OK guys. I used the search feature untill i read everything there was about throttlebodys on the C4. what im looking for here is facts. it seems everytime ppl ask about TBs everyones response is that you hardly ever need a bigger one cause an engine that is stock will only flow X many CFMs and the stock 48mm flow X many CFMs and the chevy bigblock that GM made had a 48mm yadda yadda yadda...

my question is who here has done dyno tests with bigger TBs and what did YOU guys find out? also of the ppl that HAVE done this, who port matched it? i know the stock manifold it ported to 52mm so those should already fit perfectly (SHOULD!) but im curious if ppl HAVE dynoed a bigger TB and gotten a lower HP number if it was because it wasnt port matched and created to much turbulence. i wonder if most of the time ppl arent getting the whole story. Bigger TBs may actually help most of the time if they are actually portmatched so they can flow their maximum pontential without causing turbulence

 

I just put my bored 52 mm stock throttle body back on Saturday. I WILL get a dyno soon and it will show a three stage build up, with intake mods done last.

I measured both the intake openings and the throttle body openings and neither is exactly 52 mm. With my primitive calipers I measured 2 1/32" for both openings. OK, it's about 51.6 mm so that's close.


But I don't have it for you today. And if I don't back up the dyno run with track runs I'll get schmeished on here by you-know-who.

 

So you didnt do any port matching?

 

I did back to back testing and the gain was over 20RWHP

This took me from 290s in the 310s. This was with out any tunning just a straight swap. I had ported the Manifold a few years before when I had it off.

There have been a few of us on the LT1 Edit list who have shown near same gains during true dyno testing.

Many are going to yell foul but it is all true

Do search for C Millard on the net and find his site. he has dyno sheets posted.

 

WOW! was this from a 48 to a 52? or bigger?
what sizes?

 

...very interested...

 

??? I'm confused. I did put a 52mm on a TPI motor and got no gains at all... and if I remember correctly... Nathan Plemmons has a dyno graph with the before and after with no gains. How was it that you got 20hp to the ground?

 

I would imagine that a TPI motor, especially stock, would benefit alot less than an LT1 simply because the L98 is done by 4500rpm or so. I could easily see an LT1 gain a reasonable amount, but mainly in the top end.

 

I did no port matching. When you have the TB in your hand you can see that the gasket is smaller than the throttle bore diameter and doesn't block like intake port gaskets often do.

Now it might be possible to get the TB slightly offcenter and not matching? I don't know if mine is true or not.

 

I have a modded LT1 already making about 350 HP to the wheels. I would see no use of a larger TB on a stock engine, even an LT1.

 

Did a little massaging to the L98 stocker and the debatable air foil-I know the screw's missing-Seems to be plenty so far

 

Those are impressive numbers. I've always said that a modded motor will benefit from a larger TB... but I thought the 48mm was plenty for 400+hp. Nathan's 92 is far from stock and he still did not get any gains. Here is the link to his dyno graphs.

http://www.wku.edu/~nathan.plemons/h..._corvette.html

I am not doubting you and I have not done a TB on an LTx motor... but these numbers support what I had said earlier. Do you have a dyno of before and after?

 

I will know soon if the TB bumps the power, with my own dyno run. Nathan has a more radical top end with 1.7rr giving him more lift, and I have a hand grind pocket port on my heads vs. Nathan's CNC port from TEA. I also have a bigger exhaust than Nathan, so our cars are not exactly the same.

OK, my decision to do the 52mm was for two reasons.

One, last dyno run we could see it nosing over (dropping off) quickly at 6200. John had no explanation but intake restriction, as I had followed his advice and put on a whopper exhaust, and all readings were good.

Two, look at the top end 350 packages from More Performance and Doug Rippey. They both include a 52mm throttle body. Lingenfelter's 350 top end kit includes a 58mm throttle body. I'm building mine up in stages and the intake is the last stage. You can bore out a stock TB to 52mm so that's what I did, sent it to David Koldos.

