V-Twin Forum banner
1 - 13 of 13 Posts

·
Premium Member
Joined
·
158 Posts
Discussion Starter · #1 ·
I am trying to decide which flat-top pistons to buy for my 1550 cylinders and stock heads which will go on my 2002 FLHRI. Should I go with the high compression versions or not? I see in the SE catalog that the compression difference between the two piston versions, assuming the stock heads are being used, would be 9.6:1 versus 9.4:1. I would like to work on the lower end torque output of the bike and as such have settled on the SE 204 cam. So GIVEN THAT (1550,204 CAM, STOCK HEADS, EFI) what benefit is there to going with the higher compression? Or are there some negatives I should be aware of? Any info would be appreciated.
Ed
 

·
Premium Member
Joined
·
701 Posts
I went with the standard flat top 95", SERT and the 204 cam. I decided on the flat top because I didn't want any pinging issues with gasoline. I don't plan on drag racing anybody, so you won't see me going for the triple angle valve job, or the trick heads. I just want to ride with a little more torque, and without issues. I got more than what I expected.
My bike runs fantastic. It'll snap your neck when you hit the throttle. Gas mileage isn't the best, but I really don't care.
 

·
Registered
Joined
·
294 Posts
I did a 95 build with the 204 cams and the SE high compression pistons. The one differnece is that I had the heads proted.

I have 101.7 in Trque and 87.7 in HP.

Runs really strong in the lower RPMs.

The compression that you are looing at will not do any harm to your motor. You have to get over 10 to 1 be for compression get to be an issue.

You will not have to downshift like you may have done on hill or while riding with extra weight.

The higher the compression the more torque I think you will get.
 

·
0043--Licensed to Doof!
Joined
·
4,369 Posts
I had a high C/R, when I put the 98" setup on, I had GMR do the stock heads. The C/R now is like 9.6 or 9.7 with Cometic gaskets. I forget the actual. No more compression releases, no more pinging in the hot weather and traffic, no more puked starter clutches. MUCH more rideability. You ain't racin', don't bump the compression!! -2$en#e- -2$en#e- -2$en#e- Thats my thoughts.
 

·
Registered
Joined
·
90 Posts
SEDELUXE05 said:
i dont know about the higher the compression the more tq you get. i have read that the higher the commpession the more problems you can get if it is not set up properly.
That's the key, proper tuning on a professional build and you should have few, if any, problems with higher compression.
I'm running 10;89;1 in my MM Ultra with no problems in 12,000 miles. I had a very slight ping at first that we took out with ignition tweaking in the PClllr and since then it's been a real joy to ride.

TC
 

·
Ironbutt
Joined
·
7,412 Posts
SEDELUXE05 said:
i dont know about the higher the compression the more tq you get. i have read that the higher the commpession the more problems you can get if it is not set up properly.
Proper set-up is the key from what i know. My 95in is 10.25:1 compression. My builder said that getting the ignition correct in these builds is what keeps it from pinging. I had the SE adjustable ignition installed with the build and so far no problems.
 

·
Premium Member
Joined
·
701 Posts
Correct ignition?
Do you really mean retarded ignition timing?
Cooler plugs and retarded ignition timing are the only way I know of to overcome pinging. Both sap power too, so just how far ahead are you with more compression?
 

·
Premium Member
Joined
·
123 Posts
The bottom line is it all depends on what cam you are using. For instance I am using a long duration cam that benifits from higher compression. It bleeds off compression therfore you don't have issues with pinging and such. If you are using a short duration cam you can use a lower compression ratio to the same effect. Where you get into trouble is when you push the outside edge of a cam. All cams have a recommended compression range. So if you dont want to run a super high compression use a shorter duration cam. The trade off is you will fall off faster on the top end. Thats why woods cams are so popular you get the best of both worlds. Short duration and high lift = awesome bottom end and a good top end. The only short fall is it is hard on the valve train. There is always a catch. This is why the 37g is so popular it is shorter duration and lower lift. So you need lower compression and it has a great bottom end. Most people want it to be strong on the bottom and could care less if it falls off on the top. The whole key is in the cam selection. That is what you set your build up around...Just my 2 cents....Correct me if i'm wrong I am by no means an expert....
 

·
Incredible
Joined
·
3,029 Posts
Go with the stronger compression. I would go with a better cam though and some head work. If you have it apart you might as well do a few things to it otherwise you may wish you would have had done later.
 

·
Premium Member
Joined
·
78 Posts
I have a 95" build with HC cast pistons 203 cams and stock heads. Is this a good cam choice? I am having some pinging issues. I have had it on the dyno three times, two different places. I have it down now where it only pings in a high head wind (all the time in South Texas, high heat (again all the time) or if my wife is on the back (she only weighs 125 lbs). So I am thinking about an oil cooler or new cams or both. Any advice would be great.
 

·
Hellbound Train
Joined
·
5,595 Posts
Bullrider said:
I have a 95" build with HC cast pistons 203 cams and stock heads. Is this a good cam choice? I am having some pinging issues. I have had it on the dyno three times, two different places. I have it down now where it only pings in a high head wind (all the time in South Texas, high heat (again all the time) or if my wife is on the back (she only weighs 125 lbs). So I am thinking about an oil cooler or new cams or both. Any advice would be great.
Get the cooler and run synthetic oil and 93 octane gas. You shouldnt have a problem with that cam if the tune is right.
 

·
Ironbutt
Joined
·
7,412 Posts
George C said:
Correct ignition?
Do you really mean retarded ignition timing?
Cooler plugs and retarded ignition timing are the only way I know of to overcome pinging. Both sap power too, so just how far ahead are you with more compression?
87 HP and 107 lbs torque...i'd say i'm pretty far ahead...of the stockers anyway.
 
1 - 13 of 13 Posts
Top