Need Opinions

[mattmck13]

I have a 86' wellcraft 21' scarab the motor has been bored to 355 c.i and has a mild cam( haven't got exact numbers yet going to call them and get soon. I just spun my coupler this year like 2 weeks ago and i'm thinking i'm going to leave it out for the winter (i pulled my motor) and maybe do a few mods... I want to gain some rpms it rev'd about 5000 when i got it but i ended up with a broken exhaust valve spring after a year or two and i think in the process of finding it my friend may have messed with the carb and not put it exactly back where it was (holley 750 double pumper) my boat now tops at about 4700 4800 ropm and about 5-8 mph less top speed. what would you recommend to go a few hundred rpms more so i can step from my 14 1/4" x 21p prop to a 23p prop....do you think he might have richened my carb enough to lose 300 rpm?

 

[Bondo]

Re: Need Opinions

the motor has been boredto 335 c.i

Ayuh,... Unless you can do Better than That for a discription of what you're workin' on,...
Don't expect to many replies...

 

[mattmck13]

Re: Need Opinions

no one can giveme any opinions?

 

[Apollo75]

Re: Need Opinions

I may be confused --- you drove the boat hard for two years and lost 300-rpm and speed ?

If I got it right then you have just lost some power -- typical from wear --- don't worry about it.

That is too much carb for a boat of that cubic inch --- if that engine was in a light car with gears ---- maybe --- I would drop down to a 600-cfm if running 5000 rpm or less..

Is that a marine cam or RV cam ? It makes a difference as to what rpm range you need to run for best torque. I am sure you can use the cam manufactures recommendations to get a general idea. Also, check out the prop section "prop questions and topics" for additional help.

My best opinions

Have Fun

OFM

"If you get a couple torpedoes slammed into yer sides ---> You have my permission to panic."

 

[wca_tim]

Re: Need Opinions

Bondo's point as well as the others are good ones. first, you should run the engine to the rpm it was designed to make peak horsepower - a direct result of the cam, heads, compression and intake used when it was put together. I will guess that based on what you're saying that 5000 is probably about right. although knowing cam and head specs would make guessing a lot easier... for best performance you want to prop the boat to set wide open throttle rpms right at peak horsepower...

if you broke a valve spring... were new ones installed when the engine was rebuilt (as has been noted on here a number of times, a large portion of small block engine failures are related to valvetrain problems... weak springs are a common one...).

if you put more info up, I'm sure people can help out more and will try to do so. Don't feel put off, just understand that folks want to give you a realistic answer and can't do so without more information.

I definately second the carb being too big. while it won't take away top end, you're leaving a good bit of throttle response and low to midrange torque on the table with that carb...

 

[mattmck13]

Re: Need Opinions

i never rebuilt the motor after spring broke just put all new springs, and i know the carb is rediculous but the guy i got it off of said it gave it more powerand speed when he put it on..here are my cam specs i got them from the company who builds motors..cam lift .296/.311 ADV lift .444/.466 Duration 214/224 ADV dur 288/298 overlap 69 degrees Separation 107/117 degrees I'm thinking of a little work this winter maybe a bigger cam, roller rockers ,fluid damper,shave the flywheel a bit, and some new springs, maybe shaving the guides if i have too and a valve job off course so they seat well.

 

[mattmck13]

Re: Need Opinions

and btw the carb didnt sacrifice much low end torque i can plane with a full tank (60 gallons and two people in about 4-5 seconds

 

[Maclin]

Re: Need Opinions

Your plan with that big cam sounds like a recipe for ingesting water from the exhaust thru inversion at idle and just above. Speaking of idle, if it won't idle at 650 rpm in gear then your drive is going to suffer against the higher idle rpm's required. The carb is just too much period.

 

[wca_tim]

Re: Need Opinions

Your plan with that big cam sounds like a recipe for ingesting water from the exhaust thru inversion at idle and just above. Speaking of idle, if it won't idle at 650 rpm in gear then your drive is going to suffer against the higher idle rpm's required. The carb is just too much period.

If you're running factory exaust you're running about as much duration as I'd be comfortable with - you'll have reversion problems (the same overlap that gives a nice lope at idle can pull water from the wet exhaust back up into the engine... not good.). Lift can go up some but if you've got factory heads, it won't do a lot of good. You ned the weight on the flywheel to keep it from stalling when you shift into gear...

the big issue with idle is shifting into gear at higher than 600 or so. You can always wire a bypass botton for the neutral safety switch so you can start it in gear, but that has drawbacks obviously.

 

[Apollo75]

Re: Need Opinions

I have read what modifications you want to do --- I would suggest the following.

I am sure that is a manual carb --- disconnect the secondary link and secure the secondaries --- see how that feels to you. If the throttle response feels better consider a smaller carb with vacuum secondaries --- change secondary vacuum diaphragm spring to your liking

Critical is valve spring bind with a huge cam --- the piston follows that exhaust valve --- spring pressure must increase --- consider roller cam for reduced wear.

Great idea with roller rockers:
The good high ratio roller rockers and / or cam can increase your horsepower by 20-hp with less heat and much less wear at 5000-rpm.

