Ported Throttle Body Question

[Mikz86ta]

So I been reading on some threads with people doing home made port jobs. This is basically on LS1 and Vortec TB units. Very similar in design.
I know on my 4.3 Votrec TB, they say going with the Marine TB Blade (or CFM-Tech Blade in which I did a long time ago), you up the flow to 75mm. Without the 'deflector' there was def a throttle response difference and upper RPM pull difference. No ill effects on mileage. Been in there since 2004.
The I read some going to 78mm which is been bored.
Some of the do-it-yourself guys are smoothing out the bore, making a sharper entry angle, taking off the inside ridge and the marine blade mod. No biggie I dont see except maybe you should do the MAF and VE tuning after. What do you think?
But my main concern lies in where some guys epoxy in the IAT opening (very large on these TBs) and leave a much smaller hole or two. Will that mess with the IAT function in controlling idle, corrections for AC, etc? Should adjustments be made if such a mod was made?

Thx in advance!, Michel

[Mikz86ta]

Anyone with input on this?
I got a NOS TB unit on the way and wanted to take my stock TB and start playing with it Be nice heads up if I need to adjust the IAC someway to compensate
I had heard in the past, some with the VaraRam intake TB filler part they had some idle issues

[hog]

By removing the diffuser device(which is larger on the 4,.3 than the 5.0/5.7) your are effectivley accomplishing the same thing as installing the marine/cfm tech t-body blade. In doing so you will introduce more air per degree of TPS opening at low throttle settings.

I just read an article in a 1996 isuue of Popular Mechanics magazine, and it explains the device is there to "smooth" low throttle manouevers such as backing with a trailer. The older TBI trucks would surge even with small throttle applications, engineers are trying to avoid that with teh newer TB design.

I simply drilled out the 2 rivets which held the diffuser plate in place, then reinstalled rivets to close up the holes. If you plug up all teh openings on the t-body blade, this will force teh IAC to do more work. It might not be able to effectively control idel as easily, but I'm not sure.

I have had my L31 t-body modified this way for years as well. I have not ported or polished the t-body in any way. Since teh same t-body is essentially used on the L18 8.1 340hp truck engine, which is exactly the same engine as the 375hp Mercuiser HP1 8.1, swap the cam you have the 425hp HP2 8.1 engine. Port the stock heads, change cam, and up the rail pressure to 4 BAR(58 psi) and you hav ethe 525hp Mercruiser HP3 marine engine, all with the same 75mm t-body. I think gains would be small when portiing this 75mm t-body for my 255 sae net hp L31 which equates to about 310 gross hp.

BTW I have heard that a secondary benefit of this diffuser device is to stir the EGR gasses with the incomming airflow form the throttlebody. IIRC EGR was dropped in teh early 00's.

peace
Hog