What´s the best replacement for AQ271C (or 570) 5.7 GM engine, ideally stroker?

[Scott Danforth]

the edelbrock is a good manifold. same as the stock Volvo Penta vortec manifolds that I ran. go with a 1" minimum, 2" preferable carb spacer to increase plenum volume under the stock carb. will give you some tuning tips on the holley later

a good timing set (melling, cloyes or comp cams), a high volume oil pump from melling (and no, it wont suck your pan dry) https://www.melling.com/product/gm-cast-iron-oil-pump-select-performance/

threaded oil galley plugs vs pressed in

what RPM do you want to run? that determines cam selection

I would have the stock vortec heads modified for screw in rocker studs as well as the guide towers cut down for the better seals (about $100 charge). this is a must as the press-in studs will come out with eventually and unless you run beehive springs, you will mash the stock umbrella seals leading to oil consumption.

stamped roller rockers unless you want to upgrade to lighter valve train. then spend the extra $100 on aluminum

coated bearings is about a $100 charge. you may never need this, however if you ever loose oil pressure, it will save the engine from eating the bearings for about a minute giving you enough time to key off.

 

[Returntrip]

the mercruiser camshaft is same for the 350 and 383, only difference is the 1.6:1 rockers.

they use a flat top 4-relief piston (not a proper piston for building a 377 or 383)

Hi Scott, new member today. What a blessing to see this post you have going on about the stroker/Vortec info. By the way, the 24 Rouges are pissah boats, especially 496. Ive been a diesel marine mechanic for years & done my share of engine work. Im building my !st. gas engine & i have a mercruiser 377 forged crank (unmolested) and 2 sets of 906 heads. Also one 350 block, 1 pc. seal 4 bolt main, roller.
I could really use some help picking out what type of rods i should use with I assume Ill buy KB forged d-shaped pistons, who makes a decent roller cam with the correct dur. & lobe. would like to stay around .480 to .500 lift. I can do all the cylinder head work myself.
I will be following your thread. I would like to figure how much to deck .010?? proper gasketing & quench. Sorry for all the rambling on, look forward to seeing more good sbc info.

 

[bollerwagon]

After several ups (engine doens´t need a rebuild, just heads were too hot) and downs (engine needs to have the chambers drilled) the situation balanced out at down:
- Heads were too hot and the valves formed tulips, as they say here. So the top is not flat any more, several of them were concave. Maybe carb running too low?
- Head gasket had a passage between two cylinders
- rust holes from the water in the cylinders are too deep to be just honed out
- crank shaft bearings look weird and worn

So this engine needs a full rebuild. Advantage for me is, that after disassembling it I finally undertstand way more of what you guys were talking about.

On my search for some vortec heads I talked to someone who upgraded his (older version of a) SBC marine engine with some Edelbrock Performer heads and a Torker manifold and is very happy with it. He says idle speed is down to 500 RPM and fuel consumption down to 2/3.
I have to admit this sounds very appealing to me, rebuilding the engine not with these heavy iron parts, but the more efficient aluminium parts. Since I intend to use a closed cooling system, that seems to be a good alternative to the vortecs. Also it seems to be difficult getting a good paid of vortecs, since many of them seem to have hairline cracks between the cylinders.

After working with this heavy stuff, almost killing myself by putting the engine on a engine stand alone, thinking about the numbers my engine workshop asks for (drilling the engine >1.000 USD), I wonder if it is worth putting in the extra effort to stroker this engine, or if it would be a shortcut, just throwing more sophisticated parts at it like roller tappets or aluminium heads.

So this is my update, wonder how you think about these topics.

Ahoy!

 

[Scott Danforth]

dont do aluminum heads unless you do a full heat exchanger conversion

no real advantage of the aluminum heads other than weight. however the weight you save on the heads, you add back with the heat exchanger

since you pulled your motor apart, the only way it can go back together is a full rebuild.

if you did not label the bores the lifters came out of consider the lifters junk. they mate for life with the cam lobes.

I would simply build or buy a stroker. you can build the longblock with better parts for the same amount of $ it takes to buy a stroker crate motor.

 

[bollerwagon]

Aluminium heads
I will for sure rebuild with a HX, seems to be better for the engine and gives me the freedom to use aluminium parts. Also I do not want to grow sea shells in my engine block again.

bores and lifters
I would like to have these roller things. My block has these three points to attach the retainer that holds them in place that newer engines have (see picture). So I assume it is a easy bolt on upgrade?

Buying a stroker vs building
everyone over here who has purchased engines from the US warns me about the build quality. I can not judge, but literally every car- or boat workshop, every engineer or whoever tells me horror stories about (cigars and rugs found in) US-assembled engines. This pushes me a bit more toward building instead of buying.
Also I have to use my block to keep the boat permit to run on some lakes here.
But the question is, does the extra effort for clearing the block and so on pay off? is the stroker worth the extra effort?

 

[alldodge]

but literally every car- or boat workshop, every engineer or whoever tells me horror stories about (cigars and rugs found in) US-assembled engines

Unable to say for sure, but we here the same thing from rebuild shops on this side about buying foreign. The local shops want to do the work. The cigar and rugs is a new one and a bit extreme

Now if you heard it from someone which bought and installed there self, it could have some legitimacy.

 

[Lou C]

Aluminium heads
I will for sure rebuild with a HX, seems to be better for the engine and gives me the freedom to use aluminium parts. Also I do not want to grow sea shells in my engine block again.

bores and lifters
I would like to have these roller things. My block has these three points to attach the retainer that holds them in place that newer engines have (see picture). So I assume it is a easy bolt on upgrade?

