Skip the next 2 paragraphs if you don't want to hear me sob story and make this a bunch shorter.

Alright, a little background. My car had a number of small issues, including timing, plugged up cat, etc, that were found while troubleshooting a hunting idle and a problem where the car would stall when you put it into gear unless you gave it just a touch of gas.

In the process of troubleshooting, lots, and I mean lots of stuff got replaced, tuned, etc. One thought by the guys at fast chip and at Scoggin Dickey was to swap out the 58mm BBK throttle body with the stock one. I did this and the car got better. Not great, but a little better. And that's how I drove it around for a little while. A mechanic friend suggested that I try running a vac line from the intake out to the airbox so that the motor would get a little more air, filtered, through a controlled vac leak. I tried this with the BBK before swapping to the stock on, except I had the line going from the duct between the maf and t/b. With the stock t/b on and the vac port on the intake capped, a week later, I was tinkering and decided to try to run the line to the airbox. And it worked great. I backed the throttle blades off a bit and readjusted the tps voltage.

Going to the track tonight, I figured it was a good oportunity to test out the stock 48mm throttle body.

Here's my setup:
-GM Perf ZZ383 shortblock(3.8" stroke crank, 350 bore) decked to give a 10:1 compression, balanced and blueprinted, some stronger bottom end parts etc
-Edelbrock E-Tec 200cc heads
-LT4 hotcam
-1.6 roller rockers
-SDPC/Edelbrock vortec head bolt patterned lower intake
-Super ram runners/upper intake

The track I run at is at 4900ft and the air density is usually much worse. It also doesn't yield good 60ft times, 1.9's are my best, with most being in the 2.0 and 2.1 range, regardless of whether I'm on drag radials or ET Streets. Seems like I need to go to a higher stall converter, since the one I'm running now is a few hundred rpm higher than stock. The track is consistent though, and is great for testing mods. Using the NHRA conversion for altitude, times in the 13-15 range are about a second off, with the slower you go, the more you would gain at sea level.

Anyhow, back to the point.....

I made two runs with the stock throttle body. Both were much slower than I'm used to, both in mph and et. My times were 14.07@96.4mph and 14.23@96.8mph. These seem really slow, and they are, but at 4900ft, the 14.07 would correct(only for alt, not weather and these runs were all made with the temp between 85* and 97*, with about 40% humidity and 29.8 barrometric pressure) to a 13.21@102.6mph, which isn't great, but not horrible either.

I swapped back to my BBK 58mm and on the very next run, without changing anything, I went 13.80@101.9mph. This would convert to a 12.96@108.4mph. The rest of the 5 or 6 runs were very similar in both et and trap speed.

Now, I know that's not that great for my setup, but this was also my first time on the tires I was running. The best the car's done with the 58mm t/b was 13.5@101.2mph. I'm sure I'll get better once I figure out the tires, since my 60ft times aren't very good. I know I'll never see 1.6 or 1.7 at this track, but 1.8's should be there with the et streets.

Enough explaining, the point is that with just a t/b swap, on a high flow motor, I picked up nearly 3 tenths and 5 1/2 mph. I know a lot of guys that would kill for 3 tenths.

I was also assured by several mechanics, friends, motor builders, etc, that going to the smaller throttle body would lose a bit of top end, but pick it all back up in torque and run similar times. Not so. On a built motor, the stock throttle body can't flow enough to support it. There was a very, very noticeable loss of responsiveness, top and mid range power, part throttle power, etc with the stock throttle body as compared to the 58mm.

All in all, it's much less fun to drive, both on the street and track with the stock throttle body. I didn't have a 52mm to bolt on, but I think I'm going to stick with the 58mm for now. BTW, the test was a little biased. The computer never had a chance to learn the bigger throttle body. I reset the ecm when I got the stock t/b running right, but not when I bolted on the 58mm. I suspect the slower overall times I ran tonight with the 58mm t/b have a lot to do with the computer not really knowing what's going on. Last time out, I was running 13.7's with very similar weather.

I don't think a t/b would help much on a stock motor, especially an L98, but maybe a little bit on an LT4, but if you're running a head, cam and intake package, you may want to look into it, if you haven't already. It's a difference that's very noticeable sotp on the street.

Chris

 

When my car still had the stock LT4 with all bolt-ons, I swapped to a 52mm TB with no other changes. I picked up a .10 to .15 consistantly with the same weather conditions and 60' times. I forget about the MPH though.
In the winter I swapped to a 58mm for the 396 but haven't had it to the strip much yet in good weather to see if it helped any. The car feels like it has less traction. Maybe I'll throw it on the dyno at Carlisle to compair it to last year.

 

The debate about when to switch and to what size will no doubt rage on forever here. But it only makes sense that at some point as the breathing is improved on an engine that benefit can be derived from increasing the TB size. Like many other things, researching results from those with similar combinations and then just trying different things is the only way to optimize anything for a given car. Good post and I'm sure some will benefit from your experience.

 

Nice to see some facts related to an ACTUAL experience.......

