5.7L Non-Vortec to Vortec conversion

[Panoguy]

I have a 5.7L crate engine (home build) with low compression on several cylinders, likely cause is a bad head rebuild on my behalf. Assuming all goes well with my (wet) compression tests & I don't have piston/cylinder issues, I'm thinking of replacing my non-Vortec heads with (guaranteed) remanufactured Vortec heads & intake manifold.

So my question: If I replace the heads and intake manifold, are there any other items that also need to be replaced? - I've seen several posts (not on this forum) stating that I might also need new rockers, a different length pushrod, different springs... etc., it's enough to make a guy paranoid!

So, are there any surprises that I should be wary-of? Thanks in advance!!!

 

[Scott Danforth]

Just gaskets

 

[Panoguy]

Hey @Scott Danforth, really great hearing from you!

Thanks for your quick reply - I guess I've been reading too-much internets, & losing my confidence, I appreciate your reply (which makes sense to me, until I started reading too-much).

 

[nola mike]

I had some plumbing/wiring issues; I did the same on my 4.3 and ran into some trouble because the 4 bbl carb sat differently on the manifold than the 2bbl. My fuel lines didn't fit right, and my throttle and shifter cables were routed differently. I needed to get a different bracket for those, and needed to reroute the fuel lines. Don't know if the same would apply you are set up, but nothing insurmountable

 

[Panoguy]

Hi:
Well, the "wet compression test" has passed (no change in compression with oil squirted into the cylinders), so it's almost certain it's my heads that are problematic.

I'd like to step-back a bit, & offer details on my engine block, & while at-it, also ask a few other questions...

I bought my short block from Mabbco:
- 5.7L SGI - block#14093638 (1987-1995), 2-bolt main
- "performance reground camshaft" - I believe it's 270/276 lift .452/.465
- Hypereutectic flattop 4-valve relief pistons installed.

QUESTION 1: I DO NOT have roller lifters - will I need them?
QUESTION 2: I also bought with the short block new push rods - I don't know their length offhand (engine is just now being stripped) -will I need new push rods - if yes, what length?

I've attached a close-up of what my rockers & push rods looked like before clean-up, (new rods were the same length as these, old ones). Will I also need new rocker arms?

I'm just really paranoid that I'm going to end-up pushing a valve thru my pistons! Thanks once-again, folks!!

 

[Scott06]

Hi:
Well, the "wet compression test" has passed (no change in compression with oil squirted into the cylinders), so it's almost certain it's my heads that are problematic.

I'd like to step-back a bit, & offer details on my engine block, & while at-it, also ask a few other questions...

I bought my short block from Mabbco:
- 5.7L SGI - block#14093638 (1987-1995), 2-bolt main
- "performance reground camshaft" - I believe it's 270/276 lift .452/.465
- Hypereutectic flattop 4-valve relief pistons installed.

QUESTION 1: I DO NOT have roller lifters - will I need them?
QUESTION 2: I also bought with the short block new push rods - I don't know their length offhand (engine is just now being stripped) -will I need new push rods - if yes, what length?

I've attached a close-up of what my rockers & push rods looked like before clean-up, (new rods were the same length as these, old ones). Will I also need new rocker arms?

I'm just really paranoid that I'm going to end-up pushing a valve thru my pistons! Thanks once-again, folks!!

View attachment 359287

So you bought a rebuilt short block and put heads on it? Vortec heads will certainly be better performnace but before you tear it down did you rule out improper valve adjustment as the cause of low compression?

you only need roller lifters if you use a roller cam. is the cam you got a marine cam?

 

[Panoguy]

Hey @scott - Yep, long story short, I bought a thrashed Mercruiser 5.7L engine from a guy who was parting-out his boat, just for the heads, manifolds, tin, power steering... etc. then bought a Mabbco short block to hang it all on to.

I'm quite sure that I messed-up on the head rebuild (turns-out, the heads were a mess - engine was out of a salt H2O boat - live & learn!).

