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

[bollerwagon]

Ahoy! I have managed to toast my Volvo Penta AQ271 within 4 months after purchasing it* and need some advice for a resonable replacement. Since I found frost cracks in the exhaust manifold and it was sea water cooled for 30 years, I would not like to reuse the block, so at least I need a long block.

Also from a European perspective the ratio of 275 horse power and 5.7 liters of displacement is a bit odd. So more power would be very appreciated. From my non educated guess, cost´s should not be significantly more, since all the parts used in a stroker kit need to come new anyway.

I found offers like this, that looks nice from the specs to me, but trigger my trust issues. Also I found this offer, that is a bit over my budget, especially if you add 1.5k for the stroker kit.

So is there anyone, who was in the same situation and now, maybe after some months or years of boating experience wiht that replacement can say he (or she) made a wise choice?

Jonas


*I bought the boat with zero knowledge and did not see an obvious frost crack in the manifold. Also the gaskets between riser and manifold were old and leaking, so water came into the combustion chamber. There are rust rings visible where the water was at the piston rings. Honing in almost all of the cylinders is gone and with it the compression (around 6 bars most of them). One is without any compression.

 

[alldodge]

Don't like the looks of Raptor engines. They don't list where there located and when you go to there contact info it has something embedded which my virus software doesn't like and blocks it.

Michigan Motorz has been a good place to buy from, many on this site have done so. The one you chose is the same as your old

If you go for turn key motor I would get a newer vortec motor. It will plug and play. You could just rebuild your old motor

Motor HP when installed in a bot is at the prop, and when purchased as just a motor its measured at the crankshaft. So a 315HP motor at the crankshaft equals a 270HP at the prop. The raptor motor listing 420HP at the crank, well I'll just say I would like them to prove it on a Dyno

 

[bollerwagon]

Just to share my misery, see attached some pics from the disassembly. My favorite picture is the cylinder with the deep crater in it, I call it "sports stripes".
Compared to the tinkering with my audi this engine feels a bit more like lego bricks, a tad less complex. So I hope I won´t get get nuts and dare to fix it myself...
Since I don´t really know what w ay go do down now, let me also share some open questions and thoughts with you:

The Vortec engines - is this the same engine but with different heads and intake manifold? Or does it come with a different carb also - or even EFI?

I would like the idea of getting rid of the fuel smell with a closed EFI system, also with some less fuel consumption. But I dislike the idea of spending more than 5k on this.

Also after seeing the crack (frost damage) on my exhaust manifold, I like the idea of a closed cooling system, but these seem to be very expensive also (>1k).

 

[alldodge]

Vortec motor has different heads and cam, and yours would accept just a head change

EFI and closed cooling cost, no way to get around it. Just depends on if its worth it to you. I've spent 3 times what my boat is worth because i like the boat

 

[bollerwagon]

So I can not just replace the head to the vortec, also the cam shaft needs to be replaced to properly control the valves?

IF I change heads and cam, the vortec heads seem to have different bolting. Mine has 6 bolts per side, the vortecs don´t have the middle ones. So I need a different manifold, correct?

 

[alldodge]

You can put just vortec heads on your motor without the cam change. With cam change you will get all the power that originally came with the change.

The heads may have bolts in other locations so ancillary items (alternator, power steering, dip stick) may not bolt up, don't know have to look at your motor.

If heads are changed then the intake must also be changed

 

[Senior B]

The easiest and most economical will be to replace your current motor with a 5.7 Vortec long block. Not much sense re-working a 30 year old raw water block and adding a new cam and buying a set of vortec heads. You will need a new intake manifold but should be able to use your current carb. You will notice a good increase in power over your current motor.

 

[bollerwagon]

so you think, there will be a big price difference between a 5.7 Vortec long block and a stroker long block?

Michigan Motors offers a Vortec long block with the #906 heads on them. My googled superficial knowledge tells me, the 906 heads are less performant compared to #062, due to a modiefied exhaust seat that loses 20 percent of its flow at 0.120-inch lift (http://www.superchevy.com/how-to/97458/). Whatever that means...

@Scott Danforth, you seem to be quite familiar with the exact same topic - what would be your conclusion, after your journey?

 

[Scott Danforth]

first, please understand torque is what makes the boat go. HP is just a function of torque and RPM

lets break down the 271C
its a generic 5.7 short block with small chamber (64cc) police package / performance crate motor heads and a 715CFM vacuum secondary 4-barrel carb

hence the 271-275hp compared to the mercruiser 260hp for the same vintage

you can take the same motor, swap cam and move up to vortec heads, swap manifold, and with some tuning.... get close to 330hp prop (about 350hp crank)

I have done just that...... and once the mods find where the thread went, I could post it.

if you want more power, then you need to build a 377 or 383 (vs buying a GM crate motor with the god awful flat-top 4-relief cast crap pistons. you can build 420hp 6.2 liter

the drive will handle all the power you can throw at it, including if you decide to go big-block

most importantly, how fast can you afford?

 

[Scott Danforth]

so you think, there will be a big price difference between a 5.7 Vortec long block and a stroker long block?

if you buy it, there is well over $1500 difference. if you build it yourself, there is about $300 difference

 

[bollerwagon]

just out of curiosity and to learn something new, I would love to build it myself! I would need some help to build a solid shopping list and someone virtually holding my sweaty hand while doing it.
I have some guys here who are generally familiar with the hardware, but everything what is beside the usual (stock) - is witchcraft to them.

Budget wise I would prefer not to burn more than 5k, ideally including VAT and shipping to Europe. Would it be too much to wish for a fresh water cooling system to be included as well?