My view is bigger, up to 58mm, done properly will never be detrimental, so why not......

 

Well, I don't know. I can see where loss of torque and throttle response on a very mild, read stock, motor would be a factor on bigger t/b. I don't think a 52mm would be an issue on any motor, but obviously, going to a 58mm on a 245hp or 300hp motor probably isn't the best idea.

I was quoted by the Ed Wright guys that when they swapped from a 48mm to a 58mm throttle body on a 500+hp LT1, they could lay the dyno curves right over each other. I really didn't buy this for a second. I can maybe see torque going up and hp down with the smaller t/b, but there just no way they'd make the same power curves. Using that logic, a super ram, mini ram and stock tpi would all have the same curves, despite the vast differences in flow characteristics.

I would also imagine that the altitude I run at would make a difference more apparent. At 4900ft track altitude and 6500-7000ft where I drive it on the street, anything you can do to get more air into the motor is going to show.

Chris

 

I'll vouch for Ed's observations. I had two dyno runs about 18 months apart. In both runs, the motor was a 383 with a Superram and hooker headers.

The first run was with 24 lb/hr injectors, the stock TB, and version 1.0 of the PROM...no speedo meant the Torque converter wouldn't lock up.

The Second run was with appripriately sized in jectors (28? I forget), a 58 mm TB, and a lockup switch for the TC.

Before the TC lockup, the dynos were virtually identical. (after the lockup, the motor produced a good additional 25% of area under the curve.)

BUT. I'm starting to question the veracity of comparing dyno graphs. They just don't paint the whole picture. Sure, they're great for feedback in tuning the car, but this piddly little 290 rwhp motor is faster than a Z06, mostly due to the _other_ things that have been done to it.

I'm just now finishing up hardening the driveline and swapping in 3.54 gears. (From 2.52) Will it affect the dyno? It shouldn't. Will the car be a TON faster? You betcha!

When swapping the TB, I noticed an immediate improvement in part throttle response as more air per degree of blade opening happens. Will it flow more on the dyno? Perhaps not, but it just might make a difference when the fresh air source isn't just a fan pointed at your radiator.

 

FWIW, LPE says that their SuperRam requires at least a 52mm TB to be fed enough air, with a 58mm being optimal. When you buy the SR/219 package from them it includes a BBK 58mm. I've got a 52mm (ported stock) on my SR right now but eventually will go to a 58mm.
[RICHR]

 

The problem is testing on a dyno on 2 different days. ON some of the blower cars that are really sensitive to heat you can see 20 hp difference without any changes on 2 different days. For instance I did a car that only put 500 down in the summer, but without any difference in his setup the car did 520 base the next go around.

I find it interesting that the car picked up so much, One day when I have tons of extra time I would like to try a back to back on the dyno. That would be very concluesive also.

I went to the track immediately after I swapped to a 52 and didn't see any gain from the week before.

I appreciate the test, its always nice to hear first hand expereience.

 

I picked up 3-6 on both numbers when I jumped to the 58MM.

My dyno runs where about a week apart, and fairly similar weather conditions, and around the same time of day!!!

 

On a 383, I don't know where the difference would be, but on a 350, unless you are spinning over 6K, I don't see where you need a larger TB.

Tom Piper

 

Mine was on a 350, and those are RW numbers from a Mustang Dyno.

It does make a difference, or at least in my situation it did!

 

Just from what i have seen on this board, every back to back run on a dyno I have seen with a modified motor has produced more HP with the bigger TB. I agree that a stock motor might not gain a thing but even there I have yet to see anyone post back tp back results with a 52MM TB. I had a 52 and after reading a post of a set up almost identicle to mine that gained 6 RWHP with a swap from 52 to 58 I decided to get the 58 and have never looked back. I think post like this one are great data for us all to learn from and if any one has lost power with a bigger TB and has documented it, hopfully the same day as that would be best, that would also be good info to stick into the databank.

 

Well, to be honest, I'm playing 'find the bottleneck'. Before lack of tranny cooling cause it to get unhappy, we weren't sure if the rear gears or the crappy rear y-pipe in the exhaust was causing it to make less power than it could.

Now the tranny's repaired, the driveline's hardened with a better gear, and the TC is customised for the car (it originally came off a heavily modded Typhoon, when the trany let go, I had them rebuild it for my needs.)

So, it could very well be that the 58 makes a difference in a bigger motor, I'm just not producing enough power for the TB to be the bottleneck.

 

The main reason I don't think a larger throttle body will make a difference on my modified (350 cubic inches with AFR heads and a Crane cam) '92 LT1 with an A4 is because I datalogged a WOT run.
I only spin to 6K.

That datalog shows that the MAP sensor (kpa reading) is telling me that the intake manifold vacuum at WOT is almost the same as atmospheric pressure.
If I had any restrictions before the intake manifold (air cleaner or Throttle body), I would have some vacuum in the intake -- the MAP sensor says there is none.
Unless a larger throttle body is going to start to put positive pressure in my intake, it won't make any difference on mine.