According to my invoice, the short block has a non-roller cam - but I purchased (for extra) what Mabbco describes as a "HP MARINE Custom Reground Performance Camshaft".

I'm guessing that I can use my current non-roller rockers & lifters... right??

I know I'm over-thinking this!!

Thanks again!

 

[Scott Danforth]

Hey @scott - Yep, long story short, I bought a thrashed Mercruiser 5.7L engine from a guy who was parting-out his boat, just for the heads, manifolds, tin, power steering... etc. then bought a Mabbco short block to hang it all on to.

I'm quite sure that I messed-up on the head rebuild (turns-out, the heads were a mess - engine was out of a salt H2O boat - live & learn!).

According to my invoice, the short block has a non-roller cam - but I purchased (for extra) what Mabbco describes as a "HP MARINE Custom Reground Performance Camshaft".

I'm guessing that I can use my current non-roller rockers & lifters... right??

I know I'm over-thinking this!!

Thanks again!

do you have a cam card?

My 1988 motor got an upgraded flat-tappet cam and vortec heads

vortec heads only care if the cam lift is above .420. then the heads need some machine work.

 

[Lou C]

Also you will need a Vortec intake manifold & convert the Quadrajet to an electric choke if you are still using a choke. No exhaust crossover passage in the Vortec head design.

 

[Panoguy]

@Scott Danforth - No, I don't have a cam card... didn't come with the short block. I'm now realizing that I should have obtained much more info, when I got this short block, 4 years-ago! Will there be a way to check clearances, say with a micrometer & hand-cranking?

@Lou C - Yep, I'll get a Vortec intake manifold... I'm old-school with the choke, I have a cable that I pull on my console(!). (Hey, don't judge me!! )

 

[Lou C]

Nothing wrong with a manual choke, I would actually prefer one!

 

[Scott Danforth]

FWIW......I havent run a choke in 2 years.

 

[Scott Danforth]

@Scott Danforth - No, I don't have a cam card... didn't come with the short block. I'm now realizing that I should have obtained much more info, when I got this short block, 4 years-ago! Will there be a way to check clearances, say with a micrometer & hand-cranking?

you can use a dial indicator on the cam lobes and get total rise on the cam, then use your rocker arm ratio and calculate valve lift.

 

[nola mike]

FWIW......I havent run a choke in 2 years.

But how does it start when the temp dips into the upper 60's?

 

[Scott Danforth]

But how does it start when the temp dips into the upper 60's?

starts the same regardless of temperature from 90 all the way down to 45. first start is always, one full prime, then part throttle and turn the key. with two 30cc squirters, it fires off about the 4th or 5th revolution when cold, and about the 2nd revolution when warm

 

[nola mike]

starts the same regardless of temperature from 90 all the way down to 45. first start is always, one full prime, then part throttle and turn the key. with two 30cc squirters, it fires off about the 4th or 5th revolution when cold, and about the 2nd revolution when warm

That was me making fun of your frigid climate

 

[Lou C]

Here the coldest I have run the boat is about 40*F and I think a choke is needed for reliable starts at that temp.

 

[Panoguy]

FWIW......I havent run a choke in 2 years.

Yeah - I was rarely using it also - just on those cold early mornings, sometimes.

 

[Panoguy]

Well if I don't get a response from Mabbco (they certainly haven't been the most forthcoming in the past), I'm thinking that I should probably change my camshaft to stock (or perhaps something better???), to be safe.

I'd like to keep it as stock flat tappet (looks I'm getting into really BIG bucks if I were to convert to roller!) - does anyone have a recommendation of ideal camshaft lift & duration specs for this conversion?

Man-o-man, I really don't want to shove a valve thru a piston head - that would really wreck my day!!

Thanks!

 

[Panoguy]

Summit Racing has a replacement cam & lifter kit... <<HERE>>
Any thoughts on this??? Hey, what's an extra $140. - right??