Throttle bodies

hytorksc

Registered User
I max bored a stock TB leaving no inner ridges, and made a new heavy brass throttle plate for it. Took me 6 hours to complete, installed it, and it worked very well idle-wise. However, I noticed that it did not respond as crisp as the old one (I have 2 of them, 1 unmodified). I went this route to avoid buying a 70mm. The modded one did not make much of a difference in performance- in fact I think it made no difference. I think it reduced some lower and midrange torque (softened the response). I was expecting better top end performance WOT. Does a larger TB necessarily improve drivability and acceleration? I'm thinking that it helps during high air flow conditions (3rd gear above 90mph) although I didn't notice anything with my modded TB. What are your experiences with the 70mm TB- does the low end torque increase? Does the engine respond quicker? The stock one seems better maybe because of better air velocity at street speeds. I get more wheelspin with the stock TB. I have max ported my M90, ported just about everything else except heads, 73mm MAF, modded air box, 5% pulley, underdrive pulleys, raised top (even bored this out more), max adjusted the TPS. Why does the stock TB make the car feel faster? I ran with a new WS6 easily past 110mph with power reserved with the stock TB- it felt like I could overtake him. I'm getting globs of torque throughout the power band with a stock TB and very mildly modded exaust. I don't get it-

Randy
'92 SC w-AOD

Sorry about the long thread-
 
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What do you mean max adjusted you TPS? That’s probably your problem. On a fuel injected car drivability should not be affected by the size of the throttle body.

On a carbed car it can make all the difference. Going from a 750cfm to a 600cfm carb, made a noticeable difference in drivability. In a carb the velocity of the air through the venturi makes a difference in the way fuel is atomized. The larger the bore the slower the air moves and the lower the signal strength. On an SC it doesn’t really matter, especially since the air is really churned up anyway.

Jeff
 
TPS adjustment

I adjusted it very, very slightly rotating it in a clockwise direction as far as it will go with the screws in place (if it has any play in it at all). What this seems to do is increase throttle response, probably increases fuel and/or timing very slightly for a given throttle opening. The pcm will probably re-adjust the system for this setting using it's adaptative abilities, but it still makes it run harder. I know it's sort of a crude way, but it works well for my SC. It doesn't throw any check engine codes either. You ought to try it.

Should I look at installing the 70mm TB? Can I actually feel an increase in response and performance from a street driving perspective? Or is it not worth it- I'm not going to be driving the car at constant triple digit speeds.
 
Id say you would loose a tad bit of throttle responce with a bigger TB..However WHat you did with the tps is a nono...Generally I get best rersponce at around.91...if teh computer sences mor evoltage from your tps it will in turn make your car run richer..To rich...less Throttle responce..Check with a voltmeter and see what reading your actually getting
 
Id say you would loose a tad bit of throttle responce with a bigger TB..However WHat you did with the tps is a nono...Generally I get best rersponce at around.91...if teh computer sences mor evoltage from your tps it will in turn make your car run richer..To rich...less Throttle responce..Check with a voltmeter and see what reading your actually getting
 
Please explain why you would loose throttle responce with a larger TB on a Fuel injected car.

Jeff
 
To Damon and J57ltr-

Thanks to both for your prompt response. Damon, I will return the TPS to the original position and reinstall the larger TB and see what happens. I don't mind losing a little low end throttle response if there is some strong compensation in other areas of performance like a top end increase THAT YOU CAN FEEL- otherwise it's not worth it from a street perspective. From a racing perspective it's worth it. You hear about guys installing bolt ons that yield 10-20hp on the top end (5-6k rpm), you will hardly feel any difference down low- in fact you may perceive a loss of power if driveline components are still stock. At this point you must install a slightly higher stall converter with bigger rear end gears to really feel an instant benefit from these bolt ons (but again you compromise top end speed). How does one get around this? Can't afford this right now.