Tom Piper

 

Tom Piper,

You're also relying on the ECM and sensors to tell you what the engine is doing. I don't know if I'd trust the sensors that far... especially when you're talking 6-10HP out of 320+ or so. I won't debate the sensor resolution versus power change with you but it seems that to find one factor that supports a theory and subsequently ignoiring all other signs for the opposing view is just bad science.

And of course every combo is different - some people like to say VE % vs supported airflow, etc etc - but my limited experience says you just never know until you try it. And third-party testing (ie dynos and or ET's) is just about the best you're going to get for these cars as far as "proof" is concerned.

My hat's off to the original poster - great read. I have a SR/219 built combo and I may consider upgrading to a 58mm at some point in the future.

 

I posted because there's a number of myths regarding throttle body size. I hope it helps some guys decide which t/b to run. I knew there was a loss of top end the moment I bolted up the smaller throttle body, but I wanted to see if the extra air velocity would produce enough extra torque to run similar times. It just didn't.

Now, on a stock motor, I don't think there would be much difference. I've also never heard of anyone losing power, at least sotp. I wouldn't mind trying a 52mm out at the track and seeing how it does. Then again, it'd be another 250 or 300 I'd have to spend to find out.

Another thing that will be interesting to see is how the car does after letting the ecm learn and correct to the bigger t/b. The car was driven for about a week with the 48mm one after I reset the ecm, but only driven from the pit area to the staging lanes, then through the burnout box before it hit the track. I believe it could see even better times(as it has in the past). I've seen consistent 13.7's(at altitude) with the 58mm and the same setup, but with drag radials instead of et streets.

Overall the car does feel much better than it did before. The effect of the smaller t/b is similar to how the car feels when the fuel pressure is set low and I'm running at wot. Just feels like it falls on its face after 3k rpm.

BTW, I didn't mention it before, but I have the wot shift points set to 6000rpm, which, according to SDPC, who built the motor and dyno'ed similar combos, is a few hundred rpm higher than where it peaks.

Once again, glad this may help someone. Figured you hear so much "my friend dyno'ed this," and "a guy I know ran that," that it would be nice to hear it from that guy.

I also have to say that I don't think the car picked up 5 or 10hp from the swap. 5 or 10hp just doesn't make the car run nearly 4 tenths and 6mph faster. Neither do weather conditions when the runs were made within 30 minutes and a few degrees of each other. And actually, the first run on the 48mm was made at 97* and was 2 tenths quicker than the second, which was 95*. The first run with the bigger t/b was about the same temp as the second, maybe a degree cooler.

Chris

 

not a bad read at all, but does anyone have any experience here with the monoblade tb that flows something like 1300cfm?? i was thinking about that one for the maro i just picked up with a 396 bottom end, stage II heads and fully ported LT1 intake, Comp Cams XE NOS cam, etc...

 

Long before making the mods to my engine (about seven years ago), I did several calculations on a 350 cubic inch engine at 100% VE and determined a larger throttle body would not help me up to 6K rpms -- I wish I had the figures, but I didn't keep them.

If I remember correctly (but don't quote me on this), it sticks in my mind, at about 6200 - 6400 rpm and 100% VE, a 350 cubic inch engine will start to flow the maximum of a 48mm TB. And, at 85% VE, the 48mm was good to about 6800 rpm on a 350 -- way beyond my 6K limit.

That's part of the problem -- I did all of this many years ago to prove to me what I wanted to do. And, it was so long ago that I moved way beyond this discussion.

And, about five years ago, the datalog of the MAP sensor confirmed it.

Another thing I should point out:
When I bought my '92, I did some initial scan-tool tests of the system.
My throttle body opening with my foot to the floor was 85%. And, I have seen other C4s with the same problem. I fixed that problem with some minor adjustments to the throttle system -- including getting the mat out from under the throttle pedal.
So, I can easily see where someone may have a less-than-maximum throttle opening, install a larger throttle body (at 85% a larger throttle body is going to flow more than the smaller one at 85%, and maybe fix a linkage problem) and see an improvement.

My suggestion is to do the math (even at 100% VE, which you probably won't see) and see how many CFM a 350 cubic inch engine will flow at 6K and compare it to the stock throttle body CFM rating.

Tom Piper

 

Tom,
It was said earlier, that the combo I was running was a 383 but I have heard similar on the 350 about not using all the air.

I also noticed mine wasn't getting 100% throttle opening when on the floor. My throttle cable had about 3/4" of play. I did the simple thing, swapped positions of the cruise and throttle cable. Now the cruise has to open a bit more to hold the same speed, but the gas pedal gives me full opening on the t/b. This was about a month ago, long before the other night at the strip.

Something to look at, since I also suspect many aren't getting true wot.

Chris

 

who mkaes that monoblade TB? i think ur right it flows about 1300cfm. i think you might actually want something like that if you are spinning over 6500rpms with a motor that is making well over 500 flywheel horsepower