I have nothing but respect for what you've done for the rover community in regards to your mods but I doubt you've gained all that much in terms of actual additional horsepower. There is not doubt that the delievery of power has been improved but adding actual hp isn't probably all that much.

I wrenched on Audi's and Vw's for over 10 years and those folks would claim all sorts of power increases from doing similar mods but when put on the dyno the results tended to be negotiable

 

Oh, I agree. I'd bet maybe ollnly 10-15hp peak improvement. That said, it's all about the area under the curve. If I gained that much across the RPM range, maybe more in places other than peak, that's the real ticket.

 

[QUOTE=Alex_M;642777]I certainly wouldn't recommend paying the big bucks at a machine shop to have it done, but I did notice a difference with my home brew job. Not to be argentative, of course, but I don't think many guys can boast 9.02 second 0-60 times in a D2 on 33s.

Stock gears Alex?

 

Differential gears. Ring and pinions in the axles.

 

I think he was asking where you using the stock ratio?
And you are not, correct?

 

https://www.summitracing.com/parts/sum-g1060

https://www.makitatools.com/products/details/GD0600



I thought I should update this. Above are tools etc.

To practice I started by polishing the plenum chamber, and found that the process was easier to control than expected. Unfortunately, the long mandrel did not stand up to the rpm, so I could only go 1.5" in.

I double checked my markings on the intake and heads, and they held up so I darkened them, and started grinding with the cartridges. They will not move too much material, but you do need to pay attention, I found the Die Grinder to be easy to use, and did like the paddle feature, but you could getaway with a cheaper model I am guessing, but considering I am a total noob with polishing I went for the paddle so I could easily control the tool.

The cylinder head frankly did not have much to remove, the top of the intake ports could have been really ground down and enlarged, but I did not want to mess with how the injectors are seated in the chamber, and also the cartridges are limited by their circumference so you can only create so much of an angle.. I took a little bit off around there, but mostly just polished.

Some of the ports required nearly zero enlargement, and I did not push it. I worked Left to right, and from coarse to fine. Spending approximately the same amount of time, and going only 1.5" deep, which is about all I could reach anyway. I worked on some ridges, and widened where it seemed appropriate, but did not go crazy.

The exhaust ports needed more removed so I used the 60 grit in places, but again did not get crazy. On the intake side I used 80 grit, and on the exhaust side 120. I did use a Dremel to polish the Throttle body interior, but didn't get too nuts.

The Cartridges can be frustrating when you need to remove a lot of material, but I was not going to learn how to use a carbide bit on the expensive parts. That will be for the exhaust manifolds.

I could not get good pictures, so I apologize about that, but will get some when heads come back from the shop.


Alex M was a huge help. Told me to use water for the Cartridges and Oil for the Carbide when I get to it, so a big Thank you to him. Also, helped me avoid the big mistake of trying a carbide bit with a drill.

Here are some videos I found instructive:

 

Nice work!

 

Thanks! I went out and measured the distance between the chambers where they are thin, and I appeared to have kept them wide enough. I was pretty conservative, while at the same time doing enough so I did not waste 5 hours of my life. I can see how it could get out of hand or you could spend days doing this work. I could pull them out and spend all day obsessing about the portholes.

I had to do it on an old deck high top table we have, so it was tough to really angle the parts to get a great look, plus the lighting outside is not great.

I would suggest having the heads clean prior to doing it, but I don't have the facilities for that. I have a toddler and I am not cleaning engine parts in the tub that I wash him in.

If you had a workshop with a spotlight and lots of time, you could do a lot more, but I just would have felt like I missed an opportunity if I had not.

If you had to do just one part of it I would do the Exhaust manifolds, they are way smaller than the ungrinded exhaust ports, 2mm, and with the ports wider probably 3 or 4mm. That is nuts to me. I don't see how restricting air flow at the exhaust manifold does anything but decrease efficiency.

 

Ah, my bad. Actually I am still on stock ratio. I thought I had said stock gears, but didn't double check...

 

Glad I could be of help, Tony! I can't wait to see how it went.