96-98 Cobra N/A Dyno graphs (with IMRCs)?

[Razorback]

Anybody have a link to, or can post a picture of your dynograph? I'm just interested in looking at some dyno graphs of Naturally Aspirated 96-98 Cobras that were using IMRCs at the time of the dyno. Thanks.

[Michael Clements]

Just posted mine in another link. Mostly stock with a few bolt-ons. Here it is again:


Note the broad, flat torque curve. Torque peaks at 5000 but 90% of peak torque is available at 2200. That's the IMRCs doing their job.

The torque rolloff past 5500 RPM is largely due to California 91 octane pump gas. On normal 49 state 92 octane gas the high RPM torque rolls off more slowly and it dyoned 9 RWHP stronger.

The A/F stayed between 12.5:1 and 13:1 through the entire run.

Edited so the picture shows (I hope).

[Blown46Cobra]

I'm not sure specifically what information you're looking for, but I'll provide what I've garnished from real-world testing.

From results provided to me and those from experiments I've done myself, IMRC deletes do little for performance gains and, in many cases, result in driveability issues. The driveability with deletes can be made to be pretty good, but nowhere near as good as with the IMRC's in place. I recently re-installed a set of functional IMRC's on Chris98Vobras car (as well as my own car) and the improvement in driveability is dramatic, even with someone as competent as Chris98Vobra doing the tuning.

Below are some same-day, same-car numbers showing the effect of deletes and intake (testing done by Chris Yates). The car's tune was optimized for each configuration. I've done similar tests on my stock bore NA set-up and my big bore set-up, and found these results to hold true.

IMHO, unless you're building an all out fourced induction drag car, deletes generally do not offer any real performance gains.

Baseline _______ Deletes ____________ Deletes &
Combo _______ Only ______________ SSR Intake
1900 _______ 90 _______ 84 _______ 91
2000 _______ 96 _______ 90 _______ 97
2100 _______ 101 _______ 95 _______ 101
2200 _______ 107 _______ 100 _______ 106
2300 _______ 113 _______ 106 _______ 112
2400 _______ 119 _______ 112 _______ 118
2500 _______ 125 _______ 119 _______ 124
2600 _______ 131 _______ 125 _______ 130
2700 _______ 137 _______ 131 _______ 137
2800 _______ 142 _______ 135 _______ 143
2900 _______ 148 _______ 140 _______ 148
3000 _______ 154 _______ 145 _______ 154
3100 _______ 160 _______ 152 _______ 159
3200 _______ 165 _______ 160 _______ 165
3300 _______ 170 _______ 169 _______ 171
3400 _______ 175 _______ 175 _______ 177
3500 _______ 182 _______ 180 _______ 184
3600 _______ 189 _______ 185 _______ 191
3700 _______ 196 _______ 192 _______ 198
3800 _______ 204 _______ 201 _______ 204
3900 _______ 213 _______ 209 _______ 209
4000 _______ 221 _______ 218 _______ 214
4100 _______ 228 _______ 225 _______ 221
4200 _______ 233 _______ 230 _______ 229
4300 _______ 240 _______ 236 _______ 237
4400 _______ 245 _______ 242 _______ 244
4500 _______ 251 _______ 247 _______ 251
4600 _______ 256 _______ 254 _______ 257
4700 _______ 263 _______ 261 _______ 262
4800 _______ 270 _______ 267 _______ 268
4900 _______ 276 _______ 273 _______ 273
5000 _______ 282 _______ 278 _______ 278
5100 _______ 285 _______ 282 _______ 282
5200 _______ 288 _______ 285 _______ 287
5300 _______ 290 _______ 287 _______ 291
5400 _______ 291 _______ 290 _______ 294
5500 _______ 293 _______ 292 _______ 298
5600 _______ 291 _______ 291 _______ 301
5700 _______ 287 _______ 291 _______ 302
5800 _______ 284 _______ 287 _______ 303
5900 _______ 286 _______ 286 _______ 301
6000 _______ 285 _______ 284 _______ 304
6100 _______ 283 _______ 284 _______ 305
6200 _______ 280 _______ 281 _______ 306
6300 _______ 280 _______ 279 _______ 305
6400 _______ 278 _______ 275 _______ 304
6500 _______ 271 _______ 272 _______ 301
6600 _______ 267 _______ 266 _______ 296
6700 _______ 259 _______ 264 _______ 289
6800 _______ 250 _______ 255 _______ 285
6900 _______ 250 _______ 251 _______ 270

