1987 4.3 litre gmc engine HP and RPM questions

[tlmn1987]

I have a 1987 4.3 litre gmc engine (OMC set UP) with a 2bbl carb. To be able to design a prop for my home built 23 ft aluminum bartender (double ender a Caulkins design) I need to know the spec's for MAX HP and at what is the RPM. I think the range is 4200 t0 4500 rpm. and the MAX cruising RPM would that HP be? This is the info I need to design a prop for that boat.

 

[tlmn1987]

Re: 1987 4.3 litre gmc engine HP and RPM questions

I have a 1987 4.3 litre gmc engine (OMC set UP) with a 2bbl carb. To be able to design a prop for my home built 23 ft aluminum bartender (double ender a Caulkins design) I need to know the spec's for MAX HP and at what is the RPM. I think the range is 4200 t0 4500 rpm. and the MAX cruising RPM would that HP be? This is the info I need to design a prop for that boat.

I am at a loss to find this info

 

[blueoval1]

Re: 1987 4.3 litre gmc engine HP and RPM questions

I take it you have a OMC Cobra 4.3L.
The HP for your 2bbl version is 175HP.
The WOT range for that motor is 4200-4400rpm.
I'm not sure what your looking for as far as cruising rpm. My 17' boat cruises at about 2800rpm in my opinion , but your boat is likely to be way different.
By the way....welcome to Iboats!!;

 

[180shabah]

Re: 1987 4.3 litre gmc engine HP and RPM questions

Also note that the 175hp is at the crank. At the prop it will be closer to 150.

As for cruising RPM - that will depend on the final package. Mine will hold plane just under 3k, but is really happiest(and so is my wallet) at about 3500.

 

[MikDee]

Re: 1987 4.3 litre gmc engine HP and RPM questions

That vintage 4.3 2bbl OMC is 190hp! I know because I had two 4.3 4bbl 205hp OMC Cobra's on my 86' Celebrity Cuddy. I don't know what Mercruiser rated them at for that yr? But, yes, it's crank hp, not prop hp. Mine were rated for 4200-4600 rpm WOT, I'd say it was probably a bit less for a 2bbl version.

 

[blueoval1]

Re: 1987 4.3 litre gmc engine HP and RPM questions

MikDee ,
Where did you get the info that the 2bbl 4.3 OMC Cobra was 190 HP?
I can only find 175Hp(2bbl) , or 205HP(4bbl) listed for the 4.3 from 1985-1990. Did you use block #s or what? It would be nice if they were 190HP!
I just can't find any info on 190HP 4.3's other than a mercruiser.
Talk with you soon!

 

[Gary H NC]

Re: 1987 4.3 litre gmc engine HP and RPM questions

I used to have a 1987 4.3 Cobra and the Factory service manual rated it at 190hp with a 2bbl.....That was right out of the book.
Max rpm was 4600...

Here is a Factory manual....They are getting really hard to find.
Email the seller(Don) and ask him about a 1987 manual.He probably has one just not listed.
Tell him Gary in NC sent you and he will help you out.
http://cgi.ebay.com/ebaymotors/1986...62QQcategoryZ26453QQihZ010QQitemZ200260677758

 

[blueoval1]

Re: 1987 4.3 litre gmc engine HP and RPM questions

Gary ,
I'll be darn:redface:
I do have a factory manual somewhere. Gotta dig it up!
Thanks for the heads up. Makes me happy for sure , and probably make tlmn1987 happy too!

 

[Gary H NC]

Re: 1987 4.3 litre gmc engine HP and RPM questions

Gary ,
I'll be darn:redface:
I do have a factory manual somewhere. Gotta dig it up!
Thanks for the heads up. Makes me happy for sure , and probably make tlmn1987 happy too!

Lol!...i have an extra one somewhere too.Its buried it my pile of old boat parts books i guess...I may have gave it away..

 

[mthieme]

Re: 1987 4.3 litre gmc engine HP and RPM questions

My '89 is rated at 170 hp at 4400 rpm.
I can keep her on plane at 2800-2900 rpm which is usually good. Typically, I never cruise above 3500 rpm. I almost always blow out the carbon the last 1/2 mile or so.