540/B&M 250 Issue
 

Recenlty rebuilt 540/250 combos. New hydraulic rollers/top ends from Bob. Problem - Both engines start idle great and run perfect until around 2500 RPM's. At that point the port engine starts requiring more stick to keep up with the starboard. At 3K the port starts building boost and the boost guage is moving in unison with the throttle. At this point the sticks have about a 1.5" spread and the engine is really not making power. SB engine runs great well past 3K... Running TB IV - V6-14's with the initial set at 20*. Single 1050's. Engines have about five hours on them. I have pulled the heads thinking stuck valve, and checked the intakes for trueness. Thoughts?

You need to have a little more information; do some more troubleshooting first.

I have to ask; did you dyno engines?
Make sure the throttles are moving in sync.
Insure timing advance is equal at specific rpms.

This is a basic start.

Mark

Swap the carbs and see if problem follows .Then try swapping the blowers.
Do the blowers have the same hrs ?

check to see where timing is at various RPM'S 2000, 2500, 3000 ETC..See if they are the same ? personally don't like the merc dist...but thats just me...

What's the fuel pressure doing

I would swap the SC's and carbs. It sounds like you're not making boost.

Did it run good since rebuilding it 5 hours ago and just start doing this now or did it do it since you fired it?

Sounds like he's saying it does make boost but just doesn't have any power (port motor)?

+1...would have been a lot less work than pulling the heads!

I would verify timing and fuel before tearing things apart!!!!

Thanks for the replies... Guess I should have been a little more clear. This engine has behaved this way since the first time it was started. I did swap carbs and blowers before I tore it back down. Since then I have swaped ignition modules and no change. Timing is all in (30*) at around 2800. I will check if it is falling off. AFR's abiet rich, are around 10.5 at 3000 running 98's and 6.5pv's. all the way around. As far as making boost - the guage is moving as I push through 3000 but there is no additional power. It actually seems the power falls off. I will go back to timing and fuel and report back. Thanks!

Sounds stupid but...check your blower belt and make sure its not slipping.

I`m sure you`ve checked the plugs... my story was when i was running rich and had a few long idles on the boat, I was making full boost but both motors were turds and weren`t making any power, they hit a wall and didn`t go over 4000rpms..; changed plugs power came back, turned out the plugs fouled out

i have a few questions were cams degree checked,what is the compression ratio,do you have powervalves in the secondarys.it sounds like it might be so rich it cant burn the fuel,also you need more ignition timing.

Yes
Around 8.5
Yes - Carbs were done by Nickerson originally but had 90's and 6.5's all around. I installed 98's before I installed the O2 bungs because the plugs appeared to be too lean. I agree now it is too rich, but the SB engine is running just fine.
Timing - I think this is more than likely the issue. Why do you think it needs more than 30* total?
Thanks!

If the intake is making boost pressure, it sounds like the Intake valves aren't opening and you are developing boost pressure quickly. If they aren't opening the pressure has no where to go?

Put a fuel PSI gauge on it and make sure the FUEL PSI isnt dropping. If fuel PSI is good, and timing is showing up at 30* on the balancer, I'd look at secondary ignition, and or carb. Your boost is going up so the air is there.

I'd look at plugs, wires, cap, rotor, and coil if fuel psi is good.

I have to agree with you. cigrocket
What is your cam firing order and how did you adjust the valves?
If you have swapped all components and checked timing advance, something is not sounding correct. Have you done any type of cylinder leak down, besides a compression test?

The cam is a 2-3 4-7 swap. Adjusted the valves using EOIC plus 1/2 turn. Did a leakdown before I tore it apart the first time. Have not done one since.

Why, did you tear it apart, the first time after rebuild?

What type timing sets did you use, one that you can only install one way or has key-ways for advancing or retarding cam? Did you use a degree wheel and properly locate TDC 1 st?

Could be a broken intake rocker, loose rocker not seated, leaving the intake valve closed

Compression test would show it immediately, especially on a new build. Don't run it until you figure it out

That's what I was wondering too-is cam timing correct? If NOT you will see a small acrossed the board difference in compression, who assembled the motors? I recently fixed a Oldsmobile that's cam timing was whacked off in left field built by a supposed engine builder, the engine builders response to me finding the cam timing off was IT CAN'T BE OFF- I LINED THE MARKS UP!!!!!:evilb:

question for the op,why did you go with a cam with a non traditional firing order.

first off thanks to everyone for the input...