Do you balance ?
Balanced assembly is the key for long life --- find a good shop and tell what rpm you will be running.


Added: This is good believable information.

http://www.popularhotrodding.com/enginemasters/articles/chevrolet/smallblock/0412em_small_block_chevy_engine/index.html


I like you ideas --- modest --- good hp gains


Have Fun


OFM

 

[wca_tim]

Re: Need Opinions

I have read what modifications you want to do --- I would suggest the following.

I am sure that is a manual carb --- disconnect the secondary link and secure the secondaries --- see how that feels to you. If the throttle response feels better consider a smaller carb with vacuum secondaries --- change secondary vacuum diaphragm spring to your liking

Critical is valve spring bind with a huge cam --- the piston follows that exhaust valve --- spring pressure must increase --- consider roller cam for reduced wear.

Great idea with roller rockers:
The good high ratio roller rockers and / or cam can increase your horsepower by 20-hp with less heat and much less wear at 5000-rpm.

Do you balance ?
Balanced assembly is the key for long life --- find a good shop and tell what rpm you will be running.


Added: This is good believable information.

http://www.popularhotrodding.com/enginemasters/articles/chevrolet/smallblock/0412em_small_block_chevy_engine/index.html


I like you ideas --- modest --- good hp gains


Have Fun


OFM

amen on balance... and I like that article. note that some of the people I know running marine engines do the mixed 1.5 / 1.6 rocker arm thing to helpa ccount for the really poor marine exhaust combined with the exhaust flow weaknesson the heads. Also, the comp xm series of cams are quite a bit like the xe series but ground with a little more lobe separation to help offset reversion. the 262 or thereabouts is a good cam... as is the 270, but the 270 is probably too much for a stock wet exhaust.

and definately have fun with it!!!

also... run a good sized oil cooler with a thermostat if you're going to run the boat. it'll make a big difference on life. the loading on the bearings is a lot heavier on a boat engine...

 

[Apollo75]

Re: Need Opinions

Good call WCA_TIM

The sheering forces / bearing loads are much heavier on boat engines operating most of the time pushing high torque..

Maybe consider looking at oil properties since you will be running high torque @ 5000-rpm

I will give you this link and leave the research to you.

http://www.bobistheoilguy.com/index.php?option=com_content&view=article&id=53&Itemid=61

"After the base oil has sheared or squeezed out, The last line of defense is an additive that puts down a barrier film. This additive usually has higher levels of strength against shearing so it helps keep the wear down. Alright, here's the catch. In 96, the lubrication industry changed from the SH to SJ API rated oil by reducing the barrier lubricant additives to help preserve cat converters on cars. Why?, It appears that the manufactures / lubrication experts are concerned with contaminating the cat converters with the standard antiwear additives in the motor oils so they have reduced the levels of antiwear additives to preserve the cats. Hmmm, guess what, When they introduced the new SL GF-3 oils, They left it the same. Ok, not out of the woods yet... Now the new GF-4 oils are in the works in hopes to be introduced next year around April. Have a guess one of the things they are going to do?, YEP, reduce the current antiwear additives again."


OFM

 

[wca_tim]

Re: Need Opinions

Don't want to start an oil thread! even rotella t, the old standard for breakin oils is getting marginal in terms of zddp without adding break in additive... currently running mobile 1... again on the advice of engine builder. Amsoil, Redline, syntec, some others good as well. along with 3" merc big block oil cooler, 8 quart pan, standard volume pump. need thermostat to let temp get over 200 and let water boil off so condensation doesn't build up. take oil pressure off the front of the block so you can see how the oil is holding up under shear. If you're going to run it hard, forged crank, H-beam rods and forged pistons also highly recommended. 4 bolt mains optional under 500 horsepower or so.

 

[Apollo75]

Re: Need Opinions

I have always used Moly for assembly --- it has never let me down.

I like the properties of Moly ---- researching the new additives now --- report back later.

An oil post would be good if it could be based on research --- instead of a lot of heated opinions.

OFM

 

[wca_tim]

Re: Need Opinions

Hear you... unfortunately, a lot of the published literature that's available on the web was sponsored by the company supplying the oil - not saying it's junk science, but the tests are skewed and results chosen to best highlight the interests of the one paying for the research... or they aren't published. The primary literature has a lot of good information in it but it takes a lot of time and effort to cross reference the scientific literature with US and foreign patents to work out which oil furmulation(s) are using what type of chemistry... I've also done some analytical work to see whether or not the chemistry in a few of the lubes I was interested in really reflects what is advertised. there is a lot of leeway regarding how companies portray products in the lubricant areas and you might be suprised how "misleading" some of the so called literature is...

sorry to digress...

back to work here...

ps. to the OP, that 750 is probably fine on your set up (as you indicated). If you don't have them, a set of tunable metering blocks will let you dial the carb in even better. The advantage is even more apparent when you're running a bit more carb than needed...

 

[mattmck13]

Re: Need Opinions

Good call WCA_TIM

The sheering forces / bearing loads are much heavier on boat engines operating most of the time pushing high torque..

