new motor disappointment
 

Built a 454 330hp stock what I did was forged crank and .030 over pistons file fit rings, balanced assembly high volume oil pump, i am running large oval port heads 2.19/1.88 valves ported and bowl blended, 8.79-1 comp, a complete crane valve-train with the 420 cam gold roller rockers 3/8 pushrods all arp bolts, running a eldelbrock performer intake and a 750 marine carb, revolution marine exhaust no mufflers and a stock thunderbolt ign. I am running a bravo 1 prop 24 pitch I have put 3.5 hours on it I finally opened it up it runs up to about 4700 rpm and thats it it falls flat on its face. I have a ton of mid-range power the boat is very quick the motor sounds good very strong. Also I am running 20w-50 oil and the motor carries 54psi of hot oil pressure. I just think it should run better than it does what does every-one else think

Re: new motor disappointment
 

Which Tbolt pack are you running and what is thetop timing set at? Does it spit cough or what ever or does it just run out of power?

Phil

Re: new motor disappointment
 

What fuel system are you running? What is the fuel pressure at w.o.t.?

Re: new motor disappointment
 

My previous motor was the merc 330hp motor. I do believe that the Merc thunderbolt ignition module has a built-in rev limiter. Set at 4750? Sounds like with the additional power, you are running on the rev limiter.

Recommend you take off the thunderbolt module, bolt on either a Crane or MSD ignition module. The MSD does not come with a built-in rev, so you will have to purchase it separately. Good luck.

Re: new motor disappointment
 

tend to agree, or just try a stiffer prop go up a couple of inches in prop and see what kind of power and top end she has... its alot safer then running without a limiter you can always change the mod later if you still feel you want the revs


keep in mind that the general rule is 1 in in pitch = 200 rpms

Re: new motor disappointment
 

I'm running the stock fuel pump eldelbrock 750 marine carb it acts like it hits a wall or runs out of gas you will be running say 4200 open it wide open and it goes to about 4700 if it was up against a rev limiter wouldn't it pop or miss because it doesn't

Re: new motor disappointment
 

What year? If it's a t-4 ignition, it has no rev limiter. You need to check timing at 4000 rpm and fuel pressure at wot. Also need to do a plug check at wot to see if its lean. Then try a 23 mirage to get the r's up and into range.

Re: new motor disappointment
 

What boat is it in some/ most boats have a check valve to keep the fuel from going back into the tank it can resrict your flow and you run out of fuel
also what fuel seperator are you using some older stock ones have a 3/8 hose but at the filter the fittings are about 1/4 inch
I took a piece of rubber FUEL HOSE and by passed my seperator and gained 400 rpm that was only to check to see if it was the problem
then I ordersd a new seperator with larger openings

just some thoughts to check out
good luck
Darryl

Re: new motor disappointment
 

the motor is 1993, wellcraft nova spyder 23ft, that is true on the fuel seperator I have a large fuel line frim the tank and 1/4 in lines coming out of it it is a mercruiser seperator

Re: new motor disappointment
 

That boat might ofhad one I knoe the late 80s wellcrafts did have a check valve from the factory, it looks like a regular nipple comming off the fuel tank if you remove it and look inside you will see the ball you can take a punch or a phillips swewdriver and punch the ball out then reassemble

Re: new motor disappointment
 

I agree with everything formula31 said. The Thunderbolt 4 does not have a rev limiter and is a darn good ignition system. I would make sure that you are jetted correctly because you are requiring more fuel than your stock 330 set up. Also, a fuel pressure guage is not a bad idea.

Re: new motor disappointment
 

how do i know if i have a thunderbolt 4 ign?

Re: new motor disappointment
 

What prop were you running before? From reading your post you have not done any changes that are going to yield a bunch more torque in which would be able to spin a bigger prop. Everything you have done is going to gain you more horsepower more so in the upper rpm's. You may try the same prop and see where she stops pulling at. Or check the dyno sheet if you have one. Remember, Torque tells you what you can move and horsepower tells you how fast you can move it. Thanks, Cam-shaft.

