First a bit of backstory:
Last spring I got my FB project on the road. I installed a S4 NA engine out of a 88 vert that had a scrap title. The S4 EFI harness has been spliced into the FB chassis and it ran fantastic (14.5 at the strip). Due to some bad luck the engine came with a mild compression leak that would aerate the coolant during autox/spirited driving.

Up until recently I was planning on rebuilding the engine and taking the opportunity to do some porting and grind out the exhaust pitch diffusers. That all went out the window when I came across a great deal on a known good running S5 NA engine.

My question is this; Is the risk of getting metal shavings in my good engine worth the performance increase of grinding out the diffusers?
I have the skills and equipment to easily do the grinding, and obviously I'll be taking precautions to minimize getting debris into the engine.

The final setup of the engine will be:
Stock S4 EFI and Intake manifold
Atkins 6port sleeves
Mindtrain Header with full 3in piping from the collector

 

Evan?

anyways. If you are planning on keeping the engine together its basically an all around bad idea.

Even if you can grind the old ones down or grind away at the spot where the pins are. Its worse to run it without inserts vs the NA ones.

You wont be able to install new inserts without having the engine apart.

Now having said that, if you have the engine apart:
I hate taping the roll pins so if your going to remove the NA inserts (and nobody wants to buy them ever) I get my carbide and grind through where the pin goes into the insert then once I've broken the surface I use a pin or a punch and just knock it out from the inside. Install is easy.

 

lol Yeah its me.

I'm not looking to completely remove the inserts, just grind out the diffusers.

 

Not work the risk, I would just wait on those until its rebuild time. I got a pair of nicely polished T2 inserts too FYI.

 

I just did it the other day. The engine has to be apart. The sleeves have to be removed (pull the roll pins). They turned out similar to this:
https://www.rx7club.com/2nd-generati...leeves-986906/