be inactive at WOT because there shouldn't be any measureable vacuum.

In either (both) case, their should be no measureable difference in ignition advance between the two and as such no measureable performance difference either, providing this was the only variable. Can anyone think of a reason for this ?

B.) I as well as I am sure several others are extremely interested in what total timing was. A timing light costs 40 bucks, if I have to buy one and ship it to Mraley I might do it - anyone want to pitch in?

C.) I find the discontinuity @ approaching peak HP interesting. Did whoever was driving the car do something odd like jump in and out of the throttle near peak HP?

D.) Stock motor w/ Stock Autolite (I am assuming this is a Pony rebuild?) made max power @ 5650 RPM?

E.) Nice torque non-curve

just a thought on ported vacuum.

Ported vacuum is a little fuzzy on some carbs. Some take the signal from just above the throttle plate such that at idle, there is no signal and as soon as the plates open, the port is exposed to manifold vacuum. In this case, the vacuum signal is the same at WOT.

There is another version of 'ported' vacuum which is actually venturi vacuum. The signal is generated in or just below the venturi and as such (generally) gets stronger with velocity.

I don't know which is the case here and maybe I'm out in left field (again), but it might explain the difference.

-- jay

My guess is that the vacuum port on the Holley carb was somehow malfunctioning. Not being a carb expert, I'm not exactly sure how a vacuum port goes about being broken or something, but with only 1 data point my testing mindset says it is a bum data point.

This might be one of those areas where conventional theory is disputed by actual results.

This also may be an indication in a difference between carbs and how they may affect advance. My limited experience is this: The original carb I used on my modestly built 300 was a Holley 4360/8002 spread bore. There was little difference if any between using ported or manifold vacuum. With my current Holley 4160/0-1848-1 there was a considerable difference at idle. On ported vacuum idle was erratic unless the idle speed screw was turned up a bit. On manifold vacuum I was able to turn it back down to a smooth idle at 600 rpm. On the 4360 I could achieve a smooth idle down to 500 rpm. In both cases manifold vacuum is at 17.5. I can only assume the difference is that the ported vacuum source is different between the carbs. (What jswhite said) On the 4360 it is in the base of the carb. On the 4160 it is up on the body of the carb. Timing is set 8* idle with 41* total...a little much I think but there doesn't appear to be any problems with that much total advance.

Without any evidence I can only theorize this difference in ported vacuum source v different carbs v manifold vacuum might also cause a difference in power band readings on a dyno.

Venturi vacuum fundamentally makes sense. Venturi vacuum would increase with velocity and as such RPM. It is possible that the "ported" source on the holley carb is in actuality a venturi source and as such was pulling in some advance at peak.

This could have pushed the total spark (Initial + Mech + unintended Vac) past ideal and even into pre-ignition territory, causing the 35 hp drop in power.

That does seem like a bit of a stretch to me however. I wouldn't expect more than a few inches of venturi Vac (perhaps my intuition is wrong) and as a result would not expect much Vac advance.

I've got a buddy with a timing light....Give me few days and I'll post what it's set at.....How's that?

mraley":3lcexq6j said:

I've got a buddy with a timing light....Give me few days and I'll post what it's set at.....How's that?

Click to expand...

Would be very good to know for everyone involved

8)

@mraley:

By chance would you happen to know what the static compression ratio is with the aluminum head?

Also, If I recall correctly you have done some open track time with this car. Have you had a chance to drive this car with new head on a track yet?

Id be interested in your seat of the pants evaluations if you happen to get some time in.

mraley":whh6stac said:

1966 Ford Mustang
200 CID Custom Built
T-5 Tranny
Dual Flowmasters-New Classic Inline Aluminum Head and Intake, Ported, Polished, Stainless Steel Oversized Valves, 264H Cam 110 Lobe Center from FSPP
Autolite 4100 Spreadbore 4-barrel
Custom K&N Air Intake
DUI Ignition System

Click to expand...

