Boost / Octane / Timing
 

Hey Guys, Changed the upper pulley on my blower (b&m 174 w/chiller on my 489 chevy bb with a 6 inch bottom pulley) from a 3 1/4 to 2 1/2. Found out I was in the 11500 rpm range at wot and the blower can go to 14000 ish . With the last pulley I was at 5lbs at 5200rpm with a 27p and 6lbs with a 24p double cupped at 5900rpm. With the new pulley it pulled like crazy (with the 27p) and I was at 7lbs at 5000 with a lot more throttle to go. I run mid grade 89octane fuel and never had a problem (28 total timing) but with more boost should I cut back on the timing to ease detonation or am I needing to run premium fuel? Motor runs in the 120 degree range. This is my second season with this blower so I'm still on a bit of a learning curve.
P.S. I did pull a few plugs and they look good.

Thanks for any help.

I would say 93 would be a good idea. Steel heads?

Yup, 502 marine. Keep the timing at 28?

You don't want to take to much out cause it will make more heat and the motor will be somewhat fighting itself especially with a 4" stroke. Actually turning it up a little may be beneficial but camshaft would come into play also.

You're crazy for running boost without 93 IMO, LOL.

Run 93, keep timing the same like Baja said and run it hard and check the plugs. It may want a little more fuel b/c of the boost increase.

Definatly run at least 91 octane, and preferably 93 octane. What is your static Comp ratio???

Do not reduce the timing any further. It will create more heat in the cylinders.

I'm just gonna throw this out there I had a 540 efi that was a 500 efi with a procharger on it. The initial compression was 9:1. At 8lbs of boost the CPU was pulling timing out of the motor cause it was knocking. I ended up settling for 5.5lbs of boost and it made more power cause I could put timing into it. About 35 more at 5.5 compared to 8...

I'm not looking to make 800 hp (it would be nice) but from what I had found on dyno pulls with my blower @ 6000 rpm with a 2.5 it was making 620hp. Griff, My static comp is 9:1. This past winter I pulled motor for a freshen up and had no scuffing from detonation and I ran 89 octane all last year. I have all good bottom end parts, Flat tappet 576 with a 114 and HS roller rockers but do have stock head gaskets. I didn't think 8lbs of boost was to much but like I said, having this set up is new to me. Figured it doesn't hurt to ask!

May be ok for short WOT bursts but no way I would run that sustained high with 89 octane. I think if you really want to play around without hurting your engine you should invest in a knock sensor gauge, and or have an AFR installed on the odd cyl bank side and see where you are at. The summer heat will play a factor as well, you have no chance of hearing detonation over that little blower spinning that many RPM. Chilling that little heat pump is also inexpensive insurance.

Are you running 89 because it is all you can get, or are you trying to save some money? .15 cents a gallon savings is only $15 bucks each 100 gallon fill up, not a lot of money when dropping $400 bucks at the pump

4Bus, 89 is on the water around here. I am going to keep a few cans of octane boost on board this season. Putting in 91 isn't a problem when its on the trailer. I'll call today about the knock sensor. I was thinking about that this weekend and yes I have a chiller from Teague. So far this small package has got the boat to 80.7mph on gps. I know its not flying but I'm happy so far. Thanks for all your info

Who told you that is not flying? That speed could embarrass a lot of performance boats :D

The chiller is a big deal for fighting detonation in the summer heat, along with that 120 stat. My guess is you are still on the cusp of detonation, and I am not sure the octane in the bottle is going to help you....never been a fan. A five gallon can full of race fuel to mix with what you have on the days you are going to run hard is a better choice IMO.

Keep that other pulley on the boat and don't be afraid to switch it out on the days you plan on holding it to the bar for sustained periods. Going up a jet size on the top end is not a bad idea either, too many variables in the marine world to rely on a plug reading you took today. Changing temps, baro pressure, humidity could bite you on a different day.

9:1 CR with 8 lbs of boost is pushing the limits of even 93 octane fuel.