I do like the instant wheelspin that the smaller TB brings. If I use a large TB (like a 70mm) I guess that means I will have to install a higher stall converter when it comes time to repair or replace the AOD. All I want out of the SC is to maintain strong low end torque and to increase and maintain mid-high end torque at the same time. I am looking for ways to do this without compromise. Most every posting I see in this forum relating to a bolt on there is some loss in one area for a gain in another. Our cars are just too heavy to lose any low end torque- thats why Ford originally designed the 3.8 SC to put out 315 lbs-ft at 2600 rpm. Thats why this car is fun- otherwise it would be a slug. I would say that Ford intentionally neglected air flow through the heads to prevent big horsepower numbers (and other marketing reasons). Aside from what Coy Miller and Fred has done, how does one on a miniscule budget fatten torque dramatically all the way up the rpm band? I guess there's not much you can do but improve air flow where you can and experiment (in a conservative way). I would love to see 500+ lbs-ft from the low end all the way up (just a dream for me, I can't afford this).
 
You know I suppose that with all the nasty plumming and bends in the intake/exhaust system that the only thing that would really help increase power significantly is to open up everything from intake to exhaust including the heads, installing the proper fuel management components, and overdriving the supercharger as much as can be done to compensate for air velocity losses without destroying it's reliability or engine reliability.

I mean you see Toyota Supra twin turbos pushing 20-23psi into their motors and those cars perform unreal (and they don't have all that plumming we have and their engines stay somewhat reliable).
 
If I use a large TB (like a 70mm) I guess that means I will have to install a higher stall converter when it comes time to repair or replace the AOD. All I want out of the SC is to maintain strong low end torque and to increase and maintain mid-high end torque at the same time.


Where did you get the idea that your going to loose torque or bottom end power by going to a 70 MM TB? That is simply not true. If anything the throttle should be more responsive.

If you were adding an 83MM with stock heads and cam you might have some problems with too much air when you first crack the throttle plate, but even that won't cause a loss of low end torque or HP.

Good luck, David
 
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I really don’t see why a lot of people think that putting a larger TB on their cars is going to reduce drivabality, and low end torque. It doesn’t make any sense. You can throw all the bolt-ons you want they are not going to lower your low end if anything it will increase it. Unless you have sewer pipe exhaust then that isn’t going to lower torque either. Most people claim that they loose torque when they add a larger better flowing exhaust. I am pretty sure that they will run out of fuel and start running lean so they perceive a loss in torque, Especially when a 10% pulley is used.

Jeff
 
So what you are saying is that a large TB will not reduce low end power, but it will maintain it at the very least and increase power progressively thru the upper rpm ranges (if the TB was a restriction).

Maybe my reaction was psychological. I put a larger TB on the car and I just didn't feel any more power. It seemed to be less responsive on the low end (softer pedal response or maybe the power slid up the band a little) and it did not feel any different all the way up to 90 mph WOT. Maybe I would have felt something beyond 90 where larger CFM numbers are generated.

Smaller bore TB within a defined speed range=high velocity air (lower volume)
Larger bore TB within the same speed range=lower velocity air(higher air volume)

Just because you enlarge a TB does not mean that more air is going to flow thru it than required. The engine is only going to pull the amount of air that it requires for that same speed range. But if you are full out racing (rpms high all the time, using much more fuel), the larger TB would work better because you have higher velocity and volume.

In the street driving mode I guess the difference can be registered by the MAF relating signal to the EEC in terms of how fast the heated wires are cooled thus changing the fuel and advanced timing- changing the acceleration characteristics accordingly.

Please correct me if I'm looking at this all wrong. All criticisms welcome.

thanks-
 
Well it looks like you got it, but I think you are putting to much on the velocity of the air through the TB. On an FI car it doesn't matter. All it is doing is limiting the amount of air entering the engine, nothing else. Problems occur when people just bolt everything back on without checking the TPS to make sure it is set correctly and not setting the air bleed that is in the side of the TB for proper idle.

