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Avia8tur

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Hi All,

I have the 5.7 Gi-GF 280 hp. I need more power, especially low end out of the hole.

Two things:

1. After checking the VP specs comparing the 280 to the 300 hp, the block numbers (bore, stroke, compression ratios, displacement) are all identical. That leaves the top of the motor (heads, intake, injection) to be the difference. (Assuming it's not an air restriction problem, exhaust manifolds etal, as the problem.) What is the difference and can I reasonably modify the existing motor to gain the additional power I need?

new heads, intake...??
reprogramming?

2. I have a dual prop.. Any prop recommendations?

Digging out out up here in NH so boating is just around the corner!!

Thanks to all!!
 
RicardoMarine said:
Most any Marine OEM SBC, or Marine SBC from GM today, is going to be fitted with the dreaded Full Dished pistons.

If you want true Marine HP and Torque, start reading at post #7 here.
http://www.marineengine.com/boat-forum/showthread.php?394668-V6-to-V8-engine-swap

This involves a custom build.... and it won't break the boat bank.


Wow,

Thank you for the information! I was hoping to avoid the rebuild but that may be what will be needed. Can that be done in place or will it need to be pulled? Tight engine compartment on the boat (2007 Larson Cabrio 274) as it has a generator next to the motor. I have seen performance enhancers that send a false cold air temp to the ECM causing a richer fuel mix, theoretically, more performance. Your thoughts on these aftermarket quick fixes?

Again, thank you for your thoughts. I spoke indirectly with the Volvo rep at the marina and he had little useable or actionable information.

rough estimate on cost to rebuild?
Click to expand...
 
This is not necessarily a high performance enhancement technique or modification.
This is a technique used to build a "True" small block Chevy Marine Engine!


.
 
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RicardoMarine said:
This is not a high performance enhancement technique!
This is a technique used to build a true small block Chevy Marine Engine!

No, I didn't mean to imply that! I meant that this was another alternative, not a better alternative. I like the rebuild much better, especially for the long term.

Thank you you for your responses!

Tom
Click to expand...
 
MikDee said:
Isn't that 280 Volvo a Ford engine?
Click to expand...

When we see "AQ260" or "AQ225".... this references the engine.... of which either of these are GM engines.
When we see Volvo Penta "270 or 250 or 275 or 280 or 285", it typically refers to the drive model.

We'll also see Volvo Penta AQ260B/280.... or AQ225E/275...... for example.



If you look at this site......
http://www.marinepartseurope.com/en/volvo-penta-schematics-MarineGasolineEngines.aspx
...... up at the top section, you'll see both the AQ series and the later series model numbers being listed.
The AQ series model designations change substaintially..... in that the "AQ" is no longer used.




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I agree. I don't need more speed. Once on plane, speed is fine. I too thought props and I think I'll run this by some prop folks. The current setup is original but inadequate. Adding bottom paint, generator, people et al, over the test boat set up directly affected performance more than I thought. I wish I had gone with a bigger motor but hindsight is...well...unproductive.

What specific information should I give to the prop folks to help them give me the right set up?

thank you
 
Avia8tur said:
1. After checking the VP specs comparing the 280 to the 300 hp, the block numbers (bore, stroke, compression ratios, displacement) are all identical. That leaves the top of the motor (heads, intake, injection) to be the difference. (Assuming it's not an air restriction problem, exhaust manifolds etal, as the problem.) What is the difference and can I reasonably modify the existing motor to gain the additional power I need?


Often the only difference is the RPM at which the rating was taken....... and this is sad for many unsuspecting buyers.
Example: the first 5.7L Vortec for Marine use was rated at/near 315 Horse Power.
The RPM rated at was 5,200....... :mad: Duh!!!


2. I have a dual prop.. Any prop recommendations?

The Volvo Penta is a Duo Prop. These prop sets are not shown in "pitch" as we are acustomed to seeing.
In order to prop yourself correctly, you must observe the WOT RPM test just as you would with a single prop drive.
Click to expand...