The top ends were spec'd by Bob M. Retro hydraulic rollers in Gen V blocks. Used his custom grinds from Cam motion, Morrell lifters, Isky 9005 springs, Manton pushrods, and Rollmaster adjustable timing sets. 088 heads with some pretty extensive head work. I had the heads flowed prior to spec'ing the cams and they were good to .700 The cams have 4* of advance ground into them and the bottom ends were built and cams installed by a very reputable local builder that I have worked with on several other projects. Cams installed at 0* due to the ground in advance and the builder said they were spot on. The bottom ends are Callies/Oliver/JE. The firing change order was done by Bob. The reason I tore these back down after about an hour was because of this issue. First thoughts were a vacuum leak but we could find nothing. When I reassembled the top ends I swaped the heads from the other engine and the issue stayed the same. I am thinking either bad distributor (timing) or wrong cam grind as the other engine runs great. Thanks again to everyone! keep the input coming.

im hoping bob will chime in on my cam question as im very interested in learning why he specked these cams.

have you spoken with bob about this,if anyone can help figure out what is wrong it,s him.

can i ask who the builder is?

I never chime in on any of these types of threads but am very curious as to what is causing the issue. You said a builder installed the cams and everything was on. With an off the shelf cam this seems to be standard procedure. My question is that since you have a cam with the firing order changed is it necessary to check every lobe to verify that it was ground accurately? Don't mean to hijack but curiosity got the better of me, hopefully some of the other guys will clarify. Good luck, they should push your .38 special very nicely!

Not to answer for jamontes but when I ordered my NA/Blower cams from Bob I also did the 2/3-4/7 swap.
I believe the reason was the there was a better selection of cores to achieve the higher lift on a shorter duration that I was after.
If that makes sense. I believe they are 8.1 cores.

The reason is the side load on a traditional cam is very high and causes core deflection. Swapping the firing order balances the load on the care. That's it. Not for any performance. This is from bob last week when I ordered a cam for someone.

How did you adjust the valves, in the 1st assembly of the engine? Did you look at the cam spec sheets for each cam and verifying the numbers when you degreed the cams. The cam cores are billet and checked after grinding. I know this as a FACT, since Madara, does ALL of my cams, and I have never had 2 different cam grinds for the same build, this is over a 8 year period. Using a rollmaster timing set and Bobs cams have always come in at a straight up, installation on the numbers.
If you looked at both spec sheets and degreed the cams as spec. How can you make the statement; WRONG CAM GRIND. You should go back and find out what you did wrong before you start guessing whats wrong. That's inaccurate information at this time.

Doesn't swapping the firing order have something to do with not having 7 fire right after 5, to keep the heat down in that area?

It was just a statement. Sorry you took offence to it, but it was not directed at Bob or anyone else, but would I be out of line to think just maybe the cam was packaged wrong? If I knew what I/we did wrong, I would be boating right now. Not posting for advice. Thanks!

Shoot, I am still waiting for my cam cards for the cams that I ordered. So if he got them he is ahead of the game.
I had to have JimV lay them out and check everything for me. And I did get 2 identical cams.

I'am not going to go back and forth on your statement. Packaged wrong with the spec sheet, then you install the cam, you are 100% positive the gear marks are correct, you degreed the cam and it came in, accordingly as the spec sheet stated? Or; No, we did not degree the cam and do not know 100% that maybe we missed the degree marks?
So what is all comes down to is, everyone is trying to help. Yes; I take offence to even mentioning the cam, it's the first thing people want to blame for a issue. So you even saying the cam was not matched or packaged wrong indicates to me that; checking TDC and degreeing, may be questionable.

I would suggest; pulling the engine, oil pan and the timing cover and verifying the timing marks, if you did not degree the cam in. At that point you can degree the cam and check it.

Why did you not get any cam cards? If not; That's only a phone call away.

There were no cam cards in the boxes. There was a single card emailed to me that was used to degree both cams. I wasn't there to witness the process but have confidence in the builders ability. Hell maybe he was having an off day and DID infact fuk it up. Either way I posted this seeking input BEFORE I go the route of pulling the engine back out. Not to get blasted for making a simple comment. We can put this one to bed. Peace Out!

Wow, chill buddy...this guy is trying to figure out his problem. He is not blaming Bob or anyone else at this point. I am sure you already PMed him as no one can talk about a cam on here without doing so...geeez.