Got my Mach 1 dyno'ed

[tony-muscle]

Yesterday I went to a car shop nearby where they had a Mustang type dyno. The place is amazing, they have a race team and work on all kind of sports cars including Porsche, Ferrari, Lotus, etc.

My goal was to have a baseline so I can see what my improvements over the winter will produce. This was a Mustang dyno and the numbers were on the low side. After researching and reading a lot it seems that there are many rule-of-thumbs people have to convert this results into engine HP. It seems to me that it is very hard to know what the real HP is. Even more difficult is that I have an auto trans. At least it will be a good benchmark to see the effect of future improvements. I see it more of a relative measurement rather than absolute.

My M-code Mach 1 hit 200 rwHP @ 4600 rpm and 258 lb.ft @ 3000 rpm (ignore high torque reading at beginning of run) My engine appears fairly factory except for a 670 cfm Holley carb, a 272H cam and a dual 2" exhaust system with an H. The factory specs are 285 bhp @ 5400rpm and 370 lb.ft @ 3400rpm.

The guy stopped the run at 5000 rpm based on the HP dropping. As far as I know it should have gone to 6000 with no problem. You can see that torque peaked 400 rpm earlier and HP peaked 800 rpm earlier. I don't know if he would have continued the measurement past 5000 rpm if the HP would have bounced back. Maybe the 2" exhaust is choking the engine too much.

In this dyno the RPM is measured based on the wheel drum rotation. They first sync the engine RPM to the wheel RPM by making a 3000 rpm run. For this they picked up the RPM from the spark plug wire.

There could be a delay between the engine RPM and the wheel rpm, but it should be relatively small. I also run it in 2nd gear. Ideally would have been in 3rd gear which is 1-to-1, but I calculated that it would have the wheels spinning at 160 mph due to my 3.0 axle ratio. I did not feel comfortable rotating those tires that fast. In 2nd gear 5000 rpm was about 90 mph, which is more manageable.

Does any of you have experience with Mustang dyno results? Thoughts on these results?

 

[71mach351]

I had mine chassis dynoed several years ago. It has a similar set up to yours. 71 M-code. C6 auto, Holley 670 carb. Long tube headers. My rwHP was 251. I can't remember the torque off hand . I'll have to find the sheet. We did run it up to 6200 rpm where the valves started floating.

I'll dig out the specifics tomorrow.

 

[tony-muscle]

I had mine chassis dynoed several years ago. It has a similar set up to yours. 71 M-code. C6 auto, Holley 670 carb. Long tube headers. My rwHP was 251. I can't remember the torque off hand . I'll have to find the sheet. We did run it up to 6200 rpm where the valves started floating.

I'll dig out the specifics tomorrow.

Thanks. I am very curious to see your power curve. Did you have stock cam and valve train?

1971 M-code Mach 1

 

[Don C]

It looks like the advertised power range of that cam is 1600 to 5200 rpm, so what you got on the dyno is fairly close. I would make sure the rear barrels on the carburetor are opening and check what your total advance is, you might pick up a little more with around 36 degrees total.

For comparison purposes, the stock cam for a '71 M-code should have been 268/280 and 0.42/0.45 lift. The Crane cam is 272/272 and 0.524/0.524 lift.

 

[mjlan]

Mustang dynos are regarded as being one of the most conservative, so best used to compare performance before/ after changes.

I'm assuming your M-code is running a C6? They are pretty inefficient, probably safe to assume about a 20% loss in power through the drivetrain. Based on that, you're looking at about 250hp at the flywheel...

I would agree that the 2" exhaust might be hurting you at the power peaks, and based on the drop in power after 4700 rpm your valve springs might be a little worn or not up to the increased lift of the aftermarket cam. It looks like A/F ratio was not being logged?

 

[tony-muscle]

I would agree that the 2" exhaust might be hurting you at the power peaks, and based on the drop in power after 4700 rpm your valve springs might be a little worn or not up to the increased lift of the aftermarket cam. It looks like A/F ratio was not being logged?

I think the A/F would be hard to measure unless you had an air mass sensor and fuel flow gauge. I think that function is more for newer cars where they can plug the dyno to your OBD2 connection.

Mustang dynos are regarded as being one of the most conservative, so best used to compare performance before/ after changes.

+1 That's my plan. Create a baseline for later comparisons.

I would make sure the rear barrels on the carburetor are opening and check what your total advance is, you might pick up a little more with around 36 degrees total.

I am at 12 advance at idle, but don't know where I am at full advance. That's a story on itself. I tried to do it but did not have marks past 30 on the damper. I then bought a MSD timing tape that has options for like 6 different damper size and none were the same size as mine. My damper I think it is 6.5" in diameter. I guess I could use a conversion factor.

In regards to the secondaries, I tried the clip trick and it is moving. Not sure if they were opening all the way though. I am cleaning and replacing the carb kit this winter so I am sure that will be improving.

For comparison purposes, the stock cam for a '71 M-code should have been 268/280 and 0.42/0.45 lift. The Crane cam is 272/272 and 0.524/0.524 lift.

It looks like the advertised power range of that cam is 1600 to 5200 rpm, so what you got on the dyno is fairly close.

Similar duration, but higher lift. I wonder what was the RPM range of the stock cam.

Actually, I found my cam spec sheet and now it makes sense. The spec sheet indicates maximum RPM to be 5000.

 

[mjlan]

You are right, sampling of the A/F ratio is most easily done on newer EFI vehicles through the diagnostic port. Some shops that cater to pre-EFI customers have other ways of sampling it though.

