How could I lose 71 hp from one dynojet to another?

[69 Mach I]

When car was still stateside, the shop that built it tuned it on a dyno and got 351 rwhp at 6200 rpm. I was very happy with it as this correlates to 438 hp at the fly. Then to prep the car for the inspection here, I sent it to a guy whom everyone here says is an expert in mustangs. Well, long story short, he tried to undo all the work the shop in PA did because non of it was stock and "everyone prefers cars in an original state in Europe." This guy was a complete fool. So I took the car to a shop that has its own racing team based around 4.6L ford mustang engines for a proper tune.

My first dyno run was 280 rwhp and 373 torque. That HP correlates to 350 hp at the fly. This sucks because the car had 300 hp when it was stock (351W) and you cannot tell me I only picked up 50 hp by boring the motor .060 over, adding forged flat top pistons at 11:1, alum cylinder heads, new intake, long tube headers, MSD 6AL and Pro-Billet Distrib, a new holley 650 cfm 4bbl carb, and a Crower cam with the following grind.

ADV DUR: INT 297, EXH 308
LIFT: INT 538, EXH 534
DURATION AT .50 DEGREES: INT 236, EXH 242 @ 108 centerline

They are going to do another run today and I hope to pick up some power. Otherwise, I am going to be terribly bummed out.

If you look at my build, I easily should be getting over 400 hp at the fly from my engine. If there is power to find in my engine, I am sure this shop will find it. What could account for this big drop in power?

[69 Mach I]

second dyno run showed 293 hp. It is some progress but I am still less than I think I should have. The techs suspect a carb problem. In PA, my car made its peak rwhp at 6200 rpm and in these two runs, they noticed the power falling off at 5400 rpm. If they can fix the carb problem, I should keep building power past 6000 rpm. One thing the shop said that surprised me was that the power loss through the drive train on a C6 is 30% I have heard that 20% is more the norm. What does the CC brain trust have to say.

[blykins]

Mach 1.....make sure that both dynos were Dyno Jets. There are several brands of dynos.....A Mustang brand dyno will show 15-20% lower than a Dyno Jet brand dyno.

My buddy just had his 03 Cobra dyno'd on a Mustang Dyno. It made 404 rwhp. He had it dyno'd on a Dynojet a couple of months later.....it showed 451 rwhp.

This is a common knowledge in the dyno world....each dyno works or is calibrated differently and will show different results.

If you just used two different brand dynos, that could be the reason.

[Mike Simard]

What changes were made between the runs? Your title implies that the car was the same both times and 2 dynos disagree but you said "he tried to undo all the work the shop in PA did ". So what did they change? The specs do sound like a 400+ hp engine. What heads? Also, what was the timing each run?

[69 Mach I]

Originally posted by Mike Simard


What changes were made between the runs? Your title implies that the car was the same both times and 2 dynos disagree but you said "he tried to undo all the work the shop in PA did ". So what did they change? The specs do sound like a 400+ hp engine. What heads? Also, what was the timing each run?

Both dynos are Dynojets. The heads are Edelbrock RPM Performers.

The moron who first worked on my car here pulled the brand new autolite 3924 plugs and put in motorcrafts. Why? "the motorcrafts are what are used on a stock 1969 Mach 1." He said that my fuel pump was bad so he replaced it with a Scott Drake fuel pump because "that's the closest to an OEM part." WHile a perhaps a good fuel pump for a 300 hp car, definitely not the best choice for a 400+ hp car. Next, he reset the timing to spec for a stock 1969 Mach 1, not what was appropriate for a significantly modified car. He pulled the condensor from the distrib and put in a stock one for no other reason than the one that was in there was not spec for a stock car. The new condensor promply failed on the highway on my way home. There is no room in this guy's universe for any non-stock part on a classic car.

Between PA run and the NL runs and after I got the car back from the first "expert", I swapped out the ignition and distributor for a MSD 6AL and Pro Billet (HEI) Distrib. and new 8.8 mm wires. That is the only difference. Should I lose HP by installing an MSD HEI distrib and ignition?

