Tuning 5.7 GI-m

Naf · **Posted:** Thu Aug 23, 2012 2:12 am

I have a 2010 5.7 Gi-m and would like to tune the engine. I have Staineless Marine exhaust headers with o2 bungs for AFR feedback.

I am also thinkin of upgrading the 3" Throttle body for a 3.5" throttle body, as well as a KN Flame arrestor filter for about 10-15 more hp.

Currently i am gettin 56mph at 4750rpm with F6 props instead of the stock F5 props which gave me 50mph at 5250rpm.

Now i know my CPU runs in open loop, so if i were to change anything it wouldnt know and i could run lean and damage my rings and valves. I do not want to change the cam nor the heads for then i will never get the engine to run nor idle...

How may i tune the engine for better performance?

I couldnt find the usual OBDII port that i use for tuning.

Flying Sushi · **Posted:** Thu Aug 23, 2012 5:57 am

I would suggest to leave the engine alone and just enjoy your boat… Unlike cars small modification to boat engine would not make any difference in boat performance… Stable V hull is not a fast hull so small HP difference would not make effect on overall performance.. It is better off to change the engine to GXi or big block if you really want to gain something. If you want to play with boat engine look for torque and not HP... My 2C

ric · **Posted:** Thu Aug 23, 2012 6:40 am

http://www.mefi4.com/

Naf · **Posted:** Sat Aug 25, 2012 6:58 am

Flying Sushi wrote:

I would suggest to leave the engine alone and just enjoy your boat… Unlike cars small modification to boat engine would not make any difference in boat performance… Stable V hull is not a fast hull so small HP difference would not make effect on overall performance.. It is better off to change the engine to GXi or big block if you really want to gain something. If you want to play with boat engine look for torque and not HP... My 2C

Fair, but there is so much potential. if a simple prop swap got me 6mph with 250rpm left on the dial a set of proper headers should give me 200-400rpm that i need. and no need to tune the engine. The 90 degree elbow at the top of our riser is somewhat restrictive.

I could also swap the rockers and lifters for the roller type, which should give me 10-15% more power and no need to run.

Efficency is my key to my 60+mph, i just need to make sure i get the proper parts all in properly

Thanx Ric for the link, but my ECU does not have an obdii slot for tuning

ric · **Posted:** Sat Aug 25, 2012 7:43 am

You have mefi. same ecu as GM crate engines. Very tunable. Read that website.

Naf · **Posted:** Tue Aug 28, 2012 6:00 am

Thanx, i will give my engine another look over and find the terminal this connects to...

I will also be installin WB o2 sensor to see what the stock setup is givin me now. Later i will tune for proper AFR and hopefully see a positive gain.

boater50 · **Posted:** Thu Aug 30, 2012 7:49 pm

if you do get to 60+ miles per hour in your boat...please stay out of Long Island Sound!!!!!

ric · **Posted:** Thu Aug 30, 2012 8:19 pm

You might get 330hp out of it with tuning, throttle body, spacer, air filter. That's actually the ragged edge of what it's capable of cam wise.

You gotta free up that top end. The heads can do 400hp with stock ports. To really get some power you'll have to cam swap and possible injector change to bigger ones. That's now VP/MC limits the power of the Vortec 350. The vortec 5.7 leaves GM with nearly 350hp and they detune it with intake/cam/fuel restrictions.

Flying Sushi · **Posted:** Tue Sep 04, 2012 9:05 pm

Quote:

if a simple prop swap got me 6mph with 250rpm left on the dial a set of proper headers should give me 200-400rpm that i need. and no need to tune the engine.

Well…. In order to hit 60mph with 5.7 here is how you need to look at… Your 5.7Gi should have a 1.95 to 1 ratio drive and assuming you can tinker round your 5.7 to get to 5200 rpm max, your F6 (24.5in pitch) would only get you 55.7mp with 10% of prop slip. In order to get 60mph mark you would need a 27-pitch prop (F7 is closest) at 5200RPM… I hate to disappoint you but this would be a tall order for 5.7… you would not create a enough torque needed to spin F7 at this rate (with 1.95 gear ratio)… Going Big block seems very logical way to get your goal… Besides if you put these tall pitch props you would loose hole shot and will not be able to enjoy any water sports…. Also please keep in mind that your speedometer has a 4 to 5mph error in top end so if you think you are going 56mph with your speedo you are likely going 51 to 52mph on GPS…
Anyway please keep us update on your progress and we hope you have a good result in the end.

www.iFourWinns.com

Tuning 5.7 GI-m

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