Tyler09

alright i just got the mustang last week and i have read alot on here and what not look at alot of post/ pics... but have some questions might be dumb to some but im new to the scene and would like to learn some stuff.

-what is IRS?
-what TB should i do? (going to be a daily driver)
-if i do H&R SS springs do i need camber casting plates?

again if these seem dumb to y'all sorry.
thanks for helping guys.

mrtstang

IRS = Independent rear suspension
TB = 70mm or 75mm
C&C plates = helpful but not completely necessary

02GTman

Welcome to the Mustang world and the Forum. To answer your questions.

1.) Independent Rear Suspension, this set up came on the 99-01/03-04 Cobras.

2.) I think most of the guys on here run a 70-75 mm TB, either will work just fine.

3.) They say if you go lower than a 1.5 drop with springs you should do caster/camber plates. There's a guy on here who runs H&R's with no plates and has no problems with out them. But it is recommended.

Hope this helps.

02GTman

Sorry mrtstang we must have posted at the same time.

mrtstang

Haha it's alright, at least we think alike.

Tyler09

thanks for the feed back, so my 98 GT doesnt have IRS.

Rockwell28

No it doesnt, the cobras have the irs unless someone put irs on there before you got it. if so your pipes/exhaust in the back would be routed sorta under your gas tank not over the axel and beside the gas tank. take a look at afew pics of the a$$ end of a cobra and look towards the bottom vs a gt and you will see it clearly.

cliffyk

The upper plenum is the weak point in the TB/plenum combination, unless you replace the plenum too a larger TB will not do much for you. Here are Accufab's flow numbers backing that up.

You can see that any aftermarket plenum (except the C&L which did not do well overall) with the stock 65 mm TB flows 30 to 50 CFM more than the stock plenum with a 75 mm TB.

You will also need a tune/tuner to see much of any gain from a TB/plenum upgrade.

Without a tune the engine will feel more responsive because for the same accelerator pedal positions you are opening up a bigger hole in the TB--however up to 5k RPM or so the same thing could be accomplished by just stepping on the accelerator harder--so the "power gain" and "faster response" reported by most is largely psychological (I.e. "in your head").

After 5k RPM, without a tune, the engine will pull harder up to the rev-limiter at WOT with an upgraded TB/plenum. However as most street drivers rarely use that end of the powerband this can be almost irrelevant from an empirical perspective.

As to the springs I agree with the others, it will be close without CC plates but they are not essential. You may have to live with negative camber at the top end of the factory range (-1.25°+) which will cause slight cupping on the inside edges of the tire--the payoff is much better handling in higher speed sharper turns as it reduces the tendency of the inside tire to roll under ("plowing"). I purposely run -1.4° camber for this reason.

The strut tower mounting holes for the OEM plates can be elongated a bit (1/8" to 3/16") which can buy a bit of camber adjustment.

Tyler09

Thanks for the good info, so its the better to get a new plenum and bigger tbI have a tuner a superchips, but it's a older one. Is it better too get all the performance parts on it and get the car tuned instead of a hand tuner?

What's Isos?

cliffyk

Hope you are ready for this?

On your 1998 non-PI engine there is really no need to upgrade the TB or plenum as the intake manifold and heads do not flow well enough for there to be any significant gain versus the stock components. That the PI engines gain a bit with TB/plenum upgrades, even without a tune, has more to do with that Ford did not change the TB/plenum when they did the PI update. I.e. the caried forward 65 mm and plenum were really inadequate for the PI engine.

If you want to add significant power then save your money and do a PI upgrade. You then have actually a slightly higher potential than a factory PI
engine as the compression ratio will be higher.

As to tuning, if you are willing to learn to do it yourself you will be able to have a better tune than can be created on a dynamometer because you will be able to tweak it out in the real world. A dynamometer is just a convenient tool for measuring engine output and thereby allowing the tuner to gauge the effectiveness of changes to the tune without actually going out and testing under actual driving conditions.

That's all, there is no magic involved.

OTH on a race track or deserted stretch of back road, all you need is a stopwatch (or better yet a accelerometer based performance tool) to measure the real world performance of your vehicle--complete with all four tires rolling resistance, real affects of aerodynamic drag, etc.

If dyno tunes were the be-all and end-all you wouldn't see pit crews making last minute adjustments to fueling and timing, during the race/between runs as conditions change.

So as to which is "better", IMLTHO (less than humble) doing it yourself is the way to go. Start with Greg Banish's excellent book Engine Management: Advanced Tuning and read it 2 or 3 times at first, then use it as a reference from then on.

The other advantage to DIY tuning is that YOU can make changes to the tune as you upgrade and further modify (and as the seasons change) without having to pay someone else to do it.