Removing Restrictor Plate on Merc 75 EFI

[Ruggybuggy]

I have a '08 Merc 75 EFI and noticed it uses a restrictor plate under the air filter. Is there any issue with removing it. I'm not trying to make a 75 into a 90 just noticed that it was a huge restriction and thought I would remove it for some added performance benefits. Really only want to hear from people who have experience first hand in doing this and the long term results. I read many posts about you will blow up your motor and shorten it's life from people who never actually had any experience doing it.

 

[Faztbullet]

Re: Removing Restrictor Plate on Merc 75 EFI

Really only want to hear from people who have experience first hand in doing this and the long term results.

Doubt you will see any.....I myself would not remove it due to you could change the air/fuel ratio in ECU and cause temp and cylinder problems...

 

[Ruggybuggy]

Re: Removing Restrictor Plate on Merc 75 EFI

Right, as a mechanic (automotive) I know that a motor needs 14.7:1 and removing the restrictor plate would cause the motor to run lean which would result in higher cylinder temps. On the other hand I've also read of others removing the plate and finding that they have a better hole shot and gained 3-4 mph and have run it this way for many seasons with no ill effect. Also reported that the ECM will compensate for the extra air being added.

So who has removed their restrictor plate long term and what were the results and was there any benefit?

 

[Faztbullet]

Re: Removing Restrictor Plate on Merc 75 EFI

Also reported that the ECM will compensate for the extra air being added.

Nope as this is a dumb EFI system and all mapping is flashed into ECM. All you got is a MAP and TPS, you would need a MAF if ECM was able to compensate...

 

[Ruggybuggy]

Re: Removing Restrictor Plate on Merc 75 EFI

So my curiosity got the better of me. After reading tons of info I never once came across anyone who removed their restrictor plate and had engine problems. Read lots of info of some doing it with good results on both the 40-60hp line and 75-115 line so I thought I might give it a try and report the results. The boat is a 2008 Princecraft 164 running a 2008 75hp Merc 4 stroke. The prop is Merc 17p and top speed is 38mph at around 5600 rpm. I removed the restrictor today and went fishing for the day. Traveled approximately 30 miles. The top speed increased to 43mph at around 6200rpm and the holeshot was considerably better. Something else I did notice that at half throttle my speed was also approx. 4-5mph faster. If I decide to keep the restrictor out I'm going to have to repitch which should result in better fuel ecomony. I'm going to pull the plugs and see how it's burning. I really don't think any harm will come to the motor. I know the the ECM has a predetermined map based on airflow and cannot make adjustments. My feeling is based on my experience with tuning motorcycles that the Merc ECM is running rich like most "simple" ECM fuel injection systems. You can add slip on exhaust on 4 stroke snowmobiles and motorcycles running very similar fuel injection systems with no modifications and not have any kind off issues. Removing a restrictor from a Merc motor is less of a modification than performance exhaust on a motorcycle/snowmobile. I don't believe that by removing the restrictor from my 75hp is going to turn it into a 115hp but the performance increase is very noticeable. To get to the 115hp with take a reprogramed ECM. Too bad they don't make a Powercommander for the Mercs. I'll keep checking the plugs to make sure everything is running well.

 

[Ruggybuggy]

Re: Removing Restrictor Plate on Merc 75 EFI

Bumped! I would really like an opinion on this.

 

[matt167]

Re: Removing Restrictor Plate on Merc 75 EFI

As said, this is a dumb system, so your probably running it a bit lean now. I'd change it back

 

[schematic]

Re: Removing Restrictor Plate on Merc 75 EFI

Nope as this is a dumb EFI system and all mapping is flashed into ECM. All you got is a MAP and TPS, you would need a MAF if ECM was able to compensate...

Although it may not apply to this engine, all that is needed to calculate incoming air is a MAP, TPS and RPM. Many engines out there use only MAP and TPS for closed loop systems. Other than timing, elevation and fuel ratio, ain't much use for MAP data........ Just sayin'

 

[Ruggybuggy]

Re: Removing Restrictor Plate on Merc 75 EFI

As said, this is a dumb system, so your probably running it a bit lean now. I'd change it back

That's an assumption made from fear.

 

[Shadrock]

Hello just joined the forum and ran across this post. Was wondering if you still had the restrictor plate out. I have a 2014 75 merc 4stoke efi. I took mine out to see the difference. And it is a big one. But didn't know if it would cause engine damage. I would love to leave it out but don't want to cause engine problems. Thanks

 

[GA_Boater]

Hello just joined the forum and ran across this post. Was wondering if you still had the restrictor plate out. I have a 2014 75 merc 4stoke efi. I took mine out to see the difference. And it is a big one. But didn't know if it would cause engine damage. I would love to leave it out but don't want to cause engine problems. Thanks

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