Re: new motor disappointment
 

I am running the same prop 24 bravo 1, the same carb and intake the same ign. I do have more mid-range power you can feel it the motor is a lot quicker. Last year 330hp 3000rpm=40mph-3500rpm=45-42-4300rpm-WOT=55mph; this year 3000rpm=45mph-3500=50-4700rpmWOT=62; this is the same prop same gauges, When you are cruising say 3500 open it up it takes off like a rocket then falls on it face acts like I run out of air/gas.

Re: new motor disappointment
 

Also, I have a mirage 23 prop for a spare I tried both props (bravo1-24) last year and the only difference in performance was mid-range speed had more cruising speed top end was the same. I just think it should more torque and rpm.

Re: new motor disappointment
 

That does not make any sense. If you are spinning the same prop as last year, your speed will be the same as last year at any given RPM. Did you change anything in the carb to accomadate feeding the engine more fuel at the hight RPM?

Re: new motor disappointment
 

That is exactly what I am thinking. the prop is spinning the same speed. Nothing has beed changed since last year only what I have said. It doesn't make any sense to me I think if you go from a 330 to a 420 you should see some more top end not run the same. From what I am seeing and been told, read etc there is a bunch of people exgerating and or lying or just misinformed.

Re: new motor disappointment
 

Seems like your running out of fuel. The stock fuel system/plumbing will probably be ok for you (I had 450hp running stock fuel setup and had 6 -7lbs fuel press at 5200). Although, you should of stepped up the jets to accomodate your upgrades. I would run it and do some plug checks. run WOT, and get it shut off as quick as possible after comming off plane. pull a couple plugs. Also, get a fuel pressure guage mounted at the carb and check pressure at 3500, 4000, 4500, WOT.

Re: new motor disappointment
 

you shouldnt speed up at the same rpm with the same prop. maybe your tach went bad.

Re: new motor disappointment
 

Bajarunner....you need to rephrase the begining of that statement to......

It's IMPOSSIBLE to speed up........ :p

Re: new motor disappointment
 

Make sure it's not the rev-limiter. I did everything mentioned on this thread and several other threads but everything ckeckout ok. All things that need to be verified on yours but last year I had the same problem with mine until I replaced the ignition module to one from a 454 mag. Now it runs up to 5050 rpms and hits the rev-limiter. Find the number on the module and verify what it is. Good luck.

PM

Re: new motor disappointment
 

For what its worth, my boat is similar to yours, if not even a bit heavier, same motor, and even worse flowing heads than yours (peanut ports). Same carb, etc.., and I can hit 5200-5300 rpm if I use your 23 pitch bravo one, at 62gps all day long, stockfuel lines, etc..stock TV4 ign as well, no limiter. I expect with your heads, I could go even a bit faster. Something is holding you back, but don't think its for lack of power in that motor.

Re: new motor disappointment
 

Well keep the ideas coming I am in the process of checking thinigs on the motor everything seems ok. My engine builder has mentioned ign and also he said to step up to a performer rpm air-gap intake. If I change the ign should i go with the crane box and leave my merc dist. in would that help. Thanks for all the ideas so-far I do have a thunderbolt IV that is what is says on the square part of the dist.

Re: new motor disappointment
 

Performer Intake is designed more for the peanut oval ports and peak power around 4k or so on a 454.

An RPM will be much better.

However, going solely by your description of going flat and falling on it's face I would strongly think carb calibration or fuel supply issues. Then again, weak spark or incorrect timing can cause the same thing. This intake will cause power loss in comparison to the RPM, but it won't make it fall on it's face at this engine rpm.

A good running TB IV should have no issue at all firing this motor. Make sure that total timing is where it's supposed to be. Bring engine rpm up to 4200rpm when setting timing just in case since some modules aren't all in until this point.

Re: new motor disappointment
 

Do a search on Thunderbolt IV rev limiter and you will see that some had them as separate units. Could save you months if there is one at 4700 or so. Just a thought.

