Injector Housing to Head Port Match Issue

[Paul Workman]

Originally Posted by KJL

** I will also try to stay away from using any "grit" based bits. I am afraid bits of grit may make it into the the cylinder. I plan on plugging the ports but you know how that goes. If a couple of small flecks of aluminum get in there probably wont damage anything but small bits of carbide grit?....

My existing port job is fairly smooth but could use a bit more polishing, maybe with ultra fine 500-600 grit wet sand paper? How smooth does a port job need to be?

Couple things:

No worries about grit, if you pack the bores tight with (I used) WD40 sprayed paper (shop) towels (the thick, heavy blue ones). Paranoid, I packed each runner twice; one primary plug, and one secondary. When finished, I used a vacuum cleaner with a tube small enough to reach into the ports and pick up the bulk of the loose debris and grit. Then with a super-long set of hemostats, the packing can be retrieved, while vacuuming again before removing the second plug. Then I used fresh towels, sprayed lightly with WD40 and wiped the bore surfaces; changing towels until they came out clean. No grit! No worries!

Like an surgical theater, the entire top of the engine bay is covered with a (I used a shower curtain), and everything but the port being modified is masked off...



Port "matching" in LT5 heads - in progress (note plug)



Surface left by carbide bit before sanding



Note finish imparted by the 60-grit flapwheel...



Far as "grit based" bits go, grinding bits load up almost instantly when cutting aluminum. So the cutting is via carbide bits. However, to remove blemishes and nicks left by the burr (and you will have some!), as Lee pointed out, a 60 grit flapwheel (seen in my photos in previous post on this thread) is ideal for cleaning those up and imparting the right amount of surface roughness to avoid boundary layer encumbrances.

But, back to port matching:

Just my 2-cents, but Flyin Ryan suggested to me that when it comes to changing the diameter of a runner, to prevent pulse reversion it is best to not exceed (if I recall him correctly) 4% change in diameter for a given linear distance (along the axis). (Other sources vary - one I read said 7%.)

I went with 4% - less is better, in some cases - which resulted in a long taper extending from the input and narrowing to just above the valve guide.

WOW! I wish like hell I had dyno'ed it at that point, cuz the seat of the pants improvement I got from top end porting alone was way beyond what I expected! There was a big improvement when I ported the heads as well, but not as much a change as I got from the top end phase - ending up at 432 rwhp, w/ stock cams, stock TB, and SW headers + X-pipe. (Someone tell me again how the stock LT5 isn't starving for air!)

Prolly more than you wanted to know, but mebby somebody will be intrigued enough to consider joining the majority of the FBI gang and port their babies too! BE A WARRIOR!

P.