LT1*C4

The debate has gone on for as long as I can remember.

Is a larger throttle body worth anything over the factory 48mm on a stock/mildly modified engine?

There's always been two sides of the argument and I suppose there probably always will. This thread isn't meant to throw fuel into that fire, but only to give you guys an idea of the differences between a stock LT1 throttle body and an aftermarket one as well as to share my experience with making the switch.


I'll start off by saying up front that I did NOT buy this throttle body thinking I'd pick up a bunch of power. I'm currently in the middle of a 396 LT4 build-up where this throttle body will ultimately end up being used on.

Having said that, I'm really in no rush to finish the 396, as the current "bolt-on" LT1 in my '92 is running like a champ and I see no reason to pull out a perfectly running motor.

To satisfy my curiosity own though, I decided to install the 58mm throttle body on my stock head/cam LT1 and see what the results are for myself, rather than just going along with internet hearsay.

Though this is not my first time upgrading a throttle body (I did so on my previous Fbodies) -This was the first time I've installed a larger throttle body on a basically stock LT1. Hence, the reason why I was so curious to see what the results would be - first hand.



Existing engine mods:

The mods on my '92 so far, are 1 3/4" long tube headers. Corsa exhaust. Electric water-pump and cut air-lid. The car also has a custom tune from PCMforless. Aside from that, the cam is stock and the heads have never been off the car.


The Throttle Body:

The throttle body you see below is made by TPIS. It's a pretty pricey piece at $450 but the product itself is an absolute work of art.

They're machined out of a solid block of aluminum. They have CNC machined throttle blades. A re-designed throttle linkage cam and come with a billet IAC housing that eliminates the engine coolant passages. Oh and then they're anodized "Plutonium Grey" - which give them a unique look that distinguishes them from other aftermarket throttle bodies.

Like I said, it's definitely a high quality piece.



Now, I'm sure you've all read the usual statements made by people who believe the factory throttle body is all you'll ever need.

THE BIG 3 ARGUMENTS AGAINST USING A LARGER THROTTLE BODY ARE:

- You'll lose all your low-end torque
- Throttle response will go out the window
- The car won't idle properly


Now that I've done the swap and experienced the results for myself first hand, I can honestly say that I did NOT experience any of those effects at all.

I just can't figure out why there are so many out there claiming the addition of a larger throttle body worsens throttle response, kills torque and causes idle problems when that's simply NOT the case. What gives? I guess it has more to do with people just repeating what they've heard/read others say on internet forums, rather than actually speaking from first-hand experience...


My results?

For starters, the very first thing I noticed, was how much stiffer the gas pedal felt.

It took a bit of getting used to because I now have to press down on the gas pedal harder than I did before. It feels as if the throttle blades are either closed all the way, or fully open. It made it kind of difficult to drive off the line normally without chirping the rear tires from a stand still.

Once the car's up and running at speed, again, pushing down on the gas pedal, say, 1/4 ways down, the car lunges forward as if I just hit wide open throttle.

It really transformed the overall "feel" of the car. Once I got the hang of it though, I now actually prefer it.

At wide open throttle, (and take this for what its worth) the car definitely feels as if it pulls a lot harder up top. I know, I know, without actually putting the car on a dyno, this is only an "opinion" - but like I said, take it for what it's worth - but this car feels as if it's making more power than before at any given RPM. I can only assume the reason for this, is because at any given pedal pressure, the larger throttle blades are allowing more air into the engine than before with the smaller 48mm blades. Hence, the sharper throttle response and "feeling" of the motor pulling harder...

Coming to a stand still, I literally had to "re-learn" how to launch my car as the first few attempts had me lighting up the tires and hitting the rev limiter like crazy. Like I said, the pedal feel is totally different now and launching "gently" is an exercise in restraint.

Whomever said you lose low-end torque with a larger TB is totally out to lunch on that one.

Idle remains the same as it was before. No choppyness at all. It remains rock-solid.


My conclusion:

All in all, I'm definitely happy with the end results. True, that's a lot of money for a throttle body, and although I'd still recommend a set of headers/exhaust/gears before I'd recommend a larger throttle body, I can now honestly say, that a larger T.B. will definitely NOT hurt performance on a bolt-on LT1, only improve it.


