98 Cobra Swap into 98 F150

[Anddy_C]

Hi Everyone,

I'm new to this forum and fairly new to the Ford world so a quick little aside about me. I started wrenching on RX-7's when I was younger, got tired of rebuilding rotary engines and moved on to pushrod V-8's. Specifically 350's. I hate to admit it sometimes but they are far easier (and cheaper!) to work on and customize. Anyways, I am hoping you can help me decide which way to go on my upgrade path for my new (to me) F150. My last truck (yes it was a Chevy) was stolen in January of this year :-(

One thing before I get to the point - I am posting this here because you guys seem to be the most knowledgeable about Mustangs. I don't think the folks on the F 150 forums are going to have the know-how to answer my questions. So, I apologize for posting about my truck on a Mustang forum.

Starting point:

• 1998 F 150
• 4.6L 2V
• 3.55 gears non limited-slip (sigh....)
• 160,000 miles
• Automatic transmission
• All seems to be in good working order. Recently tuned up (plugs, wires, coolant flush, etc) by me
• I'm not sure if the engine is Windsor or Romeo. Need to research it and identify it I suppose
• I think those are probably the only relevant details. Let me know if you need more

My (modest) goals:

• 300 hp and 300 ft-lb to the wheels on pump gas (preferably 87 octane)
• The beautiful Ford V-8 exhaust growl
• Something that is civil enough to be a daily driver (AC, power steering, etc)
• It must pass emissions since I live in Atlanta, Ga. Here, on 96 and newer vehicles, they do a test where they plug into the OBD-II connector. From there it is a simple pass/fail. There is no sniff test, etc.
• I want to retain the existing automatic transmission (Atlanta traffic really is as bad as you think)
• Gas mileage greater than 10 mpg
• Make friends jealous
• Turn heads on the street
• Attract women
• World domination..... etc

I am considering two options

Option 1:

• Purchase these Patriot Performance 2V Stage II cylinder heads from Summit Racing
• Add these Comp Cams
• Custom tune, etc

I don't really have many questions about this option and I think it will be fairly straightforward. I just wanted to put it out there for reference to my other idea. I have read two different writeups online that have installed and tested this and I think I can get to my goals of a square 300/300 with this setup.

Option 2:

• Purchase and install a used Cobra engine (there is one available locally that I have my eye on for significantly less than the cost of the cylinder heads and cams)

I have only been able to determine from my research that I will need:

• 8 bolt flywheel
• 4V exhaust manifolds
• imrc delete plates (what are those?)

I know I will need larger fuel injectors, a custom tune, probably a higher flowing fuel pump, etc. I really need some help on the big picture questions like:

• Can I use the existing ECU?
• Will it bolt up or do I need custom motor mounts?
• Can I use the existing transmission?
• Can I use the existing ignition system?
• Will it pass emissions (and what would I need to get it to pass emissions if not)?
• What other "gremlins" are out there that I am not thinking about?

I would love to see a thread or a writeup somewhere online from someone who has done this before.

I really like the idea of the Cobra motor because it is unique, I can build it in the garage on the stand at my leisure, it has less than half the mileage of my existing engine, and the future upgrade potential is much greater. I could also rebuild the stocker that I pull out and re-coup some of my $.

I really like the idea of the Patriot heads because it's a simpler project that I can finish in a long weekend.

Any and all input is appreciated. Thanks everyone.

 

[Three50won]

If you put 4 valve heads on a stock 2 valve engine you will have very low compression. 4 valve heads have a larger combustion chamber (52cc I think) compared to a 2 valve head (44cc I think).

Also, you have to make sure the engine is an actual Cobra engine...not a Mark VIII/Cobra engine. Post pics of the engine and most anyone here will be able to tell you.

For what its worth, I'd just buy the Patriot heads and Comp cams. Others might opine in favor of other companies for heads and cams. I personally like and trust Patriot and Comp. There names have been around for a good time and they haven't had to change their name or management so I'd personally go with them.

IMRC plates were put on 4 valve engines to restrict airflow and thus create more low end hp/tq. They did this because the 4 valve heads flow soo much that without the plates there is no low end power. They are closed below 3200 rpms (approx) and open above that to increase top end power. A lot of people remove the plates with high boost setups. You'll find arguments for both sides but I say keep them on if you go the 4 valve route.

All in all, the simplest route for less headache, great reliability, and to get the hp/tq you desire is to just do the heads and cams on the 2 valve. When you put the heads on you can also go with a thinner head gasket to increase your compression slightly...because the Patriot heads have a slightly larger combustion chamber (46cc) so you will lose some compression. Then you can do UDPs, and a tune and you should be well over you desired hp/tq AND you will have a reliable DD that will be decent on gas, and you will even be able to detune it a bit and use 87 octane if you ever need to.

Swapping a 4 valve will cost you much more in time, money, parts, curse words, etc. If you were gonna build something with the focus on power and speed and world domination then 4 valve is the way to go hands down. But if 300/300 is all you desire then a 2 valve will make that all day in a simple easy and affordable package.

 

[Anddy_C]

Thanks for the input 351. Just to clarify, I was not considering putting the Cobra heads on my existing block. My plan was to swap the entire Cobra engine into my truck. That remedies all of the concerns about compression, etc. Also, I don't know for sure but I would have guessed that the Cobra has a better rotating assembly (forged goodies, better bearings, etc) than what Ford puts in the run-of-the-mill 4.6 2V.

As for IMRC, I think I would leave them. I would even consider going with the truck intake manifold. It has very long intake runners and would probably make lots of torque down low

Thanks for the input on the Patriot and Comp Cams combo. I think it would be a lot of fun and you can't beat the price. I don't have $4500 to put into a pair of cylinder heads.

Here are the pictures:

 

[Three50won]

My bad. I saw "head swap" and assumed you meant swapping 4 valve heads onto a 2 valve block. So I change my vote to head swap. Sorry for not reading thoroughly.

The Cobra block has a forged crank but the bearings, rods, and pistons are the same material as the GT.

If you do get the Cobra block then I'd advise you to take your time with it and put new bearings in it. It is already halfway disassembled so you might as well put fresh stuff in it. You could even buy some new rods and pistons for a few hundred dollars. That way you'll know that everything is reliable. But I still say go with the heads and cams swap!!

 

[Maxpowers]

How many miles are on the trans? Will it take more abuse?

I would not be doing a head swap on a motor with that many miles without rebuilding it. You will be half way there already, and there's no reason not to.

We need more info on the Cobra motor. How many miles, what car it's in, ect.

Patriot has cleaned up their reputation a bit, but is still not the best.

There is only so much hp to be squeezed out of the 4.6 without boost. I would rather buy a supercharger kit and run low boost. You will have reliability with the possibility to go higher. The tuner kit Kenne bell can be had for less than $4k.

 

[1987stangman]

Personally, I would not toss bearings into a engine unless I was going to disassemble it all and have it machines and checked and re checked by me. Knowing it runs well and has reasonable miles and you don't have much $$$ in it, go with it. I would, however pull a cap or two and check them.

I have done several engine exchanges on same year f-150's at my home shop so I will tell you what I think you will need to investigate. I'm sure someone with more Cobra knowledge will be glad to add to or critisize my post.

The DOHC Cobra engine will essentially bolt into your truck using the F-150 mounts. The only real thing I can see you will have to deal with is the intake side of things as the F-150 has a rather tall and bulky intake that is designed to optimize the 4.6L to be m ore suited for a truck. I would assume the fuel rails, exit from a different location and some wires will probably have to be extended and you will have to decided on using a stock F-150 style water pump to use the stock mech. fan or install a e-fan.

Also, I would research the cobra crank. Can't recall bolt pattern (8 bolt vrs 6) on the Cobra crank vrs a stock 2V depending years. I would research those that have done an 5spd to auto swap into their Cobras for that info. That's territory I have not been down yet. IMRC plates are integrated into the into the Cobra intake? Not sure if you can use the stock F-150 intake on the 4V heads. Use your PCM with the trucks coil packs, I would assume the PCM should do the job but I would get a dyno tune afterwards. Do some more research on the exh manifold. They could be very similar (not sure on that one). If they are not then you will have to use the cobra's and could be looking at a custom, manifold back setup depending on if the 4 valve manifold exit in a slightly different location than the 2 valve's did.