Avia8tur said:
I agree. I don't need more speed. Once on plane, speed is fine. I too thought props and I think I'll run this by some prop folks. The current setup is original but inadequate. Adding bottom paint, generator, people et al, over the test boat set up directly affected performance more than I thought. I wish I had gone with a bigger motor but hindsight is...well...unproductive.

What specific information should I give to the prop folks to help them give me the right set up?

WOT RPM test just as you would with a single prop drive.


thank you
Click to expand...

kimcrwbr1 said:
Rule of thumb is 1 inch pitch for 200 rpms. You want to achieve proper WOT rpms for both engine performance and wear and tear on the motor.
Click to expand...
Kim, the OP has the Volvo Penta Duo Prop drive.


Just an FYI re; the single prop: Propeller diameter differences, hull size, final/over-all gear ratio, etc, will all throw a curve ball at this rule of thumb.


.
 
kimcrwbr1 said:
Once you cross the T`s and dot the I`s check the WOT rpms the engine is producing and the spec for the motor. Rule of thumb is 1 inch pitch for 200 rpms. You want to achieve proper WOT rpms for both engine performance and wear and tear on the motor. You will find 3/4 throttle will give you alot better fuel economy anyway once you get the prop pitch correct. Less pitch allways means faster out of the hole just keep an eye on the tach if you decide to run it under propped. Are your props cupped maybe just get some standard non cupped props and see how she performs the prop shop can help you decide but trial and error is allways the best way.
Click to expand...

Thank you for all the advice. I wouldn't have come up with the game plan with out your input.

1. Check engine, WOT test, progressive advance to spec.
2. Confirm existing prop setup, gearing on out drive.
3. If required, lower the pitch to increase RPM's and test hole shot to see if there is any improvement.

She's only has 120 hrs. since new (2007) and has always been dealer serviced, including the out drive. I will certainly talk things over with the mechanic.

Thanks Guys, you been a big help.

tom
 
Ricardo,

Thank you for adding on to the post. I will pass along all the information I have to the prop guys. Seems to me this set up is fairly standard, but I don't know. In recollecting, I don't think I'm making WOT unless I'm trimming up the engine. Of course,Mathis was last fall so I'll know more soon. I recall only seeing, at full throttle, 4400-4500.

Thank you,

Tom
 
Avia8tur said:
Ricardo,

Thank you for adding on to the post. I will pass along all the information I have to the prop guys. Seems to me this set up is fairly standard, but I don't know. In recollecting, I don't think I'm making WOT unless I'm trimming up the engine. (you mean triming the drive!)
Click to expand...
Tom, you are welcome.

Just an FYI for you.
A WOT RPM test cannot be performed until the engine is in full tune.... and I mean "full tune", inluding your Ignition TA.
Only then can we perform an accurate WOT RPM test.


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kimcrwbr1 said:
You said you added a generator and people and your happy with WOT performance maybe all you need is to know how to shift the weight in the boat and proper trim angle to pop it out of the hole quicker some issues can be overcome by simply getting to know your boat. Try a bunch of different combinations of weight distribution and trim angles if your still not reaching proper WOT rpms then you need to first ID your props then the prop guys will better get you to where you want to be. Most people dont build the motor to fit the prop. You probably have plenty of power you just need adjust the props for the added weight.
Click to expand...

The boat is a 28' Larson Cruiser so weight distribution is tougher. (Unless I want to ask people to go below decks to get on plane.) I do have trim tabs and, without them, I'd have a hard time getting out. I've owned the boat since new so this would be the 7th season at the helm. I do know how the boat handles and have lived with the problem. I like the idea regarding a re-prop. I think Ill chase that angle as well as having the WOT testing completed. I have read my posts and forums and do tend to agree that the power may already be there and the boat wasn't set up right by Larson with the added weight.

thank you for the input, it all helps.

Tom
 
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