VW Engine Build: Top End Install Part 1, compression ratio, pistons

Aircooled Volkswagen Type 1 engine building video: Top End Install Part 1, Type 1, 1500-1600cc.
In this segment, VW engine building guru Mike Smith shows how to measure the combustion chamber volume inside the head, in order to calculate the compression ratio of the engine. Other subjects covered here include proper positioning of the piston rings inside the jug, and assembling the piston/piston pin/jug on the rods. The deck height of the VW engine is also measured here, and that volume is included in the compression calculations.
Formulas for setting compression ratio:
Swept volume of one cylinder = Engine size divided by four
Bore (in mm’s) x Bore (in mm’s) x Deck Height (inches) x .01996 = Deck Volume (in cc’s)
Head cc’s + Deck cc’s + 1 cylinder swept volume
---------------------------------------------------------------------- = CR (:1)
Head cc’s + Deck cc’s
Depending on the octane you are running, your target compression ratio should be set at factory level, or preferably lower, for street gas. Use machined, not stamped, spacers under the jugs to lower the C.R. Note that the compression ratio on an engine assembled with stock, brand new parts is almost 7.7:1. The exception to the new-parts rule might be if you were using the very latest Mexican factory dual-port heads, because some of them have 57-58cc combustion chambers, which allows you to run the smallest possible deck height.
These C.R. recommendations revolve around running a stock cam. If you are building a performance motor that uses a more radical camshaft, there is some room to run more compression. The reason for that is because cams with more duration are less efficient at lower rpm's, so the dynamic C.R.(which is the C.R. actually seen by the motor) is less at lower rpms. The tendency to detonate is also most prevalent at lower rpm's. However, as the octane level of pump gas continues to plunge, there still isn't much room for high C.R. on the street. In most of California, for instance, the best pump gas you can get is only 91 octane.
The compression ratio used on the 1970’s Beetles was 7.3:1, but the chemical composition and octane level of the gas was different back then. That octane rating system(RON) involved a different testing procedure than the rating system used today, which is (RON+MON)/2. It is now called the CLC rating system.
In 1978 or so the VW factory tried to end the confusion over what gas to run by claiming that “91 RON equals 87 CLC”. This statement was made in the 1978 bus owners manual, but it is conspicuously absent from the 1979 Bentley manual, which recommends only RON-rated fuel.
If your compression is set too high for the octane you are running, there is a risk of engine damage. The best way to maximize your engine's efficiency is to run the tightest deck and the biggest possible squish area. You will need the largest possible head cc's to do this.
There is further relevant information on octane ratings and compression in the excellent internet gasoline faq. Here is an excerpt regarding octane requirements for carbureted engines with non-management systems (ratings are CLC):
Compression Ratio: Octane Number Requirement: Brake Thermal Efficiency( Full Throttle )-
6:1 81 25%-
7:1 87 28%-
8:1 92 30%-
9:1 96 32%-
It appears that, at 7.0:1 compression, a minimum octane level of 87 is required. Since the octane test engine used here is water cooled, you must increase the octane requirements slightly to compensate for your hotter air-cooled engine. For instance, that 7.0:1 compression setting could require an octane level of 88 or more on the VW engine.
For more specific information on the problems caused by running high compression with street gas take a look at the writings of Gene Berg. He goes into detail discussing the damaging effects of things like engine pinging and knocking that isn’t loud enough to hear.

[@markrussell8223]

thanks for the positive reply, I use the method of making them all full floaters and use the teflon buttons , seen lots of failed circlips and upgraded snap rings also.

[@robjasmin3197]

brings back memories ..thanks for the vid

[@eugenemassey6853]

great information.. m new at this.. so i will be looking forward for your new videos. great work.

[@reallymadmaso]

When that plunger made the funny noise, I so desperately wanted to hear Mike say 'pardon me.'

[@toddavis8603]

Excellent instructions----THANKS ACE MECHANIC

[@DragRacingTV]

Thanks for watching!

[@benjaminjacinto2218]

Gracias por compartir tus conocimientos saludos desde México

[@DragRacingTV]

thanks appreciate it

[@robjasmin3197]

I was head unit repair mechanic 1971 to 1973 in the bug barn kiss,fl rebuilt 315 engines from crank to valve jobs all while sitting in my wheelchair severed spine 1n 1970 . most engines dropped exhaust valve in cylinder #3 because of the stupid placement of the oil cooler. i could do these in my sleep..fun times but my mom hated the dam grease tracks my work wheelchair left.

[@DragRacingTV]

grease on the wheelchair tracks is pretty hardcore vw! thanks for checking out the vids.