You got to remember doing this that the F-150's stock intake is designed for a truck in mind, thus this makes HP and TQ come at different RPM's to accommodate the truck rather than a Mustang.

I think it would be cool as hell to see this swap and I'm sure in the world we live in that someone out there has done it and has recorded it on a website somewhere on the net.

 

[Three50won]

Personally, I would not toss bearings into a engine unless I was going to disassemble it all and have it machines and checked and re checked by me. Knowing it runs well and has reasonable miles and you don't have much $$$ in it, go with it. I would, however pull a cap or two and check them.

The DOHC Cobra engine will essentially bolt into your truck using the F-150 mounts. The only real thing I can see you will have to deal with is the intake side of things as the F-150 has a rather tall and bulky intake that is designed to optimize the 4.6L to be m ore suited for a truck. I would assume the fuel rails, exit from a different location and some wires will probably have to be extended and you will have to decided on using a stock F-150 style water pump to use the stock mech. fan or install a e-fan.

Also, I would research the cobra crank. Can't recall bolt pattern (8 bolt vrs 6) on the Cobra crank vrs a stock 2V depending years. I would research those that have done an 5spd to auto swap into their Cobras for that info. That's territory I have not been down yet. IMRC plates are integrated into the into the Cobra intake? Not sure if you can use the stock F-150 intake on the 4V heads. Use your PCM with the trucks coil packs, I would assume the PCM should do the job but I would get a dyno tune afterwards. Do some more research on the exh manifold. They could be very similar (not sure on that one). If they are not then you will have to use the cobra's and could be looking at a custom, manifold back setup depending on if the 4 valve manifold exit in a slightly different location than the 2 valve's did.

I think the 98 F-150 has an electric fan. As far as the crank is concerned, Cobras came with an 8 bolt forged steel crank while GTs came with a 6 bolt cast iron crank. Some GTs, probably the ones with a 5 speed trans, came with an 8 bolt crank but it was still cast iron. Stock F-150 intakes will not work on the 4 valve heads because the intake ports are different shapes. Along with the fact that a 4 valve intake is not as long as a 2 valve intake since the 4 valve heads are considerably larger than the 2 valve heads. If he was to retain the 2 valve ECU then the only way it would work is if the ignition style for the engine matched the ignition style for the ECU (COP to COP or Coil Pack to Coil Pack). Also he would have to eliminate the IMRC plates and the knock sensors as the 2 valve engines did not come with either of these. The exhaust manifolds also have different shape ports. So a 2 valve exhaust manifold will not work on a 4 valve head and vice versa.

Not criticizing your post at all, but these are all reasons why converting to a 4 valve, while cool, is not the preferred method considering his goals. A 2 valve PI engine can make 300 NA hp all day with no headache and no conversion/fitment issues. And the price of 2 valve heads and cams vs the total price (and time) of finding all the 4 valve stuff needed to complete the conversion speaks volumes. He could even buy a vortech S/C kit for the 2 valve and have less problems than he would with a full on 4 valve conversion.

 

[Maxpowers]

A 2 valve PI engine can make 300 NA hp all day with no headache and no conversion/fitment issues. And the price of 2 valve heads and cams vs the total price (and time) of finding all the 4 valve stuff needed to complete the conversion speaks volumes. He could even buy a vortech S/C kit for the 2 valve and have less problems than he would with a full on 4 valve conversion.

Bolt on 300 whp NA 2v is difficult. You will need every bolt on, and maybe a set of cams to go with. Add all that up, and you could have the Vortech kit for much less.

 

[Three50won]

Bolt on 300 whp NA 2v is difficult. You will need every bolt on, and maybe a set of cams to go with. Add all that up, and you could have the Vortech kit for much less.

The OP was asking about a 300 hp engine for his truck. HCI and bolt ons is the cheapest and easiest route. He never specified if he wanted RWH or just a 300 hp engine. I assumed he was talking about engine hp. If he was talking about rwhp then you are absolutely correct, a blower is the way to go. Maybe he could clarify which one he is talking about.