TBI Throttle body 88-95 ridge removal

[Horntoad]

On a number of forums, including this one, removing the ridge from a 350 throttle body (Rochester 220) is discussed and recommended. The reasons given are that it removes an air flow restriction and deshrouds the injectors.

While not disputing those recommendations, I'm just wondering what the reason for the ridge being there is. Having put time and money into designing their systems and parts, why did GM put the ridge there? If I'm not mistaken, there is no such ridge on the 454 TBI throttle body, and if so GM must have chosen to have the ridge on the 350 but not on the 454. Why? Couldn't GM just as easily produced the 350 TBI without the ridge? Is there some functional benefit from having the ridge there?

 

[Schurkey]

I've thought for years that the so-called "Ultimate TBI Mods" were a waste of time, money, effort, and enthusiasm.

I can hardly wait to hear other responses.

 

[PlayingWithTBI]

I saw on another forum (thirdgen.org) where one guy gained .6 sec on 1/4 mile with ultimate mods AND some timing. That muddies up the waters a bit with the "timing" thing. I see lots of guys claim gains but I haven't seen any definitive proof. When I got my 46mm bored TB with pod spacer and "Ultimate Mods' I also changed a whole bunch of other stuff like fuel pressure, intake manifold, heads, cam, headers, cat, and straight through muffler so, I have no proof other than what the machine shops that do this stuff claim. One thing, when I get up into higher RPMs, like 4000 to 5300, my logs only show 90 KPa MAP instead of 95 - 100 I see in lower revs. It could have something to do with my throttle blades don't open all the way (maybe 90%?) with the skinny pedal mashed. My AFR is also running a little rich (~11.3:1 with WBO2) then too - maybe still not enough air flow? I'm working on that.

 

[Horntoad]

Thanks for the responses. I've seen some of these testimonials, too. I'm rebuilding my throttle body and have sent the injectors out for cleaning, so I've got it off and could very easily grind down this ridge. It's just that as I was considering that, I wondered why GM designed the ridge into the part and what if any trade off there is to removing it.


Does the ridge have to do with the shape or location of the power band, with airflow turbulence and/or balance, air pressure or something else? Or, and I know nothing about metal casting, is it simply a casting artifact (as I think I've read suggested on some forum or another) that restricts airflow and serves no purpose but would have been an added cost to remove that GM couldn't justify?

 

[Frank Enstein]

Wild stab in the dark it may be for noise reduction. The air box often has a restrictor in it too. That for sure is to reduce noise. The big block engines were heavier trucks that had a more relaxed federal drive by noise standard.

 

[Frank Enstein]

An injector spacer TRD 2457 $44.99 @ Summit spaces the injectors up a little to get them out of the air flow. A Hypertech 4001 power charger can help too. I looks like a cereal bowl with the bottom cut out and helps the engine pull air from the sides. It has been discontinued but it would be easy enough to make. I saw some photos here of a homemade one. An AID-200-540 throttle body spacer can help a little especially at part throttle but they don't do much at WOT.

 

[Frank Enstein]

TBI isn't very flexible due to the primitive computer but it can be made to run better. A dual snorkel air filter (cut and weld from a boneyard air cleaner) a high flow filter and remove the restrictor in the air box. and it can run a bit better. I do not recommend removing the heat stove from the snorkel as it can hurt performance during cold weather. The thing slams shut and feeds the engine cold at at heavy throttle. Also don't listen to "My Buddy". That guy should not have access to tools. You know who I mean...

 

[Pinger]

I saw on another forum (thirdgen.org) where one guy gained .6 sec on 1/4 mile with ultimate mods AND some timing. That muddies up the waters a bit with the "timing" thing. I see lots of guys claim gains but I haven't seen any definitive proof. When I got my 46mm bored TB with pod spacer and "Ultimate Mods' I also changed a whole bunch of other stuff like fuel pressure, intake manifold, heads, cam, headers, cat, and straight through muffler so, I have no proof other than what the machine shops that do this stuff claim. One thing, when I get up into higher RPMs, like 4000 to 5300, my logs only show 90 KPa MAP instead of 95 - 100 I see in lower revs. It could have something to do with my throttle blades don't open all the way (maybe 90%?) with the skinny pedal mashed. My AFR is also running a little rich (~11.3:1 with WBO2) then too - maybe still not enough air flow? I'm working on that.

Has it been on a dyno to know at what rpm torque peaks?

 

[PlayingWithTBI]

Has it been on a dyno to know at what rpm torque peaks?

Nope, just a 1/4 mile time. I've been looking for an apples to apples comparison for a long time, all I see is people claiming benefits but no real data. It does stand to reason, if you have a modified engine and are running higher revs than the 4400 these 5.7s normally go, you need better air flow. This TCI calculator (go to the bottom) shows somewhere ~650CFM for a 5.7L @ 6000RPM. Will you get 650CFM just by shaving the horns and throttle bar? NO but, it'll help along with other mods like, boring and opening up the flow around the injectors. Stuff like the pod spacer, the "salad bowl" intake spacer, the air box, etc.

https://www.tciauto.com/racing-calculators

 

[alpinecrick]

Based on a friends complete removal of the ridge—which results in an almost instantaneous and almost uncontrollable throttle response—I would say the ridge is there to make the throttle response plumb drivable.

Based on what I read on the internet, partial removal of the ridge is more controllable.

Although I wouldn’t want to try to jack around a hairpin turn on a two track trail hanging on the side of a canyon in 4 low with the ridge modded.....

For a stoplight to stoplight boulevard cruiser, slight removal of the ridge might be more reasonable.