350 stock heads verses vortec
 

i would like to know the hp increase over stock heads and high rise manifold verses vortec heads and manifold.can i use the same ditributer and carb?and does anyone know who might have to pairs as i have twins.1991 350 s

For a idea, one article I had read was that the vortecs produced 25-40 hp over earlier cast iron heads. If you change to vortec heads, you just have to buy new vortec intakes, like edelbrock has a air gap dual plane which is a very nice intake, I ran vortecs and this intake on a 383 a few years ago. Only thing is the heads need machining to handle cams bigger then .460 lift, I spent a good chunk of money, getting them machined for, screw in studs, guideplates, bigger springs and guides had to be cut down..

Yes you can use the same disributer, and for the carb depends on if its a holley or stock quadrajet, I don't know if they make vortec intakes for quadrajets or not, if not you will have to use a adapter or use a holley carb.

You can get these vortecs for $480-$500 a set.

Travis

The flow potential and resulting hp increases will be severely limited in this application without a cam change. The stock Merc cam is the roadblock to making more power due to its limited lift and duration, it does not exceed the flow potential of the stock heads and intake, let alone optimize your aftermarket pieces. It has been my experience that just the head/intake swap, without the cam change, will yield very minimal increases.
Protopline offers a "906" Vortec replacement head that is cut for high lift w/ screw in studs that flows very well for nearly the same money as the Vortecs.
Bob

thanks guys what cam can i use? i don't want to cause reversion.im running emi exhaust with ss risers and silent choice.

also running in salt water.yes i do flush but i would like to stick with an intake with bronze water jackets or cast manifold.

http://www.sallee-chevrolet.com/Inta...on_Vortec.html

Here is your intake, Stock cast appearing, fits Vortec, and taked a Quadrajet.

http://www.sallee-chevrolet.com/Cyli...ds/Vortec.html

and your heads.

I am interested in doing this same conversion, lets hear about the Cams.

I didn't do it, but looked into it. Remember to optimize your quench. A stock 350 should have a deck height of about +0.025" above your stock flat top pistons. If you use the stock composite marine head gasket (0.039") that'll give you a quench of about 0.064", which is really no quench at all (especially for vortec heads). If you use a high quality shim gasket (0.015 to 0.018), you'll get good quench. But watch your compression ratio. You may want the 72cc Vortecs rather than the 64cc to keep the CR within reason.

As for cams (I assume you are flat, not roller), the Comp XE262 would do good, although the exhaust lift might be a problem (I think its around .480). Also the XM 262, XM 256 or XE256. I like the XE's LSA of 110 (versus 112) better.

Not an expert, but I got an opinion.

OK, this may be a "Stupid" question, but, Has anyone tried to replace the cam with the engine in the boat??? I have the manifolds off, so it would be no problem to pull the intake, and heads, anybody think I can get in & around it enough to lower the oil pan, pull the timing cover, and regasket the pan & get it back together???

It was easy on my boat. A removable engine cover (ie no front bulkhead) makes it easy. You don't have to remove the oil pan, only drop the front lip enough to get the timing cover back in. I jsut removed the first 5-8 screws on each side (and front) and loosened the rest

That is what I thought, I have done this several times with success on cars, but didnt want to sound like a hack on OSO, figured I would let someone else post it first, Just kiddin, good to hear, I think this is the route I will go since it is halfway apart anyway, and Florida seems to be a "little" too cold for boatin' lately anyway. Thanks for the info.

The Swap is a simple 40hp increase. With no other changes. You will need to change the intake. Carb and disrtibutor can stay.... I did the swap. If you are going to change the cam just make sure you keep the lift to under .490 otherwise you will need to change the springs....You can get the heads new and complete from Salee performance pretty cheap. As far as compression ratio with the heads you can run up to 9.5-1 pretty safely with the vortec heads. Keep the quench around .25 and you will be fine. The stock Mercruiser motors that use the Vortecs heads run 9-1. You will want to keep the Timing under 32degrees...
Also if you are dressing up the motor valve covers are hard to find..... Here's my 355 vortec. Im pushing about 375hp at 5200......

