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borninabus Samba R&D Dept.
Joined: May 18, 2006 Posts: 4539 Location: Arizona Highways
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Posted: Wed Aug 24, 2011 8:16 pm Post subject: i need to lower my compression ratio |
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i will open this for discussion:
the engine of reference is in my sig line and lives in a 71 bus.
it runs on 87 octane cheap shizz.
i bring this to you boys because i have a few options at this point and i need to decide where to go from here...
please keep in mind that this a $100 (cyl hone & rings / shims?) top end job that i will be doing myself.
i will not be splitting the case or springing for any NEW parts whatsoever
this is not a race engine! just a 'built' engine that gets me & family where we need or want to be every day in a fun, economical & peppy manner.
this is what i built:
AH 1600
69x85.5
stock cam, stock longblock basically, save the C/W crank.
040 heads w/ 48cc chambers
.053 deck
o19 (please, no timing questions)
zenith on an old EMPI manifold (isolated runner) ((jetted with an AFM))
in 20,000mi it always ran hot---head temp 350+ mounted on a head stud--and it started pinging when the weather turned hot.
i have it apart now and it turns out my heads have the step cut out and my chamber cc is only 48cc
plug those #s into CBs super computer and it comes up w/ 8.1:1 which is too much for a bus w/ a stock cam and leanish jetting, IMO.
so i want to lower my C/R to 7.5:1.
OK, i have some options:
1) shim cylinders .020 and have .073 deck and 7.8:1
2) add CC's by either dishing the pistons, sinking the valves, or manicuring the heads. i need about 5cc's.
3) all of the above.
it doesn't appear that i can 'restore' the stock step in the head because copper gaskets are not available in the size i need.
i think that i would like to keep a tight deck (.053, no shims) and possibly unshroud the intake valves a bit. but there is no way i'm gonna come up with 5cc's that way.
someone with deep VW lineage--the deepest, deeper than mine and yours combined, i promise; recommended that i hemi cut.
what says you _________________ 88 Van WBX, A/T - 13 JSW TDI 6M/T - 2012 Touareg TDI Sport |
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baked beetle Samba Member
Joined: September 23, 2006 Posts: 1162 Location: Alberta, Canada
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Posted: Wed Aug 24, 2011 8:24 pm Post subject: |
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stick a .020 copper shim on top of the cylinder and drive it. don't worry about your deck height. it' not a race engine
At least if it does fix your problem then you did good diagnosing. _________________ These days people like me are hard to find- we don't give a damn what you think, about what we think. - JR
____________________
66' His
57' Theirs
63' Hers
62' Drag Bug - Theirs 13.1 @ 101 mph (GONE) |
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borninabus Samba R&D Dept.
Joined: May 18, 2006 Posts: 4539 Location: Arizona Highways
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Posted: Wed Aug 24, 2011 8:30 pm Post subject: |
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i cant find copper gaskets in ..010"-020" or 85.5mm _________________ 88 Van WBX, A/T - 13 JSW TDI 6M/T - 2012 Touareg TDI Sport |
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Cusser Samba Member
Joined: October 02, 2006 Posts: 31379 Location: Hot Arizona
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Posted: Wed Aug 24, 2011 8:52 pm Post subject: |
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On my 1835 engine (in 1986) I added shims underneath the cylinder, between case and cylinder, to decrease the compression. So I use regular unleaded. _________________ 1970 VW (owned since 1972) and 1971 VW Convertible (owned since 1976), second owner of each. The '71 now has the 1835 engine, swapped from the '70. Second owner of each. 1988 Mazda B2200 truck, 1998 Frontier, 2014 Yukon, 2004 Frontier King Cab. All manual transmission except for the Yukon. http://www.thesamba.com/vw/forum/album_page.php?pic_id=335294 http://www.thesamba.com/vw/forum/album_page.php?pic_id=335297 |
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borninabus Samba R&D Dept.
Joined: May 18, 2006 Posts: 4539 Location: Arizona Highways
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Posted: Wed Aug 24, 2011 9:02 pm Post subject: |
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so VW thought that approx .050 deck was OK but they used a step to keep combustion in the chamber is the way i'm understanding it.
