My 540 lost some power...need some advice.
 

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!

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.

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

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

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!! :)

check the throttle linkage

Talk is cheap, homeboy. ;)

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.

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

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.

depending on the dist. you may even be able to lock the dist advance and see how it starts, should not be running any more than 8-1 comp at that boost, and 28 max timing..no wonder you took out a piston, a goos water/alchol injection setup would help. the only way to know your compression is to know what pistons and head cc's you have, whoever did the engine should know, at this point the pin has been pulled !
have you done a plug check ? what heat range ? feel free to give me a call if you wish, 540-786-8111, Rob

Check out allot more pics here! ;) http://www.offshoreonly.com/forums/s...d.php?t=165627

Thanks for all the input guys! I talked to the guy who freshened up the motors and told him about all the repsonses on here. We are going to back the timing to 28-30 at full advance.

If i lock the timing will it crank at 28? I was told that it would make it very difficult to crank but did read about a MSD crank retard kit that brings the timing down on the start only.

Blowers have 160hrs on them.

thanks again for all ur help!

Wire in two switches- and ignition and a starter. Hit the ignition and let the motor spin up, then switch on the ignition. No push-backs.

Holy $hit. I'll be right down to get you boat running like a Swiss watch.

Unfortunately, they'd probably be polite enough to call me "sir". :(

damn, those pics would make me move to the south

Great pics for sure !!!! anyway....what was i saying.....oh yea...at 28 deg and low compression I don't think you will have a issue starting, running more compression and timing in my race car and it's a MSD and is locked @ 36 so you should be fine, still need to do some plug checks to make sure the jetting is ok....lean blower =$$$$$$$$$$$$$$$$$$$$

I had run lock timing for a number of years before I went efi. No problem starting and engine idles great. I would set timing at 30 max if you have alum. heads and 28 if iron. You may now have a valve, piston, and/or piston ring problems after running that much timing & 8lbs of boost. Detonation will distroy an engine quickly. Do you have intercoolers? Backing your timing down would give you less HP unless the motors are detonatioin so bad with all of the timing.

I would start with a compression test, easy to do and gives you a starting point. Not as good as leakdown but easier to do. If compression test shows all the same then you should know you have not damaged engines when you were running that much timing. First cylinders to go are #5 or #7 since they fire right after each other.

Give us a time frame as to all of these events, and results. I think you lost a drive first, then replace drives. Did you lose any rpm or speed then?

When you lost a motor did you redue both at the same time? Did motor go back the same or did you make changes? We need more details.

Here is my time frame:
1. Last year (april) running 5800-5900 rpms...broke a xr upper. Replaced both uppers w XR new style upper. Still turning the same rpms after this change.
2. Put less than 93 octane in boat.burnt up piston n one motor. Replaced 2 pistons and freshened up motor..no changes at all done to motor. Other motor was still running fine so I did nothing. This was in august. Set timing on freshened motor to 32 to match motor that did not burn a piston. Was turning about 5400 rpms w both motors at the end of last year.
3. This past winter i freshened up the other motor. All pistons were fine. Freshened up motor and made no changes.
4. Replaced both distributors caps w new ones (same ones just new)
5. We set the timing at 32 @ 3000 rpm. But after a few runs this year, the timing has creeped up to 36 @ 3000 rpms. Very hard to idle, crank and surge(which I need to put into gear) Acts like the carbs are loading up badly. When the motor is hot, I have to give the throttle to almost halfway for it to fire up. Pain in the butt.

Checked the plugs...very black w some sort of deposit build up on them.

No intercoolers.

Throttle linkage is fine.

I'm going to take all of your advices and lock the timing at 30. Also, going to adjust the carbs again after we set the timing. I will let you know my results.

Could be air leaks, could be blown power valves.

Check your float levels as well. A trip to Eddie Young would have them singing a sweet tune in no time.

That's exactly where I was headed here...

Blower motors aren't for the novice- or the intermediate. Mistakes happen swiftly and expensively. Let a pro get them right and then learn how to keep them there on a DIY basis.

lets get chattviper dialed in soon, so he can get us some more pics :drink: good luck

Chattviper.....I was anchored behind you in my 38....white with a yellow and purple strip at the chattanooga races last year. Eddie Young built my 598CI 750hp mills and I could not be happier. He has done all my buddies supercharged motors with awesome results and he is getting ready to whipple mine. I would highly recommend him......and he is only 2 hours away. Give him a call.....you will be glad you did.
(615) 216-7449. Your boat sounded good and had a nice looking crew aboard!

Chattviper,
You have gotten some good advice. I would first do a leak down test to be sure the motors are mechanically sound before you spend anymore time chasing problems that may not exist. I would be happy to talk to you and help any way I could, or take a look at it. It may require me to make several trips with your crew to iron out the problems. But I'm willing to go out as many times as it takes:D
Give me a shout if you get a chance and I will help you in any way that I can. 615-216-7449
Thanks, Eddie.

Thanks everyone else for the referral and the kind words.
Eddie

Eddie just built my motor. It makes 872+ hp and will be out on the water in Chattanooga in a couple of days

Eddie - it looks like you may need to come down to Chattanooga to finish tuning my boat! :cool-smiley-027: