View Full Version : Wanna Make my cobra faster

02-22-2010, 08:29 PM
I am a proud owner of a 1999 rio red convertible cobra. The only performance mod I have on the car as of now is a JLT CAI. The next part is probably going to be a slp catted x-pipe. I would like to know what I should do next. Is there anyone that could give suggestions on parts that would up my performance. I am wanting to atleast make 500hp. I was also wondering if anyone knew how much a stock 4.6l motor can hold. I am a little new to the cobra world, but I am loving every moment.

02-22-2010, 08:44 PM
I'm just learning myself about the Cobra world but just like with any other sports cars that run 305hp on up to 390hp, to hit 500hp the quickest way would be supercharger or turbo.

02-23-2010, 11:13 AM
I am not sure on the 99's motor, but on the 96-98 expect up to 420 rwhp before problems occur. Building the engine up for for more Hp can cost anywhere from $3-7,000 and the same for Hp upgrades and tuning, depending on the routes you take. There is some good info on svtperformance.com as well.

02-27-2010, 02:49 AM
The 99/01 Cobra's are fast cars. However, what I can remember with mine was waiting for 2nd gear to wind out. Unfortunately, the rear gear ratio of 3.27 is a little short from the fun factor. Either 3.73 or 4.10 rear gear will wake up the performance of your engine considerably. Changing from a steel flywheel to an aluminum flywheel will also improve performance.

For starters, the first mod I would make to a 99 would be the coolant bypass fix. There is a kit for it (used to be made by Apten) which connects both heads together in the rear of the engine. This can only be done with the transmission removed.

There are many articles in MM&FF (muscle mustangs and fast fords) magazine that were done on intake plenums for the 4v motors that are better than the stock plenum. This would be of interest if you plan on keeping the engine naturally aspirated. No this will not get you too 500 hp, but if money is of concern, the intake plenum may be a lower cost than a roots or twin screw supercharger. A different plenum will help in the low rpm and high rpm range an could be used with a turbo and or centrifugal supercharger.

To get to 500 hp would be difficult with just bolt-ons without having to rebuild the engine. Of course bolting on a power adder such as a turbo or supercharger is a bolt-on item but the amount of boost that could be applied would be limited due to the hyperetic pistons and powdered metal connecting rods used by ford. When coupled with a 10:1 compression, something will give (hole in the piston, or broken rod) eventually.

Also, you will need to upgrade the fuel system to support the 500hp.

Once you get there, you will also need to upgrade the rear end. There are options for the differential cover, either use a brace or LPW differential cover (more than likely too late to order the Fore differential cover since it is now discontinued).

then there will be the transmission, will it survive the increase torque? It all depends on which transmission you have. I am not sure if the 1999 had the T3650 or the T45 transmission.

As for how much the motor can handle, the 1999 year ended the Itallian made block and is very strong for aluminum casting. If you replace the pistions, connecting rods, and cam shafts along with upgrades to the fuel system you could produce alot of power. However, with the stock internals, fuel system and transmission there will be limits, even with power adders. The limit may not be how much power, but how long will the engine last before it gives out.

02-27-2010, 03:36 PM
One weakness is the plenum. It is not bad but there are better plenums.


The FR500 intake offers variable geometry to improve low end and high end torque. Considering the cost of the plenums, that is a huge chunk of change for the power gained. Since the 99/01 Cobra engine was not build for forced induction, adding a supercharger (roots/twinscrew/centrifugal) or turbo will roughly cost the same once tuned and ready to run. By the time you add up all of the costs, how does that compare to swapping out the engine that is built for more power?

Replacing the rear gear ratio would be the best cost alternative. You could opt for rebuild on the differential traction-loc or replace it with a true-trac differential. Changing the rear gear will make your Cobra quicker but not necessarily faster in terms of top end speed.

03-03-2010, 01:17 PM
I know 550 hp is a hard task but I have always wanted a fast build ride. I know I am going to have this car for a long time. The only thing holding me back is money since I am still a college student. I was wondering if anyone knew bang for your buck parts that are beneficial on the 1999 cobras.

03-03-2010, 01:52 PM
best bang for the buck would be nitrous, and a good tune

03-03-2010, 02:28 PM
The best bang for the buck bolt-on part(s) that would get you close to your goal without need to rebuild engine internals would be a positive displacement(whipple or Kenne Bell) supercharger set for 5-6psi of boost. A tune would also be required to ensure safe operation. Methanol injection could also be added to reduce charge temperatures. A non-intercooled configuration with the stock MAF would net 400HP with a larger MAF that would change to 426Hp. For an intercooled configuration the HP figure would jump to 462hp (non-stock MAF).
Considering the cost/Hp the average comes to $45/Hp.
non-intercooled $4799.00 for 106Hp increase
intercooled $6799.00 for 150Hp increase

Then there would be the additional cost of the tune.

