boost at 6250 ft altitude
 

Hi everyone, need some expert technical advice. Have 2003 38 ft cat with twin 598 CI 900 hp supercharged intercooled engines. Fooled around with different props but just didnt run like it did at sea level, especially not getting up to plane even though I could hit the rev limiter with the smaller pitch props. Big difference from a 16 inch 4 blade 32 and a 16.5 inch 5 blade 36. Talked at great lenth with BBlades and they were very helpful.

Theoretically, couldn't I just up the boost enough to make up for the lost O2 at this altitude??? Then, the only difference woud be thinner air for an air entrapment hull - cat - but I can deal with that. I could continue with my original 36 pitch props ( That ran great at sea level - of the line it jumped up to plane and took off, picked up rpms and screamed past 130MPH before I shut it down. Was the most outragious powerful boat I have ever been in (I don't have a lot of high performance experience....).

Besides from running rich at this altitude, the chillers cool the intake charge so much (Thanks to Lake Tahoe cold water) that unless the motors are really warmed up if I drop the drives down at a start and start to push the throttles it just floods the engine and dies. The atomized fuel charge is pooling..... Once really, really warmed up then it's OK. I think I don't have any thermostats in these....

I have talked to various shops. Paul Phaff, Sterling, The Blower Shop, and my local guy. Phaff said they could send a guy to Lake Tahoe and tune both motors for this altitude after changing the pulleys. The blower shop said that 2 or 3 teeth would be equal to 1 pound of boost and that he thought I would need 1 pound of boost for every 1000 ft of altitude over 2500 ft elevation. About 3-4 pounds more boost. But, I have to know exactly what boost I am pulling now, and frankly, I am not sure... Have to take it out and give it a WOT high speed run...! Keep an eye on the boost guages at WOT and 5400 RPM(?).

Phaff said that they could send a guy here who could tune my "EFI" brand injection, even said he could install two tunes and a switch to change from one to the other, one for sea level and one for Lake Tahoe. All I would have to do is change the blower pulleys each time I went to a different elevation and flick the switch.

Here is the kicker, my local guy said: "if you are running rich now, and you want the same O2 level as sea level, why not just change the blower pulleys ( once I am sure what I am dealing with now) to be equal to sea level and the injection should be spot on.....

Phaff most likely would charge $1000+ per motor.....

Anyone here on OSO with experience with this or have any ideas?

Great winter project!

Rick

rick,i dont know if you have afr meter or bungs installed in your exhaust,but if your tune up is for sea level,no doubt you will be very rich at 6500 ft above sea level.you need to spin the blower faster to put more air in the engine.what do you currently have for top and bottom pully,s?

also keep in mind if you up the boost levels your going to make more heat in the blowers..you may have to either install coolers or bigger blowers..turn the bigger blowerd slower at sea level amd up the boost at 6500 feet..

The top pulley has the number 47 stamped on it, don't know yet what the bottom pulley says. I will see if I can count the teeth tomorrow. Send me a pm and i can send you pics of pulleys. No bungs, sterling said they built some of the motors for KE back in 2003 and badged them as KE's. Said it works two ways. One, off of throttle position or two, boost pressure plus throttle position. It literally says on the fuel injection box : "EFI". It's a blue anodized aluminum box with fins.

Rick

It has inter coolers and is way cold blooded. As to heat, the blower shop said I should not go over 8 pounds. I need to find out what it does now...

If the bottom pulley is any number lower than 47, flip those b!tches and hammer it down for a pass :daz:

Actually, after looking at a pic I think it says IFI...

It's logo looks like it says IFI but on the side of the box with the serial number it says EFI Technologies

Funny guy!!! Will find out tomorrow

Rick, in theory you could pulley up to make the same boost and roughly the same power as sea level without changing the tune. But... your idle, part throttle transition, acceleration enrichment, and cruise AFR are all still going to be pig rich. Unfortunately it sounds like you just don't have a very good base map as the EFI should compensate for the altitude. Yes, you'll be down on power but, you shouldn't be running rich and stalling. At 900hp with a 598 I'd guess you're probably only running 5-6lbs boost. I don't know what blowers you have but it should be easy to add a few more pounds to get your 900hp back. You shouldn't need two tunes unless the EFI software has very poor resolution. I'm not sure what system you're using but it should be possible for a good tuner to set you up so that if you're at 6000' one day and want to boat at 3000' the next day all you have to worry about is fuel.. Might want to get the tune dialed for the higher boost at sea level too! :boat: