I have a 468 BBC circle boat engine that I am converting from injected on gas to a Littlefield 14-71 (fresh) injected on alcohol.
Engine is fresh and is at 13-1 comp now. Dyno's at 750 HP with the gas set up.
I want to start with 5 lbs or so boost and be able to sneak up on 15 lbs with some seat time.
Any suggestions on what drive ratio (pulley sizes) to get the boost I am looking for?
Also, what drive size would you go with? 8MM, 13.9MM, 14MM and why.
Looking for a std. deck BBC tented intake if anyone has one used.
Be good, Jim
8mm because of the fact you can change the blower by 2% easily without changing belt lengths.
13 to 1 ? Not sure I would go there. 14/71? Fresh? I have to wonder just what "job" you are looking for this boat to do.
I'd certainly be underdrive. Too many variables to guess at lbs of boost.
I would guess that I would put the blower 10 under to start.
13 to 1 ? Not sure I would go there.
Bob, I know you like 11 or 12 to 1. Is 13-1 just too much?
I am going to take the heads off and see how thick the gaskets are and may be able to take some off the pistons. I know in a perfect world that would require a re-balance but could I get away with a slight shave to get the compression down a touch?
Got a really good deal on this 14-71. I am shipping it to RBS superchargers soon. I could trade it for something else with them......
Be good, Jim
14-71 at 25 under would give you somewhere around 8lbs. I just sold my 14-71 to go down to a 8-71 on a 496.
I'm just not sure how far the envelope can be pushed on compression. I've always run 6 or 8/71 blowers and they were never tight alcohol blowers. I never needed and more than that for what I was doing.
You may not have an actual 13 to 1 compression ratio. Head gasket thickness is an option as is cutting dome (if solid dome). Cutting dome would result in a very slight overbalance....nothing to worry about.
As far as the 14/71...I'd hope that it was rather on the loose side....and if it turns smoothly and looks good inside...I'd run it as is. Or you might send it in and have someone look at it...but I would refrain from tightening it up. I doubt you need a tight blower. I'd still be underdrive tho.
What kind of boat is this going in and what is it's purpose? Play or race or ???
Fiat,
I dont have the specs on the engine yet but should get them this week.
Pretty sure it's a honest 13-1 motor. I thought cutting the pistons gives over balance. Thanks for confirming that.
The 14-71 is loose now but is missing about 2" of nytralon stripping on 1 rotor. I thought I would send it in for a going over and have it re-stripped loose.
Motor is going into a ex circle boat. Will use it for lake fun and with seat time may get down to Kentucky for some drag racing.
Will try and attach a pic.
Jim
I don't know anything about
blowers, but would like to
see you at the Ky. races. I
run a TE jet now #678, look
me up if you come racing with
us. I have a dolly trailer if you
need one.
Paul
ME 678
After working on my motor for 10 years now you tell me you don't know anything about blowers. What's that supercharger doing in your avatar?
I assume you have an offset for the dist/mag you are going to use as you need one for 10/71's and up.
I'd send the blower in and have it stripped and checked. I'd have it set for gas specs rather than tight for alcohol.
I'd definately get the compression down to 12 to 1 or under. Either by way of thicker/larger bore head gasket or piston work. Of course the block needs to be O ringed or use one of the special head gaskets they make nowdays.
Deal like this I guess you should run the 110 pump. Probably hat and port nozzles and a couple extra nozzles over the back end of the blower(most guys do this to lubricate the long rotors in this area). And of course a high speed bypass. More complication.
Since there is no particular "job" this boat/motor combination has to do I would opt for a smaller bower (6/71 or 8/71), forget the offset mag, forget the 110 pump, hat and port nozzles and high speed and do an 80a pump....one main jet and no high speed.
Here's why I say that.
With a 475" similar motor to what you have and a 6/71 gas blower which was certainly nothing special and the 80a pump I ran 7.5 seconds in an altered/roadster at any corrected altitudes of 1000 ft to 7500 ft. Only at 7500 ft corrected did I have to overdrive the blower...which I did at 6%. All other places I ran underdrive...sometimes as much as 12% under.
That motor when removed from the drag car and placed in my 1976 Cole Tr-1 (heavy boat with no bottom work) ran in the low 8's at 3000 ft corrected with the same blower driven at 2% overdrive. And the boat had not been worked out yet. At 6% overdrive I could not set the boat (due to not enough down peddle to hold it).
Two different hydro's I know of using the same setup I have are 468's...one with a 6/71 and the other with an 8/71....either one will break the 7.70 rule if we start overdriving the blowers. Even 2%.
I just hate to see you head down the road of "complication" when there is a simpler and easier way to probably give you the thrill you are looking for.
So just some food for thought.
Jim,
13:1 static compression is too much on a blown alcohol motor, unless you're an NHRA ProMod guy who really knows what you're doing. From what we've experienced, 12:1 is the upper limit with 11.7:1 or so being just about right.
I also saw a few guys trying to drag race circle boats in Phoenix...they bounced all the way down the track. Then again, I'm pretty sure it's because they were underpowered (running in the 11 second class).
Just my opinion.
Adam
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