swap. 350 for 305

[krisnowicki]

After finding the crack in my block, that was the source of all my problems, I have found a crate 305 from a marine tech here in jacksonville. I was going to pick it up today or tommorrow. Will I notice a huge difference from the change? It is a total of 30 hp....

 

[Bondo]

Re: swap. 350 for 305

Ayuh,.....

I gotta believe it'll be Noticable,.... Huge is a relative term...

 

[krisnowicki]

Re: swap. 350 for 305

the boat is 2800 lbs with no engine ... Will i need to prop down I have a 21 inch on my mr 260 out drive

 

[wca_tim]

Re: swap. 350 for 305

My guess would say yes... especially if it's a heavy boat. but it is goign to depend on the specs for the 305... There is likely an even bigger difference in torque which has more of an effect on out of the hole and seat of the pants assesment... I'm assuming you're outdrive gear ratio is 1.5....

I'm curious why you're going with a 305 rather than a 350 long block?

 

[Haut Medoc]

Re: swap. 350 for 305

Go with a 350 if possible, the 305 is a dog compared to it.....
If you must go with the 305, leave on the prop you have now & see what your wot is.....
I'm thinking a 14 x 17 will put you in the proper range.....
But you will need to test for yourself.....​

 

[John_S]

Re: swap. 350 for 305

A heavy boat like that you will feel the difference. You will probably have to drop down to 19", and maybe to 17". Any chance your old 350 is non-vortec and the 305 crate is vortec? That would narrow the gap some.

 

[krisnowicki]

Re: swap. 350 for 305

no ... its the exact opposite. My old one was a vortec. The 305 is not a vortec. The reason I am going for this 305 is i am getting an amazing deal it is a complete plug and play engine for 1400.

 

[krisnowicki]

Re: swap. 350 for 305

from 260 to 230 will make that big of a differece? I mean it will still cruise fine just low end torque right ? So i may see a differnce pulling a wake boarder. But I go to smaller prop which is what I am thinking of doing I will make up for it on the low end by sacrificing top speed?

 

[QC]

Re: swap. 350 for 305

How easily does the boat plane now? Lower peak torque affects the ability to get on plane, the lower horsepower will affect your top speed . . . Both will be poorer with the new engine. You can recover some of the low end with a pitch change. Your top speed will suffer no matter what you do short of a blower . . .

Edit: We need to know more of your current situation to comment on the changes you should expect. Cruise may not be affected at all . . . What is/was your top speed with the old engine? At what RPM? Trimmed out to go as fast she can possibly go with a typical load. What speed do you cruise at?

 

[krisnowicki]

Re: swap. 350 for 305

as is now the boat planes on demand... I mean right when I accelerate.

 

[krisnowicki]

Re: swap. 350 for 305

The tech that is selling me the engine is telling me it is more then enough that is why I came here to see If he is "just saying that "

 

[John_S]

Re: swap. 350 for 305

Mercruiser Specs (at prop):

350 vortec 2brl: 250hp
350 vortec 4brl: 280hp

305 non-vortec 2brl: 190hp
305 non-vortec 4brl: 205hp

305 vortec 2brl: 220hp
305 vortec 4brl (est): 250hp

350 non-vortec 2brl: 210hp
350 non-vortec 4brl: 250hp

 

[QC]

Re: swap. 350 for 305

Well we could still use some more info. If you have to push the throttle all of the way down for it to "plane on demand": than I am concerned. If she planes with part throttle application, then less so. It woudl still be really helpful if you posted what we are asking for, RPM at top speed now, and what that top speed is . . .

It doesn't matter who says what, with all other things equal (a 305 and 350 weigh the same) less horsepower equals lower top seed, and less torque equals poorer hole shot or more time to plane. Period! With that said, there are 305s today that make more ponies than 350s 10 years ago. Not all 305s and not all 350s. Each different iteration matters . . .