Maybe consider looking at oil properties since you will be running high torque @ 5000-rpm

I will give you this link and leave the research to you.

http://www.bobistheoilguy.com/index.php?option=com_content&view=article&id=53&Itemid=61

"After the base oil has sheared or squeezed out, The last line of defense is an additive that puts down a barrier film. This additive usually has higher levels of strength against shearing so it helps keep the wear down. Alright, here's the catch. In 96, the lubrication industry changed from the SH to SJ API rated oil by reducing the barrier lubricant additives to help preserve cat converters on cars. Why?, It appears that the manufactures / lubrication experts are concerned with contaminating the cat converters with the standard antiwear additives in the motor oils so they have reduced the levels of antiwear additives to preserve the cats. Hmmm, guess what, When they introduced the new SL GF-3 oils, They left it the same. Ok, not out of the woods yet... Now the new GF-4 oils are in the works in hopes to be introduced next year around April. Have a guess one of the things they are going to do?, YEP, reduce the current antiwear additives again."


OFM

i run Cen-Pe-Co oil 15-40w i dont know if you've heard of it its privately sold and my uncle in a distributor here in maine.... its parrafin based oil and from what i've seen and heard its some of the best you can get... also i'd like to add i have stock exhaust but its straight off the elbows and out the back about 6-8 inhse above the waterline would that make reversion less likely or no? I was looking at the marine cams on summit also how much lift did you recommend?

 

[mattmck13]

Re: Need Opinions

www.cenpeco.com



Engineered to save you money

Cen-Pe-Co lubricants enable your equipment to achieve maximum performance while at the same time maintaining the lowest overall operating cost. This is accomplished by our unique combination of high potency additives and 100% pure paraffinic base oils. The result is performance and protection that exceeds the best. Engine life is extended up to 50% longer through reduced friction and wear, cooler and cleaner operation, maximum acid neutralization, and minimized oil breakdown. Maintenance and operating costs are in turn lowered due to increased fuel economy, extra protection for extended oil drain intervals, longer engine life, reduced oil consumption, and an overall reduction in downtime.

 

[Rippenlips]

Re: Need Opinions

Any body run a break in additive? I heard that if you race or run and engine hard it helps with the protection package.

I'm putting a 95 mustang HO motor in a old Searay. A boat guy said it would last 2 hours and blow because its not a marine engine. I hope not. Just want to get out and do a little fishing.

Don't want to hi jack but I was searching and found this thread.

Jon T

 

[wca_tim]

Re: Need Opinions

the primary issue with reversion is how far away and how far down from the riser top that the water is injected. reversion happens because with longer duration camshafts, the exhaust valve is still open a bit while the piston is filling the cylinder. the resulting vacuum pulses will pull water up the exhaust pipe.

Any high quality oil is a good thing - especially if you change it often enough...

adding break in additive to oils - especially for flat tappet camshaft engines, is a smart thing to do.

The caveat being that a lot of the higher grade racing and offroad oils - especially those based on alkyl ether or ester chemistry - already have addives for that purpose.

Used to be that rotella T had a large amount in it to protect diesel engines, but under pressure from epa even that has been cut down to the point wher it is smart to add additional zddp additive.

oils like some of the amsoils, redlines, mobile one (v-twin as well as 20-50) and some others are formulated with high quality additive packages that have anti-scuff properties...

 

[Apollo75]

Re: Need Opinions

Any well made engine will work in a boat --- but, it is under load and the way prop selection is usually made is to select a prop to maximise torque at the correct rpm.
A good cam to create this torque at the correct prop speed for the application is a must. Leave that old Vega 4-cylinder where it is at hopefully on it's way to Japan to make a Toyota.

Moly seems the best as an assembly lube --- wouldn't stay in suspension long --- I guess they have found a way now.

It is hard for an engine to get a good fuel charge in a cylinder with a big cam ---- overlap ---- the intake valve opens long before the exhaust closes --- long tube headers and other things can be used on an street engine to help get a better cylinder charge at lower rpm by keeping exhaust speed up, this helps to scavenge the exhaust from the cylinder --- on a boat this is not feasible with normal exhaust and riser set-ups.

"Waves behave much differently than gas particles when a junction is encountered in the pipe. When two or more pipes come together, as in a collector for example, the waves travel into all of the available pipes - backwards as well as forwards. Waves are also reflected back up the original pipe, but with a negative pressure. The strength of the wave reflection is based on the area change compared to the area of the originating pipe. "

More on this :

http://www.burnsstainless.com/TechArticles/Theory/theory.html

Added: Excellent book --- on Ebay and may be in your local library.

http://books.google.com/books?id=ze_w0i3xZmAC&pg=PA131&lpg=PA131&dq=gasoline+engine+exhaust+gas+speed&source=bl&ots=mZ_z49YphX&sig=fHO1VOiWwVHP_INk9k4B3tYCTBU&hl=en&ei=MHO1StPIIYH8tQPa08XQDA&sa=X&oi=book_result&ct=result&resnum=6#v=onepage&q=gasoline%20engine%20exhaust%20gas%20speed&f=false

OFM