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Cyl head switch ? AQ151B SOHC head for a AQ171 DOHC head ?

dearborndeuce

New member
Anyone know if this will work ?
Reason: I'm looking to squeeze more get up and go from my 4 banger. 18' open fishing rig which is a dog out of the hole.
If the DOHC head will work, at least I'll get an extra 20 horses. Already done the prop thing and WOT is good. Thks Dearborndeuce in BC
 
The prop you have is it a Volvo prop or aftermarket.Aftermarket props don't work as good as the Volvo standard equipment.
Aftermarket props work,just not as good.Post a pic of your prop.
My neighbor had a 22 ft.with the same motor as yours.He call and said he was having trouble with performance.I went and checked EVERYTHIING twice.Could find nothing wrong.
Then I noticed the prop was new.I asked when did the trouble start.He says when the new prop went on it started.
Switched props and it was fixed.Not saying that's the problem but were just guessing anyway.
The old prop was a Volvo the new a Michigan aftermarket.J
Post a pic.
 
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Yes the c171 cyl head will bolt on.However 20hp is not worth the expense of the exhaust manifold,cyl head,timing belt setup and gaskets needed to complete the swap.
http://en.wikipedia.org/wiki/Volvo_B230_engine How many hours on your engine?? If tired rebuild it with a little bit of hotrod tech,back cut valves and port job on cyl head can give you a big boost.What cam are you currently running?? Find you a V,VX or VX3 camshaft,you will notice the difference.Im running a modified AQ151 in my 20ft citation and loving it!! Keep your dual solex carbs,they flow more air then the single 2 barrel weber conversion,I know,they dont have chokes but in good condition they work great except for the cold start!!
 
Jerry, sorry for delay in my response to your adv. Possibly the prop as you say as I think its a michigan wheel.
Also, just got the bad news from my machine shop ( my 151Q head is gone re too much corrosion ) but the rest of the eng is very good so, I'll install new rings, bearings. Now looking for a nother head and found 2 used AQ145 eng's. do you know if I canuse these heads on my AQ151?
Cheers
 
mftopgun; Eng hrs are 1350 ( on the clock ) not sure if accurate as I just got the boat and refreshing motor/drive/wiring etc.
Eng & drive now out. Drive prefect ( no water ) engine is now dismantled at my machine shop and only bad news in the head ( corroded beyond repair ) I've found a couple of AQ145's w/new manifolds last yr and might buy them both for parts. See my post to jerryjerry05 re head ?
Are the cams you mention Stock VP items ? How far should the valves be "cut back " ? Still tempted to go the 16V head if I can fins some good stuff. Appreciate your help & adv. regards
 
The 2.30:1 Duo Prop lowers don't bring quite as much in the used market as do the 1.95 and 1.78.
Have you considered adding the DP lower unit?
The performance gain is not quite as much as is with the V-8's, but there is a considerable improvement.

.
 
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Thks Ricardo for your prompt reply & adv.
My Drive is the 290D Power trim model gear ratio I believe is 2.15:1 No, I have not considered changing to a DP. Do you think my little Aq151 can turn the DP's ? What drive ratio works best with this setup ( DP ) ? Are saying I need a 2.30:1 ?
 
Im running a solas 21 pitch 4 blade left hand prop on my 290 drive,2.15 ratio.This is a good combo for the AQ151.
 
Your quite welcome,im not in here enough im sure,I have much experience with these engines and would rather not run anything else!!
 
Thks Ricardo for your prompt reply & adv.
My Drive is the 290D Power trim model gear ratio I believe is 2.15:1 No, I have not considered changing to a DP.
Do you think my little Aq151 can turn the DP's ?
What drive ratio works best with this setup ( DP ) ?
Are saying I need a 2.30:1 ?
Yes, the 2.15:1 in a single prop drive is the correct over-all ratio for the OHC 4.
NOTE: all transmission in this series use the same gear reduction.... so they all interchange with on another given the same model number.

Volvo Penta has deliberately come up with the 2.30:1 DP ratio for the OHC 4's, and for some of the 4.3L engines.
Your only option for the 4 cylinder engine, is the 2.30:1 ratio, and is why I mentioned that ratio.

Again, some say that the Duo Prop improvement on a 4 cylinder engine is not as great.
I can tell you first hand, that the improvement when used with the 4.3L and any of the V-8's, is tremendous.
Often being much more effective than if more horse power were added.

.
 
Many thks to all for your adv on my AQ151 head swap possibility and other ? re: prop, perf etc. Heard lotsa horror stories on those 16V engs.
Finally made my decision to just replace my head ( found a 530 model from a boneyard & it looks perfect ) so, I'll swtich my cam from my old head, & install new rings & bearings. Engine now being finished at the machine shop ( lapping valves and making sure all surfaces are cleaned up on the block & head ). New manifold also on order.
Now, I have another question re: the advice from the forum to stick to a VP prop & no aftermarket stuff ?
My props are Michigan wheels 16x16 RH & well used. I need everyones best guess as to what VP ( Diameter & Pitch ) to buy pls ? My boat is approx 18' length, open runabout style ( no cuddy ) a 25 gal tank in the bow. Dunno the weight yet. So, any ideas on what prop to start with ? I have not had her in the H2O yet but was told by the prev owner " it was a dog out of the hole " ! Eng was also a little weak due to the rear exh port starting to leak......with my new rebuild, should not be a factor. I'm a AQ151B/290 2:15.1. You are all very helpful and I appreciate your time to respond.
 
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Now, I have another question re: the advice from the forum to stick to a VP prop & no aftermarket stuff ?
My props are Michigan wheels 16x16 RH & well used. I need everyones best guess as to what VP ( Diameter & Pitch ) to buy pls ? My boat is approx 18' length, open runabout style ( no cuddy ) a 25 gal tank in the bow. Dunno the weight yet. So, any ideas on what prop to start with ? I have not had her in the H2O yet but was told by the prev owner " it was a dog out of the hole " ! Eng was also a little weak due to the rear exh port starting to leak......with my new rebuild, should not be a factor. I'm a AQ151B/290 2:15.1. You are all very helpful and I appreciate your time to respond.
I don't know why anyone would suggest that a MichiganWheel prop would be substandard! That's their biz...... manufacturing props! I've had great luck with this propeller in years past.
As with any propeller, you'll just need to try/test an array of props until you achieve the correct WOT RPM, just as any of us would.
See your OEM spcecs for this info, and shoot for the correct RPM range.

As for the fresh engine, I'd strongly suggest that you set your ignition BASE Advance, and then follow this by checking your TA (total advance).
TA is much more important than BASE on any gasoline marine engine.
Again, see your OEM ignition timing specs for this engine.

.
 
Rick;

The prop issue I know I will sort out once I'm in the water. I was hoping to get a " base starting point " with a new VP prop but I'll try & borrow a few to get started.
I agree the Base Advance must be bang on also the TA. I've ordered an electronic ignition ( I've heard good things on them ).
Great Forum and sound advice ! Thks again
 
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