BH

Huh?

just helping...only flat top pistons can be run with vortecs, cause if you used a dome piston, the dome hits the heart shaped point in the Combustion chamber.

Correct me If i am wrong, but "quench" head to piston clearance should .035" minimum! I used these heads on a stock block with a shim .015" gasket. had .040" quench.

my .02

UMMMMMM,

I kinda know what your sayin, BUT I have no clue what pistons are inside the stock 1992 5.7 non mag??? I am assuming Flat top, as far as Valve covers, I will just paint the stock ones, and put em back on, I am not into the flash, as much as a few extra MPH. Long story , but lets just say one side of my motor got a little HOT, (somehow water flow got restricted to one manifold, after disassebly, water was gettin to the manifold, but not out the other side?????) I know the manifold is bad, but I am afraid I may have caused a little damage to the head also, so if I am gonna replace, why not VORTEC, and if I got the intake, and heads off, I might as well throw a stick in it!!!!!

If its a 1992 Merc 5.7L (350) its like mine ('92 5.7L lo rise intake with Q-jet), and has flat top pistons with 4 valve reliefs cut into them (about -3cc, maybe -7, can't remember). The only other piston Merc used on pre-vortec SBC was a dished piston, but I'll bet you don't have them.

What travis said. Deck should be +0.025 so add a .018" shim gasket for a quench of .043 and you're set. Just make sure your static compression is ok. I seem to recall my calculation showed 64cc vortecs with .043 quench put me above 10:1 static compression.

Thanks,

sounds good, I am gonna look further into it after the Holidays.

when i replaced cylinder heads i quickly blueprinted a couple of my bores for static compression calculations... 1997 250hp 5.7 2V. my motor has the dished pistons which measured 13 cc. the highest point on the piston at TDC (indicated) was 0.024 inches down from the deck (depth mic).

utilizing a 0.015 shim head gasket i end up with a quench distance of .039 inches... distance is good but piston style is bad... if you are gonna use high turbulance heart shaped chambers the flat tops or (better yet) a D-dish quench style piston are the best. the dished piston accomplishes very little in the quench scenario.

these measurements with a 64 cc combustion chamber yield 9.39:1 static compression ratio on a 4 inch bore 3.48 inch stroke motor (350 chevy).

on the camshaft front, GM has been doing factory roller cams since about 1987... if the motor uses a flat tappet be aware that the block MAY already be machined to accept a roller camshaft thrust plate, spider and lifter tiebars so that you CAN run a roller... these parts are pretty easy to come by.

Again, good advice, anyone got a set of heads collecting dust???? Intake also?????? Holley 650???????

Sorry....My bad.......Quench should be around .038-.050...I would run the Edelbrock Performer RPM for a stock or mild cam. If you plan on running alot above 4000 or havin a decent sized cam run the RPM Air-Gap. If you are running below 5000rpms and under 325hp run the Holley 600. You will be fine. If you are going higher than 5000 or 325hp run a 650. Barry Grant makes a AWESOME carb for the small block marine motor. Its a 650 vaccum secondary with electric choke.....You would be well advised to get Dennis Moore's book on Small block chevy marine motors. A MUST READ...

BH

I offed my holley for a BG demon late last season... world of difference in component quality and out of box performance... the initial cost is a bit steeper but the BG comes with all the bells and whistles that you'd spend another 50-100 bucks on adding to the holley. I'm a satisfied customer and their customer service and support are pretty good too.

i also run an rpm airgap... she runs pretty well but takes a while to build some temp in the runners so it helps to have a choke in the carb (which i don't)... makes things a bit cold blooded. performance is going to suffer ever so slightly until you begin to build some runner velocity... generally 3000 rpm or so... i've considered swapping to a single plane for some more WOT punch but from what i've seen on and off the dyno... there isn't a whole lot of variance between the RPM and a single plane under 6000 rpm... 10 hp at most on similar motors to mine...

if you are gonna do intake, carb and heads don't choke her off by neglecting the valvetrain... you'll regret the extra few hundred bucks in the long run... (ask me how i know this :rolleyes: ) stock merc exhaust is adequate (although HEAVY) into the 350 or so hp range...

