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Alexander_Monday
Samba Member
Joined: November 09, 2007
Posts: 407
Location: Springfield Missouri
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 Posted: Mon Aug 11, 2025 11:03 am Post subject: Re: Need higher compression ratio |
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| chrisflstf wrote: |
If you have 5.4 rods, switching to 5.325 would reduce your deck from .120" to .045"
There are other methods. Shorten cylinders, deck case or change shims, if used |
Maybe I am not thinking correctly, but wouldn't a shorter rod increase it?
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Danth’s or Parker’s Law:
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Alexander_Monday->What were the rings gapped at?
bedlamite->Almost enough.
| andk5591 wrote: |
The original german engineers have attained sainthood and it is impossible to improve perfection.
Anything that anyone does to deviate from the original designs will be made to wrench on 20 year old Yugos with Harbor Freight tools in hell. |
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chrisflstf
Samba Member
Joined: February 10, 2004
Posts: 4108
Location: San Diego
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| Posted: Mon Aug 11, 2025 11:56 am Post subject: Re: Need higher compression ratio |
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Yep, my bad. disregard my comment about the shorter rod  |
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SGKent 
Samba Member
Joined: October 30, 2007
Posts: 42754
Location: at the beach
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| Posted: Mon Aug 11, 2025 5:42 pm Post subject: Re: Need higher compression ratio |
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| BFB wrote: |
| for some reason in the vw community its been thought that running more compression equals more heat. probably another one of the " so and so said it so we believe it" scenarios. good to see ppl are finally breaking away from it more and more. |
Running more compression always generates more heat. That is why the amount of produced power goes up with more compression, and why engines increased compression as computers allowed engines to manage that heat better. The incoming charge expands more than with lower compression. Basic physics and engine design 101. Managed higher compression also increases engine efficiency.
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BFB
Samba Member
Joined: November 03, 2014
Posts: 2752
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| Posted: Mon Aug 11, 2025 8:05 pm Post subject: Re: Need higher compression ratio |
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| SGKent wrote: |
| BFB wrote: |
| for some reason in the vw community its been thought that running more compression equals more heat. probably another one of the " so and so said it so we believe it" scenarios. good to see ppl are finally breaking away from it more and more. |
Running more compression always generates more heat. That is why the amount of produced power goes up with more compression, and why engines increased compression as computers allowed engines to manage that heat better. The incoming charge expands more than with lower compression. Basic physics and engine design 101. Managed higher compression also increases engine efficiency. |
keep running your Gene Berg 7:1 CR then. same bullshit as the old 7psi rule, and can't boost with stock internals.
guaranty you a 9:1 runs cooler and more efficient than 7
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WaterBuggy_24
Samba Member
Joined: January 19, 2024
Posts: 73
Location: KCMO
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| Posted: Tue Aug 12, 2025 11:14 am Post subject: Re: Need higher compression ratio |
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| Brian_e wrote: |
The math isn’t mathing.
According to my calculations, with a 1929cc, 50cc chambers, and a .01195 deck, it should be 7.8:1.
Still way too low.
Not trying to be an asshole here, but your heads were just about ruined when they were flycut so far. I never understand why a builder would Flycut the crap out of the heads, just to add it back in with deck height. 
The .01195 average deck is terrible, but I think if you re-arrange a few things, it might be salvageable into a decent little combo.
If you took the top end apart, and got the deck height down to a proper .045”, that wil get your compression up to 9.3, which will be just about perfect for the cam you have.
I guarantee you it will be a totally different engine. It will run cooler, have WAY better throttle response, and make quite a bit more power.
Should be an easy, inexpensive fix also. You will need to re-check your rocker geometry because the heads have moved a decent amount. This is good, because judging by the deck height, the chances of the rocker geometry being set up correctly right now are pretty slim. I am gonna guess it probably has roller ball Mazda adjuster screws on it also???
Last, post some pics of the heads. Those outlaw heads are just stock castings with big valves tossed in. If you pulled them apart, blended the bowls, did a little unshrouding, and recut the seats, they would also transform the engine.
If you spend the time to dial in the deck height, and fix the heads, your engine will all fall into place, and it will actually be a pretty correct combo, and it will work quite well.
Brian |
I did have the heads off and checked the geometry of the rockers. It has 1.1:1 rockers w/
Stock adjusters and everything lines up correctly. I did notice it uses aluminum pushrods. I was having a problem with fuel soot faulling up the combustion chambers and I at first thought it was a carb issue but I no longer think thats the issue. I was wondering if it wasn't evacuating the cylinder because of the overlapp. It runs great at high rpms but I kknow it could be much better performance wise.What grade of fuel would be required at 9.3:1 cr?
