I agree ( about head work and that your post sounds sexual). Good porting and valve work would definitely be a plus, I was just suggesting to op that shaving down the cc's be kept to a minimum as to not raise compression too much since he would already have the 10:1 pistons. Finish your smoke...

 

Not to disagree my friend but the more the head is shaved the better the squish. Squish does not so much raise compression but puts the compression in a smaller compartment to be exploded. The true trick to head building is air flow and squish.

 

Setting squish is an important factor to consider. A thinner hg and domed pistons will reduce it somewhat. Once you start milling things down cost becomes a factor as well, such as extra machine work and purchasing adjustable pushrods (op did say he was on a budget). I guess it just comes down to how much money you've got to squeeze out all the power. I'm a poor man, so mine will get an EV27, (maybe) some 10:1's, a .030 cometic, and the heads will be cleaned, valves lapped, and stem seals replaced (all by me). It may not be optimal, but I'm sure it will work on my ol' street bike.

 

This is why I prefer shaving the heads to raise compression instead of changing pistons. A bathtub shaped combustion chamber with tight clearances used to set squish is very effective at increasing efficiency for higher output. With high compression pistons, you are somewhat limited on how material you can remove from the heads for a regularly ridden street bike, thus making setting squish harder. At any rate, the thickness of the various gaskets comes into play in making small adjustments.

Something a lot of people tend to do is use valves that are too big which results in less velocity thus less filling of the combustion chamber. Big valves are good if you also have other components to support it.

In my opinion, Jerry Branch of Branch Flowmetrics wrote the foremost authority on head design. Now the company is called Branch O'Keefe due to merger.

Buzz Buzzelli is also a very knowledgable guy and most of what I know regarding Harley performance I learned reading his books. The one he wrote about Sportster performance is especially good. In it he explains why keeping the stock 883 heads and installing wiseco 1200 conversion pistons with compression relief dishes will smoke a stock 1200 sportster. The smaller 883 valves increase the velocity of the air fuel mixture and the resulting compression is significantly higher than stock but still safely low enough due to dished recessed type pistons.. The 883's lighter flywheel aloso allows it to spin up faster.

I know we are not talking about sportsters and I went off on a tangent but same concepts apply. Set your deck height by selecting base gaskets of appropriate thickness then shave the heads after determining resulting volume so you know how much you can take off. Then make final adjustments to the squish with the appropriate thickness head gasket. With high compression pistons, this can still be done but is a bit more complex and you starting having to pay even closer attention to valves contacting pistons.

Damn I wish my bike was ready. I think they will finally start on it tomorrow.

 

Ok guys there seems to be some confusion as to what "squish" is. Squish is the distance between the flat portion of the piston and the corresponding area of the head and is set by deck clearance and head gasket. You can shave material off of a stock D-shaped or bathtub cylinder head and the squish area will not change unless you get way up to where the head tapers in and no way can you cut that much. Now with the Hemi Design heads cutting the head will change squish.
Before cutting any head we first CC them so that we can balance them off. Then we decide if we want to "blueprint" them down to factory specs or take more off for additional compression. A flat top piston and a combustion chamber that is as small as practical to allow good flow around the valve and into the cylinder will make more horsepower due to better, consistent, propagation of flame front. Check out the heads on the super racing engines. Pent roof, four valve are an exception as they run two plus per cylinder. If you look at the big drag hemis running a large dome so that they can get the 15+-1 compression they also run multiple plugs so that they get good flame front through the combustion chamber. Just be sure to mark the heads with the cut that was made so future owners/mechanics know!! Hope this helps.
John

 

I guess thats why head work is more like math where all the componets need to work together. Way above my pay scale. My heads got the full treatment and they work well.

 

Yeah, a lot goes into it and there is so much misinformation out there. Branch heads have most of the homework done for you then it is just a matter of setting deck height, squish, clearances, etc. using the right combination of gaskets. That convenience comes at a cost. Branch heads are not cheap, but you get what you pay for. Most normal guys don't need to spend that kind of money to get a good running reliable bike with good performance.

In other words, the dollar per horsepower scale is not linear. Instead it's logarithmic. 80 hp or less is relatively inexpensive. Beyond that it starts adding up quick. Of course I am talking evos here, as I don't know very much about twin cams.

 

John brought up some good points. One about cc'ing your heads. Because of manufacturing variances you have no idea what the combustion volume is on your head. Needs to be the same in order to have a balanced motor. I looked at this, & a lot of other factors before I decided on a set of these aftermarket heads, by S&S (part #106-6064 ). Heres a link for specs: http://www.sscycle.com/product/Repla...ns-p24754.html Already cc'd at 76 , with a .030 hg, gave me roughly a cr of 9.21:1, & sets the squish band between .030-.035. They have a bathtub shaped combustion chamber, similiar to what Branch O'Keefe produce. They have 1.900 in. valves & actually smaller ex. valves than stock at 1.575. They do , however, require a little extra work to be compatible with a short duration cam, because of the airflow characteristic's. The cam I use is .236 in. & .236 ex. They are also set up with high-lift springs. I know these are not for every application out there because of cost & most don't run high-lift cam's on the street on a evo. Just another choice.
Link for setting squish area: http://www.nrhsperformance.com/tech_squish.shtml
I got to keep my stock heads, unmolested, stored away in my shop for a rainy day. One other thing, these are the same heads S&S uses on their V96 motor, ( Part # 106-4603/ #31-9956) One more reason I got these , to build a stroker down the road.
Ride Safe,
Harold

 

WOw! A lot of feedback that is greatly appreciated! So what I'm gathering here is to go with a 10:1 piston, have the heads at least cleaned and resealed. Go with a .030 head gasket, cometic of course (personal preference). I dont want to shave the heads if not neccessary. I may port n polish tho. But just to make sure, what head type piston should I use wiht the cam I have? Domed, dished, valve relief....??

 

The only way to get 10:1 with an '80" is to use domed piston, unless you cut the heads. Heads should at least be CC'ed to factory specs to ensure equal combustion chambers. Head gasket thickness depends on deck clearance, the total should be between .030 and .035. I prefer going closer to .035 on street engines as you will get some carbon build up and have some problems with the carbon hitting the heads. Hope this helps.

John