Cuss: your 1835 is in a light Baja or something, right? _________________ 88 Van WBX, A/T - 13 JSW TDI 6M/T - 2012 Touareg TDI Sport |
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modok Samba Member
Joined: October 30, 2009 Posts: 26790 Location: Colorado Springs
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Posted: Wed Aug 24, 2011 9:19 pm Post subject: |
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most 040 heads did not have a step
grind a few cc outa the chambers, it won't take much |
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craigman Samba Member
Joined: March 28, 2004 Posts: 2397 Location: redding
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Posted: Wed Aug 24, 2011 9:23 pm Post subject: |
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I'd bet $$$ that your running WAY hotter head temps than you think you are.
The temp probe does NOT belong on a head stud. You need to put it as close to the heat source that you can. And that's under the spark plug.
And, too low of compression can make it run hot.
What makes you think you need to lower the compression? |
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DarthWeber Samba Member
Joined: November 24, 2007 Posts: 7543 Location: Whittier,CA
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Posted: Wed Aug 24, 2011 9:52 pm Post subject: |
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modok wrote: |
grind a few cc outa the chambers, it won't take much |
Agreed. Open the chambers up 5cc, that will get you where you need to be and it's the proper way to acomplish the job. Don't add shims, keep the deck tight. Don't dish the pistons, you'll lose critical piston crown thickness that acts as a heat dam. _________________
Mitey62 wrote: |
Swapped the Compufire for a Bosch blue and some points I had sitting around, started 1st crank. Took her out for a drive, pulls harder, more RPM, and runs smoother. I think I'll be sticking with points from now on. |
RockCrusher wrote: |
JB weld the case halves....that'll keep the fretting to a minimum. |
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jfats808 Samba Member
Joined: December 10, 2007 Posts: 5022 Location: oahu hawaii
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Posted: Wed Aug 24, 2011 10:44 pm Post subject: |
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I agree with craig that you are running hotter th an you moght think. I read your post and know that you dont want to run a better octane , but that coupled with running a fatter jetting might get you running cooler. Sorry gotta mention also, might want to play with timing a bit. I wouldve tried these two options first before tearing down. My two bits. _________________ 2276 IDA's 86C 11-1 DD !
2017 48 Trijet DRLA's W125
Rockstar Suzuki wrote: |
You might as well put 10 year build in your bullshit sig, as it will NEVER run. Also your a dick |
You can always learn something new, even from a fool.
Check your oil levels routinely! |
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craigman Samba Member
Joined: March 28, 2004 Posts: 2397 Location: redding
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Posted: Wed Aug 24, 2011 11:23 pm Post subject: |
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Also i just don't understand why people refuse to use higher octane fuel.
What extra does it cost at fill up time? A dollar or two? That's the price of a burger or a pack of smokes.. |
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borninabus Samba R&D Dept.
Joined: May 18, 2006 Posts: 4539 Location: Arizona Highways
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Posted: Wed Aug 24, 2011 11:30 pm Post subject: |
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craigman wrote: |
I'd bet $$$ that your running WAY hotter head temps than you think you are.
The temp probe does NOT belong on a head stud. You need to put it as close to the heat source that you can. And that's under the spark plug.
And, too low of compression can make it run hot.
What makes you think you need to lower the compression? |
couldn't agree with you both more.
thinking that the head temps are 100+* hotter @ the plug YIPES!
that's hot
the facts are:
it pings like crazy when pulling a load and i've discovered 8.1:1 compression.
that leads me to believe that i need it needs to be lowered.
jfats808 wrote: |
I agree with craig that you are running hotter th an you moght think. I read your post and know that you dont want to run a better octane , but that coupled with running a fatter jetting might get you running cooler. Sorry gotta mention also, might want to play with timing a bit. I wouldve tried these two options first before tearing down. My two bits. |
believe you me; i have tried these options.
OCDish changing jets in a zenith--in a bus--carb installed.
i have been down this road...
sure, you can run it FAT, retard the timing and it'll do OK.
but it still runs hot and it's still not right.
soooo.....
can i get 5cc's out of the intakes or should i be thinking hemi?
or both? _________________ 88 Van WBX, A/T - 13 JSW TDI 6M/T - 2012 Touareg TDI Sport |
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craigman Samba Member
Joined: March 28, 2004 Posts: 2397 Location: redding
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Posted: Wed Aug 24, 2011 11:46 pm Post subject: |
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8.8:1 compression is NOT making your engine run hot. You have other issues.
Lowering your compression is NOT going to help you.
I'm willing to be you have no idea what your A/F is. Too lean can run hot, as well as too rich can run hot..
Find out what is making it run hot and fix the problem. Masking the problem won't do your engine any good. |
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borninabus Samba R&D Dept.
Joined: May 18, 2006 Posts: 4539 Location: Arizona Highways
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Posted: Thu Aug 25, 2011 8:29 am Post subject: |
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craigman wrote: |
8.8:1 compression is NOT making your engine run hot. You have other issues.
Lowering your compression is NOT going to help you.
I'm willing to be you have no idea what your A/F is. Too lean can run hot, as well as too rich can run hot..
Find out what is making it run hot and fix the problem. Masking the problem won't do your engine any good. |
i don't really want to get into a pissing contest here...
i understand what you are saying even though i'm not too receptive to the way you are saying it.
the whole point of what i'm doing is to eliminate variables and C/R is a big variable that i've found.
so i'm going to lower it and i'll let you know how it works out.
AFRs: mid 12s WOT, 14s & 15s under light throttle & load _________________ 88 Van WBX, A/T - 13 JSW TDI 6M/T - 2012 Touareg TDI Sport |
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craigman Samba Member
Joined: March 28, 2004 Posts: 2397 Location: redding
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Posted: Thu Aug 25, 2011 8:48 am Post subject: |
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Not pissing at all, just trying to help!
John at aircooled.net recommends (and i agree) that:
range of 16:1 for light throttle (progression circuit), and 12.75-13:1 from 1/2-Full Throttle.
But you seem to have it figure out already.
Good luck! |
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baked beetle Samba Member
Joined: September 23, 2006 Posts: 1162 Location: Alberta, Canada
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Posted: Thu Aug 25, 2011 9:08 am Post subject: |
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i run 10.9:1 (2234cc) on Shell 92 octane fuel with no pinging and heads temps of 375 (which is probably low considering the vdo gauge) after 3 hot lap runs in my race car going full throttle. I have simple fans cooling the heads but have not even seen 400 on the gauge.
I too, do not think .5 of a drop is going to fix your problems. _________________ These days people like me are hard to find- we don't give a damn what you think, about what we think. - JR
____________________
66' His
57' Theirs
63' Hers
62' Drag Bug - Theirs 13.1 @ 101 mph (GONE) |
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borninabus Samba R&D Dept.
Joined: May 18, 2006 Posts: 4539 Location: Arizona Highways
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Posted: Thu Aug 25, 2011 9:43 am Post subject: |
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baked beetle wrote: |
I too, do not think .5 of a drop is going to fix your problems. |
i'm not looking at the C/R as the magic bullet either.
just thinking it's a step in the right direction and am asking for advise on the 'best' way to go about it _________________ 88 Van WBX, A/T - 13 JSW TDI 6M/T - 2012 Touareg TDI Sport |
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jsturtlebuggy Samba Member
Joined: August 24, 2005 Posts: 4496 Location: Fair Oaks/Orangevale, CA
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Posted: Thu Aug 25, 2011 9:49 am Post subject: |
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Volkswagen keep dropping the compression ratio for stock engines as the gasoline changed.
The last engine in the 1970s where at 7.3 to 1 and recommended 91RON.
You have a stock camshaft with very little overlap and want to run 87 octane rated gasoline with 7.5 to 1 compression ratio. Not a good idea unless you think you are smarter than the VW engineers.