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Brian_e
Samba Member
Joined: July 28, 2009
Posts: 4058
Location: Rapid City, South Dakota
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| Posted: Tue Aug 12, 2025 11:26 am Post subject: Re: Need higher compression ratio |
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Running rich with low compression, and a huge deck is what is fouling up the chambers. The tops and bottoms of the piston tops should be almost clean when your deck height is correct.
I build everything to run on 91. Its available everywhere, and the cost difference is minimal to be on the safe side. Its also usually the ethanol-free stuff.
Brian
_________________
So more or less the lazier and stupider you want to be, the nicer quality parts you need to buy.
-Modok
Narrowed beams, Drop adjustable spring plates, Bus disk brake and IRS kits.
www.type-emotorsports.com
Type E Engine Parts and Supplies
https://type-emotorsports.com/collections/engine-parts |
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sled
Samba Member
Joined: February 16, 2005
Posts: 6256
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| Posted: Tue Aug 12, 2025 11:50 am Post subject: Re: Need higher compression ratio |
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get your deck height down to .058 by whatever means necessary. Remove shims or shorten cylinders. Then Let 'er rip!
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drive your split. |
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SGKent
Samba Member
Joined: October 30, 2007
Posts: 42754
Location: at the beach
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| Posted: Tue Aug 12, 2025 12:08 pm Post subject: Re: Need higher compression ratio |
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| BFB wrote: |
| SGKent wrote: |
| BFB wrote: |
| for some reason in the vw community its been thought that running more compression equals more heat. probably another one of the " so and so said it so we believe it" scenarios. good to see ppl are finally breaking away from it more and more. |
Running more compression always generates more heat. That is why the amount of produced power goes up with more compression, and why engines increased compression as computers allowed engines to manage that heat better. The incoming charge expands more than with lower compression. Basic physics and engine design 101. Managed higher compression also increases engine efficiency. |
keep running your Gene Berg 7:1 CR then. same bullshit as the old 7psi rule, and can't boost with stock internals.
guaranty you a 9:1 runs cooler and more efficient than 7 |
boy you jump conclusions for someone who knows nothing about me or my background and experience. One chooses the compression ratio that serves their needs. This kiddy I know more than you bullshit 16 year old crap gets really old. Shed your adolescent temper someplace else.
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redhot
Samba Member
Joined: February 05, 2005
Posts: 527
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| Posted: Tue Aug 12, 2025 12:29 pm Post subject: Re: Need higher compression ratio |
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Two things can be right at the same time...
The theoretical understanding and what drives then the engineering - as in this link; https://www.sciencefacts.net/otto-cycle.html
The practical implementation (engineering) and daily language where there are good and poor designs that results in an unncessiarly warm running engine given the power it produces (losses basically).
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BFB
Samba Member
Joined: November 03, 2014
Posts: 2752
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| Posted: Tue Aug 12, 2025 4:56 pm Post subject: Re: Need higher compression ratio |
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| SGKent wrote: |
| BFB wrote: |
| SGKent wrote: |
| BFB wrote: |
| for some reason in the vw community its been thought that running more compression equals more heat. probably another one of the " so and so said it so we believe it" scenarios. good to see ppl are finally breaking away from it more and more. |
Running more compression always generates more heat. That is why the amount of produced power goes up with more compression, and why engines increased compression as computers allowed engines to manage that heat better. The incoming charge expands more than with lower compression. Basic physics and engine design 101. Managed higher compression also increases engine efficiency. |
keep running your Gene Berg 7:1 CR then. same bullshit as the old 7psi rule, and can't boost with stock internals.
guaranty you a 9:1 runs cooler and more efficient than 7 |
boy you jump conclusions for someone who knows nothing about me or my background and experience. One chooses the compression ratio that serves their needs. This kiddy I know more than you bullshit 16 year old crap gets really old. Shed your adolescent temper someplace else. |
The problem with this is you assume i give a shit about you and that you matter to me and you think your life’s accomplishments are special. I dont, you dont, and they arent.
Dont want to hear my b.s. then dont address me because I’ll reply and then you’ll have to hear my “b.s.” then you’ll get all upset and feel your expertise has been challenged.
if you were half as smart as you think you are youd know this already from my previous posts that apparently you are well aware of because it “gets really old” for you.
Really seems pretty simple to me, dont like me or my b.s. then dont talk to me or quote me, OOORRRR theres this little button that says “ignore”, im sure if you dont know how to use it someone here will assist you.