(In case any of you plan to upgrade the stock throttle body, be sure to reset the computer by disconnecting the battery for a minute ow two and then adjust the TPS sensor to .54 volts (reading with the key in the start position) using either a scanner or multimeter, before you take the car out. I just got a dremel tool and"ovaled-out" the openings on the factory TPS sensor and now had enough "front to back" play to manually adjust the TPS.


Anyways, here are some comparison pics.

I'm interested to know of other peoples experience's with larger T.B's.


..

..

..

..

..

..

..

..

..

..

..

dogfish246

Thats awesome! Looks like a really great piece and sounds like it was worth it! I wonder if there is anyone out there who has a stock or slightly modified vette that took her to a dyno for a before and after run? I always like your threads, a lot of good info, pics, and its always an interesting read!

JackDidley

Looks like a work of art. Nice report. I'd like to see some timeslips.

rodj

But was it a cost effective mod?
I have previously documented my back to back testing ;
stock vs 58mm TB on a big tube TPI setup .Same track / same day over 30 runs
The net results was no observed difference ;Good or Bad.
Car had excellent throttle response , ran same 60ft time, trapped almost identical and was no different on the street except for very low speed tip in on account of mentioned stiffer spring making it hard to "tickle " throttle in bumper to bumper traffic

Need another option for your poll
"Made no difference"

StealthLT4

You need a third selection for the poll.

Neutral! Increased throttle response due to higher actual flow than what my foot tells me, but max hp and tq are unaffected! Overall, simply a waste of money, no gain, no loss (performance wise).

I have a 52mm TB and I will be the first to tell you that, unless you are significantly modified (cam, LT's, full exhaust at the very least), it is a waste of money. It feels faster because when you give the pedal 50% throttle the engine actually gets 75% airflow, but that just means you lose precision in the lower ranges, and the last 25% of throttle travel doesn't do anything because the engine is already getting all the air it can use.

VetteMed

Sums it up very nicely.

ch@0s

LT1*C4

I'm afraid I'm going to have to respectfully disagree with you on that statement. I think it would be much more appropriate if you'd said "Overall, simply a waste of money...IN MY OPINION". Since that's exactly what it is. Your opinion.

I happen to think the end result of this upgrade was well worth the effort. That of coarse, is just my opinion...

The car feels completely different now then before. I'd even go as far as to say it's a night and day difference and that's not an exaggeration either. I've said it before and I'll say it again, if I had to equate this upgrade to any other "mod" - in terms of it's ability to change the entire "feel" of a car, I'd compare this, to installing a set of lower gears.

Gears might not show any meaningful power increase on a dyno either, but that doesn't mean people don't "feel" the difference driving the car.

Everybody always makes the claim that adding lower gears makes the car more "fun" on the street. Guess what? A larger throttle body has the same effect on a car's "fun-factor" as well.


So what exactly is the problem here? You freely admit that the car does in fact "feel faster" (the whole point of my post) but you're acting as if I'm somehow misleading others as to what to expect from this upgrade.

I never made claims of a huge power increase, nor did I claim it reduced my ET's. I simply reported my results that the larger throttle body changed the feel of the car. Improved its throttle response in "day to day" driving and made the car more fun to drive.

That's it and that's all.

If someone's looking for a "HP" mod, yes, buy a set of headers. Install a more aggressive cam. Throw on a set of aftermarket heads. etc. etc.

For anyone looking for a quick, easy way to make their car more fun to drive, consider a larger throttle body.

PLRX

Very Nice Indeed

5abivt

Someone summed it up before i could write an essay. Nice looking throttle body indeed.

The TB is basically just a valve. GM looks at maximum airflow at peak rpm and then chooses a size so that 50% throttle will give you 50% flow and so forth. it is just more accurate this way again as mentioned above.

