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Discussion Starter · #1 ·
95" fxst, scottsman build, andrews 37b, SE adj pushrods, flattops, cycle shack slip ons.

I have been asking alot of questions and I appreciate all the input while I figure out what to do. I was speaking to the mechanic at the HD dealer who assembled my bike with stock gaskets rather than cometic .30 gaskets. He said that increasing compression would not make a difference for my bikes power. SBC said with stock gaskets I am around 9.4 or 9.5. Ideally I should be around 9.8. My question is, will increasing the Compression from 9.4 to 9.8 make much of a difference on my bike? To do so I need to take the heads off have the compression checked and possibly have the heads milled. If it wont make much of a difference to increase the compression, I am going to spend my money on something else. What do you guys think? is it a waste of money and time to check and increase the compression?
 

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killer sperm
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It seems to me the compression being off a point or two isn't a deal breaker. The squish band is the critical thing here. Those heads were designed to work with .030's.
If you spec'd .030's I'd insist they correct their mistake.
 

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Arrogant Bastard
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Milehog said:
It seems to me the compression being off a point or two isn't a deal breaker. The squish band is the critical thing here. Those heads were designed to work with .030's.
If you spec'd .030's I'd insist they correct their mistake.
The big problem with low compression is loss of low end torque and throttle response. Like Milehog said if you spec'ed .030 cometic and they put something else in without your approval you need to have them correct it. Your off half a point on compression thats actually significant. If you were off half a point due to engine wear you'd be looking at re-building so I sure wouldn't accept a new engine like that.

Joe
 

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I saw on some other site some discussion about the difference in horsepower between an 8.5 build and a 10.5 build, and it was about 10 horsepower difference. I'm not sure how they arrived at this, because I would think the cams would have to be different for these different compression ratios. Anyway, just from my reading a lot of posts about the 37 cams, I think 9.4 is still in the ball park. I think 9.8 is max for that cam. I'm sure there's some difference, but I'm not sure you could really tell by a seat of the pants determination. I have a mild build with a roughly similar cam, with a .040 gasket, and from what I can tell my actual compression is about 9.2, based on some of the spread sheets available, which puts it at the low end of the cam cr range as far as I can tell. The build is definately better at low rpm than stock, and the throttle response is fine. I do note that HD states that with the flat top pistons and the 95" cylinders, the cr is 9.5, but the spreadsheets for cr calculations would put it much lower. With a stock gasket, I think it would be closer to 9.0. This may be because the heads are supposedly 83cc but are actually closer to 85 or 86.
 

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There is a comp calculator that you can play with and determine static comp and dynamic comp based on the cam choice. Most builders AFAIK target a 180-190 psi dynamic comp for a good street build. Playing with the spreadsheet will show you the impact of cam intake closing and static comp on the dynamic comp. Comp need s to match the cam, if comp is too low for a given cam, sluggish torque down low. Too high, ping city.
Have fun toying with it


http://v-twinforum.com/forums/showthread.php?t=66831 post 18
 

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This is a hard one. I know a lot of guys use the .030, but I am uncomfortable with them for long term. It's a cheap way to gain a few compression points, while possibly sacrificing reliability. I also know that I wouldn't want to ruin a relationship with my dealer.
They should meet you in the middle here..
I think I would talk to your dealer and tell him that you KNOW what compression you wanted, ordered and needed, and see if he will do the labor if you pay to have your heads milled.
Then ofcourse, you might as well have the heads done while you are at it. The 37 seems to react very well to cleaned up heads also..
A few bucks more, but a win-win situation with more HP & TQ.
JMO..
 

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Discussion Starter · #7 ·
Its a long story but the dealer did me a favor fixing my bike. He did call and tell me clearance was an issue and he needed to use stock gaskets rather than the cometic. I ok'd this. My dilemma is whether or not to dump more money into this to increase compression or not. If its not worth taking the heads off measuring compression, milling, then reassembling the heads, I dont want to spend the money on all the labor to have it done.