People disagree and most of use here are men that can take some ball busting, ever read threads on here from 10 years ago? Sorry you cant though, i really didnt think my comment was so hurtful though, especially considering things ive said before, i thought i did real good.
Also didnt know we were considering that OP would be wanting to run something like 12:1 CR, so didnt think we’d be addressing the issues that might arise from that kind of compression ( hence my 9:1 comment ) but feel free to twist things around to fit your agenda and make your point.
Maybe post some temps on a 7:1 vs 9:1 or hell even throw in a 12:1 too. If your so impressive and background is so noteworthy then im sure you have all kinds of data.
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"how am i supposed to torque the rear wheel nut to 250 ft lbs??? " - clonebug
An interesting thing happens in forums where everyone starts parroting the same thing and "common knowledge" takes over.
Most experts aren't. |
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WaterBuggy_24
Samba Member
Joined: January 19, 2024
Posts: 73
Location: KCMO
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| Posted: Tue Aug 12, 2025 10:54 pm Post subject: Re: Need higher compression ratio |
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| Brian_e wrote: |
Running rich with low compression, and a huge deck is what is fouling up the chambers. The tops and bottoms of the piston tops should be almost clean when your deck height is correct.
I build everything to run on 91. Its available everywhere, and the cost difference is minimal to be on the safe side. Its also usually the ethanol-free stuff.
Brian |
Non-ethanol is what I run. It doesn't draw moisture as bad. Moisture and ethanol will cause aluminum oxide crystals to form in my aluminum fuel tank. It is also hard on rubber seals and lines as it shrinks rubber over time. I think Im going to go with a trim on my cylinders when it gets cold out. Thanks for the input.
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One day, I may learn.
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Brian_e
Samba Member
Joined: July 28, 2009
Posts: 4058
Location: Rapid City, South Dakota
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| Posted: Wed Aug 13, 2025 9:03 am Post subject: Re: Need higher compression ratio |
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I am guessing there is a big stack of shims that need to be removed. Then measure where you are for deck, and trim or shim accordingly.
Brian
_________________
So more or less the lazier and stupider you want to be, the nicer quality parts you need to buy.
-Modok
Narrowed beams, Drop adjustable spring plates, Bus disk brake and IRS kits.
www.type-emotorsports.com
Type E Engine Parts and Supplies
https://type-emotorsports.com/collections/engine-parts |
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SGKent
Samba Member
Joined: October 30, 2007
Posts: 42754
Location: at the beach
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| Posted: Wed Aug 13, 2025 12:17 pm Post subject: Re: Need higher compression ratio |
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| Quote: |
| The problem with this is you assume i give a shit about you |
actually I have you pegged for a 16 year old in maturity with "Narcissist in Training" on your hat.
I stand by my statement that increasing compression increases the amount of heat that the engine must shed. One chooses the compression ratio to meet their needs. If they want to run cheaper lower octane gasoline in it as a daily driver, a lower CR is used. If they plan to win drag races, they run the highest CR that can be run with a very high octane fuel to prevent detonation. Most people who build high performance engines, and there are many of those people here on TheSamba, use this principle when they design and build their award winning engines. VW on the other hand detuned some of their engines due to inability to shed heat. VW Buses are famous for melting pistons, dropping valve seats from overheated heads, tossing rods from excessive bearing wear due to overheated hot oil etc.. If VW could have solved these things by just raising CR they would have. Instead they solved it by lowering CR down around the mid 7's, detuning timing, lowering cam duration, and adding more restrictive exhausts. They went the total opposite direction than their higher performance cars and sibling cars like Porsche models. A 2L bus type 4 engine (GD or GE) runs 7.3:1 with all the methods above to detune it. The same 2L engine in a Porsche 912e (GA) runs 8:0:1, a much higher duration cam and substantially lower restriction in the exhaust.
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oprn
Samba Member
Joined: November 13, 2016
Posts: 14872
Location: Western Canada
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| Posted: Wed Aug 13, 2025 1:26 pm Post subject: Re: Need higher compression ratio |
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There are 2 schools of thought about the type 4 Bus engine. Some believe as you do that VW detuned the engine to get better life out of it while others believe VW created a hot valve and head eating monster by doing so.
The fact of the matter is that the type 4 engine exhibited NONE of the problems in the 411/412, 914 and 912E that it did with the detuned version they put in the Bus. If VW's intension was to make them run cooler by lowering the CR... it was a complete and utter failure!
