Vortec Upgrade Question....

[mohead1]

Ok, Im back with some more wonderin's.....over the winter, I want to upgrade to a Vortec top end on the '88 260 Alpha in my Wellcraft. I keep hearing alot about the dished pistons and whatnot....

So, I want to put on the upgraded Vortec heads (valve springs, guideplates, set up for more lift), intake to match (prob one of those aluminum hi-rise with the brass inserts), mild cam (268 dur. around .460 lift), and prob change the Quadrajet to a marine Holley (600 cfm awta do it).

I was running some compression numbers, trying to guess at the ratio if in fact I have dished pistons. Was using two variables on the piston dish, one at 8cc and one at a guessed 10cc. With a 64cc chamber on the head, .010 deck, and gasket I guessed at .025, it comes out to 9.5 +/- C.R. With the little more cam it will bleed some of that off, so what is the issue?

On hot street cars these days, the youngsters are putting mini chambered heads on and using a piston dish to make the ratio size to work. I havent had the heads off so unless i buy a borescope, I dont know if I have flat tops or dished.

Someone wanna chime in here? If Im using 93 octane fuel, does detonation really come in to play here? I think not, hell I have run 10.5/1 in street cars w aluminum heads, stiffer gearing, and no issues....

 

[Don S]

Re: Vortec Upgrade Question....

Your standard 1988 260hp 5.7 engine from Mercruiser was 8.5:1 compression ratio.

 

[mohead1]

Re: Vortec Upgrade Question....

Ok, so I raise the CR up a point.....Im keeping it reasonable overall, I dont want to hurt the drive....but I figured 300 horse easy, with decent torque gains...the right prop....drive shower and bearing girdle....and we're off !!

 

[Tail_Gunner]

Re: Vortec Upgrade Question....

Ive read a few of your post's ....Nice boat you have there i take it it is new to you and you have in mind to do a little tinkering or rebuilding. You may want to start a thread on just that opinion's on 88 350 rebuild you may find it cheaper to buy new and dont limit your thoughts to the big Marine word...

You will get many opinion's and thoughts allowing you to take a good course of action..the down falls and expense. As to higher compression...not a good ideal in marine.. detonation is always around the corner in a boat engine constant high rpm and heavy loads. A marine motor has a cold block yet high cylinder temps...funny combo

Ive seen where you might want to run in salt a bit that too takes a little differnt approach or a different approach can be taken..Start a thread it will amaze you

http://forums.iboats.com/showthread.php?t=555885

http://forums.iboats.com/showthread.php?t=524489

 

[John_S]

Re: Vortec Upgrade Question....

If your valve covers have perimeter hold down bolts, you most likely have 76cc heads with a flat top pistons. If you have center bolts, they are 64cc with dished pistons.

 

[mohead1]

Re: Vortec Upgrade Question....

John_S, thanks for the info, it does have the center bolt valve covers, but not a roller cam, model before those. So the only advantge of the Vortec is the breathability of the head (flow rates). So it should be a good addition, along w corresponding intake and carb....I think I will leave the cam alone for the time being, due to stock type exhaust (GLM upgraded type) unless I cna go one step up. People keep talking about 230 deg duration, they are talking at .050 data point, right? Isky has a good looking cam:

HYDRAULIC 2000-4800rpm .450/.465 264?/270? advertised, 214?/221 @ .050 112? lobe sep

 

[Tail_Gunner]

Re: Vortec Upgrade Question....

Cam Change for my 406? - Offshoreonly.com

Note: RMbuilder is one of top cam engine guys in the country. Services | Marine Kinetics - Marine Engine Shop

He will build a cam for your application if you choose to call, Notice he is recomending a very well known cam for a marine application.

Umm GLM manifold's???? make sure they are planed flat prior to installation. They do not have the highest reputation

 

[mohead1]

Re: Vortec Upgrade Question....

Wow, he will build cam, like spec it out....thats pretty dam cool....and yes I know, the GLM menace....but it think their design is good for power, i used a straight edge and checked flatness at the riser to manifold surface and it was good, also checked the riser fit-up without a gasket and no issues apparent. I added some hi-temp rtv on the gasket/surfaces also as an extra precaution.....not so sure how I will check these other than pulling spark plugs.....

 

[Maclin]

Re: Vortec Upgrade Question....