I guess I could do it myself to save the labor cost but the last time I did that my piston detonated on a valve. Not sure it was my fault. But I am kind of paranoid about touching my engine after having to drag my broken bike to the dealer to spend $1500 to fix it. Since its winter I was toying with the idea of pulling the heads off myself bringing them down to dealer to measure compression, but again I am not sure I want to tear into my engine again especially if increasing the compression wont give me too much in the way of gains.
 

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How do you like the way your bike performs now?? No pinging..good throttle response..good power where you ride?? If the answers are all "yes" ..then leave it alone. If you want all the cam can deliver..then pull the heads and have them done and go with the 030 at 9.8.
In other words its kind of hard to advise you, because we are not "you".
I look at a modification to achieve a desired outcome...the hell with the cost..I want what I want. If your goal was specific numbers on a Dyno sheet ..and you dont have them..then proceed further. If it was a good performing build over stock..goes back to my first questions..and you have it..you have answered your own question.
.... percent improvement = cost . for a .4 bump in comp.....I 'd ride it as is.
 

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George C said:
This is a hard one. I know a lot of guys use the .030, but I am uncomfortable with them for long term. It's a cheap way to gain a few compression points, while possibly sacrificing reliability. I also know that I wouldn't want to ruin a relationship with my dealer.
They should meet you in the middle here..
I think I would talk to your dealer and tell him that you KNOW what compression you wanted, ordered and needed, and see if he will do the labor if you pay to have your heads milled.
Then ofcourse, you might as well have the heads done while you are at it. The 37 seems to react very well to cleaned up heads also..
A few bucks more, but a win-win situation with more HP & TQ.
JMO..
And please do tell us how an .030 headgasket(or any gasket of varying thickness) used to set up a proper squishband and chamber volume is going to sacrifice reliability in any manner? Thats the most rediculous thing Ive heard to date on head gaskets. Where did you get that info from? May want to stay away from that source in the future.

Using the proper thickness gasket is critical for setting proper squishband in conjunction with your pistons and heads and in helping to achieve the correct chamber volume.
 

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Discussion Starter · #10 ·
I just talked to the guy who is going to install my Mikuni 42 carb in the spring. He said .4 in compression wouldnt change the feel much. However, since I am having him look into a ticking noise in the front head I might as well have him check the compression. If it truly is 9.4 I will leave it alone. If its lower I may get the heads milled. I find it hard to believe that Charlie at SBC would not have already milled these heads to achieve 9.8 CR. Maybe its just a matter of putting the cometic gasket on after checking the head and putting it back together.

As far as the build? I am somewhat happy with except for the loud ticking noise. Power is ok. I think I need to get it tuned once the carb and ignition are installed. Then I should get the most out of the parts and see if I really enjoy it.

One thing that annoyed me was riding with a person two up on a bagger that had aftermarket pipes (No Baffles), stage 1, and thunderslide kit. On the highway doing 90 - 110 MPH he could stay with me the whole time even with him and his girlfriend on the bike. I weigh 230, they probably weigh 340, and they are on a bagger. I didnt think they would be able to keep up (Since I had 95" with headwork and cams) but they had not problem. I know with no baffles his bike should have more top end. I just figured I should be able to pull away.
 

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95CDman said:
And please do tell us how an .030 head gasket(or any gasket of varying thickness) used to set up a proper squish band and chamber volume is going to sacrifice reliability in any manner? Thats the most ridiculous thing Ive heard to date on head gaskets. Where did you get that info from? May want to stay away from that source in the future.

Using the proper thickness gasket is critical for setting proper squish band in conjunction with your pistons and heads and in helping to achieve the correct chamber volume.
I certainly agree. The only failed Cometic .30 head gaskets I know of were from incorrect torque sequence and lbs which is different for the .030. The Cometic .30 will give you a better squish band making combustion more efficient. A few dealer wrenches will tell you different because of fear by not complying with the HD manual. I don't know of any well know builder that does not use the Cometic .030
 

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Discussion Starter · #12 ·
I just talked to the guy who is going to install my Mikuni 42 carb in the spring. He said .4 in compression wouldnt change the feel much. However, since I am having him look into a ticking noise in the front head I might as well have him check the compression. If it truly is 9.4 I will leave it alone. If its lower I may get the heads milled. I find it hard to believe that Charlie at SBC would not have already milled these heads to achieve 9.8 CR. Maybe its just a matter of putting the cometic gasket on after checking the head and putting it back together.

As far as the build? I am somewhat happy with except for the loud ticking noise. Power is ok. I think I need to get it tuned once the carb and ignition are installed. Then I should get the most out of the parts and see if I really enjoy it.

One thing that annoyed me was riding with a person two up on a bagger that had aftermarket pipes (No Baffles), stage 1, and thunderslide kit. On the highway doing 90 - 110 MPH he could stay with me the whole time even with him and his girlfriend on the bike. I weigh 230, they probably weigh 340, and they are on a bagger. I didnt think they would be able to keep up (Since I had 95" with headwork and cams) but they had not problem. I know with no baffles his bike should have more top end. I just figured I should be able to pull away.
 

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cdirk: Its not just the slight difference in compression, but a combination of the correct cr and your correctly set squishband. Combine the both together and you could be leaving some significant power on the table. If they were supposed to put a .030 gasket on there, then they are obliged to do so.

Charlie at SBC probably milled your heads to set compression under the assumption your using .030 gaskets. Your head gaskets in essense are really part of your heads combustion chamber, and different thickness gaskets change the volume of them.
 

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cdirk said:
95" fxst, scottsman build, andrews 37b, SE adj pushrods, flattops, cycle shack slip ons.

I have been asking alot of questions and I appreciate all the input while I figure out what to do. I was speaking to the mechanic at the HD dealer who assembled my bike with stock gaskets rather than cometic .30 gaskets. He said that increasing compression would not make a difference for my bikes power. SBC said with stock gaskets I am around 9.4 or 9.5. Ideally I should be around 9.8. My question is, will increasing the Compression from 9.4 to 9.8 make much of a difference on my bike? To do so I need to take the heads off have the compression checked and possibly have the heads milled. If it wont make much of a difference to increase the compression, I am going to spend my money on something else. What do you guys think? is it a waste of money and time to check and increase the compression?
I have a similar budget build. SBC milled my heads .040 and set me up for 211 cams and told me to use a .030 cometic for a 10:1 compression. The bike does not ping or have trouble with any available gas. I have not had it on the dyno yet but the difference in power from 88" Stage 1 is like night and day. The bike runs very strong and does not have any soft spots in the low end RPMs. But...my reference points are 88" Stage 1 bikes I have owned and not bikes with radical builds.

If you haven't had the bike on a dyno, I would suggest a good tune before you spend more money. One question I always ask is are you using all the power you currently have? Are you twisting the throttle wide open?

When I get tired of the 95, I am going to the 107. It's only money...?prty:
 

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Shithead
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95CDman said:
And please do tell us how an .030 headgasket(or any gasket of varying thickness) used to set up a proper squishband and chamber volume is going to sacrifice reliability in any manner? Thats the most rediculous thing Ive heard to date on head gaskets. Where did you get that info from? May want to stay away from that source in the future.

Using the proper thickness gasket is critical for setting proper squishband in conjunction with your pistons and heads and in helping to achieve the correct chamber volume.
He said "May", not "Will". Any number of factors could cause an .030 to be less reliable than the stock part, not least installation procedure.

Perhaps you would care to quote us a reliable source that says the .030 is going to improve reliability ?

If not, then perhaps you would care to quote your own experience of the relative reliability of .030 and stock parts in similar builds ? Actual miles between build and part failure would be useful information.

Or, as a new guy here, I suppose if you got really desperate, you could try having some fucking manners about how you put your points. You might find they would get across better.
 

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Discussion Starter · #16 ·
Strat.

I think I am going to put ignition and mikuni carb on the bike, see if I can get that lovely top end ticking noise fixed then throw it on the dyno and get it tuned. I dont have any experience riding a 95" either. I just hear so many people have rave reviews. I guess I just expected more. It is fast, just thought it would be faster. especially when I cant seem to beat a stage 1, drag pipe, thunderslide kit, bagger bike with 2 people on it. Maybe I needed to twist the throttle a bit harder. I think the mikuni 42 may help bring out the throttle response. We will see.
 

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cdirk said:
Strat.

I think I am going to put ignition and mikuni carb on the bike, see if I can get that lovely top end ticking noise fixed then throw it on the dyno and get it tuned. I dont have any experience riding a 95" either. I just hear so many people have rave reviews. I guess I just expected more. It is fast, just thought it would be faster. especially when I cant seem to beat a stage 1, drag pipe, thunderslide kit, bagger bike with 2 people on it. Maybe I needed to twist the throttle a bit harder. I think the mikuni 42 may help bring out the throttle response. We will see.
You should be able to wipe up Stage 1 bikes. Friend of mine has a fuel injected Heritage and his brother has a fuel injected Road King. They are both stage 1 88s and these guys are hot dogs to ride with. I can pass them at will within 2 gears and coming from behind. If you can't do the same, something is wrong. Your bike should have the same kind of power; as our builds are nearly identical. I have the stock CV carb on mine that has been tuned with a dynojet kit. But I have not had it on a dyno since the build for a final tune and it still runs strong. I am running the cheaper nonadjustable SE ignition that goes to 6200 RPM...nothing fancy. I got most of my parts free using chrome cash. I just wanted a reliable budget build. Oh...the other thing is I am running Bassani Pro Streets. From what I understand these pipes offer very good power. This spring I will get it on a Dyno and share it here. Your dyno should be very similar to mine.
 

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cdirk said:
Strat.

I think I am going to put ignition and mikuni carb on the bike, see if I can get that lovely top end ticking noise fixed then throw it on the dyno and get it tuned. I dont have any experience riding a 95" either. I just hear so many people have rave reviews. I guess I just expected more. It is fast, just thought it would be faster. especially when I cant seem to beat a stage 1, drag pipe, thunderslide kit, bagger bike with 2 people on it. Maybe I needed to twist the throttle a bit harder. I think the mikuni 42 may help bring out the throttle response. We will see.
The Mikuni will help throttle response some. But its not going to make your bike a world beater. You mentioned getting stomped on by another rider's bike. Happen to know his gearing by any chance?Or compare it to yours? Gearing plays a really big role in how your bike accelerates.

Just curious why you went with SBC with R&R Cycles only 20 minutes from NewMarket? Their headwork is well known throughout NE. Top notch work,they have the best equipment and the owner is a class act and enjoyable to talk with.
 

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Discussion Starter · #19 ·
ignorance. If I knew then what I knew now I would have gone to R&R Cycles. Didnt have enough money to buy their heads. They are very expensive. but in the end I ended up spending as much as I would have spent using their heads. They are a very expensive place to buy heads and even parts. But they are world class when it comes to building performance bikes.

Strat,

I didnt get beat by the stage 1 bike. I coudnt blow by him though. Going 90 - 100 MPH niether of us could blow by the other. Problem is he had his girlfriend on the back of his bike. I had no problem down low blowing him away. just top end he and I seemed even.
 

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Weight is not a factor in terminal speed as it is in acceleration. Frontal area and CD (coefficient of drag) have EVERYTHING to do with top speed and the amount of power it takes to push something thru the air. If your engine doesn't make a LOT more power than the Stage1 bike or if the power curve signs off early then it's quite possible that the two would be evenly matched on a top end run. Bikes have LOUSY aerodynamics, most modern cars with any decent power will easily outrun the average cruiser type bike on top speed, they actually have LESS frontal area and much lower CD's --- they can go faster with less power than what it would take to push your "sheet of plywood in a hurricane" to the same speed.

Next time, try running in 4th gear, you may find that you can go faster top end in 4th than you can in 5th, especially if you have the stock 3.15:1 final ratio.
 
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