WOT revs on a 350 mag

[hyperlite98]

I'm currently spinning a 23P Mirage Plus on a C18 350 mag/Alpha setup @ around 4900 RPM (Tach). I'm seeing about 66mph on average, is this where I am going to top out? or are higher revs a possibility, the merc site says 5300 I believe but wanted to see what other people are running. I do have a Turbo 1 21P lying around... anyone think thats worth a try? I really dont want to hit the rev limiter.

cheers.

[MOP]

The speed if on GPS is real good, I don't think you will gain upping the RPM. With my stroker I was truning 5600 with a 21" wheel doing 63+, I went to a 23 cleaver now I turn 5100 and now go 65.3. Upping your RPM I am pretty sure will get you above your power band and cost you speed, another thing that has been said by many is I/O's don't like being spun over 5K!

Phil

[BUIZILLA]

What year package is this ??? 66 mph is pretty damm impressive if it's a stock lower unit, and a stock carbed 270hp engine.... in fact it's incredibly good. If it's an EFI Mag engine, you've got about 2-4 left in it..

Jim

[hyperlite98]

Hi Jim,

its a 1999 with a 350 MPI, stock Alpha lower. should be producing 300HP, 65.8MPH on GPS.....what would you suggest to see the additional 3-4 mph?

Jeff

[BUIZILLA]

an Alpha SS drive should do it purty easily...

JH

[Rootsy]

an Alpha SS drive should do it purty easily...

JH


what he said :yes:

[blackhawk]

How many people are really seeing 68-70 on GPS with a 350 MPI. I know Randy is but who else?

66 mph with your set-up is at about 7% slip if your tach is right. Pretty good numbers! Labbing the prop might get you a couple more mph but then again it might not! It's a gamble.

[blackhawk]

To answer your original question I don't think a 21 is the answer. Yes you will get more rpms but I don't think you will see a speed increase. You are in the "meat" of the powerband right now(4800-5200).

Labbing your prop will get you 200-300 rpm and might get you a couple more mph! :D

[Ranman]

You are about as good as you're going to get. The thinner (and more true) blades of a labbed prop may get you 1+MPH.

My 350 MAG is a bit of an anomoly. I spin a bigger prop slower that you (due to drive ratio) and my engine is just plain strong. I can get 68.5MPH @ 5100 on the tach full of gas and with 3-4 people. In good conditions she'll spin a tad faster.

I saw a significant gain when I replaced my stock flame arrestor with a K&N unit (picked up 150-200 RPM's). My arrestor is differeent that yours so I don't know exactly which one you need.

If you live on a calm lake, try this experiment to see if you gain anything: Remove the engine hatch and flame arrestor leaving the throttle body wide open. Run the boat and see if you gain anything at WOT. If you do, improve your air intake system to the engine. Good luck

[blackhawk]

I saw a significant gain when I replaced my stock flame arrestor with a K&N unit (picked up 150-200 RPM's). My arrestor is differeent that yours so I don't know exactly which one you need.

Randy, I didn't know that info! Very interesting.

[myfinancialadviser]

where did you pick up your flame arrestor????? and what kind pirice?
thanks, i've been looking.



Randy, I didn't know that info! Very interesting.

[hyperlite98]

I was reading on the forum that a K&N arrestor wasn't worth it... it was my "go to" upgrade, until i read the soft sides create a problem. Do you have a part number for a 350MAG K&N?

I am on Georgian Bay, and it does get calm sometimes... maybe I'll try it out.

thanks,

Jeff

[hyperlite98]

an Alpha SS drive should do it purty easily...

JH


Why Did Mercruiser stop producing these?

Jeff

[MOP]

If you would like to stay with a brass Merc Hi Perf arrester look at # 16 it is the one for the Tempest 300 it is about 8"X3" all brass fine mesh.

http://216.37.204.206/Shorts/mercruiser_oem/Mercruiser.asp?Type=13&SubType=111&A=98&B=3

[Ranman]

As I said my arrestor is different than everyone elses. My motor has a 454/502 MAG throttle body and therefore I was able to run a BB Chevy arrestor. (see pics)

The one I bought was from CP Performance and is a Hardin Marine "SS" Sport Series MerCruiser 454 And 502 Magnum MPI Flame Arrestor Kit

http://www.cpperformance.com/products/Fuel_Systems/flame-arrestor-hardin.htm

Dunno what you need, but CP should have a replacement for the new style 350 MAGS. Like I said, try the boat sans the hatch and arrestor to see if you get a gain.

[BaldEagle]

My 06 18 came from Donzi with a 6.2 MPI 320 Hp and Bravo-1 with 1.65 gear. Its turning a 25P Mirage plus. I only had 16 hrs on it when It let it go and it turned 65.7 Gps in pretty flat seas at 4900 Rpm. I will probably leave it until I get some more hours as many ay it is still breaking in but it should hit 70 Gps. Others i've talked to have a lower gear 1.5 turning a 23P and they are pleased.

BE

[DickB]

Hi Jim,

its a 1999 with a 350 MPI, stock Alpha lower. should be producing 300HP, 65.8MPH on GPS.....what would you suggest to see the additional 3-4 mph?

Jeff

I've got the same year, engine, outdrive, and prop (Mirage 23P). Best ever for me was 64.9 MPH GPS (cool day, light chop, not much fuel). 63 is more typical with gas and passengers.

[blackhawk]

As I said my arrestor is different than everyone elses. My motor has a 454/502 MAG throttle body and therefore I was able to run a BB Chevy arrestor. (see pics)

Randy, is this something you did?

[SMLDONZI]

I've got the same year, engine, outdrive, and prop (Mirage 23P). Best ever for me was 64.9 MPH GPS (cool day, light chop, not much fuel). 63 is more typical with gas and passengers.

DickB, What RPM are you seeing at WOT with your Mirage 23? Thanks.

[DickB]

DickB, What RPM are you seeing at WOT with your Mirage 23? Thanks.

5000 on the stock tach.

[Ranman]

Scott,

No. That vintage 350 MAG came from Mercruiser with the same throttle body as the 454/502 Mags.

[David Hartmann]

I have a 19 St Tropez and am running a 21" Mirage. I am not sure if I ever hit WOT. with the trim down I get about 4600 RPM as I trim it up I get to about 4900 by then the boat is doing about 63MPH and it starts to walk a little.

I think I could trim it a bit more but it is too scary, I am looking at going with a 22" or 23" 4 blade

it is a 2004 350 MPI with a Bravo Drive.

[blackhawk]

Scott,

No. That vintage 350 MAG came from Mercruiser with the same throttle body as the 454/502 Mags.

Ahhh, I thought you did a little "upgrade" and were holding out on us all this time! :D

[Ranman]

Ahhh, I thought you did a little "upgrade" and were holding out on us all this time! :D

Nope. I'm all stock except for that K&N arrestor. :wink: