Decrease the Compression ratio using thicker head gasket?

[slavdude]

I have a 2019 Heritage Softail 114". This winter I am going to upgrade it with 131" Harley kit with 64mm SE throttle body and SE ported heads. The heads are machined to a compression ratio of 11:1, which would be fine with the supplied SE-517 cam. This cam closes the intake valve at 40 deg ABDC. I am a low RPM guy so I want to use the SS-465 cam for maximum low end torque.  However, SS-465 closes intake valve at 14 deg ABDC. So this cam might create too much of a CR/cylinder pressure. Am I right or do I worry too much about this? To "fix" this problem, I could use 0.020" thicker head gaskets (if they make them available). This thicker head gasket "solution" would bring the CR down to around 10.5:1, which would basically be the stock CR. I plan use the D&D Fat Cat exhaust with this build. Any suggestions on the "fix" or on this build?

[rigidthumper]

IMO- The goal is to have desired compression with zero deck height and tight quench, to improve efficiency and fight detonation. Dual plug heads (stock on the M8) allow for more compression, so I'd have the material removed from the pistons & combustion chambers.
Do not trust any "advertised" compression ratio numbers, as those are based on theory. Measure/adjust as needed.

[kd]

   Great advice. BTW welcome to HTT in 2021.

[OldMike]

I have a 2019 Heritage Softail 114". This winter I am going to upgrade it with 131" Harley kit with 64mm SE throttle body and SE ported heads. The heads are machined to a compression ratio of 11:1, which would be fine with the supplied SE-517 cam. This cam closes the intake valve at 40 deg ABDC. I am a low RPM guy so I want to use the SS-465 cam for maximum low end torque.  However, SS-465 closes intake valve at 14 deg ABDC. So this cam might create too much of a CR/cylinder pressure. Am I right or do I worry too much about this? To "fix" this problem, I could use 0.020" thicker head gaskets (if they make them available). This thicker head gasket "solution" would bring the CR down to around 10.5:1, which would basically be the stock CR. I plan use the D&D Fat Cat exhaust with this build. Any suggestions on the "fix" or on this build?

I thought the "kit" would be at 11:1 if a .030 head gasket is used, I don't know what gasket it ships with. The 131 crate engine, I think, is 10.7:1 so maybe that's what the kit is shipping as. Where did you get your information?
I was going to buy the kit for my Softail upgrade but there is just too much I don't need in that kit. I only bought the heads and cylinders, having pistons fitted for a higher compression build.

[Ohio HD]

Does anyone know what the piston negative cc's are? They're a dished piston.

[Don D]

S&S, CP
JE

[Sunny Jim]

I would've thought the 465 would be too small for that application.
There are many cams that would give you
A
Great torque response with that engine displacement.

[slavdude]

  Great advice. BTW welcome to HTT in 2021.

Thank you. There is lot of good info on this forum.

[slavdude]

Does anyone know what the piston negative cc's are? They're a dished piston.

The pistons are flat with cut outs for the valves

[slavdude]

I have a 2019 Heritage Softail 114". This winter I am going to upgrade it with 131" Harley kit with 64mm SE throttle body and SE ported heads. The heads are machined to a compression ratio of 11:1, which would be fine with the supplied SE-517 cam. This cam closes the intake valve at 40 deg ABDC. I am a low RPM guy so I want to use the SS-465 cam for maximum low end torque.  However, SS-465 closes intake valve at 14 deg ABDC. So this cam might create too much of a CR/cylinder pressure. Am I right or do I worry too much about this? To "fix" this problem, I could use 0.020" thicker head gaskets (if they make them available). This thicker head gasket "solution" would bring the CR down to around 10.5:1, which would basically be the stock CR. I plan use the D&D Fat Cat exhaust with this build. Any suggestions on the "fix" or on this build?

I thought the "kit" would be at 11:1 if a .030 head gasket is used, I don't know what gasket it ships with. The 131 crate engine, I think, is 10.7:1 so maybe that's what the kit is shipping as. Where did you get your information?
I was going to buy the kit for my Softail upgrade but there is just too much I don't need in that kit. I only bought the heads and cylinders, having pistons fitted for a higher compression build.

The dealer told me about the 11:1 CR. The kit came with 0.040" head gaskets. It sounds like the best thing to do is to check the CR once it is all put together.

[slavdude]

I would've thought the 465 would be too small for that application.
There are many cams that would give you
A
Great torque response with that engine displacement.

Yeah, the SS-465 might be too small. I will start with it and see what the # are. Then I will go from there. I've looked at more then 40 M8 cams. Most of them have mid to upper RPM range. My riding stile is that I hardly go over 3000 RPM. SS makes SS540 cam, specifically made for big inch high torque engines. However there would not be enough clearance between the valves and the pistons at the TDC. Other low RPM cam I am looking at is Zippers RS-468. It has very similar timing to SS-465, bit more lift and bit longer exhaust valve opening. We will see.

