1987 Sunbird 175HP

[jeremiahbear]

I have two questions, maybe three.

I have a 1987 Sunbird with a 175Hp Mercruiser. This is a Chevy V6 if I understand properly.

This is the part# of my prop: Quicksilver48 16318 A5 21P

Can anyone tell me the pitch and whatever else I need to know to buy a new one. It is a little beat up.

Also, can a 4bbl carb be put on this motor? You know to pep it up like my old chevy pickup with the 350?

If so do I have to change the pitch and whatnot of the prop to keep the RPM within tolerance?

This is my first boat. I want to thank anyone who can help me to learn more about it. I really appreciate it.

Jeremiah

 

[mthieme]

Re: 1987 Sunbird 175HP

Prop is 13 3/4" and 21 Pitch.

You could add a 4 bbl. carb, but it's not going to be nearly the same as the 350.
To make an appreciable difference you'd need Vortec heads. You starting to get into some coin at this point.
Speed costs. how fast do you want to go?

 

[jeremiahbear]

Re: 1987 Sunbird 175HP

Oh I know that it won't be the same. I just meant I had a 350 with a 2 bbl and put a 4bbl on for a noticeable difference. I just wondered if a 4bbl would help.

We go about 42 mph top speed right now, but it will pull kids on a tube or my 215lb. butt out of the water to ski with no problem. I just don't want to over rev the engine with a different prop. Know what I mean?

 

[Gary H NC]

Re: 1987 Sunbird 175HP

If the 21 pitch keeps you in the correct WOT range stick with the same size and pitch.
A 4bbl carb would increase the HP rating some but adding the Vortec heads would be the big plus.

Going from an aluminum prop to a SS performance prop may give you a little added performance. I picked up about 2 to 3 mph on the top end going to a Stiletto SS prop in the same pitch as my factory prop.

 

[mthieme]

Re: 1987 Sunbird 175HP

Oh I know that it won't be the same. I just meant I had a 350 with a 2 bbl and put a 4bbl on for a noticeable difference. I just wondered if a 4bbl would help.

We go about 42 mph top speed right now, but it will pull kids on a tube or my 215lb. butt out of the water to ski with no problem. I just don't want to over rev the engine with a different prop. Know what I mean?

Gotchya.
There was a post last month or so "how fast is your 4.3" or something similiar. You might want to see if you can find it...good stuff for us 4.3'ers.
The bulk of the props were 19 or 21 P. I have a 21P on mine and she turns about 4400 rpm on a good day...tried the 19P which was better for tubing and getting up on plane. Never opened her up with that prop though.
42 mph is respectable for what you have. Mine is just a couple mph slower. This puts us at the lower end of what the other guys in the other post claimed.
Doubtful you have anything to worry about. I assume you have no tach?
I guessing if you added the 4 bbl with a decent aluminum intake, you might see a 10% boost in HP. The biggest problem with doing this though is that the rest of the breathing system is still set up for a 2 bbl. If you have the carb though, a manifold could be found for $100, so it's not like a major investment.
One seriously major thing I did to improve performance on mine was to replace the points with Pertronix CDI. Before that I was lucky to get 3800 rpm out of her...you could actually feel the points floating.
I take it you don't have a tach?

 

[jeremiahbear]

Re: 1987 Sunbird 175HP

I do have a tach!

It runsl in the lower 4's whien WOT if I remember correctly.

 

[mthieme]

Re: 1987 Sunbird 175HP

Sounds like that's where you should be.
You're good.

Now all you gotta do is come up with an Offenhauser intake.

 

[jeremiahbear]

Re: 1987 Sunbird 175HP

What specific advantage does the stainless steel prop have over aluminum or others?

 

[180shabah]

Re: 1987 Sunbird 175HP

Click Here and scroll down just a little bit, on the far right of the page is the propeller help guide. It will answer many question, and probably raise a few.

As for power upgrades, you got lotsa options depending on your budget. As always the easiest and often cheapest upgrade is to just swap out the 4.3 for a 5.7. If you are "stuck" with the v6 then can add the 4bbl and or vortec heads. Alpha drives "consume" about 30hp, so your current setup is only putting about 145hp or so to the prop. You have room to "add" almost 100hp to your engine, but it will need everything(heads, intake, carb, cam, additional small parts for the vortec conversion) and you might as well freshen the bottom end. You will easily have 2-3k invested at this point, and the realistic max for a marine 4.3 is only about 230hp at the prop, much safer limit is closer to 215. With this kind of power upgrade you will need a different prop and most likely the upper will need to be re-geared/replaced. A 5.7 with 250-300hp for about the same investment starts looking pretty good. And they sound WAY better.