Mraly,

What exactly do you mean by "200 CID Custom Built", are you still using stock rods and what type of pistons? Was the porting just a basic clean up of the ports and bowls? Did you see a difference when you installed a windage tray? What weight oil and is it conventional or synthetic? thanks

First off, we don't know if the manifold vac actualy went to zero. If this engine can flow more air than the carb allows, (which the 4V pull would indicate) then it still pulls vac with wide open throttle. I have seen V8s with restrictive carbs that start pulling man vac when the engine runs out of carb.
This could add some torque and HP as long as the engine can tolerate the timing.
Without manifold vac plotted on the chart, it is hard to tell.
I would speculate that the small autolites also left some extra man vac in the mix. Like you said, it could also be detonation from the ported vac, but I think the Holley looses the ported signal at wide open throttle, unless it is too small. Then it would loose the signal at WOT/low rpm's and then get it back at higher rpms.


It would be nice to know how much timing this combination needs/will tolerate. Past experience has shown that a highly effecient setup will tolerate more compression without detonation. It has also shown me that they usualy require less timing to get max HP. These high velocity ports and fast burn chamber should work with less timing.

I think the education will come from figuring out what these engines need, and, more importantly, why they need it. Manifold vac on the chart would be valuable info.


These are theories on my part. Just thoughts that have been running around in my head. These test have given the voices in my head something to talk about.

Torque "curve" was awesome...

shows how good that design is, as stated in a certain thread before, I would love to see that same motor with a bit more cam, maybe just one or two steps up, like a "hot street"/mild strip cam, some lopey, but not too radical.

In a perfect world it would be nice to see if the same results are found with carbs with a build like that as well.

This goes to show what a kick ass motor these would be with multi-port efi, they'd scream like a beamer on crack.

Kudo's to all involved, thanks for the numbers, i'll have to get a copy of that mag to see what the biggest numbers were, over 250 at the flywheel would be crazy for a N/A motor.

Stubby":f95y0675 said:

First off, we don't know if the manifold vac actualy went to zero.

Click to expand...

Good point, I hadn't really considered that. Like you said, we really need to know more information if we really want to figure it out.

Unfortunately, Unless Mraley wants to climb under his hood at WOT under load and check timing, we won't really know what true total is if any vac is involved.

Knowing what high RPM WOT manifold vacuum reads would help a lot.

AZCoupe wrote:

Therefore we came to the conclusion that our aluminum head and intake prefer a specific size of venturi to produce the best velocity and power.

Click to expand...

Mike, rather than state that the head and intake prefers a specifice size of venturi, would it be more correct to say that the engine; combination of head, intake, cam, valve size, compression ratio etc prefer that size of venturi.

I suspect with a different cam profile and compression ratio, your results may change with regards to the best venturi size.
Doug

Anlushac11":3jzikv1x said:

8)

@mraley:

By chance would you happen to know what the static compression ratio is with the aluminum head?

Also, If I recall correctly you have done some open track time with this car. Have you had a chance to drive this car with new head on a track yet?

Id be interested in your seat of the pants evaluations if you happen to get some time in.

Click to expand...

I have never put the Stang on the track, must have been thinking about someone else..

I have no idea what the static compression is...Sorry...

sp_alloy_head":zggtwezw said:

mraley":zggtwezw said:

1966 Ford Mustang
200 CID Custom Built
T-5 Tranny
Dual Flowmasters-New Classic Inline Aluminum Head and Intake, Ported, Polished, Stainless Steel Oversized Valves, 264H Cam 110 Lobe Center from FSPP
Autolite 4100 Spreadbore 4-barrel
Custom K&N Air Intake
DUI Ignition System

Click to expand...

Mraly,

What exactly do you mean by "200 CID Custom Built", are you still using stock rods and what type of pistons? Was the porting just a basic clean up of the ports and bowls? Did you see a difference when you installed a windage tray? What weight oil and is it conventional or synthetic? thanks

Click to expand...

Custom built was more of a term than anything else. It's not a back yard build. The guy who built mine is known in my area for his race engines. Yes I'm using stock rods and sealed power pistons, with chevrolet rod bolts. Stock Timing Chain and gear. The windage tray was done during the byild. My mechanic thought it was good for 7 or 8 horses....Don't really understand how???

The head was more than a basic clean up. He took his time and did as much as he felt would help the head perform better.

I'm running Shell Rotella 10W-30....Hope that helps

Bort62":1yopjogw said:

E.) Nice torque non-curve

Click to expand...

8) contrary to popular opinion torque curves are not always smooth curves. in fact i have seen engines that have two torque peaks.

I have argued with several people who contend that ported vac is what is supposed to be used for performance. Emission era carbs & distributors have been around so long that many folks have never known that the manifold vac delivers better performance.

