404 RWHP vs. 435 with a plug change?

[Ron]

<FONT face="Comic Sans MS">Gentlemen;

I've run my 1996 GTS on a dyno 3 times since I bought it.

1) At 2,200 miles, smooth tubes, K&N's and Snake Oyl rear muffler eliminator - 412 RWHP SAE - Run began at coolant temp of approx. 185 degrees - Dynojet 248

2) At 8,500 miles, smooth tubes, K&N's and homemade H pipe rear muffler eliminator - 404 RWHP SAE - Run began at coolant temp of approx. 207 degrees - Dynojet 248 - different unit than 2,200 mile run

3) At 8,800 miles, smooth tubes, K&N's and homemade H pipe rear muffler eliminator - 434 RWHP SAE - Run began at coolant temp of approx. 185 degrees - Dynojet 248, same unit as 8,500 mile run

The only variance between runs 2 & 3 was a fresh set of stock Champion plugs (old ones looked fine) and the coolant temps.

Question, can coolant temp have that much impact on RWHP (30 HP) or is plug appearance not a very good judge of functionality or are Dynojets runs just not that repeatable?

Thanks much for your comments....

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[GONABITE]

Ron,

There are so many variables when dynoing, biggest is air quality humidity and temp,maybe it was more humid and hot the first time you ran it engine temp will have some effect but probably not 30 hp.

 

[treynor]

In my dyno experience, the coolant temp has a dramatic effect on horsepower. Without controlling for that variable, I don't know how much if any of the power increase to ascribe to your spark plugs.

 

[Ron]

<FONT face="Comic Sans MS">Ben;

I tend to agree, no way plugs had anything but a minor HP impact if any, but I am surprised that the coolant temp has such an affect on power. I know the intake charge is denser if the manifold isn't hot, but what else in the engine produces more power if it's cooler?</FONT f>

 

[Ron]

<FONT face="Comic Sans MS">Gonabite;

Agree on the variables and the impact on HP, but doesn't the SAE correction factor account for that?</FONT f>

 

[Tom F&L GoR]

I actually don't know whether the fuel injection lines have a return to the tank or not... but if they do, and if the fuel tank was low (say 5 gallons or so) I know the fuel will get surprisingly hot from the multiple passes through the hot engine compartment. Then you also have the issue of hot fuel that heat the intake air charge, which can add to the confusion.