 

[erikgreen]

Re: swap. 350 for 305

Here's another thought - I don't know that a 305 non vortec will be a drop in engine for you if the 350 was vortec... there were a few changes made in the years between to the bell housing, flywheel, ring gear, and starter.

Just FYI, you can find a reman 350 engine for close to the price you want... if it was your block that was cracked, the you can replace that for less than $1400 (new short block). I paid about $1750 last summer for a reman 350 non-vortec long block from rapido marine, and other vendors have similar prices.

At any rate it sounds like you'll be dropping too much power for this to work... a 350 vortec four barrel is pretty close to 300 HP, and a 305 would be a quarter to a third less hp, and maybe more torque than that. Big change.

Erik

 

[MikDee]

Re: swap. 350 for 305

Mercruiser Specs (at prop):

350 vortec 2brl: 250hp
350 vortec 4brl: 280hp

305 non-vortec 2brl: 190hp
305 non-vortec 4brl: 205hp

305 vortec 2brl: 220hp
305 vortec 4brl (est): 250hp

350 non-vortec 2brl: 210hp
350 non-vortec 4brl: 250hp

John, the non-vortec specs you have for the 305, are actually for a non vortec V6:
4.3 V6 2bbl. - 190hp
4.3 V6 4bbl. - 205hp

The early non vortec 305's were:
305 V8 2bbl.-198hp 2bbl.
305 V8 4bbl.-228hp 4bbl.

I know because I had a 79' SeaRay 20' (a heavy boat) with a 228hp/305-4bbl Mercruiser with a 19" pitch aluminum Merc prop, unpainted bottom, and thru hull exhausts that would do 48mph! trimmed out.

 

[John_S]

Re: swap. 350 for 305

The numbers are straight out of Mercruiser Service manuals #17 and #24. They only cover SB 305 and 350. The numbers you posted are for older engines that were rated at the crankshaft. The numbers I posted are all for rating at the prop.


PS: I'm feeling some Deja Vu. I bet we have had this discussion in the past.

 

[whywhyzed]

Re: swap. 350 for 305

....

 

[MikDee]

Re: swap. 350 for 305

The numbers are straight out of Mercruiser Service manuals #17 and #24. They only cover SB 305 and 350. The numbers you posted are for older engines that were rated at the crankshaft. The numbers I posted are all for rating at the prop.


PS: I'm feeling some Deja Vu. I bet we have had this discussion in the past.

Well I think the book is wrong (a misprint) just regarding the hp of the 305, it's too much a coincidence that the pre-vortec 4.3V6 was rated at 190hp 2bbl, and 205hp 4bbl., I had 2- 4.3 4bbl 205hp V6's in my last boat, and I doubt the 305 was ever rated less then 198hp 2bbl, or 228hp 4bbl. iregardless of, if it was crank, or prop hp, that didn't enter the picture when my 305 had 228hp in big block letters tagged all over it. Previous to this they were using 327motors, & 302, & 351, Fords, and previous to that 283's.

 

[QC]

Re: swap. 350 for 305

In the '80s the 305 was rated at 200 at the crank and then in 1990 Merc started to publish both propshaft and crankshaft hp and they listed the 305 as 180/200 respectively. In 1991 they started rating them at the prop only. This is consistent with Outboards and also a NMMA standard I believe. The 305 remained 180 until 1993 (which is probably Vortec, I don't know) when the 5.0L was rated at 190 and the 5.0LX was rated @ 205. They stayed that way until 1996 when there were no 305 ratings. The 305 reappeared in 1998 carbed at 220 and TBI at 240. It stayed like that until 2002 when the TBI was replaced by the MPI at 260 propshaft, the carbed stayed at 220. Today the 5.0L carbed is still 220 and the 4.3 MPI is rated the same.

Edit: Source, Mercruiser manual, thanks Bondo

 

[Bondo]

Re: swap. 350 for 305

Edit: Source, Mercruiser manual, thanks Bondo

Ayuh,..... Which reminds me,..... I found a way to send you the other 2....

I'll PM ya with the Details........