Diesel VS Alcohol RPM October 10, 2015 03:21PM
Curious if anyone has any insight on the max rpm variance between a diesel vs a converted alcohol in aprox 400ci or less? Say a 5.9 cummins, is there really much of a difference in RPM between the two motors or does taking away compression ignition just make it seem like they are screaming compared to their diesel brothers? I am sure a lighter rotating assembly could free up some rpm but unsure just how much more!
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Re: Diesel VS Alcohol RPM October 11, 2015 01:41AM
Single turbo?
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Re: Diesel VS Alcohol RPM October 11, 2015 02:24AM
Yes, 3"x4 single for either one? Again just trying to compare between the two
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Re: Diesel VS Alcohol RPM October 12, 2015 06:53AM
The RPM difference between the two isn't a lot but the difference between the two is that you can build an alcohol motor with more horsepower than you can a diesel. In order for them to be the same you would have to spend a ton of money on a diesel motor. However a diesel motor with with stand more pressure and can also handle more heat as where the alcohol motor may warm up hotter and and will stay hot and will be able to preform a little better. And with the 3x4 turbo that won't be a problem trying to get enough RPM's to spin it.
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Re: Diesel VS Alcohol RPM October 12, 2015 07:42AM
You can make the same power from both diesel and Alky for LLSS class. Your looking at 1300-1500hp. The bottom end on the diesel will be more expensive to build. Typically on the diesel you will need a girdle, and possibly a deck plate and sleeves, and steel billet rods. The rest will be about the same. The alky tractors will turn more RPM, but will typically run a little bit slower gear and not have as much torque. The diesel will need a little faster gear and have more torque, and little less rpm. The alky tractor will probably turn about 5000-6000 going down the track, depending on the track, gear ratio, tire cut, and engine tuning. The diesel will be from 4000-4800 typically with all the same variables.
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Re: Diesel VS Alcohol RPM October 12, 2015 02:40PM
Thanks for the details NoLimit. You mentioned the diesel bottom end...how much different would the alcohol motor be? are you talking about just a stock bottom end or Aluminum rods and stuff like that?
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Re: Diesel VS Alcohol RPM October 13, 2015 12:29AM
I know quite a few are running aluminum rods. Not sure if the stock rods will hold up. We change them to billet typically around the 1200-1250 hp mark. You could probably get a way with out a girdle, but I like to girdle the bottom end to stabilize the mains. You will also want to convert the block to roller lifters, and do a roller cam. You need to have the cam tunnel aligned bored to put bearings in all 7 journals. That is what I would at least do on the Alky. On a diesel I would start with a 6.7, and girdle it, deck plate it, sleeve it down to 5.9 bore , align bore cam tunnel, billet rods, convert block to roller lifters, and tie the mains to the deck. That would be a very solid short block for the diesel.
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