Problem with bigger throttle bodies ?

[Chuck 98 RT/10]

It's been common knowledge that larger throttle bodies on a mostly stock V10 will lower torque.

 

[Vipermed 97.01]

youve just taken one step forward and two back,short of headwork,S.C ect you may gain a modest amt. of H.P but you are going to loose a considerable amt of torque which is where you want your real gains.Also you have a M.A.P sensor which will not change your problem

 

[99 R/T 10]

I am getting ready to add 62 mm TB's to my car, (it has headers), but woulnd not add them unless I was going to also put on 1.7 rockers due to the problem your experiencing. You need to add to you mod list to make use of the bigger TB's. Good luck and let us know how it works out. By the way you can always puat a set of stocks back on.

Mike

 

[MadMaxx]

Hi

I have a little question about bigger throttle bodies for you.
I have a '94 RT/10, just installed the K&N Performance Air Box, opened up the Throttle bodies to 63.5 mm, and the same to the Intake Manifold. Now stragely enough, the car is suddenly not so aggressive anymore, it seems that it has lost some torque in the lower RPM's. My question is, do I have to recalibrate the computer ? Does my model have a 'mass air meter' or a 'manifold absolute pressure sensor' ? Because if I understud it right and I have a 'mass air meter', then there is another problem, because the computer should realize that it gets more air, right ?

Friends of mine said that I should change the headers too now. Others said that it's a good idea to change the headers because I did some modification at the beginning of the chain, but this is not an absolute must.

Now I'm confused, what should I do and where could I suddenly have my problem ?

I would really appreciate, if someone could give me a hint.

A mass air flow meter (or MAS) is a device that measures the amount of incomind air via a tiny heated wire in the center. A viper does not have a MAS, rather it relies on a Manifold Absulute Pressure sensor (MAP).

Now, with that in mind, lets move to the larger throttle body question. Going with a larger throttle body (either by Gen2 swap or porting) will not gain any HP, while most of the time it actually decreases power. On most cars, the throttle body is one of the mods done after a large amount of engine work...gains are nill with just a throttle body swap on almost any vehicle.

Re-callibrating the computer consists of disconnecting the battery for about an hour, and hooking it back up. This will cause the computer to "re-learn" your driving habbits and such, but will NOT affect the lack of low-end torque caused by adding the throttle bodies.


Headers are a good start to making power, but putting on headers while leaving the stock 2.5" (2.25 in some areas of the pipe) is not going to be worth the hassle. Everything on a car should be done in ballance, matching components will always yeild the larger gain. If you have the money for headers, I suggest you pick up a 3" exhaust system w/ hi-flow cats (or no cats) to a dynomax bullit muffler. You have side-pipes, so you might want to just have a exhaust shop fab up a 3" setup for you. The result will be an engine that not only can inhale a good bit of air, but can also expell it without much effort.

If you haven't already, go ahead and do the re-sync of the throttle cables. This can make a world of difference in throttle response! The article on this is located in the tech section, but feel free to email me if you have questions on it.

The real restriction in the intake system is the plenum itself.. but that's a totally different thread

MM

 

[Tom F&L GoR]

Analytical approach:

If the runners are the restriction, then size of throttle body shouldn't matter.

Fuel mixture quality is not dependent on air speed through throttle body (as with carburetors) so mixture preparation is not different.

MAP is MAP, regardless of throttle body.

What is different is the TPS senses a certain throttle position, which normally would indicate a certain amount of air flow. With a different size TB, the same opening angle is now a different amount of air flow. At idle and WOT the TPS should be correct. From this logic, I would assume idle and peak power/torque should be the same, but part throttle driveability might be off.

I am still confused, although lots of you engine guys say it, as to why the amount or quality of air reaching the cylinder is so different because of the throttle body that is 12" or so upstream. The runners are all picking up air from the left and right side plenums (which are larger in diameter than the TB), so the intake runner length does not include the TB.

If I were a molecule of air I would think of the intake system as starting at the plenum, or maybe even at the runner; the TB is merely the barn door that lets me in. I guess I come back to the TPS signal being off.

Engine electronics guys?

 

[joe117]

Giuseppe,
I've got a 94 with 105K. I don't drive much so keep driving and you can catch up.
If I were you I would look on ebay for a set of stock throttle bodies. I saw two sets on there yesterday. One set was $49 at the time. One other set was much more. They are for sale on ebay all the time.
Don't try to mod the car to catch up with the oversize throttles. Put the stock ones back on and keep your mod bodies for some other time after you mod the engine.

 

[joe117]

Tom, Fuels & Lubes,
I think you must be right in your analytical approach. I can't remember if the TPS goes high or low on WOT but there might be a way to experiment by adding a resistor either across or in series with the TPS. Changing the resistor value to match the new, larger, TB opening might prove your idea that this is what causes the engine to be sensitive to TB size.

 

[GTSTF]

you're attaching larger throttle bodies onto openings on the intake that are smaller then the diameter of the new t.b.'s. it's like trying to force more people through an open doorway. i have 70mm t.b.'s installed on my '01, but i had the openings on the intake manifold grinded out to 70mm to match. i have experienced no problems.

 

[GTSTF]

sorry. i didn't notice that you matched the intake openings to the t.b.'s. never mind.