scotth48

I was reading on my mpg thread that the throttlebody had a smaller butterfly opening for cruise and better mileage any pictures or how that system works? The stock lt1 is 48 mm, what is the size for the lt5?

FASTAZU

The primary plate is 22 mm the two larger secondary plates are 59 mm

ZR1Bob

When Marc Haibeck does the 510 package he enlarges the 59 mm plates to 63 mm.--Bob

scotth48

Having never seen a lt5 throttle body, is it bigger in physical size than the lt1? Would it work on a lt1? How do the plates open, small one first before the larger? Could a lt1 be machined to be like the lt5? Are there aftermarket throttle bodies for the lt5 and if so, do they do away with the smaller plate!

FASTAZU

Tom400CFI

It doesn't work (for gas mileage). The purpose is easier management of the "valet" feature. Today, that would all be done w/software controlling the TB blade action. Back then, it had to be done mechanically.

Tom400CFI

1. It is physically larger, different shape, and different flange/bolt pattern
2. No.
3. Small first, larger second....like an '80's VW.
4. possibly. Anything can be done w/enough $$
5. No aftermarket TB's for LT5. No need, IMO.

FYI, there is no practical advantage to adding this style TB to an LT1. Would be a total waste of time and money.

FASTAZU

Tom while agree with most of this I don't think the primary throttle plate has anything to do with the "valet" feature. The valet key controls the secondary port vacuum system and 8 secondary injectors, it was primary for emissions.

"Quote" From Graham Behan, one of the original LT5 Engineers now working for Lingenfelter Performance Engineering:

"The intent of the "Valet" mode was actually to allow the engine to operate on eight injectors whilst on the emission test cycle. The primary lobe of the LT5 intake cam is 20 deg shorter in duration than the secondary lobe. On a 90 MY car the power key could be left in the full power mode at all times, unfortunately for the 91 MY and above we were forced to adopt a strategy whereby the system would be in "Normal" mode(8 injectors) at every start. Hence the change in the key system for the later cars, this strategy prevented the power key from being considered an emission defeat device."

DRM500RUBYZR-1

The Doug Rippie DRM 500 conversion also uses the larger 63mm throttle plates.

Marty

scotth48

So does the car get better fuel mileage in valet mode or is it restricted in speed also? Is tuning a better choice on the lt5 for better economy? Why couldn't there be a ecm with two proms with a switch to go with a economy mode to a performance mode?

Tom400CFI

Yes, I agree w/all of that...however, when in Valet mode, only the small throttle plate opens (in addition to only the primary runners, function.).

At least, that is what I've read. Otherwise, why spend the $$$ on machining, parts etc, for that itty bitty throttle plate and bore? You can get a progressive throttle much more cheaply and simply by using a cam on the throttle arm.

Rkreigh

no, your foot determines MPG, sorry but the ECM doesn't work that way and the secondaries only open on load which would wreck gas mileage.

for the LT1 there are numerous high flow throttle body setups

I've always wanted to port the "primary" on my throttle body but I've never heard of anyone doing it.

I agree that for stock LT5s a ported TB is a waste and there is some debate if it's even needed on the big doggies.

bet cool to do a back to back dyno test. my bet is that it's not a restriction even stock.

FASTAZU

You are correct in all but the small plate, it operates as due the larger at all times.

Tom400CFI

Copy that. I had read (probably in Motor Trend, as that is what I subscribed to back then), waaaay back when the LT5 came out, that the small throttle plate was the only one activated when in Valet mode, limiting the engine to 250 hp.

I think the author must have been confused at to which throttle plates he was writing about. I can't see an engine making 250 horse through that sized orifice, I don't know of any device that would limit the secondaries from opening, since it's all mechanical.

What you're saying makes more sense than what I had read. Thanks for the correction.

scotth48

Thanks for the picture. That is a pretty small opening to let enough air in! Even a 3 horse power Briggs and Stratton engine is bigger than that!

Paul Workman

While driving, there isn't much throttle input above idle when I can feel ever so slight of a power (I hesitate to say) "surge". I'm not sure it is the main throttle plates opening or just a ripple in the AF tables or when the secondary injectors come on in the "secondary deleted" mod config that I have...or both?

wfot

Hey guys I have done a lot of tuning with the LT5 computer. the throttle body is all mechanical and the secondary plates start to open at about 25% throttle opening. Your foot goes down and and the throttle opens. the Valet part of it is all computer controlled, there are two sets of fuel and spark tables, one set is for 8 throttles and another set for all 16. the throttle blades being open can overlap on these tables based on tps position. there is a tremendous amount of tuning for all tables and varying sensor input.

hope that clears up some questions. It is almost too much to play with really

JaySS

IIRC, the primary throttle blade was originally intended to supply the air shrouded injectors that were eliminated during development.

These should give an idea of the differences between & LT1 & LT5 throttle bodies (LT1 throttle bores have been enlarged to 58mm for this example):

Front:



Back:



I'll let someone else ponder the concept of using an LT5 throttle body on an LT1 with the primary throttle feeding the under-manifold transfer passage

Tom400CFI

Interesting input. Very little info "out there" to confirm anything....that *I* am aware of. In "Heart of the Beast", there is a brief mention about the LT5 idling at ~400 RPM to meet EPA/CAFE fuel requirements....but obviously, that strategy wasn't employed in the final, production engines. So was the little throttle necessary for final production? Or left over from design process that was trying to cover all bases? I suspect we'll never know.



Those are currently fed by the IAC. Don't know what benefit you'd get by feeding them w/a mini throttle. No "ROI" that I can see there.

Dominic Sorresso

The dual mass was installed to dampen the rattling on the ZF trans which were. Close to square cut, especially in the Black Label model. The primary throttle blade is there to keep intake air velocity up for better low end. It's all mechanical so it works progressively with or without valet. Valet mode disabled the secondary injectors and throttle mechanism
under the plenum.