Jeff
 
It is not that you are running too rich (that I can tell). The TPS tells the EEC where the throttle plate is, and the rate of change. IE Are you cruising, coasting, idling, WOT, etc. and are you easing into the throttle or did you just slam it wide open (for accel function). Your missing the air bleed also needs to be adjusted.

How exactly did you bore the TB larger?

Jeff
 
Like always opinions are a dime a dozen..I have mine, you have yours, he has his, she has hers....I'm personally going on personal experience as well as what I have seen on a dyno with my own cars..With a bigger opening you do indeed loose velocity and in turn can loose some throttle responce and generally do...Perhaps Ill do a little experimenting at the dyno with my car when I get my blower back..Havnt dynoed the good ol SC as of yet
 
Opinions are like a**holes, everyone has one.

What you fail to see is

1. There isn’t any sensing device in the TB for measuring air. The TB doesn’t care how much air passes through it.

B. The velocity of the air through the rest of the system is the same for the same amount of power produced (except where the power is going to be higher, the top end). Meaning toh only place where the air velocity is going to be different is though the TB. It won’t, can’t, doesn’t care how much air flows through the TB, and that’s a fact.

Years ago I watched along as Car Craft put a 1000 CFM throttle body on a early-mid 90’s trans-am. They actually lost power, the car had a hard time idling, and drove like crap. Well a few issues later they fixed the vacuum leak.

In summation, Big TB Good, No problems unless you are the type that bolts stuff on and wonders why you are having problems, you just blame the part.

Jeff
 
Jeff-

You must have a ton of patience to do this but here it goes-

I bored out the TB the old fashion way since I don't have the proper tools- I removed the throttle plate, and carefully used round coarse and medium metal files by hand to get rid of the inner ridge of the body where the plate/shaft is housed and made it flush- yes it is not perfectly round and you wouldn't notice it by just looking at it anyway- but I didn't care about that (took several hours). I also used a ryobi drill press with a fat roto zip bit to cut down the thickness of the fat shaft that the plate is bolted to. Then I fabricated a thick brass plate (.018" approx. thickness) and used a pair of large metal shears to cut out a rough circle (used old plate as a template). The process after that took 1 hour to trim and work the metal down to match the inner circumference of the throttle bore (very, very difficult to do). I trimmed it far enough until i could insert the plate to near the proper seating on the shaft (a little oversized at top/bottom), then started trimming the edges using a combination of metal file and shears. When I did this the first time i did not have much faith in it working successfully. But when i finished to my surprise the plate actually matched the bore pretty good- no large gaps. After rough matching the plate, used sandpaper to smooth down the edges. Marked the screw holes on the plate and used the drill press to bore the mounting holes- very, very carefully. Compared the stock TB and the modded one to match plate position and trimmed down as necessary. Smoothed and rounded plate edges again. Whew!!
ensured throttle plate movement did not bind, trimmed as necessary, fabricated and pressed on one brass shim on the shaft at the TPS side of the bearing to prevent side to side movement. readjusted plate position and tightened it.

adjust air bleed screw to closed position, installed TB, fired up the engine, made final adjustments to balance idle at 700 rpm in D.

Is this enough? Probably more than you wanted to know.

Results: very good performance-wise, no major gains on low end power, but slight gains in upper mid to high rpms.

long thread-
 
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TPS

I did reset the TPS to it's original position, and re-installed the larger TB. I think this answered my question about acceleration feel difference from the stock TB. I made a test run last night and noticed slight power increases in the mid to high rpms.

Bottom line: bigger TB's are better for overall performance improvement especially high end.
 
yeehaw!!!!!!

J57ltr said:
Opinions are like a**holes, everyone has one.

What you fail to see is
Jeff
Wait a minnit! Let me go nuke a bag o' popcorn, this oughta be good! :)

When ya get done, get yer butt over here an' help me strip some parts off that white 5spd. I got a case of Coronas waitin' on ya!

'bird
 
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