[Ohio HD]

Does anyone know what the piston negative cc's are? They're a dished piston.

The pistons are flat with cut outs for the valves

If the compression of 10.7:1 is based on an OEM CVO thickness head gasket, around 0.070" thick, assuming it's 10.7, I think I read that here and elsewhere. You would be ok with the S&S cams, maybe 230 ccp. But if a better fit head to piston as Rigidthumper said is planned, using an 0.030" head gasket, would put that compression pretty high, about 255 ccp. If I'm assuming correct, you need to add about 9cc to 10cc to the combustion chamber volume.

As Rigidthumper said, it really all needs to be measured, then decide what direction and how much volume the combustion chamber needs.

I think the motor cubic inches will give you plenty of natural low end torque. I wouldn't under cam the motor.

[Don D]

You are making assumptions that would need to be validated. The cr480 will run fine and dandy all day at 11:1
Tdc lifts will need to be checked then fix if need be. Any decent builder should feel very comfortable doing this.

[Mogollon]

The S&S465, and RS468 cams are both too small for a 131" engine, even for a 131" TQ engine.

The Gen II SE CNC Extreme head's valve springs can surely handle .517" valve lift and probably a tad more. I assume those are the heads you are using. Don't bother using the Gen I SE CNC heads; ported stock head castings are better. 

If you want a bolt-in torque cam for your mild combo, consider the S&S 475 or RS472. These cams were intended for 114 & 117 engines, but have sufficient duration for a 131 TQ motor.  They close the intake at roughly 29° and 24° abdc, respectively, and will work with well your combo.

The S&S540 TQ cam is another option, closing the intake at roughly 30°, but you will probably need aftermarket high-lift springs.

If you want a more balanced cam, consider the Red Shift 552, Andrews 554, or maybe the Max-Cell M837B cam. The RS552 closes the intake at 29° abdc, while the Andrews and Max-Cell close the intake around 34-35° abdc. But all three of these balanced cams have about .550" valve lift, and I suspect the valve springs in the Gen II SE CNC Extreme head may fall slightly short of allowing that amount of lift. If so, you will need aftermarket high-lift valve springs. Also, you would have to check valve-to-piston clearance with these cams, just to be sure.

Has anyone on this forum checked the max cam lift the Gen II SE CNC Extreme head valve springs will handle? I suspect it is somewhere between .520" and .540" lift.

The advertised static compression ratio for the SE 131 engine is 10.7:1, but it may be lower. You will have to blueprint and check everything to really know. The Gen II heads should have 94-95cc combustion chambers, the head gasket should be .040", and the pistons should be about -6cc dome volume. But again, you need to verify these numbers.

Use the stock head gasket, and machine the cylinders to get zero piston deck height. For the non-bolt-in cams, check the valve-to-piston clearance and valve-to-valve clearance.

Also, verify that your 2019 engine has the latest 8-rotor oil pump with the O-ring in it. 2019 engines shipped with the latest oil pump model starting sometime during May 2019. You can get the latest pump and O-ring backing plate for roughly $125 - $150.

[OldMike]

I'm going to use the Max Cell 837b (550 lift) cam, stock 131 SE Extreme heads and flat top pistons and .030 head gasket.

[slavdude]

The S&S465, and RS468 cams are both too small for a 131" engine, even for a 131" TQ engine.

The Gen II SE CNC Extreme head's valve springs can surely handle .517" valve lift and probably a tad more. I assume those are the heads you are using. Don't bother using the Gen I SE CNC heads; ported stock head castings are better. 

If you want a bolt-in torque cam for your mild combo, consider the S&S 475 or RS472. These cams were intended for 114 & 117 engines, but have sufficient duration for a 131 TQ motor.  They close the intake at roughly 29° and 24° abdc, respectively, and will work with well your combo.

The S&S540 TQ cam is another option, closing the intake at roughly 30°, but you will probably need aftermarket high-lift springs.

If you want a more balanced cam, consider the Red Shift 552, Andrews 554, or maybe the Max-Cell M837B cam. The RS552 closes the intake at 29° abdc, while the Andrews and Max-Cell close the intake around 34-35° abdc. But all three of these balanced cams have about .550" valve lift, and I suspect the valve springs in the Gen II SE CNC Extreme head may fall slightly short of allowing that amount of lift. If so, you will need aftermarket high-lift valve springs. Also, you would have to check valve-to-piston clearance with these cams, just to be sure.

Has anyone on this forum checked the max cam lift the Gen II SE CNC Extreme head valve springs will handle? I suspect it is somewhere between .520" and .540" lift.

