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Discussion Starter #1
What compression are you using? I have been told that 9.8 is the min. for this cam to really perform. What CR are you running and how did you figure it out? Did you measure the chambers and deck? Or just go by the manufactuors CR that is published? If you are running below 9.8, how do you like the cam? Is it what you expected or do you wish maybe you had gone with the 31g or 26g? What piston and head combination are you going with? And one more do you have /use compression releases?
THanks
Paul
 

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9.8 is MAX not min

9.8 is near the top of the CR for the 37. I would not go any higher. If you don't have good gas, I would keep it in the mid 9's.

Some the pros will have more to say I hope.

David
 

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With 9.8 you shouldn't need compression releases , and as Bagger Dave, and many of the forum Guru's as well as Andrews rep I've talked to said 9.8 is at the top of optimum. When you get into the 10's you can run into pinging and detonation problems per Andrews. As far as the 26 goes , if you are running a bagger and ride at lower rpm ranges it may suit you better, although the 37 from what I've seen and read can pull harder across the rev range.

There are tons of 37 posts here , and quite a few on the 26.
 

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Hi Paul,
Yes, my chambers were measured and the heads were decked along with a street port job, new valves & springs.

My wrench decided 9.9:1 was the limit and so he set it there. I ran some dynamic compression numbers with the cam in my build and it came out to 9.15:1, as I recall.

Zero problems with pinging, using the SERT in the data log mode, I've seen my tune hit the knock sensor once for a very momentary 2* retard. That's been about it.

Cam choice is the key to the whole build outcome. Pretty much everything revolves around this choice and it depends on your bike weight and riding style. Are you on a bagger? a super glide? are you a leisurely rider? a street terror?

SE flat tops with ported stock heads should do the job. What year is your motor?

No compression releases were needed.
 

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Discussion Starter #5
Hi, and thanks for the replies. I am riding a carbed fxst 03 and am going to go up to 95" next month. I plan on using the 37g since it seems the one to fit my style the best. So if i understand correctly it seems the the 9.8ish is the top for the 37g? meaning that 9 to 9.8 is acceptably for it to run strong?
thanks
Paul
 

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Sometimes I wonder if I should put the compression releases in my SE Performance heads. I was running the SE 251 cam. But since I went to the S&S gear drive and Woods TW5-G a couple weeks ago, occassionally during a hot restart it does not turn over quite as fast as if it were cold. The lifts between the cams are only a difference of about .005. But the durations and overlaps are different. Maybe thats the deal. Definitely the TW5-G is a torquey ass cam with those SE heads. Mucho better than the SE251 IMO.

Not real sure what the comp ratio is, I forgot. I think it's 10.1 or 10.25.
I don't know. With my combo, what should it be?

95" SE cyl's
Flat top pistons
SE Performance Heads
Stock headgaskets
 

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shrike96 said:
Hi, and thanks for the replies. I am riding a carbed fxst 03 and am going to go up to 95" next month. I plan on using the 37g since it seems the one to fit my style the best. So if i understand correctly it seems the the 9.8ish is the top for the 37g? meaning that 9 to 9.8 is acceptably for it to run strong?
thanks
Paul
Paul,
As I understand it, when the heads are cc'd and the numbers are crunched for your motor's heads, the final CR number will be determined based off of this information. The higher you run the CR within the limits of the cam valve timing, the more power it will develop allowing you to get the most out of the build for the same money spent at little or no reliability risk. My wrench saw that 9.9 was safe when he crunched the numbers for decking my heads.

I would not go with 9:1, I would discuss it with your builder and steer more towards the 9.5:1 and up range.
 

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Discussion Starter #8
as it stands right now, my heads will go out next to be ported and polished etc. We will measure the chambers and at that point we'll know about where our CR range will be. It then will be come a matter of matching the pistons to accomplised the CR. Its either the cast flat tops or the cast high compression. Which ever will work to get it to about 9.5 to 9.8, which at this point is my goal. I felt that Cr in that range would require no releases to to cut in to the heads. I checked the andrews sight and they said the range is stock to 9.5 so may be 9.8 might be a littel to much? i could go with a thicker head gasket to lower it a touch?
Paul
 

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shrike96 said:
as it stands right now, my heads will go out next to be ported and polished etc. We will measure the chambers and at that point we'll know about where our CR range will be. It then will be come a matter of matching the pistons to accomplised the CR. Its either the cast flat tops or the cast high compression. Which ever will work to get it to about 9.5 to 9.8, which at this point is my goal. I felt that Cr in that range would require no releases to to cut in to the heads. I checked the andrews sight and they said the range is stock to 9.5 so may be 9.8 might be a littel to much? i could go with a thicker head gasket to lower it a touch?
Paul
Just get a good street port job done by a reputable porter. Who are you using for the heads??? They need to be in tune with the builder and knowing the cam being used to set the deck height right. Who's the builder???

Polished is the wrong way to go, they should be roughed up a bit actually and it's critical they understand where to pocket and take away material in the ports.