But as Ian pointed out, the 35 hp difference is perplexing. I wonder if the ported source was bleeding off some vacuum via an air bleed. I find it strange that the AFR was the same forthe ported and manifold vac source dyno runs even though there was a 35 hp difference in power. It seems that much differnce would result ina a differnce in the AFR since one run should be combusting more thouroughly.

With regards to the question about the blip in the curves caused by a "throttle blip"... Is it possible that something funny with the vacuum secondaries occured and that may also have accounted for the 35 hp difference? I have little experience with vacuum secondaries. Could the rate that the throttle is openned affect the actuation of the vacuum secondaries and the level of engine vac to explain the 35 hp?
Doug

That's some real cool stuff there! Kinda makes me think hard about one of the new 1100s with the 200 venturi. 200 HP. WOW! Even with an iron head that carb must rock!

Harry

66 Fastback":31skxqu1 said:

I have argued with several people who contend that ported vac is what is supposed to be used for performance. Emission era carbs & distributors have been around so long that many folks have never known that the manifold vac delivers better performance.

But as Ian pointed out, the 35 hp difference is perplexing. I wonder if the ported source was bleeding off some vacuum via an air bleed. I find it strange that the AFR was the same forthe ported and manifold vac source dyno runs even though there was a 35 hp difference in power. It seems that much differnce would result ina a differnce in the AFR since one run should be combusting more thouroughly.

With regards to the question about the blip in the curves caused by a "throttle blip"... Is it possible that something funny with the vacuum secondaries occured and that may also have accounted for the 35 hp difference? I have little experience with vacuum secondaries. Could the rate that the throttle is openned affect the actuation of the vacuum secondaries and the level of engine vac to explain the 35 hp?
Doug

Click to expand...

Well, we all know that ignition advance can pretty drastically affect peak horsepower and performance as a whole. That to me is the most important piece of information to get out of the testing that was done. (Other than the peak numbers, which are exciting and informative)

IE, if I built the exact same engine as Mraley and didn't get the timing right - I could easily be down 30-40 HP without really realizing it. Knowing that he was running X * of total advance however would really help people know where to start tuning.

If it is true that the motor was pulling sufficient vacuum @ WOT to engage the vacuum advance then it is seriously undercarbed.

More food for thought....

A.)I am extremely iterested in the 35 hp delta in performance between ported and manifold vacuum. There are two reason this makes no sense to me, and I'm not sure what that means.

1.) Ported and Manifold vacuum should be equal at WOT.
2.) Vacuum advance should be inactive at WOT because there shouldn't be any measureable vacuum.

In either (both) case, their should be no measureable difference in ignition advance between the two and as such no measureable performance difference either, providing this was the only variable. Can anyone think of a reason for this ?

Click to expand...

When we ran ported vac, the motor stumbled and mis-fired thru the entire RPM range. I have no idea why this happened, just that it did. I wish we would have had the time to dig into it and find out what was going on, but it was early in the day and we had countless dyno runs ahead of us. Our goals were to test carbs, not figure out why the ported vac was so screwed up. In retrospect, I wish we would have tried ported on the 480cfm 4V. Would it have acted in the same manor, or disapeared? And would it have made any difference in the numbers?

C.) I find the discontinuity @ approaching peak HP interesting. Did whoever was driving the car do something odd like jump in and out of the throttle near peak HP?

Click to expand...

I went over all the runs tonight and found something interesting. In the runs using the 200cfm-1V, the 200cfm-2V, the Holley 500-2V, and the 240/287-2V with larger jets, the dip and spike were still there, just not nearly as evident. They became more severe as power went up and as the AFR's leaned out? This is also why we tossed out the best run, thinking the peak numbers may have been in error. However, if they were not, then we were clearly over 250hp at the flywheel.

D.) Stock motor w/ Stock Autolite (I am assuming this is a Pony rebuild?) made max power @ 5650 RPM?

Click to expand...

Two mis-typo's here. This was the new 1100 annular dicharge carb (200cfm), not a stock carb (185cfm). Also the peak was at 4650, not 5650. Sorry about that.

All this gets me pretty excited and makes me wonder what my 250ci with the fully ported head, 292 cam, and EFI will do??? Hopefully I can start putting it all together after we get back from Carlisle. The short block and head are done, I just need to install the cam, put it all together, and drop it in.