Ported 2.5 Block

[CLAYC]

I saw a 2.5 block which had the entire exhaust system ported. The exhaust ports weren't enlarged, just everything from the port had been removed and polished. The (what I would call) exhaust flow directors (from each cylinder) had been ground out and smoothed into the larger exhaust flow channels. From there it looked like they had flowed the entire system by removing and polishing everything that may create exhaust flow restrictions as the exhaust flows toward the tuner.

I know changing the tuners can either help or hinder a particular set-up. But what will this type of exhaust work provide or hurt?

Thanks,

 

[CLAYC]

Re: Ported 2.5 Block

Any thoughts?

 

[sschefer]

Re: Ported 2.5 Block

Without seeing it, it sounds like the motor was cut for higher RPM. The trade off is a lost power on the bottom end. Addditonal porting in the cylinders is often done as well as head modifications to increase compression. Depending on what was done, these engines often require high octane fuel between 96 and 106.

The average life of one of these motors can be reduced to a measily 100 hours in some cases.

They sure are fun though!!!!

 

[Dukedog]

Re: Ported 2.5 Block

Any thoughts?

If your not runnin' a very, very light boat or a ton of N2o its gonna be a turd on tha bottom side of a "normal" boat...............

 

[CLAYC]

Re: Ported 2.5 Block

Interesting. Well that answers my questions. I've done a lot of port/polish work on hot rods, but never on an outboard. I saw that and wondered if it would help or hurt a stock engine.

I saw the block again after I posted this. What they did was open the entire exhaust system (not changing the exhaust timing by opening the exhaust ports in the cylinder/bore) by blending in all the humps and bumps the exhaust must flow over. Looking at each idividual cylinder, I could see where the exhaust flow directors had been blended into the adjacent material of the block (which appears to give the exhaust flow a cleaner, faster exit) lessening turbulance. Wish I had a pic to post.

I thought this may be a good idea to do on my stock 2.5 EFI, but, with the posts, I think not.

 

[sschefer]

Re: Ported 2.5 Block

Interesting. Well that answers my questions. I've done a lot of port/polish work on hot rods, but never on an outboard. I saw that and wondered if it would help or hurt a stock engine.

I saw the block again after I posted this. What they did was open the entire exhaust system (not changing the exhaust timing by opening the exhaust ports in the cylinder/bore) by blending in all the humps and bumps the exhaust must flow over. Looking at each idividual cylinder, I could see where the exhaust flow directors had been blended into the adjacent material of the block (which appears to give the exhaust flow a cleaner, faster exit) lessening turbulance. Wish I had a pic to post.

I thought this may be a good idea to do on my stock 2.5 EFI, but, with the posts, I think not.

What you need to realize is that the exhaust chamber dumps three cylinders and the key reversion source is the pulse felt from the other cylinders. If you reduce the pulse to nearly nothing, you hold less fuel in the cylinders and the first thing to go is bottom end power. After that you have to dump a lot more fuel in them to keep the squish band supplied or you risk heating up the piston and then detonation or preigntion.

This exactly what you want in a Drag motor but not so good in a sport motor with mutiple uses.