For example the VW Bugs in Mexico drop the compression to 6.6 to 1 and recommended 88 octane as minimum.
Even the 36hp engines use less than 7 to 1 compression ratio in the 1950s.
What you are asking to do with using the cheapest fuel and higher than stock recommended compression ratio is not possible for an engine to run cool and live very long.
Drop the compression ratio, yes you will notice a lack of performance, but your engine will run cooler and live longer. _________________ Joseph
Fair Oaks/Orangevale, CA
Elrod Motorsports
Motion Tire Motorsports
Having fun with Dune Buggies since 1970
Into Volkswagens since 1960 |
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jfats808 Samba Member
Joined: December 10, 2007 Posts: 5022 Location: oahu hawaii
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Posted: Thu Aug 25, 2011 9:50 am Post subject: |
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Cheapest route at this time is stick shims/copper gaskets in there and see. Head shaving is next. Guess .070 + deck is your next option. What about plumbing in an oil cooler-fan? _________________ 2276 IDA's 86C 11-1 DD !
2017 48 Trijet DRLA's W125
Rockstar Suzuki wrote: |
You might as well put 10 year build in your bullshit sig, as it will NEVER run. Also your a dick |
You can always learn something new, even from a fool.
Check your oil levels routinely! |
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yamaducci Samba Member
Joined: March 30, 2010 Posts: 2335 Location: Mount Airy, Maryland
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Posted: Thu Aug 25, 2011 12:30 pm Post subject: |
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How was the carbon build up in the chambers and piston tops?
Was it measurable?
You say it started pinging which leads me to believe either carbon increased your compression ratio or mearly the ambient temp changes your air density just enough to mess with the engine tune. I say given your take on this with not wanting to spend excessive money on new parts and not knowing your skill level to do chamber work or have the time / tools to do it; just go for the $6 shims under the cylinders that CB sells and give it a shot.
Don't get me wrong; if you wanted to do it right I would have a whole 'nother answer for you.
Don't under estimate carb and ignition tuning as has been mentioned. I understand it can be trivial but a lot cheap on time and money to correct. _________________ -John Cox
My 2498 Turbo Re-Build Thread: http://www.thesamba.com/vw/forum/viewtopic.php?p=5578697#5578697
3rd Brake Light Safety Stars- I still have a couple with blue light left. Email me if interested. |
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Gary Massin-Ball Samba Member
Joined: March 10, 2004 Posts: 377
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Posted: Thu Aug 25, 2011 12:37 pm Post subject: |
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No to the Hemi cut! it's best to leave the "quench" area in the heads for proper combustion.
If you cut a dish in your piston 1.5mm deep and 70mm diameter this will give you 6cc of extra combustion chamber and still leave active quench area on the piston..
What wieght oil are you using? what is your cruising speed and RPM?
Deep sump? 2.5 qts in the stock sump is too little I think.
Could be at hwy speeds you are overwhelming the stock cooler.
Thinner oil could help and a 3.5qt deep sump is a no brainer.
3x on trying the shims in the head to check your theory.
These are steel head shims avaiable at cip1.com
C13-21-5008 - EMPI -CYLINDER SPACERS - BETWEEN HEAD & BARREL - SET OF 4 -.030 INCH THICK - 15-1600cc BEETLE ENG.
Website Discount Price US $7.95
C13-21-5009 - EMPI -CYLINDER SPACERS - BETWEEN HEAD & BARREL - SET OF 4 -.060 INCH THICK - 15-1600cc BEETLE ENG.
Website Discount Price US $7.95 _________________ Warrior sand rail:
2276cc 82x94
Engle FK-41 with 1.25:1 street style rockers
40x35.5 stock cast single port heads
Single 40mm Kadron w/32vent
Equalizer 5lb pulley
Stock lifters
Stock aluminum pushrods
26mm aluminum oil pump full flow
*Poor mans rack and pinion up front*
-------------------------------------------
The Ugly Bug is on the road!
Last edited by Gary Massin-Ball on Thu Aug 25, 2011 1:07 pm; edited 1 time in total |
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