Chev Roller Cam

[redjmp]

I want to build a replacement for my '78 898 305.
Will I be able to use my stock 2bbl carb while using a set of vortec heads and manifold?
I also want to use roller gear on the valvetrain. Can I use stock vortec gear if I get a pre '86 305 block or will I need to go aftermarket?

Will a complete vortec motor bolt up to my type 1 outdrive?

 

[John_S]

Re: Chev Roller Cam

Go with a 350 of your vintage era. Go with vortec heads and a 4brl carb. If you want a roller cam, you have to go aftermarket. I'd stay with flat hyd. That would give you about 280hp. 250hp if you stay with standard heads 4brl.

BTW, there is not a merc vortec roller cam. The current roller cam came out before vortec heads. The main advantage of a roller cam is longer lobe life.

 

[Bondo]

Re: Chev Roller Cam

Ayuh,.......

I wouldn't Waste the Time,+ Money going to Roller Lifters in an Old vintage Block,.....
The Machine work,+ Hardware don't come Cheap.....

A New Vintage Block will bolt up to your outdrive,....
But,....
You'll have Coupler Issues......

 

[redjmp]

Re: Chev Roller Cam

A New Vintage Block will bolt up to your outdrive,....
But,....
You'll have Coupler Issues......

Ok then! What specifically are the issues and what is a workaround?
Will I need to redrill all the holes on the coupler or lengthen or shorten it?
Aftermarket maybe?

One more question. Are vortec heads all the same for sbc's or are they differently CC'd for each displacement of engine.

 

[Bondo]

Re: Chev Roller Cam

What specifically are the issues and what is a workaround?

A New aftermarket Coupler,....
The Crankshaft Bolt Pattern changed from 3, 1/4" to 3"......

Are vortec heads all the same for sbc's or are they differently CC'd for each displacement of engine.

There are 2 castingg #s,....062s,+ 906s,....
The 906s have abit thicker Exhaust seats,......
Both are the Same Volume though......

 

[John_S]

Re: Chev Roller Cam

I know of three different cast-iron vortec heads available from GM.
- "Standard" Vortec head - used in truck and marine engines
- GMPP Vortec small port - Larger valves than standard
- GMPP Vortec large port - larger exhaust ports than one above


I think what you are asking, is there a specific vortec head for the 305. I don't believe so, but you can check merc part numbers between a current 5.0 and 5.7.

 

[riverjet502]

Re: Chev Roller Cam

Part # 12558060

SBC 350 Vortec Head, Cast Iron Assembly.
This production Vortec iron cylinder head was first used on the 1996 pickup truck RPO L31 with fuel injection. The intake and exhaust port are very similar to the Corvette 350 LT1 heads. This head includes 1.94? intake valves and 1.50? exhaust valves, with pressed-in 3/8? studs. This head with compatible valves flows more air than bow tie head P/N 10134392, but the casting may not be as durable. The water passages are the same as the original 1955 small block design. Vortec heads fit all small block engines produced 1955 to present, excluding LT1/LT4 reverse coolant flow engines and current LS1 style ?GEN 3? engines. The eight-bolt intake bolt pattern is totally different than the early model V8 12-bolt design. Use new manifold P/N 12366573, 12496820, 12496822. The valves seats in these heads can be machined to 2.02? intake and 1.60? exhaust. The rocker arm studs can be pinned or drilled and tapped 3/8?. (Casting P/N 10239906 or 12558062.). It is not recommended that the heads be modified to accept early design intake manifolds (They will never match up right.).

 

[redjmp]

Re: Chev Roller Cam

Alright then. Thanks for the input everyone!
So for the added cost of an adapter, I will be able to use a newer style block that can accept chevy roller gear? Correct? That's to say anything post '87? I can add the vortecs later if I choose?
It matters not whether I opt for a 350 or 305 because they can use the same vortec heads?
Hmmmmmmmmmmm........ Won't that cause issues with compression ratio if using stock pistons?

Will a TBI engine accept my carb and be suitable?

 

[Bondo]

Re: Chev Roller Cam

So for the added cost of an adapter, I will be able to use a newer style block that can accept chevy roller gear?

Ayuh.......

That's to say anything post '87?

Ayuh,........ I belive that is correct.......

I can add the vortecs later if I choose?

Ayuh,....... That would be a Head,+ Intake Manifold swap.......

It matters not whether I opt for a 350 or 305 because they can use the same vortec heads?

Sort of, but Not exactly.........
Large Valves will hit the Block on a 305 sometimes........

Won't that cause issues with compression ratio if using stock pistons?

Possibly,.............

Will a TBI engine accept my carb and be suitable?

Ayuh,.......
The motor doesn't care How you feed it, as long as the Proper Intake Manifold is used.......

 

[John_S]

Re: Chev Roller Cam

On the stock Merc 350s with vortec heads (64cc), they have dish style pistons (around -12cc) to keep the compression ratio managable for a marine engine. I am not that familiar with 305 and configurations.

IMHO, you are putting too much emphasis on the roller cam, where the money is better spent on a 350 block and vortec heads.

 

[John_S]

Re: Chev Roller Cam

938-802556 HEAD ASSEMBLY-CYLINDER (5.0L) $1,166.60 $981.33
938-803860T HEAD ASSEMBLY-CYLINDER (5.7L) $999.90 $861.23

Mercruiser parts lists two different part numbers for the head assemblies for '98-'01 engines (both have vortec). Doesn't mean they won't fit, but does mean more research needed to determine differences.

PS: Google on "vortec head 305 chevy" and you will find lots of info to start pawing through. Including putting the 350 head on 305 and visaversa. I didn't spend much time reading, but it appears that the 305 vortec has the smaller intake valve and smaller chamber than 350 breathern.