[Modular John]

OK, here you go. I appologize if the pic is a little hard to see. For a better view, you could always save them and open them in whatever photo program you use and zoom in.

First one:
The red line shows the dyno pull when the car was BONE stock, down to the paper filter and 45k miles on the clock.
The blue line shows a pull a few months after a k&N and VRS off-road x-pipe had been installed. I never did a dyno immediately after, but after a few months, I suddenly noticed a loss of performance, so I took it in for a dyno session to see what was going on. With the help of corral I found out my IMRC controller took a crap.


I got the car fixed, thanks to a donated IMRC controller (thanks jslagel), and immediately went in for another dyno session.

Red = The same pull as the blue line from the above pic.
Blue = The pull with a new IMRC controller.

Ignore the green line.

[missouri_guy1973]

Here's my dyno page:

http://webpages.charter.net/horrom/dynos.html

The top 2 are with BBK CAI, BBK pulleys, BBK catted H-pipe, and flowmaster catback, the bottom 2 are the above mods with P&P/short runner intake, IMRC Deletes, UPR Powerpipe and Pro-M 80mm MAF...

Heres a comparison page with a chart like Dave has above...

http://webpages.charter.net/horrom/comparison.html

[slosvt]

[bitemark46]

Lloyd, did u feel any gains after you ditched your tailpipes? -Mark

[JohnnyReb]

Don't have a scanner so I can't post my graphs. With a dyno tune by Jerry, keeping the imrc's and port matching them to the gasket and one of David Simmons' SSR ported intake, my car gained 8 hp and 15 ft. lbs. of torque at 3000. Real peppy down low unlike everyone else with a ported intake that went with deletes. At 6250 picked up 20 hp and 44 ft. lbs. of torque. I'm real happy with the results.

[Razorback]

Thanks very much fellas, that's EXACTLY what I was looking for. Thanks for your time.

[Nate281]

But how would deletes react to a 700rwhp turbo cobra? Would the high end gains be worth the low end torque? Should I even give a damn with that kind of torue? Probably not, making my post completely moot.

[Razorback]

I personally feel that deletes are necessary regardless. The IMRCs themselves are just too much of an irritant with their constant problems (dirty, sticking, actuator failure, check engine codes) to warrant keeping them. I have them on mine right now, but I'll be pulling them as next winter's project with a new lower manifold.

With your setup a turbo or nitrous will create all the low end torque you could possibly need.

[Michael Clements]

Forced induction reduces the need for IMRCs. When you have forced induction, you've got a compressor force feeding your engine. IMRCs still help, but the engine is so much stronger there is less need for them at low RPM, and at high RPM when the boost is really kicking hard the airflow rate is so much higher that even when open the IMRC plates are just in the way obstructing flow.

But for N/A applications the IMRCS work well. Look at all the dynos above and see how flat the torque curves are on these '98-'98 Cobra engines. The '99-'01 engines are a little stronger but their torque curve is more peaky. That doesn't matter much for drag racing but for autox and road racing the flatter torque curve really helps.

[slosvt]

Originally posted by bitemark46
Lloyd, did u feel any gains after you ditched your tailpipes? -Mark

I cant say that I did. I took them off because the either rubbed the tires or rattled on the frame when I pulled them away from the tires.

[97svtsnake]

do you guys have Tweecer or Custom burned chips with your cars.......if these changes i make don't bring on any bigger gains i'll be TT come may

[missouri_guy1973]

Custom burned chip here with my short runner...my graphs above don't reflect the best tune...that better tune yeilded more midrange power and 292/272 peak...