As far as your RPM range comments about the cam card: I don't think a 4V-headed Cleveland would lay down at 5000 because of the cam, I think that symptom or trait is more a by-product of the state of the engine as a system. I think the exhaust is a little on the restrictive side as well as valve springs possibly being weak. Perhaps it runs out of fuel on the top end as well...

Boss 351 cars had a larger exhaust for a reason- the bigger solid cam that extended the RPM range needed more breathing!

 

[Don C]

A/F ratio isn't that difficult, you just need a wide-band sensor and a way to display it.

http://www.summitracing.com/parts/sum-g2996

I would be surprised if the dyno shop didn't have the type that has the probes that insert up the tailpipes.

 

[71mach351]

I had mine chassis dynoed several years ago. It has a similar set up to yours. 71 M-code. C6 auto, Holley 670 carb. Long tube headers. My rwHP was 251. I can't remember the torque off hand . I'll have to find the sheet. We did run it up to 6200 rpm where the valves started floating.

I'll dig out the specifics tomorrow.

Thanks. I am very curious to see your power curve. Did you have stock cam and valve train?

1971 M-code Mach 1

I have a comp cam 268h, pertronix, edelbrock performer intake. They really had to jet up the primaries to get the power but it ran terrible on the street. I think they had .073 jets in it.

 

[tony-muscle]

I had mine chassis dynoed several years ago. It has a similar set up to yours. 71 M-code. C6 auto, Holley 670 carb. Long tube headers. My rwHP was 251. I can't remember the torque off hand . I'll have to find the sheet. We did run it up to 6200 rpm where the valves started floating.

I have a comp cam 268h, pertronix, edelbrock performer intake. They really had to jet up the primaries to get the power but it ran terrible on the street. I think they had .073 jets in it.

Thanks.

I think the raw numbers compare relatively well. Both engines are very similar but tested on different dynos. However, based on my research the Dynajet and Mustang typically show similar power numbers: http://www.hotrod.com/how-to/additional-how-to/hrdp-0405-chassis-dyno-guide/ . However, Mustang dyno's may differ in torque readings.

The big difference is that yours have headers and I assume a better breathing exhaust than mine. The other issue mentioned is weak springs on mine affecting higher RPM power, which may explain the earlier drop, or that's maybe caused by weak exhaust and/or carb setup.

Interesting is that my torque curve is fairly flat at lower RPM all the way to 3800 compared to yours. Your HP is fairly constant above 4700, which is were mine peaked.

I look forward to how my next dyno run will look after my planned work this winter.


Anyone has dyno runs to share?

 

[Jim and Jutta]

I recall a previous discussion on this site that the C6 alone robs 40HP or more which is why some go with a built C4.

The main thing is like you said, you've established a base line that'll allow you to determine future modifications results, it'll be interesting, keep us posted.

Jim

 

[MeZapU]

Yes, the C-6 is a power robber but you said you were just after a baseline anyways.

What intake manifold are you running? The old Performer 2v I had on my engine would really lay over past 4k rpm's.

This is my car with a 4-speed and a small Crane HR cam.

 

[Paul of MO]

Dittos on mustang dynos reading low. -20

Dittos on C6's robbing power. -40

2 inch exhaust with an H pipe should not have hurt you any.

Single plane intake (?) -10

200 + 20 + 40 + 10 = 270 at the rear wheels or just over 300 at the fly wheel.

That is what your set up should be making give or take a bit.

I would tap a hole in your h pipe and install an 02 sensor as you can not really tune without knowing your AF ratio's. Might be the best $150.00 you can spend before you start making changes.

AEM 30-4100 UEGO - Digital Wideband Gauge

I have an older AEM sensor/guage that I have moved from car to car to car over the years with no issues.

- Paul

 

[captthundarr]

When we ran Amys landspeed car on the dyno we compared the in car A/F meter to the dyno A/F sampler tube. The car is carburated and there was a 1% difference between the readings. A/F meters are worth their weight if used correctly. Don't just set the A/F ratio at idle, check it around 2,000 - 2200 rpm as well. I changed the jets 6 times during the session and we ended up 2 sizes up (stagered) from where we started. The motor turns 6350rpm befor the springs start to float.

 

[barnett468]

hi;

your headers need to be at least 1 1/4 but no more than 1 3/4".

your 2" exhaust is just big enough if you have a cross over tube and free flowing mufflers . . 2 1/4" - 2 3/8" pipe would be better [a safer bet] . . 2 1/2" is a hair too big.

your compression absolutely must be at least 9.5:1 with that cam to optimize the potential of that cam, otherwise i would increase it or yank the cam out and run a comp xe262h or xe268h.

your gears are too low for that cam, you need at least 3.23 and 3.40 would be better.

that cam should make power up to at least 5400 rpm in your particular engine before it drops off guaranteed.

any afr from around 11.5 to 13.5 will provide nearly the same hp.

as mentioned, timing is critical . . insufficient timing can cost you up to 25 hp and 300 rpm easy, easy, easy all day long.

if you have a stock intake you need to dump it and get a better one . . a dual plane medium rise eddy with the big ports is fine in your case.

put the optional white spring in your secondaries . . they will open early and fully by around 4000 rpm . . this is the most common upgrade to the holleys . . if your car falls on its face when they open, simply put the next heavier spring in until it just barely stops falling on its face when they mopen . . the spring kit is 15.00 and has around 7 different springs.

...

 

[tony-muscle]

Never thought of an AF gauge.... great idea

Thnks for all the recommendations.... my plan is to focus on car chasis and safety first before investing heavily in the engine...... I would like to go the stroker way some day....

1971 M-code Mach 1