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BFB
Samba Member
Joined: November 03, 2014
Posts: 2752
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| Posted: Wed Aug 13, 2025 5:00 pm Post subject: Re: Need higher compression ratio |
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| oprn wrote: |
There are 2 schools of thought about the type 4 Bus engine. Some believe as you do that VW detuned the engine to get better life out of it while others believe VW created a hot valve and head eating monster by doing so.
The fact of the matter is that the type 4 engine exhibited NONE of the problems in the 411/412, 914 and 912E that it did with the detuned version they put in the Bus. If VW's intension was to make them run cooler by lowering the CR... it was a complete and utter failure! |
You preach it Oprn!
| SGKent wrote: |
| Quote: |
| The problem with this is you assume i give a shit about you |
actually I have you pegged for a 16 year old in maturity with "Narcissist in Training" on your hat. |
Im pretty sure ive told you this before, and youve ignored it then as you do now, you really need to watch the “boy” name calling. That’s actually a very racist term these days and if i were to happen to have African decent youd have just gotten the Samba into some problems for allowing it. ( i dont , but since we cant see each other it could’ve been possible )
Also, you shouldnt be posting that you like pegging 16 year olds either. Ok, ok, i stretched it a little there but regardless , you should not use the term “pegging” and 16 year old in the same sentence. You can see how your comment could be misread. If you’re not sure about either of these things, google it. Im just trying to help you before you end up causing yourself and the board problems with your racist and potentially sexually deviant comments.
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"how am i supposed to torque the rear wheel nut to 250 ft lbs??? " - clonebug
An interesting thing happens in forums where everyone starts parroting the same thing and "common knowledge" takes over.
Most experts aren't. |
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sled
Samba Member
Joined: February 16, 2005
Posts: 6256
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| Posted: Thu Aug 14, 2025 9:32 am Post subject: Re: Need higher compression ratio |
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how do you guys always manage to fuck up threads? blows my mind.
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drive your split. |
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RickS
Samba Member
Joined: May 05, 2005
Posts: 605
Location: Speonk, NY
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| Posted: Thu Aug 14, 2025 9:59 am Post subject: Re: Need higher compression ratio |
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| sled wrote: |
| how do you guys always manage to fuck up threads? blows my mind. |
There are a couple of guys on the Samba that feel the need to opine about everything, whether it is meaningful or not. Unfortunately, they never see themselves as the problem. |
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Brian_e
Samba Member
Joined: July 28, 2009
Posts: 4058
Location: Rapid City, South Dakota
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| Posted: Thu Aug 14, 2025 10:24 am Post subject: Re: Need higher compression ratio |
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| RickS wrote: |
| sled wrote: |
| how do you guys always manage to fuck up threads? blows my mind. |
There are a couple of guys on the Samba that feel the need to opine about everything, whether it is meaningful or not. Unfortunately, they never see themselves as the problem. |
Been happening more and more lately. Guys posting just to hear themselves talk...
Brian
_________________
So more or less the lazier and stupider you want to be, the nicer quality parts you need to buy.
-Modok
Narrowed beams, Drop adjustable spring plates, Bus disk brake and IRS kits.
www.type-emotorsports.com
Type E Engine Parts and Supplies
https://type-emotorsports.com/collections/engine-parts |
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vwracerdave
Samba Member
Joined: November 11, 2004
Posts: 15601
Location: Deep in the 405
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| Posted: Thu Aug 14, 2025 11:03 am Post subject: Re: Need higher compression ratio |
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| RickS wrote: |
| sled wrote: |
| how do you guys always manage to fuck up threads? blows my mind. |
There are a couple of guys on the Samba that feel the need to opine about everything, whether it is meaningful or not. Unfortunately, they never see themselves as the problem. |
I took a good long look in the mirror and saw exactly what you just described.
I have turned into a Karen. It takes a lot of balls to admit I've become an asshole.
Now I'm pointing my finger at Glenn, orpn, and maybe BFB.
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58 Plastic Tub
Samba Member
Joined: September 03, 2007
Posts: 506
Location: Nowhere, USA
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| Posted: Thu Aug 14, 2025 11:21 am Post subject: Re: Need higher compression ratio |
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| vwracerdave wrote: |
I took a good long look in the mirror and saw exactly what you just described.
I have turned into a Karen. It takes a lot of balls to admit I've become an asshole.
Now I'm pointing my finger at Glenn, orpn, and maybe BFB. |
Well, since you have taken that good long look -- I've really appreciated your posts. It takes a big man to admit the things you've been admitting to. A bit of introspection and self-regulation would do all of us some good.
Maybe your example will improve the climate here. Well done.
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"A single point in isolation is a reference point. Two points is a line. Three points is a trend. Trends don't lie." |
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