After my first tuning fiasco, I took the car to a second shop for a decent tune. The dyno run in PA showed the 351 rwhp at 6200 rpm on a dynojet. The two runs here in the NL were also on a dynojet and they have showed 280 and 293 hp at 5400 rpm. I guess I cannot say that these are an apples to apples comparison given the difference in the rpms. I currently have a rev limiter in the 6AL for 6000 rpm. I will have them install a 6400 rpm rev limiter and see if they cannot get close to the PA dyno numbers once they have fixed the carb problem.

[xlr8or]

Perhaps the distributor curve has changed significantly on MSD unit from what it was. Is the base timing the same? Is total advance coming in at the same RPM and same amount? Maybe your not getting enough total advance and that is why it starts dropping off at 5400.

[Mike Simard]

My hunch would be to get your timing correct first. Pull the #1 plug, poke something inside and turn the engine by hand to make sure that your timing mark reads zero with the piston at the top. Some front engine covers could have timing mark pointer at different places, you need to eliminate that possibility first.
With the engine running at about 3000 rpm and NO Vacuum adavance hooked up you should have about 32-34 degrees timing with your heads etc. regardless of what it reads at idle (which would like to be around 20 deg. but that's another story)
I believe the 3924 plugs are a good match. If you get your timing right, fresh plugs and the AF ratio is good, you should be seeing some good numbers.

[69 Mach I]

Originally posted by xlr8or


Perhaps the distributor curve has changed significantly on MSD unit from what it was. Is the base timing the same? Is total advance coming in at the same RPM and same amount? Maybe your not getting enough total advance and that is why it starts dropping off at 5400.

Good point. I don't know whether the base timing changed or not. As for the total advance, there are these springs you install inside the distributor. I might have selected the wrong ones when I installed the new distrib.

[392cobra]

Just in case you don't have it,below is the info you will need to dial in the dist..

It has what springs and bushing are needed to get where you want to go.

http://www.cobralads.com/gear/msd2.gif

[DealsGapCobra]

Simple question...are both runs corrected to standard sea level conditions? This is a very reasonable thing to do and should be done. However, this would not explain the peak power being at a different RPM.

Did the guy in PA add any numbers? This is, in my opinion, not a reasonable thing to do and was probably not done. However, I know quite a few engine shops that use engine dynos "adjust" the numbers for a bunch of BS reasons (like internal friction, estimated accessory drag, etc) and then report power produced. They do this so that the customer can say (and think) he has a 450 Hp engine when it only produces 400 at the crank.

With the loss in high RPM power I would check the total timing (the distributor curve will be inconsequential at this RPM) and the fuel delivery.

Good luck.

Rob

[69 Mach I]

Originally posted by DealsGapCobra


Simple question...are both runs corrected to standard sea level conditions? This is a very reasonable thing to do and should be done. However, this would not explain the peak power being at a different RPM.

Did the guy in PA add any numbers? This is, in my opinion, not a reasonable thing to do and was probably not done. However, I know quite a few engine shops that use engine dynos "adjust" the numbers for a bunch of BS reasons (like internal friction, estimated accessory drag, etc) and then report power produced. They do this so that the customer can say (and think) he has a 450 Hp engine when it only produces 400 at the crank.

With the loss in high RPM power I would check the total timing (the distributor curve will be inconsequential at this RPM) and the fuel delivery.

Good luck.

Rob

the PA shop says no, that the graph printed 351. I am 6 feet below sea level here. The PA shop is 780 feet above sea level.

The check of the timing is next. I asked this dutch shop (www.moritztuning.nl) whether the Scott Drake fuel pump was inadequate or not. The owner says it should not make a difference. I was under the impression that I wanted at least a 110 gph fuel pump for this engine. the scott drake (I think it is a federal mogul) is probably more like 70-80 gph. After the timing is checked, how high on the list of suspects would the fuel pump be? Can a 80 gph deliver enough fuel at 6000 rpm?