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[08_ScreaminSpringer]

Im thinking of adding cams this winter and going from 9:3:1 to 10:5:1 compression or whats best for 93 octane?
Can you mill the heads to achieve 10:5:1... Also while the heads are off maybe some port work.

[Talon]

I assume when you say 10.5:1 you are talking static compression. Probably the best corrected compression ratio for good street performance is around 9.2 to 9.5, with up to 195-210lb of cranking pressure.
Cam Lobe separation/overlap will affect your corrected compression, less overlap will give you higher compression and better torque, more overlap will give you better top end. A LSA of 100-103 will give you good torque, and good street performance. I'd be careful building to the highest compression and hoping to find good 93 octane gas every where you travel!

You can mill the heads and use a .030 head gasket, but to get to your final corrected compression, you'll need to pick cams and use the overlap to figure out the exact corrected compression before you just mill the heads to get a static 10.5:1. You should find a good engine builder in your area and talk to them, let them know your riding style and where you would like you motor to come in at. If you just go for the most HP at topend, you might be disappointed with the torque around town.

[Midnight Rider]

I'm not the resident expert on this subject, but IMO, you should talk to a competent builder in your area if you are going to have someone else do the work.  If you're doing it yourself, use a reputable shop, let them work with you to figure out what you're after, then do the build accordingly.  If you let some folks here know what part of the country you're in I'm sure you'll get some recommendations on who to use...

IMO, just milling the heads/using gaskets to raise the compression is not the only result you are after.  The SE103/110 heads are poorly designed regarding flow characteristics, which translates into how quickly the motor revs and one of the important factors in a good build.  Total HP/TQ numbers are not the only thing, but how quickly it gets there.  If you really want to do it up right, have the heads welded up and reshaped, or purchase a good pair of heads to go with the cams you want to use.

It's all about what you want for an end result...big numbers cost big money, and there is a correlation between the numbers and longevity of the engine, IMO.  You start getting a basically stock bottom end/drive train over 130, and other things can have problems, IMO.

[SE08RK]

I'm with TC and Talon on this... Attempting to only mill the heads to get the 10.5:1 is going to almost impossible with the stock 8.9:1 pistons. You could achieve the 10.5:1 with about .060 off the head gasket surface, use the .030 gaskets, and replace the pistons with a set of 9.6:1 pistons. But as TC and Talon say; you are doing a portion of what needs to be a system. Increased compression without increased port flow is liable to actually diminish the performance of your engine. You would definitely change the timing advance curve requirements not to mention the AFR mapping. Good luck.

Just thinking; removing too much from a head gasket surface will place the lower cooling fin on the head very close to the top cylinder cooling fin making it useless for air flow between them.

BC

[Talon]

I'm with TC and Talon on this... Attempting to only mill the heads to get the 10.5:1 is going to almost impossible with the stock 8.9:1 pistons. You could achieve the 10.5:1 with about .060 off the head gasket surface, use the .030 gaskets, and replace the pistons with a set of 9.6:1 pistons. But as TC and Talon say; you are doing a portion of what needs to be a system. Increased compression without increased port flow is liable to actually diminish the performance of your engine. You would definitely change the timing advance curve requirements not to mention the AFR mapping. Good luck.

Just thinking; removing too much from a head gasket surface will place the lower cooling fin on the head very close to the top cylinder cooling fin making it useless for air flow between them.

BC

SE08RK, your really close, if not right on, here's a list for 88 and 95's.

Mill Heads Compression Ratio for 80 CID Evolution     TC88     TC95         OEM TC Head/Gasket cc's
               .000"                          8.50                 9.00       9.5                     90
               .020"                          8.77                 9.33       9.9                     87
               .040"                          9.07                 9.69      10.3                    83
               .060"                          9.39                10.09     10.7                     80
               .080"                          9.73                10.52     11.1                     76
               .100"                         10.01               11.00      11.7                     72

[rednectum]

SE08RK, your really close, if not right on, here's a list for 88 and 95's.

Mill Heads Compression Ratio for 80 CID Evolution     TC88     TC95         OEM TC Head/Gasket cc's
               .000"                          8.50                 9.00       9.5                     90
               .020"                          8.77                 9.33       9.9                     87
               .040"                          9.07                 9.69      10.3                    83
               .060"                          9.39                10.09     10.7                     80
               .080"                          9.73                10.52     11.1                     76
               .100"                         10.01               11.00      11.7                     72

to clarify (without running the calculator) are those figures based on a .030 head gasket?

thanks for the data,
dennis

[Talon]

to clarify (without running the calculator) are those figures based on a .030 head gasket?

thanks for the data,
dennis

Yea, a .030 gasket.

[rednectum]

thanks, i printed the sheet for quick reference while interviewing customers for builds.

a valuable tool is not always costly.

thanks aagain!!

[Talon]

I think I got that from the nightrider web site.

Yea, here it is.

http://www.nightrider.com/biketech/hdhead_compression.htm

[SE08RK]

I took .060 off the gasket surfaces and left .020 inside the head gasket circles, used the SE forged 9.6:1 pistons in a TC 95" and had 215lbs static compression - about 10.5:1. The stock starter groaned a bit before starting to turn it over. I had to go to a heavier starter - mainly because I don't like compression releases. I already have enough holes in my head.   

BC

[SPIDERMAN]

Im thinking of adding cams this winter and going from 9:3:1 to 10:5:1 compression or whats best for 93 octane?
Can you mill the heads to achieve 10:5:1... Also while the heads are off maybe some port work.

I am dead against milling heads to add compression. My personal experience with it is it causes studs to pull out. Now that's just my opinion, so don't nobody go beatin up on poor ole BB ok. My advice is a combination of performance heads and pistons.

B B

[Talon]

Couple of other things if you mill the heads, you'll have to get shorter pushrods, or adjustables, and if you take a lot off you could run into manifold sealing problems, it can be fixed easily, but just things to think about.

Then if you go the piston route, you might want to go for a bigger bore, wouldn't cost much more and since you already have the jugs off, might as well!!

Just saw you already have a 110, probably don't want to go any bigger. 

[Midnight Rider]

Once you start down this road, it's hard to find a stopping point...

[HogBreath]

Once you start down this road, it's hard to find a stopping point...

one word.... WIFE

[JesterDecor]

one word.... WIFE