Do they make the Performer RPM for Vortec heads, and lined for Salt water use???? We dont have no stinkin Fresh Water down here in FL!!!!!!

Volvo uses an aluminum 4 bbl intake with a brass water jacket on their carbed Vortec 5.7 engines. Even the 2bbl version. They use an adapter to put the 2bbl carb on it. This intake looks just like an Edelbrock Performer. It has the carb mounting that will take a spread bore or square bore carb. I have one I'll sell for $150 plus shipping if anyone wants it.

Bob

Got any pictures????? I think I want it.

You might be interested in the spec sheet for this engine Chevy 350 HO Vortec 330 HP . It's a standard 350 block that uses the 8060 Vortec heads, a flat hydraulic cam that Dennis Moore recommends in his book and what I believe are the stock Merc flat top pistons (the ones you should have). You can look up the parts in the GMPP catalog. The pistons look like the ones in my '92 Merc. 5.7L.

The only thing that confuses me is how they get 9.1:1 with 64cc heads, flat top pistons (-3 to -7cc) and a decent quench (40 to 45 mils). I think that puts you into the tens. Maybe someone can cure my confusion.

Here are the specs on the cam in that engine, any good??? I am not really a camhead!!!!

24502476 Hydraulic Flat Tappet
This hydraulic flat tappet is used on the 350-300 and 330 HP special performance engine P/N 12355345, and 12486014. The duration at lash point in degrees (intake/exhaust) is 320/324; duration at .050" tappet lift (intake/exhaust) is 212/222 and maximum lift with 1.5:1 rocker ratio (intake/exhaust) is 435/460. Valve lash is zero/zero and lobe centerline is 112.5 degrees.

It's defnitely stronger than Merc's stock 350 flat cam. Your idle shoud be fine for docking, vacuum around 13" would be my guess. Ifyou don't have Moore's book on SBC Marine performance you ought to get it. He recommends that cam for a stock to slightly modified 350.

Not wanting to work this afternoon, I ran the numbers in a compression calculator on Keith Black's site.

For a stock 350 (.025 deck) with a composite gasket (4.155 x 0.039) and flat top pistons with reliefs (assumed 5cc), 64 cc heads give you 9.87:1.

If you maximize your quench by using a 0.018 shim gasket, the CR jumps to 10.4:1

To get 9.1:1, you need the composite gasket and 10 to 11 cc pistons, such as the Vortec reverse dome pistons.

So, my confusion has always been that to use Vortec "quench-style" heads on a stock, non-vortec engine means you don't get much benefit from the quench. You will still get more poniesfrom the better flowing heads, but not as much as if you optimized quench/compresion.

Am I right or wrong or misguided?

WELL,

I dont want to work either, but I have to build another 50 pieces by the end of the day(yeah right, thats not gonna happen, I will make up some excuse). But to keep it short, I dont know much about the whole quench deal, I know I will not get the full advantage, but still the best flowing head for the $$$, Just tell me what gasket to put in there, I think I have the head/cam/intake/carb deal fingered out.

quick little file to do compression calculations with.

Compression Calculator (EXCEL FORMAT)

Link doesnt work

OK, works now

OK, so with the flat tops, and .040 quench, it works out to like 10.26:1, is that too much for this motor??, If I use a thicker gasket wouldnt that lower it back down to a more reasonable level?

I am gonna be out of town for the weekend, and will most likely not be checking in here, so if you have a photo, e-mail it to me at [email protected]. If no picture, that is fine, just tell me it is in good condition, and we will work out the details monday.

Thanks,

Rick

My notes indicate that Merc's #7561 head gasket is GM's #14096405 and has a compressed thickness of 0.028", which should give you about 9.9

Felpro's 17030 head gasket has a compressed thickness of 0.039, which should give you about 9.7

Sorry to throw another wrinkle at you, but for 9.9 or 10.26, I think you better check the Dynamic Compression Ratio.