2.5 exhaust chest mods....

**texasvector** · 06-09-2017, 06:43 AM

ive got a lil project im planning. taking a 2.5L 150 block porting and cutting it. havent decided what to do with the front half yet....possibilities are 7 pedal laser or might throw a horn on it.

would like to get some ideas of exhaust chest work.....ive read that cutting 15* down chest then cupping and routing ports "down"...i dont really want to hog it all the way out just open it up some and route down....theres plenty of meat in the 150 to shape how i want it

lets see what yall have done to the exhaust chest.....heres a few i found researching.

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**Jay Smith** · 06-09-2017, 08:44 AM

Text me and I'll send you pics I'm not good at ensign photos or posting but I can text 832 597 2603

jay

**FORBESAUTO** · 06-09-2017, 11:14 AM

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**Steve Pope** · 06-09-2017, 04:16 PM

Unless you are going to build a high rev engine then copy a 225 promax or a 96 and later 200 and just clean up and polish.

**texasvector** · 06-09-2017, 04:43 PM

Originally Posted by Steve Pope

Unless you are going to build a high rev engine then copy a 225 promax or a 96 and later 200 and just clean up and polish.

the current blocks im running i have done that exactly.....just cleaned up and polish..maybe open channels up slightly. i prop them for 8k.......i wanna go a tad more extreme with this one and turn it up more

ive got a lighter boat this might go on later down the road.....projects....too many or not enough????

**texasvector** · 06-09-2017, 04:56 PM

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**FORBESAUTO** · 06-09-2017, 05:08 PM

Depends on what all is done with rest of the mota, but you will prob be surprised that you won't lose bottom end as you would think. The degree of angle on the bottom of the port exit has a lot to with rpm. The more the angle the higher the power band. Block in picture has 30 degree angles (cut on mill for accuracy). The motor with that chest actually has the most low end torque of my modified motors, along with a lot of other mods that help out in that area. The new mota I'm building now is cut on 45 degree angle for more higher end power. Don't have pics of it yet. I opened the mota in pic up more looking for more top end power, which it did. But at my surprise it also picked low end torque over the previous cut. Of course prob has a lot to do with the way mota is built and it just complimented the way it was (restricting mota previously)

**texasvector** · 06-09-2017, 05:15 PM

your saying if the block is standing up (running position) the bottom of the exhaust dump on each hole is angled 30* down ??

**Steve Pope** · 06-09-2017, 05:21 PM

I used to run in f1 and built a couple of steel bore engines so I could try diferent porting. The high rpm dictated the use of forged pistons and extra clearance but top ring land and lower piston skirt wear were always a problem. I reverted back to nikasil engines, invested in more props and enjoyed touble free enjoyable racing. The point I am trying to make is if you want to run high RPM then use a proper nikasil cylinder block with the appropriate exhaust chest used for high rev use.

**FORBESAUTO** · 06-09-2017, 05:24 PM

Yes, and the more the angle the higher the rpm. The 30 works good on fishing mota. When I get other mota built I'll let ya know how it goes,

**FMP** · 06-09-2017, 05:41 PM

Hey Forbes , guys
Do you know the effect of a full radius 30-45* of the port?

**FORBESAUTO** · 06-09-2017, 05:43 PM

No sense in both of us ruining blocks lol! But I can tell you the way I build my motas so far every time I've increased exhaust flow it has not hurt me yet but only helped all the way around. I'm gonna keep increasing until I break over that point of diminishing returns. I'm sure results are different depending on rest of mota combo though.

**FORBESAUTO** · 06-09-2017, 05:49 PM

Originally Posted by FMP

Hey Forbes , guys
Do you know the effect of a full radius 30-45* of the port?

You want the top of the port with no angle for the scavenging effect from the cylinder above it. Straight sides picks up velocity. The angle downward angles exhaust towards exit to prevent it from crashing into divider causing turbulence and re- entering port, which is why part of tuning for rpm you plan on turning.

**FMP** · 06-09-2017, 05:52 PM

Sounds like an old snowmobile sled trick, helps the exiting pulse/ flow stay uniform and funnels the returning pulse. I need to look at your pics on desktop, top of port you mean top not roof towards cyl head? Not sure about your scavenging from cyl above, nothing above #1

**FMP** · 06-09-2017, 06:29 PM

Are you talking about the port at the cyl or further out , the " primary" if you can call it that of the chest that has been worked? Still need to see this on desktop