[@trottierindustries3769]

why is number 3 always a problem! I have spark problems, fuel problems, overheating problems, oiling problems and the list goes on... I don't know whats with that cylinder but the problems always emerge from it!!!

[@miltona09]

@@trottierindustries3769 early motors had cooling air pass through the oil cooler before going over the #3 cylinder causing it to run warmer. Distributors for these motors actually retard the timing for #3 to help control temps. Later motors put the oil cooler in a "dog house" closer to the flywheel and hot air dumped overboard, not onto the cylinder.

[@sandramoskwa]

I guess that will work if your piston tops are perfect flush with the top of your cylinder barrels at TDC.

[@dwightgeorgecarlson]

Would really like to know exactly what the assembly lube which is in the tube which you are using. i.e. especially re the installation of the distributor shaft to hold the washers in place on the little shelf inside the case prior to dropping in the distributor shaft.

[@dwightgeorgecarlson]

Can you explain what you are doing to determine the CR? i.e. I see you are determining the volume below the plastic cover plate. Does the bottom side of the plastic plate mimic the location of the top of the piston? If so, does the piston 'top' reach the end of the barrel or is there a small space from the 'top' of the barrel to the end of the barrel? Thanks for taking the time to answer these posts!

[@da-madmodler4692]

Great Video, I have been checking out vw's and want to build a motor can you point me towards or do you have a video building a Turbo version. Being new at this I'm looking at some set ups here on youtube and am not really sure what I'm looking at. I see some set ups with dual carbs and others with a single Holly carb. I also see builders offering completes in the 2690.00 range which is cool but think it would be a little to build it myself . Thanks for any help and great video.

[@DragRacingTV]

the single holly carb version is usually going to be a draw-thru turbo, which is cheaper and relatively simple to build, while the dual throttle body/dual carb versions are probably blow-thru turbos... a blow-thru efi system will give the best control over air/fuel ratio, by far, but it's a lot more complicated, see this build for example, street-driven long distances to the track, a consistent winner: www.turbobobefi.com/ for starting at ground zero, i'd say get the old turbo book from cb performance, to get a handle on what draw-thru vs. blow-thru is, there might also be some old tech here: www.oceanstreetvideo.com/vwtech/techthreads.html with determination and a big time commitment, you could build a megasquirt cpu to control the efi, or just get all the parts from somewhere like cb performance, and bolt it up... for efi you'll probably want to use a beetle fuel injection gas tank, because it has the internal bowl to keep fuel centered over the feed line. one thing is for sure, if you go turbo you'll never want to go back to a normally aspirated vw! i've been there and done that, it's a blast.

[@nickyriffer1330]

Can you tell me , how much is the standard piston sir ???

[@dwightgeorgecarlson]

John Muir discusses 'lapping' the top edge of the barrels onto the mating face on the heads. Do you ever do that?

[@DragRacingTV]

+DG Carlson i don't recall ever doing that, because afaik, it's not a factory procedure, so i can't say how well it works.

[@dwightgeorgecarlson]

Whopps, I see you answered my question re location of piston relative to top of the barrel. Still would like to know entire procedure to determine CR. Or I guess I should google it....

[@DragRacingTV]

+DG Carlson once you have measured the combustion chamber CCs and the deck height, you can plug all of the data into this calculator: www.cbperformance.com/v/enginecalc.html

[@dwightgeorgecarlson]

Do you ever install the cylinder barrels before installing the piston pins? That way the ring installation tool does not get fouled by the studs.

[@DragRacingTV]

+DG Carlson i think that both approaches have their advantages.

[@bigred8438]

Great video, thanks. I know this might be a silly question, but are the piston pins 22 mm in diameter and the length 80mm?

[@DragRacingTV]

Sorry, I don't know what the dimensions are.

[@dwightgeorgecarlson]

I don't understand the term TDC or 12 o'clock regarding the center oil ring? Do you mean perhaps designate 12 o'clock at pointing towards the flywheel end and then the other two scraper rings gaps to be at 10 o'clock and 2 o'clock or ???

[@DragRacingTV]

+DG Carlson in general usage, the term 12 oclock typically refers to orientation, as a clock on the wall would be hung... you do not, in other words put noon/3 on a horizontal plane, and you will not see the TDC mark on an engine in the horizontal plane either.

[@gordonmack9948]

Do I need to check the piston ring gap on New piston and barrel set

[@DragRacingTV]

A lot of people don't, at least not with stock motors, but I would say that it's better to be safe than sorry.

[@dwightgeorgecarlson]

So the oil scraper rings do not have a gap like the compression rings?