Here is chart with CR's and boost # for reference. http://www.holley.com/data/TechServi...ech%20Info.pdf

Thanks Griff for the link, I was on that web site the other day. Didn't get all the way through. I see your point about the octane. Looks like I will keep it under 5700 rpm. Not sure if I will be able to even get there with the 27 but I'll find out this weekend. The game plan would be to get close to 80 with the 27p and leave the set up alone and be happy for the season. Ill keep you posted. I did keep the 3 1/4 pulley and belt on the boat.

There is always the option of putting on a methanol injection. Probably be my choice over octane boost. I would also ditch the thermostat. A motor will detonate just as fast if not faster in the cool fat fall air as it will in the dog days of summer. Good luck with your project I would take it easy until you get some kind of knock sensor meth injection or something of the sort on your motor it's definately living on the edge.

Add a wide band and meth!! LOVE THIS STUFF!! Man meth works so so well. Been running for years on boosted sled and now on my boat! How about 12-13PSI on 93 OCTANE at 32 degs!! Yea might want to try 29-30 for timing that is putting some heat in the exhaust side! She is possessed with this set up. But man watch that fuel you are running..... scary man... What temp plugs you running? 8 or 9s? Never forget i had a WRX STI all built and took to a new tuner. He added more boost and took timing out. Buy the time I got home after new tune. The turbo/exhaust side got so hot it melted my main wire harness!!! Not happy...... Car with old tune had 30,000 miles on it and never melted the wires.
Good luck be safe have fun!!!
P.S. Boost is so addicting be care full! LOL

Just an update. Ran the boat this weekend and it ran GREAT! Put 93 octane in and only ran it hard once Saturday for about 1 to 2 min to 7lbs max at 5400rpm.Topped out at 84mph with the 27p 3blade. Ran it Sunday for about 2 hrs cruising and the same today. Got home tonight and pulled the plugs and no splatter. Did a compression check ( warmed up the motor) and was between 145 and 150. Just for kicks scoped the #7 hole and it looked like cracks in the top of the piston? Spark plug showed no sign of any issues at all. I did put in some CRC octane boost previously with 89 octane (turned the plugs a weird orange color) and I wonder if its just my eyes playing tricks with a carbon/oil trail in the piston. Was going to spray some carb cleaner in the hole and see if it cleans up. Don't you think my plug would have been damaged also if I had small cracks in a piston. Seems to be running great. I have a knock sensor kit on order.

Yea u would see stuff on that plug. Plus you would see more than 5psi difference in compression. Sounds good keep 93 in her for sure!!! Screw that octane stuff....... meth man.... a real good kit is only like $500.00 so so cheap for what safety you are adding.

reconize the handle skydog on dootalk are you the same guy?

Quick up date. Brought up the #7 to tdc. Cleaned it off with long q-tips and got almost cleaned up. Cant reach everything. NUTS how nasty that octane boost crap is.
Has anyone ever put hair line cracks in a piston but not damaged a spark plug?

Yes

Water down the carb works good to steam clean the top of that piston..

IMO, your pushing the laws of physics. You're turning that little blower at nearly 13,000RPM now. Forget about the whole theory of "its ok at 6psi, or its gonna blow at 8psi". You bet your azz 8psi with a 10% underdriven blower is gonna be a hell of a lot safer than 6psi on a 140% overdriven mini roots. The heat generated by the gas law (pressurizing air naturally heats it), is minimal compared to the heat generated by that little blower. This is why we intercool to run more boost. Lower the temp in the manifold and you can run more boost. Even with a superchiller, I'll bet your IAT temps are getting up there. Suck up some crap in the chiller or feed to the chiller, and its gonna be game over in a hurry.

If your liking the power gains from boost, invest in a larger blower. 8-71, 420 B&M, etc. That 174 was designed to do about 5-6psi on a tow truck engine or a mild street engine, not a marine high performance offshore engine.

Thanks MT, I have begun thinking that way already knowing that I have reached the end of the line with my set up. For the most part I keep in under 3800pm (cruising 3400) but I know it will only take so many WOT before I have an issue. Not to mention 2 carbs look better then 1! I have to figure how to post some pics. The engine and boat look great this year.