Are you going for new valves? springs? I would along with freshly cut new seats.

What pipes are you running???????

How do you plan to do your ignition timing???????????

SE cast flat tops will be all you need. Stock head gasket is fine.

No compression releases will be needed.

The Andrews site info is on the conservative side with regard to the CR they say is max, according to my Wrench.
 

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From my talk with Andrews and alot of Forum reading you will find various opions. Some of the agreements, are using low grade gas and the 37G with 10:1 cr you will have a decent chance of ping. As far as the 31G cam, This is a cam that there seems to be many various opions on. According to Andrews it is reccomended in High cr Engines 10:1 + and is also utilized in Turbo Charged (Adder) Motors. My understanding is,It has a early closing Intake valve offsetting the High cr with a late opening Exhaust valve. Andrews claims that they have seen this Cam shine in High CR applications. I have a 95 cu, Forge SE pistons, and SE pro heads pushing 10:5.1 cr. which I will be putting a 31G in in a few days and posting a Dyno on the Forum then. As far as the 37g, if you were in a mild climate,No more than 10:1 cr and had no problem finding 93 octane. I would think that seems to be the most popular for a 95 cu. CR release is used as a cheap alternative to not having to have a beefer starter. If your running 10:1 cr I would think it would be a good Idea. If your looking for a little extra HP/Torqe I can tell you from experence that a baseline TC88 is about mid 50tys HP if you do the Stage 1 SE breather with a SE 211 cam you will gain about 20 hp. If your looking for a 90tyish HP and not turning the wrenches. Youll need about $2500 in the HOG Bank. Anyhow just my-2$en#e-
 

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I've got 9.9:1 on my build with the 37G's. I've had no pinging issues so far, nor do I expect to. I used Big Boyz for my head porting and I can tell you that Bean will work with you to achieve exactly what you want for compression ratios.
Get a good porter and they will be able to tell you exactly what will work with their set ups.
Good luck

darrell
 

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Totenkopf said:
Polished is the wrong way to go, they should be roughed up a bit actually and it's critical they understand where to pocket and take away material in the ports.
I'm interested in hearing why you think this is the way to go. I've heard three different versions, first was polishing, then everyone (it seemed) changed their mind and said no no, rough it up to get a better mix of air-fuel, but now my own opinion is that polishing is the way to go.

My opinion now is based on the way some EFI systems calculate fuelling, through calculating how much fuel goes into the film coating the intake tract, and how much comes out of that film in any instance of time, using (if I remember correctly) intake air temperature, manifold surface temperature and manifold absolute pressure or airflow.

Secondly there are performance coatings available that seem to have increasing popularity, like the friction reducing coating that comes on the side of SE pistons. One of these coatings is a low-friction oil expelling coating that when used in the intake tract basically stops any film buildup, and increases port velocity because of it's friction reducing properties. It allows the air to slip by the port walls more easily, increasing overall flow. So if they sell this I guess they could be feeding off of people's ignorance, those who think polishing is the way to do it, but it could be because it actually IS the right way.

Thirdly one of the details of making a successful performance engine is setting the right squish distance. It is possible to have an engine with a squish distance and compression ratio so set that it pings, open it up, mill the deck, which will INCREASE the CR, but also reduce the squish distance, and stop the pinging. So now the engine not only has less tendancy to ping, but an increased CR, so you're likely to also get more power and torque out of this combination, especially since you can un-retard the timing that you may have had to do to stop the pinging. Now I'm not saying in every case it will stop pinging, but using squish to mix the air-fuel seems to be a more correct way of doing it because you also don't hinder flow from roughing up the intake tract.

That's my theory, seems logical to me, but I'm open for new ideas, points of view and will change my opinion in a heartbeat if another one makes more sense. Let me know the reasons behind the roughing up technique.

Cheers. :thumbsup:
 

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Polishing the intake is not what you want to do...you have to relize that the air flow into the intake is 690 ft per second, when a column of air flows this fast it constricts and creates what we call a MARGIN between the port wall and the column of air. In this MARGIN (which should be around .030 depending on the roughness of the port) the air flow is very slow and when the air slows down the heavier gas molecules will fall out of suspension and collect on the port wall in beads if the intake is polished just like water does on your car hood after you polish it. These beads will accumalate into droplets of gas and end up driping into the cumbustion chamber and becoming after gas which WILL cause detonation. Its hard to burn droplets of fuel completely and this is why it becomes after gas.
Granted a smoother port will have less friction but a polished port causes engine distruction from the detonation. A rough port will take the slower moving air in the MARGIN and kick it back up into the air column and no fuel is dropped out of suspension. The rougher the port the larger the MARGIN will grow...so too rough of a port will lose its volume, the best MARGIN should be around the .030 as I mentioned above, you can achive this MARGIN with a slight roughness like 180 grit sand paper will give you.
A fuel injected engine won't be effected as much as a carb engine in this Margin because of the direct squarting of the fuel at the valve...ie the fuel isn't flowing down the intake runner like a carb engine does.
The most effective SQUISH chamber is between .025 and .040. Anything smaller than .025 will cause detonation and anything larger than .040 will diminish the SQUISH chamber effectiveness. The Squish does not mix the air and fuel...it makes the mixture swirll or tumble which makes the combustion chamber more efficient in a complete burn.
Hope this helps in clearing up any misconceptions in combustion chamber and intake runner design. Porters that polish the intake are doing so for a selling point, since the average Joe can't tell what a porter does he can see the polish surface which makes him feel he got something for his money.
 

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hdmd88 said:
Polishing the intake is not what you want to do...you have to relize that the air flow into the intake is 690 ft per second, when a column of air flows this fast it constricts and creates what we call a MARGIN between the port wall and the column of air. In this MARGIN (which should be around .030 depending on the roughness of the port) the air flow is very slow and when the air slows down the heavier gas molecules will fall out of suspension and collect on the port wall in beads if the intake is polished just like water does on your car hood after you polish it. These beads will accumalate into droplets of gas and end up driping into the cumbustion chamber and becoming after gas which WILL cause detonation. Its hard to burn droplets of fuel completely and this is why it becomes after gas.
Granted a smoother port will have less friction but a polished port causes engine distruction from the detonation. A rough port will take the slower moving air in the MARGIN and kick it back up into the air column and no fuel is dropped out of suspension. The rougher the port the larger the MARGIN will grow...so too rough of a port will lose its volume, the best MARGIN should be around the .030 as I mentioned above, you can achive this MARGIN with a slight roughness like 180 grit sand paper will give you.
A fuel injected engine won't be effected as much as a carb engine in this Margin because of the direct squarting of the fuel at the valve...ie the fuel isn't flowing down the intake runner like a carb engine does.
The most effective SQUISH chamber is between .025 and .040. Anything smaller than .025 will cause detonation and anything larger than .040 will diminish the SQUISH chamber effectiveness. The Squish does not mix the air and fuel...it makes the mixture swirll or tumble which makes the combustion chamber more efficient in a complete burn.
Hope this helps in clearing up any misconceptions in combustion chamber and intake runner design. Porters that polish the intake are doing so for a selling point, since the average Joe can't tell what a porter does he can see the polish surface which makes him feel he got something for his money.
I didn't understand 2/3 of what you just said HD. This might help some others though. I owned a 98 valkyrie, after I brought it home I joined a pretty good Valkyrie forum. The tech board talked how great polishing the intakes, all six of them, would be. Everyone said it would improve preformance and milage, so I did it. I had all six of them looking like mirrors with 2500 w/d paper. They looked like they were chromed inside. The preformance went down the toilet along with the milage. The term they started using was "turbulence" needed to be apart of the flow of fuel into the carbs. (whatever that meant). The end result was me and a lot of others ended "polishing" the intakes with 40 grit paper. I'm guessing we're sort of talking about the same thing. :corn:
 

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hdmd88 said:
In this MARGIN (which should be around .030 depending on the roughness of the port) the air flow is very slow and when the air slows down the heavier gas molecules will fall out of suspension and collect on the port wall in beads if the intake is polished just like water does on your car hood after you polish it.
Everything else I knew, but the above I didn't really think about. I understand that creating turbulence in the outer layer of the flow would exchange fluid (air or fuel) between it and another "layer" closer to the middle of the flow. Wow - an example of creating turbulence in a laminar flow as a benefit.

I guess if you 180 grit the intake, you could probably still use the oil-repelling coating as well, (it burnishes to <0.001" IIRC) and gain back some velocity at the margin, and thus overall as well.

I now agree that polishing is not good. My definition of polishing was more like smoothing though, and my immediate thought of "roughing" the intake was a little over-zealous.

Thanks Doc, you're a very helpful man!
 

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Route666 said:
Everything else I knew, but the above I didn't really think about. I understand that creating turbulence in the outer layer of the flow would exchange fluid (air or fuel) between it and another "layer" closer to the middle of the flow. Wow - an example of creating turbulence in a laminar flow as a benefit.

I guess if you 180 grit the intake, you could probably still use the oil-repelling coating as well, (it burnishes to <0.001" IIRC) and gain back some velocity at the margin, and thus overall as well.

I now agree that polishing is not good. My definition of polishing was more like smoothing though, and my immediate thought of "roughing" the intake was a little over-zealous.

Thanks Doc, you're a very helpful man!
Its my pleasure for sure...
 

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Discussion Starter #18
Well back to the orginal line of questioning. I am using big boyz for the porting and will follow his recomandation for pistion and head gasket. I am sure that he will steer me in the right direction.
Any way for pipes i use V/H straight shots with thunder monsters installed.
For ignigtion i plan on going with a SE race ign. module.
Paul
 

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Doc,
I interpreted that as the SE Adjustable Map Ignition System p/n 32704-01 but it's just a guess on my part.

By the way, that was a great description of how the boundary layer works in the port to keep the fuel in suspension. That's exactly what Otto described to me and why he roughed up the ports in my heads.
 
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