[@DragRacingTV]

+DG Carlson that is a good question... wiseco has an illustration showing how the expander ends are butted up against each other, and they talk about clocking the oil rails(aka scraper rings), but given that our engines have horizontal jugs, it may not be right to put a gap at the bottom... so it's v-8 stuff, but largely applicable... there probably is a gap spec for the oil rails, but if they were somehow too tight it would be difficult to file the gap on such a thin ring... i'd want to see that they were at least as wide as the rest of the rings?? www.wiseco.com/PDFs/Manuals/RingEndGap.pdf

[@fashionstarjagguwithasort6427]

Please tale me about cnc programme related of piston machine

[@DragRacingTV]

+jagannath yadav - i don't know anything about that, so i googled it, and came up with this link: www.practicalmachinist.com/vb/cnc-machining/newbie-question-piston-skirt-programming-machining-319351/ it looks like the equipment used to do it is expensive, can't do it on a normal lathe? and it can get complicated.

[@markrussell8223]

i think your snap ring orientation is off, and if your block is decked, you want to get as close as possible to zero deck to maintain quench and cop ratio..right?

[@DragRacingTV]

Mark Russell snap rings that hold in the piston pins? there isn't a spec for clocking those... or probably you mean the piston rings, they should be clocked per the bentley spec, with the object being no straight path for the oil to get into the combustion chamber, through the ends of the rings... the deck height settings in the video give the same compression ratio that the engines were set with from the vw factory, using all new parts... imho, taking full advantage of zero deck height usually means that the piston and head are mirror images of each other, with quench directing the air/fuel charge into the most desirable part of the combustion chamber, at high velocity... can't get there with flat-top pistons and a vw head design, but there are custom pistons and matching vw head work, that have been rather controversial over the years... see the chassis dyno video that i posted, the robert kong ghia 'vert: kzbin.info/www/bejne/goHWl5hpo71sitE

[@moreshok]

Mark Russell I believe you are correct. The end gaps of the wrist pin clips are supposed to be either pointing towards the piston or the big end of the rod. The theory is that the inertia of the piston going up and down at high revolutions can cause the pin clip to flex and possibly pop out of the groove. Good catch.

[@DragRacingTV]

Tim Schaecher I looked at page 27 of the orange Bentley, Type 1, 1970-1979, it did not mention piston pin circlip orientation. The photo of the circlip installation shows the circlip gap in about the 4:00 position, not pointing towards the top of the piston nor towards the big end of the rod. The blue instruction sheet for Gene Berg GB203: Wrist Pin Keepers does not mention gap orientation at all, only that the sharp side of the keeper has to be away from the wrist pin. It does state that crank flex creates harmful side loads on the keepers, and that taper on reground crank journals can cause piston pin keepers to come out. For those who don't know, Gene Berg took every technical class that the Volkswagen factory offered, and back in the early '90's, his Super Street VW motors won PRA points class titles.

[@kadi7471]

Mark Russell i

[@casimirobuenabista]

Are all the arrow s pointing to the flywheel or the pulley?

[@DragRacingTV]

Arrows point towards the flywheel. Here are some more relevant tips: hotvws.com/content.php?contentID=203

[@davidduffy2046]

Do you use sealer on the bottom of the cylinders?

[@DragRacingTV]

yes, definitely

[@chadburkle1461]

@@DragRacingTV is their a paper gasket or a rubber gasket? What is the sealer that can be used? And where can you get it?

[@DragRacingTV]

No gaskets of any kind, the sealant could be high-temp RTV or similar, thx for checking out the video.

[@wolves356]

don't the barrels have copper washers ?

[@DragRacingTV]

not from the vw factory, but i've seen people put washers between the barrel and the head, in some applications.

[@zzzz1192]

DragRacingTV you mean between the barrel and the block? At the base of the cylinder?

[@betareybill9400]

That's crazy...most modern vehicles have indicators on the piston that are supposed to point to the front of the engine but VW beetles are the opposite...is this accurate or did he just install this incorrectly?

[@DragRacingTV]

Since the air-cooled VW engine is in the back of the car, it depends on how "front" is defined; does it refer to the front of the car, or is the VW flywheel actually the front of the engine? I've always thought that a flywheel was at the back of the engine, but for whatever reason, that's where the arrows point. It's a subject of much discussion.

[@betareybill9400]

@@DragRacingTV ...well for example...on Mitsubishi or Honda or any 4 cylinder engines that are placed in a vehicle perpendicular to the vehicles front and rear have an indicator on the pistons and point to the front of the engine (pointing in the direction towards cylinder #1) which isn't pointing to the front of the vehicle...that's the only reason I ask.

[@2klovesonges]

ok