Head work: worth it?
 

Hi folks,

With winter being a non-entity in these parts this year, my mind is inevitably drawn back to my trusty VTR. I was thinking of having the heads pulled off, milled slightly (say 0.010" or so) and having the ports matched and massaged. What are your thoughts? Has anyone had this done? Is it worth it?

Happy (belated) New Year to everyone :)

from talking to others my impression is that done in combination with some other mods is best. The port work, different cams, HC pistons (or decking the head as you suggest) all can add up to a nice package. I don't know about doing port work alone - might be a lot of work for little gains. If you mill the head you'll have to re time the cams as well. I'm sure some of the others will chime in with their experience - there are a couple riders on here with extensive experience with engine mods. Will be interesting to see what info they have on it.

bill

thanks Bill

I am currrently running Micron slip-ons, a DJ jet kit, and a FloCommander. I am not looking at building a race engine, just upping the performance slightly (especially in the mids, where I do most of my riding).

I had mine ported and had the valve seats hand cut when I installed JE pistons last summer, but I didn't have it decked. Since I did so many things at the same time it's impossible for me to say whether the head work was worth it or not. My gut feeling is that without hotter cams to take advantage of the porting and higher compression, the head work is probably not worth the expense. Maybe this year I'll put this opinion to the test with new cams.
The guy who did the porting work for me says that rather than decking heads for a bump in compression he generally takes apart a stock head gasket and uses one layer rather than two. If I were going to do this again using the stock cams I would do this (if there's enough clearance--I haven't measured it) along with a valve job rather than taking the time and going to the trouble of installing high compression pistons. This won't get you the compression increase that JE pistons will, but it will give it a kick and it's much easier and cheaper.

cheers

Did the guy who did the head work make any comments on the state of the stock ports,....? Just wondering as some vehicles are worse (in terms of finish, casting residue,..) than others in this regard. In other words, does the VTR benefit greatly from it or is it just a case of "fine tuning"?

G'day,

My info, is that as killer said, you really need to do the lot to get the gains. That info came from a guy who did a lot of development on his own race bike, and sold a lot of performance gear. He had customers do part jobs with minimal success, but do the lot, and you could out accelerate a 916.

My personal view of the heads when I did my engine, was that they were pretty good. I didn't touch them at all. As far as port matching, once again, there is not much to be done. You can open up your inlet manifolds a bit, as they are smaller than the head inlet. The exhaust headers could be larger in diameter as well, as they are smaller than the exhaust port. Same as the inlet side though, the head is not the problem.

The ports and chamber looked ok to me. So I reckon if you were going to touch them you would need to get a pro job done.

This is just my view of course, but they are not rough like a few car cylinder heads I have seen. They look pretty good.

When I had my first superhawk I had a friend with a 916. We did some roll ons-his had but been piped and chipped and I believe regeared, mine was bone stock...Mine still felt MUCH stronger down low (rode them back to back and the 916 felt like a 600) and used to run dead even with him all the way up the top end too so I'd imagine it would spank a 916 if you did all that work to it.

I agree with what's been said here. I would bet that you can get 2-5 HP at the top end with port work alone. When you add cams and compression, the ports probably add more. The thing you want to avoid in porting a mildly tuned engine is increasing the cross-section of the ports, because it will cause the intake charge to slow down, and velocity is critical to filling, especially late in the cam cycle.

I still think that a primary consideration for increasing compression is getting the ignition timing right. I believe that a big increase in compression should be paired with a retardation of ignition timing. But I don't have dyno results to test the theory. I wish I had done the testing that I had intended, because I was close to detonation on pump gas at sea level.

I have a friend with a 999R Fila Replica. He asked me how much horsepower I had after leading him through the twisties and pulling him out of corners. The 999R has way more top end at the expense of a little less midrange.

At least that's how I understand things.

I did some very mild port work to mine the last time the heads were off. Mostly short side radius work, but the entire runners were cleaned up. Jardine race baffles and jet kit are the only other mods. It ran a dead-heat with a RC51 on the back straight at Mid-Ohio last year, so I'd say it was worth it. This was not a drafting thing, we were right next to each other. One of my good friends was on the 51, it was the most even drag race I've ever seen!

Milling the head gasket surfaces is a cheap way to get more compression. However, you would probably want to degree your cams if you did that. You would pretty much be opening up a cam of worms in doing that. Installing some high compression pistons would be a much better choice.

I conversed with tech section at Factory Pro in regards to an ignition advancer. I advised them that my static compression ratio was 10:1 with standard cams. They advised the normal 4 degree advancer might be too much, and that 2 degrees might be better. Given that, I decided not to do it. So I think you are on the right track RC. Too much compression with standard cams could be asking for trouble. More cam overlap would help, and that is why the compression/cam combo works so well.

I have also been told that milling the cylinders or heads is not a great idea, so agree iwth that too. Pistons are a better option. Get some light ones like CP while you are at it.

I think milling the heads .010" and JE pistons are a freat combo for track use and race gas. My engine ran really well at the track. It was just on the verge of too much cylinder pressure during combustion for pump gas, which made it very sensitive to tuning. I think I could have made it reliable with some fine tuning. Moriwaki pistons are still available and have slightly less compression, which would probably be great for a street engine.

As far a s degreeeing the cams, it's not really that big a deal, if you have a dial indicator, a degreee wheel and know what you are measuring. I slotted my cam sprockets on a mill with a rotary table, but you can also do a fine job with a die grinder, if you are careful.

These engines really come alive with stage 1 cams and more compression. It was a very satisfying project.

OK. Now you know I won't be able to forget this sentence. Since I'm already most of the way there I will be compelled to "finish" the job with cams. Thanks man. Thanks a lot.-)

Once it gets you, you won't be able to sleep right until it's done!

That's why my new shop is going to have a cot in it. :) I'm sick of sleeping on the creeper!