The advertised static compression ratio for the SE 131 engine is 10.7:1, but it may be lower. You will have to blueprint and check everything to really know. The Gen II heads should have 94-95cc combustion chambers, the head gasket should be .040", and the pistons should be about -6cc dome volume. But again, you need to verify these numbers.

Use the stock head gasket, and machine the cylinders to get zero piston deck height. For the non-bolt-in cams, check the valve-to-piston clearance and valve-to-valve clearance.

Also, verify that your 2019 engine has the latest 8-rotor oil pump with the O-ring in it. 2019 engines shipped with the latest oil pump model starting sometime during May 2019. You can get the latest pump and O-ring backing plate for roughly $125 - $150.

Again, Thank you all for your replies.
As part of this upgrade I will replace the oil pump (SS), the clutch (Recluse), the compensator, hardware, bolts, engine covers etc. Some of it will be functional and some of it will be cosmetics. However I want to keep the bike look as much "Harley like" as possible hence, for instance, I want to keep the drive belt.
As far as the cams go, the RS472 is also a possibility.
The SE heads fall short of the 0.550" lift needed for some of the mentioned cams. And I honestly do not think I will need 550 lift for what I am doing. Proof me wrong and I will have the high lift valve springs installed!
Anyway, I will keep posting a progress report (cylinder pressure etc.) and hopefully in the end I will post some very good looking dyno run!

[Mogollon]

Good luck with your build. Make sure the S&S oil pump includes the O-ring backing plate. Early models did not.

You are correct, you don't need .550" lift for your application. I mentioned the three .550" lift cams for reasons other than lift, such as dual pattern design, amount of duration, intake valve close, and exhaust valve open specs. In this application, cam lift was the least important of the specs.

In fact, airflow on a stock set of Gen II SE CNC Extreme heads is mostly all done by .400" lift and tops off at around .500" lift, with only minor cfm gains above that. And the "intakes" actually flow more than a stock set of S&S B2 head intakes (de facto benchmark for V-Twin head airflow), so you don't need more than bolt-in cam lift for mild big-bore M8 applications.

M8s respond well to dual pattern cams biased toward exhaust duration because of the M8's cylinder head intake/exhaust ratio and the long, winding, convoluted exhaust system on baggers (I know, you got a Softail). Regardless, I was interested in cams with 20° to 35° more exhaust duration than intake. Interestingly, some noted M8 cam sellers who in the past favored only single pattern cam designs (same intake and exhaust duration) have introduced their M8 Gen II cams using a dual pattern design. Apparently, they have learned that dual pattern cams work with M8 heads.

And for a mild, low compression 131ci pump gas street motor, closing the intake valve somewhere between 25° and 35° degrees abdc, and not in the 40°+ range would work well. Also, a relatively early exhaust valve opening, around 60°-ish bbdc would work. It just so happened that the three selected cams (balanced-engine cams, as I called them) have valve lifts in the .550" range, but lift was the least important of the cam stats. For your street application, a bolt-in .470" valve lift range would be fine. I only listed the .550" lift cams to offer options beyond bolt-in torque cams.

And for two more bolt-in cam options, checkout the Chris Rivas 474 and Feuling 472 cams.

[slavdude]

You made very interesting point about the "dual pattern cams"! When I was researching the M8 heads and their flow bench data I read somewhere that the M8 exhaust flows at around 75% of the intake. Now, I know nothing about what kind of flow engine head need, nevertheless I was bit puzzled by this because, what goes in must come out so intake/exhaust should flow at about the same? As I said, I know nothing about this, I am just using layman's logic. Hence longer exhaust valve opening would do the trick.
Anyway, in the end my plan is to get custom grind cam, if it becomes necessary. But first I want to get the engine build and tested and get some data. The 131 "stage 4" kit is really ment for mid to high RPM application. So it will be little bit of a trial and error journey for me.

[kd]

Remember that the exhaust begins to blow off under pressure and builds velocity to discharge the spent gasses.  The effects of exhaust valve timing, duration, overlap, when the intake opens and pipe all hold hands to clear the cylinder.

[rigidthumper]

You made very interesting point about the "dual pattern cams"! When I was researching the M8 heads and their flow bench data I read somewhere that the M8 exhaust flows at around 75% of the intake. Now, I know nothing about what kind of flow engine head need, nevertheless I was bit puzzled by this because, what goes in must come out so intake/exhaust should flow at about the same? As I said, I know nothing about this, I am just using layman's logic. Hence longer exhaust valve opening would do the trick.
Anyway, in the end my plan is to get custom grind cam, if it becomes necessary. But first I want to get the engine build and tested and get some data. The 131 "stage 4" kit is really ment for mid to high RPM application. So it will be little bit of a trial and error journey for me.

Intake has to be vacuumed in, along with fuel, whereas the exhaust is blown out under pressure, and fuel has already been consumed- thus the reason for larger intake than exhaust.

[kd]

   Well said in Readers Digest terms.