In the spring I'm going to be replacing the head-gasket on my '03 disco (4.6). While I'm in there I want to do as many upgrades for performance and durability as possible. I've an email in to the folks at RPI but wanted to get some feedback from you guys as to what you've done, what you liked and what you'd do differently.

I read Landzu's post and am wondering how that turned out, if anyone knows.

This is what I was thinking:

I figured while I had the heads off I'd get them ported and upgrade the valves, guides and springs.

New cam, of course

Lifters and rods

Possibly changing to the GEMS plenum, boring it out and adding a bigger throttle body- thoughts?

timing chain

Exhaust, of course.

anyone have any idea what kind of horses the auto-box and axles can handle?

I'm still in the planning stages but want to do something a little different, get more power but still maintain drivability. I'm willing to sacrifice what may be considered off-road performance for street performance as far as the engine's concerned.

Please give me your thoughts, ideas and additional suggestions.

 

Stay away from the Gems manifold, the Bosch will flow better especially if you clean up the ports.
Add a set of 8mm Magnaor wires.
You might look into a replacement injectors with better flow and pressure.
Don't get too crazy with the exhaust, don't want to loose too much back pressure.
The t/case and tranny can probably handle 50 more HP, the diffs won't take to it because of their weak spider gears, so you will want to replace the old set up with some sort of lockers to get at least 4 spider gears.
Now if you really want to get crazy, you could go to a t/case from a 110 and get that great extra low end gearing.
What do you think?

 

Hey, thanks Mike. Isn't it amazing how it goes from just tiding things up and spending a few hundred extra dollars on performance parts to a full-on hold onto your wallet! It all started with me thinking - "hey, didn't they put the Rover V8 in TVRs? Wonder how much power I could get out of it."

Thanks for all the input, I've been kicking around boring out and bead blasting the Bosch plenum then sending it off to be powdercoated inside and out so I'll prob go that way. I was kind of afraid switching to the GEMS would open up a can of worms trying to get the trumpets right so I'm kind of glad to hear you think sticking with what I've got's the best way to go.

I've already got the 8.5 magnecores on now but just never got around to investigating ignition upgrades to take advantage, I figured not much point on a stock engine anyway, really. I'd actually completely forgotten about it. Do you have any idea what my options may be there?

Injectors- thanks for bringing that up. I haven't been able to find anything on injectors other than a passing reference to Bosch Brown something or other somewhere. I'd really like to find something proven.

Exhaust- I wish Borla made something for the 4.6 Discos. I had one on my DI and loved it. The one AB sells (superflow I think) is the only one I have found so far - any thoughts on it?

I was afraid the driveline was going to be a big limiting factor. I was hoping to push somewhere in the 300-320 range. I had never even thought about a Defender transfer case, I was looking at toddco suspensions underdrive unit. It sure is pricey though, so it looks like the 110 would be a better option. The hell of it is I just rebuilt a '04 case and put it in about a month ago.

Diffs- Got some questions here. I've been considering going with either ARB or Detroit for a while. East Coast Rovers did a hell of a nice DII and I liked the way they integrated the switches and did on-board air. Anyway, I'm just not quite sure. The ARBs will lock 100% but you've got a clutch to deal with, but they're neat. With the Detroits I really don't see the lack of 100% diff lock as a real issue and the design just seems to be more bulletproof. What are your thoughts between the two.

It seems that the Piper cams are the most widely used on this engine. Any input on real world differences between the different Pipers?

I really have no idea why I want to get 300 horses that I'll never use out of a Discovery, I guess sometimes just because is reason enough. I'd like to be quicker than a RR Supercharged but I def want to be faster than a LR3/4. Based on Power to Weight I'd need 270hp to better a LR3 and 320hp to better a RR supercharged.

 

Send me your tele number and I'll call you.

 

PM sent

 

Tried to call you, left you a message and never got a call back.