chattviper

I have a dart 540 block w a tbs blower application (8lbs of boost), demon carbs and full msd ignition. I have 4 blade 30 pitch props, xr drives w speedmaster lowers and imco extension boxes.

Last year I was turning 5800-5900 rpms at WOT. First, I broke a drive and replaced both w the new style xr uppers. Second, I put some bad gas in and burnt up a piston. I completely freshened up that motor and at the end of last year I did the same to the other motor (freshened it up).

No one is sure of where the timing was set on the motors last year so we set them at 36 at 3000 rpm and at idle is 18.

My question is. I cannot turn the same rpms anymore. I can only turn about 5100-5200 rpms. Nothing has been changed inside the motors, blowers, or carbs. How am I losing 700-800 rpms? Could the timing cause this? If not, I would greatly appreciate any suggestions on where I should start looking.

thanks!

Chris Sunkin

I'd start with a leakdown test on the engine, then I'd get an indicator on the rockers and look for a bad lobe. 36 is plenty of timing- if it's correct. I've seen pointers a few degrees off of TDC before. When you toasted the piston, I assume you had the whole thing apart- did you change anything on the cam? If you have a multi-position timing set, the cam might not be degreed properly. You may have been running it retarded an now are not. I misread a crank sprocket once and chased that one for some time- had NO power.

Chris Sunkin

P.S. Further technical information will require a larger version of your avatar picture

ezstriper

sounds like to me you have WAY to much timing for a blower setup, you only need a max of 28 and about 15-18 initial, blowers like timing in low, and not under boost, unless you are running race gas you are going to take out another piston. what compression are you running ? even at 8-1 your static compression is over 12-1 at that boost, Rob

chattviper

I'm not sure what my compression is. I bought the boat and motors from someone else and have been unable to get that info. I'm running 93 octane. If i put the timing back to 28 will that give me more rpms at WOT? How could I find out my compression? Thanks for your help...new to this stuff.

Chris.... I have lots more pics!!

johnnyboatman

iTrader: (5)

check the throttle linkage

Chris Sunkin

Talk is cheap, homeboy.

Chris Sunkin

If it was too much timing, they'd be detonating and rattling like mad- and would probably destroy the pistons.

If you don't mind a 100 mile tow to Nashville, I know the guy who can make it sing. And probably keep it from a very expensive meltdown.

RunninHotRacing163.1

Hey BIG Daddy back that timing down to 30 and crank it up , how much time on the blowers ..... If the blowers are wore and need refresh your rpm will be lost ..good luck

Budz Motorsports

Way to much timing for a blower! You should be in the 27,28,29 area at full advance. We are all just guessing since the only way to find out how much timing is correct is to do a timing loop on the dyno. But we all can take an educated guess, from our own experiences.