Dredgeking

I had my HP 500 carb rebuilt by a reputable engine builder. Mild head work, cam, CMI headers and MSD ignition have been installed. It has also been bored out 60 over. My dyno results came back below that of an HP 500 carb with GIL manifolds. Very disappointing. Can there be a significant difference between different dynos at different locations? I can understand 10 or so hp and torque, but some of the power band is 50 or so ft below where it should be. It sounds like too much of a difference to be in just dyno differences. Has any one had their engine dynoed at two different locations on different dynos with the same engine configuration? Puzzling.

kook

Are the uncorrected and corrected hp/tq values similar, or were the test conditions (e.g. altitude, temp, humidity) vasty different than the "standard conditions", making the uncorrected and corrected values quite different? The reason I ask is that we debated this topic in some length, back when I was into motorcycles. 99% of the people were using a Dynojet dyno - even though Dynojet was making claims about accuracy, we were getting variations from one dyno to the next which was substantially larger than what Dynojet claimed. I also recall something about dyno calibration, and how that (or lack of that) could influence results. I have no idea how you calibrate a dyno, and if that is even done for the larger dynos. The general concensus was that you needed to run your bike on the same dyno, in the same (as close as possible) operating conditions..... but we were looking at 3-4 hp as being "significant", not 50hp. We also *believed* that the correction factors appeared to be somewhat incorrect, at least in some circumstances.

.02

Scott

Dredgeking,
I have about 4 hours on my old hp500's, had some head work done and changed cams. I did stay with the Gill manifolds (other than the cool look I don't think the difference is that huge).

First of all I did not Dyno these so anything I type is just comparisons from the old motors. I have noticed better exeleration through the mid range and seem to be getting about 4 to 5 mph more at cruise and WOT. The motors without question make power easier than they did before. I can only assume that my torque figures have climbed up a considerable amount.

I would still like to Dyno these (in the fall). I will have to look for someone around me I can trust. If you don't mind can you post or PM me the motor info. Like what cam you used and who did your heads and of course the big HP500 carb question what springs did you use?? Thanks Scott

Dredgeking

Right now the only thing I know is that my torque and hp numbers are way low compared to HP 500's certified by Innovation for APBA. The cam was supposed to be custom ground. I don't know why. The heads were worked mildly in house. Mostly just cleaned up. One of two things has happened. a) The builder's dyno is not calibrated properly and is giving incorrect data. If this is the case, the engine goes in the boat and it shoudl run faster, it's just bad data from the dyno. No problem, just confusing. b) The dyno is correct and nowI have an engine not producing the proper horsepower after having it rebuilt and improved up by the builder. The builder had done what he said he would, but it's just not producing the HP it should. Now how do I handle that with the builder? He did what he said he would, as far as I know at this time. But the engine is running like a 454. This thing should have excellent mid range over stock and a bit more top end. It has neither. Hmmm. Now Checkmate F1 had an engine built and the dyno showed it was far above stock, but the engine has not performed back in the boat. This is a gamble.

John B

So, what are the cam specs? This is where it gets interesting.

Dredgeking

I will call and get the cam specs today.

Dredgeking

Update: Spoke with the builder and he says that my engine is making more hp stock 500 EFi's on his dyno. He will fax a dyno sheet , but hell, I can make up a dyno sheet on my laptop. He had a cam custom ground and does not want to give out the cam specs. Hmmm. Understand having industry secrets, but how do I know I'm getting what I paid for? He syas his dyno corrections are done differently than some other dynos. I just need to know if a 50 ft pd difference between dynos is possible and or acceptable. He swears my engine is making more hp than stock. I think the only real way to find out is get it back in the boat and go for a ride. What do I do if the engine is not performing as well as stock?

John B

Post your dyno results. If they're not right someone will tell you. I would consider re-installing your stock cam, you know that worked and at 5000 rpm they are tough to beat. I had a bad cam in a new 500 EFI, it took 2 months to kind it with Mercury's warrantee help. It happens and was a ***** to find it, only the replacement proved it was the cam.

I had dyno sheets on two HP500's, one was 494hp at 5200, the other was 485 at 5300. Torque was about 545 on both. They were rebuilt and had break in time only.

Good luck, JB

Dredgeking

My results:
trq hp
3000 496 283
3500 520.6 346.9
4000 536.1 408.3
4500 534.5 458
5000 528.6 503.3
5500 493.9 517.3

Dyno run was in Texas heat and humidity on a July morning. These are stated to be corrected numbers.

Innovation Marine with GIL APBA certified.
trq hp
3000 542.7 310
3500 543.5 362.2
4000 544.5 414.7
4500 545.8 467.6
5000 524 498.8
5250 507.2 507
All the certified engines are within 5 hp of each other. When you look at the stock engine with CMI it makes mine look much worse.

John B

Your new cam has more duration than the stocker, this has shifted the torque to a higher rpm, and your low end is weaker.
This does not look like a dyno difference. You may need to rejet slightly to maximize your horsepower, if you haven't already. This new cam seems to be less appropriate than the stocker.

Your other changes alone should have been worth 15 to 35 horsepower thru the entire rpm range...