Buying a stroker vs building
everyone over here who has purchased engines from the US warns me about the build quality. I can not judge, but literally every car- or boat workshop, every engineer or whoever tells me horror stories about (cigars and rugs found in) US-assembled engines. This pushes me a bit more toward building instead of buying.
Also I have to use my block to keep the boat permit to run on some lakes here.
But the question is, does the extra effort for clearing the block and so on pay off? is the stroker worth the extra effort?

Firstly if the engine was already run in salt water you can't add a H/X because the cast iron flaking rust will just clog it continuously
To accomplish what you want you can buy new, just get a new Vortec 5.7 and add the H/X in salt water use. I don't see any real advantage to aluminum heads on this engine. They are used in racing applications where weight really matters, and don't forget there are sometimes problems in mating alu heads to an iron block with head gaskets leaking. New might cost more but to run closed cooling will be better off that way.

 

[bollerwagon]

Firstly if the engine was already run in salt water you can't add a H/X because the cast iron flaking rust will just clog it continuously.

Block and intake manifold are now at a workshop for ultrasonic cleaning, I was hoping the engine will be fine to use for HS use afterwards. if not, is it viable to install a filter in the closed cooling system to clean out the stuff?

 

[bollerwagon]

Gentlemen, here are the news:
After being consulted that with repairing my engine I won´t be in the water on time, I´ve decided to get a replacement engine.
There are a couple issues though:
- Carb is missing, so I will plan to take take my old one
- intake manifold seems to be from a different engine (the black one), plan to take my old one. Had it ultrasonic cleaned, hopefully it ill not pollute the system. Will use neodym magnets to collect the rust.
- My old carb base plate gasket does neither match the openings of the original nor the ones on the new manifold. Shouldn´t I have one that seperates the two chambers?

 

[Scott Danforth]

the black intake is mercruiser. it was standard fair for the GM sourced engines. the Volvo Intake was from the GM performance crate engines along with the heads that volvo used. thats why the AQ271 put out 275hp and the mercruiser only 260. the black intake will consume just a bit less fuel at idle, however will not flow as much as the red intake from 1000 RPM up.

this would be the time where I suggest sourcing vortec heads and a vortec intake to give you a bit more power.

 

[bollerwagon]

I hear you, but at this point I don´t feel comfortable to open up this engine any further than necessary. I want it ready asap and all effort regarding performance will go to my old engine.

But do you have any ideas regarding the carb base plate gasket? What shape and thickness should I use? Looking at the shape of the manifold, this makes most sense to me: https://www.summitracing.com/parts/hly-108-18

 

[Scott Danforth]

me, personally, I would use a 2" carb spacer that transitions from the square bore to the spread bore pattern on the intake.

the 2" spacer will also give you slightly more midrange. you will need to make a new fuel line though

if not and you are using the stock VP manifold, use the stock VP gasket. its about 6mm thick if I remember

 

[bollerwagon]

Scott, I don´t know your mom, so I´m just assuming, please don´t take it as insult. But could you explain it to me like you would to your mom?
- What would a carb spacer look like, that transits from square bore to spread bore?
- what do you mean by new fuel line? The carb is currently supplied by two fuel lines, seems like there are two chambers fed by them. Would I need a third one and where would it go?

 

[Scott Danforth]

here is an example. https://www.amazon.com/Edelbrock-2696-Square-Bore-Spread-Bore-Carburetor/dp/B00062YACG

yes, the volvo fabricated fuel line comes from the fuel pump to a steel y-fitting and then to each carb bowl. to add a spacer, you need to re-fabricate the downward leg of that pre-fabricated tube.

its just 3/8" steel brake lines brazed together and painted.

 

[bollerwagon]

The adapter you mentioned seems to be exactly what I need. Translates from square to spread bore and has the holley screw pattern.

I think I get it now: since the carb will be about 1.5 inches higher than usual, the fuel lines coming from the block will not be at the right height to connect them. This height difference needs to be bridged - correct?

 

[Scott Danforth]

no, you would need to re-make the fuel line (post #74). as in re-fabricate a new line. your old line would not be usable as is

or you can get any number of holley fuel logs and run A1-15 marine fuel hose if you dont want to fabricate (per post #74).

 

[bollerwagon]

My rebuilding project makes new babysteps! I have purchased a broken VP 5.7 GS and intend to harvest the 906 Vortec heads and roller camshaft (and the push-things) from it. Can I take those parts without any changes and bolt them on my block?
And would it make sense to have the roller stuff on the top end of the valves also?

 

[Scott Danforth]

My rebuilding project makes new babysteps! I have purchased a broken VP 5.7 GS and intend to harvest the 906 Vortec heads and roller camshaft (and the push-things) from it. Can I take those parts without any changes and bolt them on my block?
And would it make sense to have the roller stuff on the top end of the valves also?

heads yes

cam, no - as the block is not machined for roller lifters

if there are roller rockers, then yes (stock vortec heads do not have roller rockers)

 

[bollerwagon]

heads yes

cam, no - as the block is not machined for roller lifters

if there are roller rockers, then yes (stock vortec heads do not have roller rockers)

What is different with roller lifters? I thought it just needs this „cage“ that holds them in place, bolted on with three screws. And my block has the holes already and I even think the threads are in also.

 

[Scott Danforth]

What is different with roller lifters? I thought it just needs this „cage“ that holds them in place, bolted on with three screws. And my block has the holes already and I even think the threads are in also.

you may want to check. if your block has the bosses and they were machined (they shouldnt be), then you are good to go