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looking to up my comp. as it does not look like the blower will be going back on due to insurance. I would like to know what comp I can safely run on 100oct. Info- currently a 540 with 7.3-1 and brodix BB2X heads. I am going to go to a larger bore size (and crank later) to up the cubes to a 632. What comp. can I change to. Thanks for any info-KELLY
Does anyone know of a website that list comp. for n/a motors similar to littlefields, moonyhams site for boost. Thanks-KELLY
As a reference, I'm running 10.8:1 on 91 octane and 36 deg timing. It runs cool though, and has ceramic coatings on the pistons, chambers, and valve faces. Also EFI w/knock sensor just in case. If I had been willing to run av gas all the time I would gone about 2 points higher. How much power are you shooting for? You can make a bunch on pump gas with the right parts.
Thanks for the info. I want to try to make around 850-900 n/a to help move this heavy boat around. Running 100oct all the time is not really a problem for me so I'm trying to squeeze out as much as possible. I was looking at 12.3-1 as a starting point. My engine builder has all the info but I kind of like to get second opinions on everything, and have a little more info in my head when I'm talking with him. I would really like to do a hi-tech setup like yours but this is just a temp. setup until my insurance is done screwing with me. KELLY
Anyone else have a high comp. setup and if so what are you running (comp-gas) Thanks
Forgot to mention one thing, idle quality. You're building an outdrive (Bravo) type setup right? That will become an issue if you try to make that much power out of a relatively small (540) motor. You will end up with a lot of compression and cam, and idle will suffer. Your drive might not like banging into gear at 1000 rpm all the time. The jetboat guys don't have to worry about this but unfortunately we do. I suppose you could put a transmission in to make it shift better!
-brian
Well since my b-max bangs in and out of gear anyways:D :D I guess it won't matter. :rolleyes: :rolleyes: . Damn I did not think about that. What does a 12-1/13-1 motor idle at with a carb, on a well setup motor. With the amount of boost that was on the blower, (if it ever gets put on this boat) I would have to time the blower surge just right to get it in gear. That sure was nice in the jetboat not to worry about that. Thank again for some info. KELLY
Mine idles reliably at 800 unloaded, but it's not a smooth idle at all. Drop it in gear and that's when the trouble starts. We have max'd out the IAC and use ignition advance control to stabilize the idle when it goes into gear, and it still dies sometimes unless you are quick on the throttle. If I set it up to 900 rpm, it probably wouldn't die any more, but it would start banging into gear harder than I'd like. I need to get a laptop back out on the water and do some more tuning in the idle rpm/in-gear load section of the map.
With a carb, the problem should only be worse. You're trying to get another 50-100hp out of a motor that's 58ci smaller. Even with more compression, I still think you will be running a very aggresive cam to make that much power up at a relatively high rpm. That means lots of overlap and high idle speeds. If you figure out how to make that work, please let me know and you can help me tune my setup as well! :D