70mm Throttle Bodies Bad?

[GeneralLee]

While I dont have a before and after dyno comparison, I do have seat of the pants. The throttle responce is MUCH better with the 70mms than with the stock. Again, the car may not be any faster, but it FEELS much better when you mash the gas.

Just my .02

 

[PhoenixGTS]

Phoenix, honestly before you shoot down my simple explanation you should try stock throttle bodies. I think you might be surprised.

I'm not hating at all. Just trying to understand why what everyone seems to agree is true is true. My car "might" be different in that I have the rear half of the air box modified to have 3" outlets and I run 3" tubes so my car does not go from the restricted smaller air box to the larger 70mm t-body holes. I'm just guessing though. I still stand by my thoughts on ease of driving. Those Roe cars must be a handful.

 

[PhoenixGTS]

Possible evidence of the problems of 70mm t-bodies

In preparation of having Dan Cragin burn my spare computer with some aggressive software, I took my car and ran it with its regular Mopar High Performance PCM on the dyno. There is a Dyno Dynamics madchine a few miles from my house and work so I went for that. Best machine out there, but reads lower than others so not great for bragging numbers.

Let me follow the air flow in my car to outline the mods: 98 GTS, airbox modified to have 3" outlets, 3" smooth tubes, 70mm throttle bodies, intake opened up to match throttle bodies, stock intake and heads, 1.7:1 rocker arms, headers, stock cats modified to have 3" inlets and 3" outlets with two straight-through mufflers on each side and a cross-over pipe out back.

I don't have runs with stock throttle bodies, but check out how flat my torque curve is when the operator hit the throttle before it gets steep. Anyone have a chart from a similarly modded car with stock throttle bodies for comparison?

Horsepower to the wheels over torque to the wheels (430+ rwhp/490 rwtq)

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Horsepower to the wheels over air/fuel ratio. What a mess. Dan should be able to smooth this out.

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[1BADGTS]

My old GTS was heavily modded.Crower Rods,Ross pistons (11:1)Rotating Assembly Balenced ,Blueprinted Mopar Street,Strip heads (Ported and Flowed )Crower Stage 2 Cam,T&D 1.7 Rockers ,Intake cut oped ,Pored then Extrude Honed.Perfect Power Dfi.One day on the dyno i switched from 68MM TO 70 mm Throttle bodys and picked up over 12 RWHP.But as people have previously mentioned motor was optimized to use added flow.

 

[ViperTony]

Phoenix, I have similiar mods yours sans gears, TB's. I'll post my dyno sheet when I scan it in. With headers, catback, cats, tubes/filters and a Vec3 I came in at 481rwhp and 529rwtq on a mustang dyno but the AFR was rich. My torque curve is similiar to yours but does not start out that flat at all. I wonder if that's the gears? I haven't dyno'd since adding rockers and leaning out the Vec3 tune but say the car feels like it came alive with the rockers. I will do a before/after with the 70mm TB's but probably not until early March. I don't think TB's are worth the bother on a relatively stock engine. They can wait.

 

[PhoenixGTS]

I don't think TB's are worth the bother on a relatively stock engine. They can wait.

When I bought my car used the 70mm throttle bodies where already installed. I would not have gone with them otherwise. Let's see those graphs. If the Dyno Dynamics unit reads 10% low we are very close to each other.

 

[Knight Viper]

When I setup the polished Roe on my car I couldn't get the stock TB to polish up and look good with the rest so that was one of the main reasons I went with the 70mm but the car runs awesome!! Lol

 

[PhoenixGTS]

Follow Up Post.

The new software did not change the power curve with the 70mm throttle bodies at all. Here the after curves in blue and the baseline cruves in red:

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[RTTTTed]

I have the Roe R larger TBs on my ride. Building about 800rwtq at 2000rpm with the Roe means we need more air to produce the much torque. I also have large cone filters, a Macedo built airbox with 3" tubes. My airbox is also open to air in front of the radiator and installed a Roe Racing front fascia scoop.

The Paxton uses a different intake system and has to flow through a single pipe, small intercooler and is a higher hp power delivery so I can undertand that system losing some power.

Ted

 

[vp97]

I have tried a set of 70mm tbs. Idle hung like crazy! So, I put a restricter in the hose for the idle air valve. I think it ended up being around a 3/8 diameter hole. Cured the idle hang. Throttle response was better and it did lean my engine out a bit on the top end. Must have been letting more air in. With such a small hole in it for the idle, the cold start up and the first two minutes of running time was very rough.

 

[ViperTony]

I decided to not install the 70mm TB's. After talking to many folks about this (Thank You), I decided it just wasn't worth it. It seems the disadvantages more than out weighed the advantages. I sold them and put the money toward my boosted fund.