The cam talk reminds me of a cartoon in an old magazine, I think it would have been with the Big Daddy character from Ed Roth. It showed the customer with head in hands in front of a parts counter and the shop owner behind it holding some bolt cutters on a long stick with a bunch of cam lobes on it, asking "Whatta ya got, a 6 or an 8?"

 

[John_S]

Re: Vortec Upgrade Question....

Your current heads , given the centerbolt comment, should have self-aligning rockers. The vortecs need self-aligning rockers. Keep track of pushrods/rockers such that they stay together.

 

[Tail_Gunner]

Re: Vortec Upgrade Question....

Wow, he will build cam, like spec it out....thats pretty dam cool....and yes I know, the GLM menace....but it think their design is good for power, i used a straight edge and checked flatness at the riser to manifold surface and it was good, also checked the riser fit-up without a gasket and no issues apparent. I added some hi-temp rtv on the gasket/surfaces also as an extra precaution.....not so sure how I will check these other than pulling spark plugs.....

At a price im sure...it would be intresting to know what that price would be. Actually that's probably more of a service for a supercharged engine..a bit over our little runabout's..

 

[mohead1]

Re: Vortec Upgrade Question....

Yeah, after looking at his webpage, I am WAY not close to that level of motor, lmao.....I just want a little more grunt in me 'ol boat....
I figured a good intake and heads w mild cam would get the torque up and not be too hard on the drive as long as I dont act like an idiot with it, and I wont. Just wanna get it to run at its optimum

 

[Tail_Gunner]

Re: Vortec Upgrade Question....

That 270 is a great cam many have used it..But you have a flat tappet i assume and wish to stay there?

 

[mohead1]

Re: Vortec Upgrade Question....

Tail_Gunner, as far as I know, its a hydraulic cam in the motor now....not having the typical clatter of solid flat tappets....I wouldnt mind having a hydraulic roller, but they are all pretty heavy on the lift/dur from what I see, didnt want to get to outta hand on the cam with stock "type" exhaust

 

[Tail_Gunner]

Re: Vortec Upgrade Question....

I cannot set here on this comp and say noo problem. I can tell you that it has 6 degree's of overlap at .050 (ground on 112) that is where the valves are overlapping..the width of a human hair..actaully less. water will not enter at that point ....maybe vapor. Opinion: Reversion in part was due to overlap. the exhaust valve stay's open slightly while the intake stroke begins and the piston pulls (vacuum) from both valves reversing the exhaust flow...... and pulls both exhaust and water into the engine....

Reversion has been a valid concern for boating for quite a while and some die hards will tell you to stay away...It can occur if you idle around at the dock for hours or idle down a no wake zone at 700 rpm...At 1200 rpm reversion is not going to happen the frequency of the pulses are far to rapid with a cam that small and it is a small cam.

There is reversion with the 270 notice the rust on the bottom...that is how far water is reverting with the 270 in my v6. stock exhaust.John has kinks to merc racing showing they actually have cams that are more radical than the 270. Smiles they would be in stock production but the concern over this overrides (warranty cost) implimentation and why develop a new cam with that in mind when there are plenty of off the shelf smog cam's on the shelf.. You are aware that cams with overlap do have a tough time making smog requirement's

There that should stir the pot some..It's a safe upgrade and good power band.

http://victorylibrary.com/mopar/intake-tech-c.htm

Reversion:
Each cylinder’s intake stroke actually begins when its intake valve opens, which is always while the piston is still rising at the end of the exhaust stroke (BTDC). No meaningful gas flow occurs at this point - the industry-standard convention is that effective flow begins at .050” valve lift. If the motor’s components are well chosen, at some useful speed gas will begin to flow into the cylinder even before TDC, despite the fact that the piston is going the “wrong” way. At speeds below this, piston motion tends to push the gas back into the manifold runner - this is called “reversion”. Generally, the degree of reversion depends on several factors, to a greater or lesser extent. The following Table gives factors and effects.

Good link on reversion..its as old as the 50..40's god knows forever.

http://waharleyriders.myfreeforum.org/archive/cams-what-does-it-all-mean__o_t__t_218.html

 

[mohead1]

Re: Vortec Upgrade Question....

Thats good info.....I think the 270 series cam will wake up the motor and give more of a powerband in the mid range, which is what Im looking for. Adding the heads and the intake will be icing....