PM

Re: new motor disappointment
 

If its a 93 its probably a t-5 and has a rev limiter. Get it out of there and try a t-4 from a friend before you spend money. Do the fuel pressure gauge. You've got to know that you have fuel at wot or you will hurt the engine.

Re: new motor disappointment
 

Remember, a fuel psi guage won't show if the needle/seat is a restriction. I've seen this a bunch of times...fuel psi guage showing good pressure but bowl(s) running out of fuel.

Re: new motor disappointment
 

I do have a tb IV ign. I just talked to a guy in florida who is retired from merc. He told me to set the timing between 3600-4000 rpm I asked about switching to a mag module he told to try this first. He also told me maybe to try an 800 crm carb instead of the 750. Also, mercruiser rev limiters will make the engine quit or (not pull any more). I keep investigating

Re: new motor disappointment
 

just pulled the module off it is a TB IV it says V8-24 2K22A those are the numbers on it

Re: new motor disappointment
 

If the timing advance doesn't work should i try a different module or just go and buy a DUI distributor i have heard some bad things about an msd system

Re: new motor disappointment
 

Stick with the tb-4. Set the timing at 4000 rpm to 34 degrees btdc. Ive seen a lot of these modules not do 24 degrees like they say. You will need a timing light that can do the advance. If you feel you must go aftermarket, the crane hi-6 is my choice but you will see no benefit other than a cleaner idle if your carb isnt set right. The 750 cfm carb will be fine for that engine up to about 5400 rpm.

Re: new motor disappointment
 

K24u, I had basically the same set-up in my 1991 25' Checkmate, but with a 365 Magnum. I called the Merc Tech on the Ignition and was able to find out about the rev limiter by giving them my engine serial number - no rev limiter on mine. My motor with a little more compression, Oval Port heads, Comp Cam, RPM Air-Gap, 830 Holley and IMCO Exhaust gained 500 RPM at WOT (went from 4900 to 5400 RPM). I balanced and blueprinted the original 23 Mirage and picked up about 7-8 mph - ran 72.2 on GPS. I'm having a larger motor put together and want to sell some of my 454 parts. I still have the Oval Port RPM Air-Gap if you're interested. Send me an email. Thanks

Re: new motor disappointment
 

off subject but as a seadoo cert tech have to ask,.... whats with the rotax 454 screen name....

and yes its the only 2 stroke that I play with, so if you have an out board 2str Ill still recommend someone else to work on it,, sorry Im old school....you specialize in something be the best you can be at it and then referrer other to someone that specializes in that product

Re: new motor disappointment
 

I'm going to put the boat in do the timing thing and see how it runs with the 24 bravo 1 compared to the week-end and do a plug check, then I'll change and put the 23 mirage on and try it. I would think I would pick up some rpm with the mirage i post later

Re: new motor disappointment
 

Well if it ever stops raining I will see what happens but I have changed the intake manifold from a performer to a performer rpm air-gap and I have set the timing at 10degrees @ 3800rpm so i am just waiting on the weather

Re: new motor disappointment
 

It will run like a turd if this is true and not a typo.

Total timing is usually between 34 and 38 degrees on a N/A BBC. That 10 # is probably your base timing # (at idle).... Total is what we are interested in since the module is fixed.

Re: new motor disappointment
 

Yea, I hope thats a typo, 10 degrees at 3800 will not work well. 10 at idle and a 24 degree advance module will give you 34 at 3800 but you should check it. I always set mine at 34 at 4000 and let the idle land where it will, the modules are not all that exact.

Re: new motor disappointment
 

Post which Tbolt pack you have, I have the chart for where Top Time comes in it varies from pack to pack, some can be set as low as 2000RPM like my HP24 most others are set at a lot higher RPM. Idle timing don't count for crap correct Top Time is the most important!

Phil

Re: new motor disappointment
 

v8-24-2k22a i have set the timing at 10degrees advance a idle

Re: new motor disappointment
 

k24u,
Any updates? I've experienced a similar problem with my set-up. I've got the MSD ignition, but am similar otherwise. Curious to hear what you figure out.