To those who say a 350 doesn't need a 3" exhaust, that's where my 358rwtq came from. The downside is with my 1 3/4" headers into a full 3" dual exhaust, I think mine is weaker than normal from off idle to about 1800 rpm. I can't launch like Mojo at just off idle. It hurts my 60 foot time a lot, but I didn't build this thing for drag racing.

I have a dyno run with H/C changes but stock exhaust manifold and exhaust. About 310rwhp/309rwtq from two sources. Then I got a dyno after the exhaust changes were done to the car. That's the 353/358 I quote in my sig. I just got the TB on and will have to schedule a dyno run with the same guy, John Sealock at Woodbridge Dynotech. When that is done he will print a chart with all three of my runs superimposed. I have to call for an appointment and hope we don't get buried in snow and salt as his shop is a good 100 miles from me.

 

If the intake manifold is ported to 52mm, why did GM slap on a 48mm TB in the first place? Fuel consumption? Emissions? I put on a 52mm and have no dyno results but it does seem to flow accelerate better, especially at high speeds.

 

Why do they put the same 48mm TB on a crate motor 502? Do they have a gazillion 48mm throttle bodies in stock, but never manyfactured a 52mm? Did the engineering teams get crossed up when specing things for the LT1 manufacturing?

Who knows? Whoever does know isn't talking on here.

 

OK, here's the pictures to replace the thousand words you guys have had to read from me.

The first dyno chart is my engine with ported heads and LT4 Hotcam kit, but original cast iron manifolds and a small chambered pipe exhaust. John told me I needed to go bigger on the exhaust, a 3 inch is good for power.



The second chart is from the same dyno with the best run of each of the trips to woodbridge Dynotech. I now have TPIS headers and the full 3 inch exhaust with Dynomax bullet glass packs on the car. (this is not the same pull as the 353/358 I have in my sig, that was at Springfield Motorsports on a good day).



I now have a 52mm TB on the engine as of last Saturday. When I can get back for another pull the best run will be superimposed on chart 2. We will see the result of intake mods in isolation.

You can see how my HP curve drops off at 6200. I hope to fix that with the 52 mm throttle body.

 

My LT4 has 58mm throttle body with intake opening matched at 58mm.....done in conjuntion with other mods.....so can't tell you gain from this mod...

Intuitively a 58mm tb on 52mm openings would perform no better than a 52mm tb, in fact it probably performs worse than a 48mm tb, which is why I suspect the 58mm tb got such a bad rap and no one understood why....turbulance...

Further I am convince that bigger is better for anything before the intake manifold plenum.....

Dyno evidence for tb's seem's minimal to nonexistant.......Lingenfelter goes 58mm and that was good enough for me..

 

You seemed to miss the fine print on his dyno run. The pull with the Holley 52mm WAS ON A DIFFERENT DYNO. I doubt you can find 2 dynos in the country that read within 5hp of each other. A dyno is a great tuning tool if you use the same one time after time.

 

Wait, I don't have a pull with the 52mm TB yet. I still have to arrange that dyno session, I just installed the 52 TB last Saturday. I'm not finished yet.

The two dynos I posted above are the SAME dyno, done at different times and different stages of buildup.

The other pull I talked about with bigger numbers I hadn't shown yet. Here it is, from Springfield Motorsports on a group dyno day.



Now this was a different dyno, and a different weather day. This pull was in December on a dry day with temps in the teens. The SAE correction accounts for the temperature difference, as the SAE correction factor was 0.94SAE. This pull might have given a false peak HP number due to a surge at shut down. You can see that the peak TQ number is true at 358rwtq.

FWIW, the operator of this dyno at Springfield said that he took a car to John at Woodbridge Dynotech for pulls and the results were dead on with the results from his own dyno. Don't let anyone tell you that different dynos are 20-30 HP off. We all go to more than one place and compare the results we get, and good dyno shops do their own comparisons.


Everything I've shown so far is with a 48mm TB and no intake mods