Touching the throttle and getting more response once again is really just letting more air in for a given throttle position. Some like it and you said you did so all is well.

one thing i have concern over is the iac. that is a beautiful unit there but on the backside there you will see it bleeds iac into the main plenum. When i was tuning for idle I came across a few posts on the camaro boards that discussed how this was supposed to be directed into the dedicated idle air port in the manifold. The stock TB doesn't allow it to bleed. I ended up taking a pipe and flattening the end so when my Callaway TB was bolted up the port strictly fed into the Iac port. My idle improved big time. This was also on a solid roller with a big duration cam so on a stock motor forget what you just read. just some food for thought.

mseven

That sounds like the lt1 fix for idle and split blm. On the mini and some other aftermarket stuff there is no direct air ports (straight to the plenum) unlike the ltx or even tpi intakes.

I have the same tb on mine for the last 2 years and have been very satisfied with the construction and quality. However with this motor I never made a comparison to any other, my choice was based on the combination.

PDQUIK95

one thing i have concern over is the iac. that is a beautiful unit there but on the backside there you will see it bleeds iac into the main plenum. When i was tuning for idle I came across a few posts on the camaro boards that discussed how this was supposed to be directed into the dedicated idle air port in the manifold. The stock TB doesn't allow it to bleed. I ended up taking a pipe and flattening the end so when my Callaway TB was bolted up the port strictly fed into the Iac port. My idle improved big time. This was also on a solid roller with a big duration cam so on a stock motor forget what you just read. just some food for thought.[/QUOTE]

Ditto.
Edelbrock is the only aftermarket T.B. I have found that still maintains the dedicated IAC passage without bleeding straight to the plenum. I chose the Edelbrock 3810 58mm for that reason on the 396. I had a 52mm BBK with plenum bleed on the 383 and did the pipe nipple mod to bring back the dedicated IAC port. It definitely helped with idle control and improved the common split BLM issues.
Rick

C4happy

That TB is to pretty to put under the hood. i love the way they cleaned up the IAC and got rid of the coolent passage that looks nice. I am currently building a 383 with a 08-503-8 CC cam with 1.6 RR with a 1.98 intake valves and I just bought a 58mm TB I though I may have messed up after reading some post here saying that a stock TB is better but I beleive after looking at this post I have the right stuff thank you for shairing your TB story with us

Charleston2012

Ditto.
Edelbrock is the only aftermarket T.B. I have found that still maintains the dedicated IAC passage without bleeding straight to the plenum. I chose the Edelbrock 3810 58mm for that reason on the 396. I had a 52mm BBK with plenum bleed on the 383 and did the pipe nipple mod to bring back the dedicated IAC port. It definitely helped with idle control and improved the common split BLM issues.
Rick[/QUOTE]

LPE had the Accell 58 MM throttle body they used on their L98 SUperram engines. They said it would work fine on an LT1 just by rewiring the TPS to the L98 style that fits it. Its IAC passage etc was identical to the factory.

mtwoolford

thanks for the post; this will be helpful later

Vette Fast

GREGGPENN

That's not completely true. The 89-92 Plenums are shaped EXACTLY like the TPIS unit in the back. IOW, even the stock IAC doesn't directly feed the IAC ports.

There are two ports directly behind the TB openings (for 89-91) and they have molded "blocks" behind those holds. Those blocks probably help to direct air into the IAC but don't force it. It could mean even air from a low level TB opening might flow more thru IAC passage. By contrast, not all of the IAC air is "demanded" to enter that passage.

I don't believe having a direct connect from the IAC passage to the IAC ports is necessary for sufficient idle. Other, it might help somewhat.

Edit: BTW, in the plenum porting the removal of the blocks I mention above is referred to as removing the humps.

rodj

Those are the ports where the EGR gas exits to intake; the humps are to promote mixing of the exh gas in plenum

The early TPI have ports in the intake base hence the tube on drv side runner to take air to base.The IAC exit hole on the TB matched up to a hole in the front of the plenum and there is a runner cast on the underside of the plenum to take the air to the tube
'89+ TPI cars did not have IAC holes in base and the TB dumped IAC directly into the plenum
See
http://www.hotrodlane.cc/Streetstories/choosingtpi2.htm

GREGGPENN

My car is an 89. There are tiny holes inside every runner of the intake base (e.g., 8 ports). There are also holes on the floor of the plenum just behind the TB ports. I thought the tiny base holes are where the EGR dumps while the TB holes are for the IAC. I don't believe the hotrodland TPI links clarify that either.