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

[bollerwagon]

This is how it looks like. Haven’t tried to put a screw in yet, though.

 

[Scott Danforth]

your motor may have a different block in it already.

post the block number

 

[Scott Danforth]

here is the picture from my 271C when I pulled the stock heads and installed vortec

 

[bollerwagon]

That’s odd. I’m relatively sure it is genuine Volvo Penta AQ271C and block is original. Is 14093638 a valid block number?

 

[alldodge]

14093638
Manufacturer: Chevrolet


Category: Engine Blocks


Type: Small Block V8


Date: 1987-1995


Notes: 350, 2 bolt or 4 bolt, roller or flat tappet cam, 1-piece rear seal

 

[bollerwagon]

2 bolt or 4 bolt, roller or flat tappet cam

…it couldn’t be more specific…
;-)

 

[alldodge]

Block is drilled for 4 bolt but Mfg can use 2 bolt mains
Same with cam

 

[bollerwagon]

i think there are only drilled holes for the two bolt:



let’s hope everything is prepared to mount the roller cam and stuff without surprises.
How about the roller rocker arms? Makes sense? Edit: internet says, boat rpm does not need roller arms. Would you agree? So i use the old stuff?

 

[bollerwagon]

There is one thing that just strikes me when thinking about it: the stock AQ271C has 275 HP (not sure what torque) with the old heads. The vortec head equipped 5.7 GS has just 270HP. What component "reduces" power on the GS model?

 

[Scott Danforth]

There is one thing that just strikes me when thinking about it: the stock AQ271C has 275 HP (not sure what torque) with the old heads. The vortec head equipped 5.7 GS has just 270HP. What component "reduces" power on the GS model?

cam profile.

however peak HP vs torque curve. always always go with the better torque curve.

 

[bollerwagon]

cam profile.

however peak HP vs torque curve. always always go with the better torque curve.

Makes total sense. I do neither know the torque curve of the AQ271c nor the 5.7 GS. But instead of using the GS cam might it be more beneficial to use another cam, e.g. one from a 5.7 GXI?

 

[Scott Danforth]

Makes total sense. I do neither know the torque curve of the AQ271c nor the 5.7 GS. But instead of using the GS cam might it be more beneficial to use another cam, e.g. one from a 5.7 GXI?

no

you run the cam designed for your induction. Carb cams are different than EFI cams

I would run an XM264HR or XM270HR. out of those two, I would run the XM264HR with 1.52:1 rockers.

with either cam, you will need to modify the heads as the stock lift on the vortec heads is only 0.420" max

Xtreme Marine 212/218 Hydraulic Roller Cam and Lifter Kit for OE Roller SBC

Xtreme Marine 212/218 Hydraulic Roller Cam and Lifter Kit for OE Roller SBC

www.compcams.com

Xtreme Marine 218/224 Hydraulic Roller Cam and Lifter Kit for OE Roller SBC

Xtreme Marine 218/224 Hydraulic Roller Cam and Lifter Kit for OE Roller SBC

www.compcams.com

 

[bollerwagon]

So you would NOT use the 5.7 GS Cam and lifters I have?

 

[Scott Danforth]

So you would NOT use the 5.7 GS Cam and lifters I have?

you can, that is up to you.

If it was me, I would be taking the heads in for threaded rocker stud conversion, and have the valves modified for the better seals and higher lift cam. Then I would probably drop in a SCAT rotating assembly for 383 cubic inches (6.2 liters)

 

[bollerwagon]

There is one thing that just strikes me when thinking about it: the stock AQ271C has 275 HP (not sure what torque) with the old heads. The vortec head equipped 5.7 GS has just 270HP. What component "reduces" power on the GS model?

I was educated that until somewhat in the 90s HP was measured at the crank and since then at the propeller. That would explain why the 30 something horsepower advantage of the Vortec got lost on the way from Aq271c to 5.7 GS

 

[Scott Danforth]

I was educated that until somewhat in the 90s HP was measured at the crank and since then at the propeller. That would explain why the 30 something horsepower advantage of the Vortec got lost on the way from Aq271c to 5.7 GS

engines after 1986 were prop rated

do not confuse peak hp numbers vs other factors.

the AQ271C was a VP spec'd Hi-Po crate motor with a custom spec'd cam. same motor that was police duty. run the casting numbers of the heads thru mortec yourself. not the same heads or intake that GM sold to Mercruiser (hence the 15hp increase). the AQ290 and AQ311 were higher output versions

the 5.7 GS is basic assembly line fodder for GM. the combustion chamber is same size slightly different shape than the vortec, however the cam is less aggressive. the vortec head combustion chamber is the LT3 combustion chamber from the reverse cooling flow heads. just with standard cooling layout

where the vortec heads shine is mid-range power. and if you choose the right cam and pistons, you can go fatter on the torque curve and increase upper end as well. however a change in the cam will require slight rework of the stock vortec heads

 

[bollerwagon]

Long time has passed, still not having repowered my boat properly, I learned some things:
- carburated technology might be simple and easy to fix, but I just don´t understand enough to make it work for me. I just don´t understand any unpredicted behaviour and I can´t fix it. I am to slow to undertstand any of the complexity of engines, rocker arm ratio, lift, whatever to make reasonable decisions.
- Also any work done in machine shops here is so expensive that it barely makes sense using used parts and having them redone.
- Meanwhile I think I can drop almost any engine in my boat and attach it to the DP290. Looking at the 880 block I can just attach my old small flywheel and my alternator (since the block also has the old screw pattern). Then the old bellhousing can be used. Just the piping and wiring is a bit different.

So I will try to throw in a MPI, because sensors speak a language I understand. I can (sometimes) make sense of their reading to troubleshoot.

Just wanted to keep you updated here, since there will most likely not be any progress on this original project.

 

[Scott Danforth]

carb or EFI, the base engine is the base engine and not a byproduct of the induction system. its the foundation.

EFI has different requirements for cams than carb. and you still have to worry about rocker arm ratios, lift, lobe separation, etc.

yes, you can drop in any GM motor with a 153 tooth flywheel in front of the DP290, including V6's, big blocks, small blocks and LS/LT motors.

 

[bollerwagon]

It seems to be quite difficult (expensive) to get a replacement for a 5.7 GXi. Volvo asks for 7k, MM wants 5.600 (plus shipping to Europe plus tax is the same as volvo).

I have a salvage block from a 5.7 GS PBYC. The only difference I can spot so far is the roller rocker arms in the GXI. Tappet and push rods seem the same, piston part numers were different, but they were changed to the same number today.

Depending on the money the machine shop asks to rebuild it - I could just replace:
- the roller rocker arms (Volvo Part no 3861167) and
- the ring on the camshaft so the crank sensor gets a signal (Volvo Part no 3862363), correct?

Also - does one happen to know the GM part numbers of these parts?

 

[bollerwagon]

you´re right, not all problems go away by running away. But at least some. ;-)

I´ve started a new topic, since it would be too far off this title. And of course it includes also a rocker arm ratios/lift question. Since VP decided it would be too much stress crank out more power of their 5.7 engine with a proper camshaft, they added roller rocker arms that mimic higher lift.