 

[Scott Danforth]

5k USD for a new to you motor with a heat exchanger and new exhaust manifolds is possibly doable if you were in the US

if you can find a good running 1996 or newer GM truck motor, you can save yourself the cost of blocks and heads

• GMPP block ~ $800
• GM vortec heads ~800 a pair
• modifications to allow the vorted heads to have a higher lift cam ~$100 (common price at most machine shops locally)
• SCAT forged 3.75" stroke rotating assembly $1500-$1800
• coated clevite bearings ~$300
• Melling oil pump, oil pump drive shaft and oil pump pickup ~$130
• Comp Cams K-kit ~$1100
• Felpro head gaskets, oil pan gasket, timing cover gasket, etc ~$150
• new vortec marine intake ~$450
• new GM marine circulating pump
• new BARR or VP exhaust manifolds and elbows ~$600
• new trick kit for the holley carb ~$60
• new 2" carb spacer ~$20
• new fuel line - $15 worth of fittings and metal line
• new front damper ~$50
• new head bolts $40

incidentals such as plast-gage, assembly lube, a degree wheel, paint, etc would all be extra.

then you can transfer over your accessories.

would recommend a new PMGR starter and probably a new distributor as the prestolite one you have most likely has spring issues.

 

[Scott Danforth]

@Scott Danforth, you seem to be quite familiar with the exact same topic - what would be your conclusion, after your journey?

depends on the boat, however if you want to go big on power, buy a different boat. here is my engine build for the replacement of the warmed over 271C
https://forums.iboats.com/threads/bbc-build-dont-tell-the-admiral.666775/

BTW, here is my warm over of the 271C....https://forums.iboats.com/threads/venturing-into-performance-upgrades-for-an-aq271c.489465/

note, long after I built the motor and started the thread, i ran the original part numbers for the stock 271C heads and the stock heads are 64cc chambers vs the 76 i assumed they were.

 

[Scott Danforth]

well...... since the beginning of the year, the cost of the blocks went up about $450

Blocks & Components: GM Performance Motor

and the rotating assemblies went up about $300 https://www.competitionproducts.com/Scat-Chev-SB-383-Street-Strip-Assemblies/products/2868/

 

[bollerwagon]

I might need to reuse my block, to avoid the permit to put the boat on some waters being revoked.
Is there a way to test my block? Whatever cooling hose I took off, red-ish water came out and a lot of sand, rust or whatever that was. How would I figure out, if it´s trash or not?

 

[bollerwagon]

And is my block one wiht 4-bolts on the crankshaft or just 2? I haven´t disassembled it so far yet. Just looked at the volvo penta replacement parts site -
This looks like it only has the two bolt thingy.

 

[Scott Danforth]

you take your motor out (its about a half hour total job if you have regularly pulled your drive for bellows service)

you take your motor to a machine shop and have it ultrasonically tested

your block is a 2-bolt block (no need for a 4-bolt unless you want to build stupid power level which requires a blower) Although a few blocks with 4-bolt mains were substituted back then.

go back to the permit thing. are they going off the serial number tag on the side of the block that is riveted to the block? if so, then worst case, you transfer the serial number to the new block or are they going off of the generic block casting number?

 

[Scott Danforth]

also, I suggest rebuilding your PDS once you get the motor out.

- read this https://forums.iboats.com/forum/eng...s-engines-outdrives/10343318-pds-shaft-issues

also, here is some library reading https://forums.iboats.com/threads/upgrading-to-a-383-stroker.727054/

 

[Lou C]

With what you want to do, I'd install a new 5.7 Vortec long block, and add closed cooling. The stroker idea is great for power but it adds significantly to cost if you are going to buy it all done. For the same $$ you can get the Vortec + a half closed cooling system and new exhaust which you will need anyway. And you'll have about the same power the boat had when new.

If on the other hand are going to have to re-use the old engine, that's a good deal more risky. You have one cyl at least with scoring, you will have to find an automotive machine shop that can go through it but even so if its raw water cooled the amount of corrosion in the water passages needs to be assessed, you don't want the cyls to be too thin after boring and installing oversize pistons.

From your pix it seems that water was in motor oil at some point, and oil changes were neglected. A shame because these simple and rugged engines don't need much to last 25-30 years....clean oil (at least one change per year) properly maintained exhaust system (inspect and probably replace exhaust elbows and maybe manifolds every 5-7 years in salt water), proper propping so that the engine does not labor pulling the boat up on plane (max wide open throttle rpm should be verified against manufacturer's specs) and cooling system has to be maintained (impellers, etc). Simple stuff but has to get done.
A lot of the options depends on what's available in your location, here in the USA its all pretty easy, there are lots of suppliers, but if you're in Europe it's not so easy I'd guess, judging from your compression test results in Bar (1 bar = 14.8 psi).....you got two really low holes there!

Good luck!

 

[bollerwagon]

With what you want to do, I'd install a new 5.7 Vortec long block, and add closed cooling. The stroker idea is great for power but it adds significantly to cost if you are going to buy it all done. For the same $$ you can get the Vortec + a half closed cooling system and new exhaust which you will need anyway. And you'll have about the same power the boat had when new.

I kind have arrived exactly there on my emotional roller coaster ride regarding the decision. I think I want this boat running again asap for reasonable costs. And when this is settled, I might take my old engine and build a stroker out of that. If I blow it, it will be financially ugly, but I still have a running boat. If it works, I have a quicker boat.

Three questions:
- Are you saying I need a new exhaust because the vortec needs it to breath properly, of because mine is damaged on the portside?
- all the vortec long blocks I found so far do have the #906, that seem to be less preferable. Any idea where I can find one with the #062 heads?
- where can I find a resaonable closed cooling system?