Flashed 4 stroke

**65gamblerman** · 11-01-2019, 08:05 AM

If a merc 200 Pro xs v8 4s was flashed to 300 would it have the same performance as a 300 Pro xs v8 4s?

**RSWORDS** · 11-01-2019, 12:45 PM

Yes. But why risk your warrenty?

**PRE-Z06** · 11-01-2019, 09:55 PM

Not sure if you’re aware 200/225 come with a smaller throttle body than 250/300.

**RSWORDS** · 11-01-2019, 10:21 PM

He is correct

**65gamblerman** · 11-02-2019, 09:51 AM

So it would be more than just a flash. TECHNOLOGY. Hard to believe that can be done... Thanks for the replies..

**PRE-Z06** · 11-02-2019, 12:23 PM

Originally Posted by 65gamblerman

So it would be more than just a flash. TECHNOLOGY. Hard to believe that can be done... Thanks for the replies..

Mercury just copied what Yamaha did as their 200-300hp 4.2L V6s are all the same including throttle body. They’re both electronically controlled and act as a restrictor plate limiting the amount of air that can be ingested. If you’re old school, think of the 200/225 as having a 2-barrel carb and the 250/300 as a 4-barrel.

**engineermike** · 11-02-2019, 08:03 PM

Actually, if I’m not mistaken, in 2005 (4 years before the 4.2 yam) merc built the verados all mechanically identical from 200-275 hp with the only change being the calibration.

The old school of thought that you can’t get much out of an NA engine went out the window when they started controlling max output with the cal. It actually makes a whole lot of sense to do it this way. Now the rest of the driveline and supporting systems can be designed for a max output not what it could make in extremely favorable conditions. Anyway, seadoo does it as well in their ACE engines.

**Chaz** · 11-03-2019, 08:51 PM

Originally Posted by 65gamblerman

If a merc 200 Pro xs v8 4s was flashed to 300 would it have the same performance as a 300 Pro xs v8 4s?

No , As mentioned the throttle body is different. As well as the intake manifold and camshaft.
Now if you think you can do as good as Mercury did with "lesser" parts , then your "new and improved tune-up" should be worth 50 more, on a 300R ...

Chaz = thinkin, the BSFC numbers are pretty good across the board on those already. It's gonna take hard parts , not the stroke of a keyboard to see any significant gains.

**engineermike** · 11-04-2019, 10:46 AM

Originally Posted by PRE-Z06

Not sure if you’re aware 200/225 come with a smaller throttle body than 250/300.

Based on Mercury’s own parts diagram, this appears to be correct. The cams and intake manifold are only different on the 300R. The 200 pro xs could be converted to a 225 pro xs with just a cal and a set of stickers. The same goes when converting from a 250 pro xs to a 300 pro xs or from a verado 200 L6 to a 275. Don’t expect to retain the warranty, though, if that is a priority for you.

**RSWORDS** · 11-04-2019, 01:07 PM

Other then the TB the power heads are the same. The R motor has different parts.

**RSWORDS** · 11-04-2019, 01:09 PM

Originally Posted by engineermike

Based on Mercury’s own parts diagram, this appears to be correct. The cams and intake manifold are only different on the 300R. The 200 pro xs could be converted to a 225 pro xs with just a cal and a set of stickers. The same goes when converting from a 250 pro xs to a 300 pro xs or from a verado 200 L6 to a 275. Don’t expect to retain the warranty, though, if that is a priority for you.

Yep. 64mm throttle body vs 80mm. I thought (ASSuMEed) they where using a restrictor ring like the do with the smaller motors and some optimax.

Also the air box, seal, and clamp is different for the 80mm TB.

The 80mm TB is only $257.17 MSRP though air box $88.08 MSRP, clamp $8.18 MSRP and the seal $9.24 MSRP.... lol

Here's a good on though. The throttle body gasket for the 80mm is $3.33... the 64mm? $40.17....

**PRE-Z06** · 11-04-2019, 03:27 PM

The OP asked about the 300 Pro XS and not R, which is why I responded the way I did. Based on the CARB dyno numbers, the 250 (R or Pro XS as the R just has different engine mounts and sportmaster) makes 276hp, the 300 Pro XS makes 296hp and the 300R makes 316hp. So there’s only actually 20hp between the 250/300 and the two 300s aren’t equal as they have different hardware as well software. I haven’t heard of any specific gains from Simon from increasing the timing since they suggest running 93 octane.

**65gamblerman** · 11-05-2019, 04:44 AM

Wealth of knowledge on S&F..

**Chaz** · 11-05-2019, 09:14 AM

Originally Posted by PRE-Z06

The OP asked about the 300 Pro XS and not R, which is why I responded the way I did. Based on the CARB dyno numbers, the 250 (R or Pro XS as the R just has different engine mounts and sportmaster) makes 276hp, the 300 Pro XS makes 296hp and the 300R makes 316hp. So there’s only actually 20hp between the 250/300 and the two 300s aren’t equal as they have different hardware as well software. I haven’t heard of any specific gains from Simon from increasing the timing since they suggest running 93 octane.

You are correct, he did ask about the sub-300 HP .... 300 . Not the over 300 HP / 300 .

I give up , what does the 200 HP model make ...

The 200 pro xs could be converted to a 225 pro xs with just a cal and a set of stickers.

Chaz = wunderin, how much power the stickers are worth ...

**Motv18** · 11-05-2019, 09:55 AM

Automotive rules are 5hp per sticker on rice

the 4s are easy but the gains are like in cars. You really need to do cams and such. Piddling with the computer will only optimize not seriously improving.

The 100hp liter cam about when people stoped caring about drivability.