For limited funds, the supercharger route is out of the question.

If you were to swap the gears to a 4.10:1, the cost would range about $159 for the gear set, $300 to $575 in labor to drop the IRS. $379 for a hand held tuner (have it customized for your vehicle which will allow for changes such as CAI, cat-back, different timming curves, etc.... ) There are some gains to be had with a CAI but I would not recommend adding a cold air induction without a tuner to compensate for change in air flow.

The gear swap will act as a torque multiplier and will improve performance. However, there is a bit more to the gear swap than meets the eye. For starters, the differential bushings allow too much movement of the differential carrier assembly that will cause excessive stress on the differential as well as the half-shafts.
cost for differential bushings : derlin $50.00
Billet Flow IRS Brace: $159.00
FRPP 4.10 gear: $159.00
FRPP Ring and pinion install kit M-4210-B : $82.00
FRPP Irs half shaft bearing kit M-4413-A : $20.00
Labor to drop IRS and install gears: $300 (this may vary and exceed $575)

Total cost of gear swap, $770.00. I have included the ring and pinion install kit M-4210-B and the M-4413-A bearing kit which has all parts necessary for rear end rebuilds. However if you are keeping the traction-loc differential, add an additional $120 for the clutch pac rebuild kit. Best to have it done at same time to avoid the labor charge to fix a slipping clutch pac later on. I did not include fluids or cost to calibrate the speedo.

I listed minimal parts that reduce differential movement and a IRS brace to prevent differential cover damage that could result from wheel hop.

The easiest means to gain some Hp other than mechanical mods would be to use a hand held tuner. You can have the tuner customized for your ECU/and motor. SCT X3 tuner with custom tune would be $379. If you change the stock induction system to an after market, JLT is the best. I have made changes to my 2001 Cobra which was a BBK CAI but had issues with running lean. I should have bought a tuner and changed the MAF to a better unit. The stock MAF will peg easily and will be affected when the intake tube in front of the MAF is altered.

The JLT CAI kits are better since the filter is attached to the MAF meter similar to stock, and all bends or curves are after the MAF and not in front of it as some other kits. JLT kits are made from composit materials that reduce the effects of heat retention, other kits that are made out of cast aluminum will heat up and retain heat for a while which affects the IAT sensor which can also result in a lean condition (hot air temperatures lean out A/F due to air density calculations by ECU and if in error due to hot aluminum plumbing expect issues). I have seen combined kits with CAI and tuner for around $499 up to $525. That would net you $20/hp since the net gain is close to 26HP if that is even possible. Most of the combined kits I have seen used the Steeda CAI which is also a good product.

For starters, I would probably do a tuner/CAI combo and hold of the rear gear change later (since now you have a tuner so you could change the speedo /gear ratio when the rear end rebuild is accomplished).

There is also the underdrive pulley kit that will reduce the amount of paracitic drag on the engine. However, slowing down the water pump may not be much of an advantage, may be cause for issues later on.

03-03-2010, 03:13 PM
What nckissfan said is also another alternative, but don't get caught using it on the street. The dry kit would cost less money. Wet kit will be more expensive. Tune is most important part. Then there comes to mind, where to refill the tank when it gets empty and what does that cost?

Overall, the kit ranging from $350 on up will offer best bang for the buck in terms of added HP. Operating costs will be affected on when and how much you use it. Of course there could be issues if there is a leak in a solenoid valve and the system has pressure. That would be adding an oxidizer to the engine bay in case of fire due to accident which is why it is not street legal. I know, take the fun out of it.... In the short term still the best bang for the buck considering the cost of kit and install time.

On the lighter side, a NOS system does not introduce paracitic Hp/Tq losses associated with superchargers or increase back pressure from the turo. Since you will not always be using the NOS system so there is an advantage to MPG when compared to forced induction which will always have a presence in some form or another (however, you can use it anywhere legally).

03-05-2010, 01:01 PM
Thank you for the recommendations on what parts I should consider. Hopefully within a few years ill be closer to my goal.

03-05-2010, 07:03 PM
There may be other options, I am no expert so take it for what it is worth. I have not had my 01 since October of 04.

I had a friend who had a 99 Cobra. Did the 4.10 swap and said it felt slower simply due to the difference in shift speeds. Many sware by it to be the best gear. Regardless of what gear you go with, hard to avoid the labor cost in dropping the irs. I have seen somewhere (may be svtperformance) how to remove the differential without dropping the IRS. Has given me something to consider since I am going to rebuild my differential assembly soon.