TheSamba.com :: View topic - Type 4

Mon Aug 22, 2016 2:58 pm

Hi everyone,

SGKent and old DKP have been a huge help over in the bay window forum(note my type 4 is going in my '83 vanagon). Here is the thread: http://www.thesamba.com/vw/forum/viewtopic.php?p=8183012#8183012

engine - type 4 2.0 CV stamped engine case. New amc heads, new mahle P&C with dished heads. Cam and crank should be stock

Right now these are my numbers:
Bore - 94mm - Brand new Mahle P&Cs
Deck Height - 0.74mm to 1.05mm - This is with a .24mm (0.01") shim. measuring from the top of the piston to the top of the cylinder. I did not include the 0.030" lip that is on the new heads. This was taken into account in the head CCing
Head CC - 72cc - I used 56.5ml to 57ml of water on every head chamber. + 15ml for heads
Stroke - 71.85mm

It sounds like I need to be shooting for a minimum deck height of 1.016mm (0.4")... The 0.74mm number I have is scaring me. That is 0.0291" and is below what people that race use (0.035") so I've heard.

Here is the "problem", If I increase my DH I am looking at 7.2-7.4 compression ratios using this calc:
http://cbperformance.com/v/enginecalc.html

I've been told I should be shooting for mid/upper 7's to low 8's for a compression ratio on a vanagon t4.

My questions are below. If anyone could tell me where the heck they get this information that would be sweet. Its not in the bentely or wilson rebuild book.
1) What is the acceptable DH range for a Type 4
2) What is the acceptable compression range for a Type 4

I think I am asking for the pistons to slap the heads with a 0.74mm DH. Then in that case how can I keep the compression ratio up and increase the DH? I'm guessing I can't without buying new pistons that are not dished.

Mon Aug 22, 2016 4:23 pm

mrcool wrote: Hi everyone,

SGKent has been a huge help over in the bay window forum(note my type 4 is going in my '83 vanagon). Here is the thread: http://www.thesamba.com/vw/forum/viewtopic.php?p=8183012#8183012

engine - type 4 2.0 CV stamped engine case. New amc heads, new mahle P&C with dished heads. Cam and crank should be stock

Right now these are my numbers:
Bore - 94mm - Brand new Mahle P&Cs
Deck Height - 0.74mm to 1.05mm - This is with a .24mm (0.01") shim. measuring from the top of the piston to the top of the cylinder. I did not include the 0.030" lip that is on the new heads. This was taken into account in the head CCing
Head CC - 72cc - I used 56.5ml to 57ml of water on every head chamber. + 15ml for heads
Stroke - 71.85mm

It sounds like I need to be shooting for a minimum deck height of 1.016mm (0.4")... The 0.74mm number I have is scaring me. That is 0.0291" and is below what people that race use (0.035") so I've heard.

Here is the "problem", If I increase my DH I am looking at 7.2-7.4 compression ratios using this calc:
http://cbperformance.com/v/enginecalc.html

I've been told I should be shooting for mid/upper 7's to low 8's for a compression ratio on a vanagon t4.

My questions are below. If anyone could tell me where the heck they get this information that would be sweet. Its not in the bentely or wilson rebuild book.
1) What is the acceptable DH range for a Type 4
2) What is the acceptable compression range for a Type 4

I think I am asking for the pistons to slap the heads with a 0.74mm DH. Then in that case how can I keep the compression ratio up and increase the DH? I'm guessing I can't without buying new pistons that are not dished.

.040" or 1.016mm.....is the common minimum on type 4 (and probably most type 1)......all other things relatively normal.

In some cases......on high performance engines and when measured/checked carefully for clearance.....and with some experience...... .030" or .762mm.....is the bare minimum....when your experience with the given engine and combination shows you that even at a peak temperature higher than maximum engine temperature of an everyday stock engine.....wiil not cause e nough expansion to cause contact between piston and valve.

The answer is obvious....get rid of that stupid .030" step in the heads. Yes.....its common for bus heads to have that.....and VW started that back in the bad fuel and early emmisions days......to keep compression low ...and aftermarket heads continued the habit. It makes it idiot proof for a bus to keep compression low for the gearing.

Also.....the step was put into the heads at about the same time ....or shortly afterwards....that the factory got rid of the head gasket rings. The head gaskets are about .031" to .033" new.....and compress to about .027" when you torque the head.

That adds .027" to your artificial deck height.

We now know a bit more about certain issues with thesd engines.....and the fuel (other than alcohol) is not an issue. Its easy to get fuel with good octane.

We know....that excessive deck causes lower efficiency and higher cylinder heat by having the flame fromt start farther into the cylinder. So having a tight deck.....that would be about .055" or less....is good for efficiency and cooler running.

Although "deck height" typically stops at the top of the cylinder......having that .030 step....is identical to having a .030" shim between the head and the cylinder. It EFFECTIVELY adds .030" to the deck height.....whether it adds to the deck or adds to cylinder volume. ....the effect in the calculation is identical.....lower compression.

Before the bus came along....the type 4 engines in 411, 412 and 914....had to cast in step....and had no issues getting higher compression.

Also you will find that when they flycut out the .030" step....just a little more...a few thousandths. ..will also shave a bit off of the quench area. This makes fast changes to raise compression.
Its far easier to add shims under the cylinder base to adjust for the missing .030" step than it is to make large deck height adjustments to try to make large compression jumps.

So....you are saying that you have already discounted the .030" step in your calculation.... (like its not there)....and you still have low compression?

What is the dish volume of your piston?
Ray

Mon Aug 22, 2016 4:48 pm

Thanks for the reply!

So I am curious if that 0.040" deck height everyone talks about should include the 0.030" step that is on the head. Is that 0.040" measurement from the top of the piston to the top of the cylinder jug? or does it include the 0.030" lip?

In my calculations above I included the 0.030" in the compression ratio calc by adding it in mL to the head volume.

My deck height measurement of 0.74mm (0.0291") is from the top of the piston head to the top of the cylinder jug. If I add the 0.030" lip then I have 0.0591" as the deck height. meaning I actually should have used a smaller shim (it is now at 0.010")

The dishes on my pistons were all 15mL.

Mon Aug 22, 2016 4:53 pm

Deck height is the closest linear distance from piston to head. Nothing excluded.
Try to get it close to 1mm (.040")

Mon Aug 22, 2016 4:54 pm

mrcool wrote: Thanks for the reply!

So I am curious if that 0.040" deck height everyone talks about should include the 0.030" step that is on the head. Is that 0.040" measurement from the top of the piston to the top of the cylinder jug? or does it include the 0.030" lip?

In my calculations above I included the 0.030" in the compression ratio calc by adding it in mL to the head volume.

My deck height measurement of 0.74mm (0.0291") is from the top of the piston head to the top of the cylinder jug. If I add the 0.030" lip then I have 0.0591" as the deck height. meaning I actually should have used a smaller shim (it is now at 0.010")

The dishes on my pistons were all 15mL.

The deck....is only from the top of the piston to the top of the jug.

That .030" step.....is actually there to represent the "gasket" space that was previously there.

In most calculators and formulas....you see this:

CR= (D +PV+ DC + G + CC) ÷ (PV + DC + CC)

D= displacement
PV= piston volume
DC= Deck clearance Volume
G= Gasket volume
CC= Combustion chamber volume

The .030" step .....is "G".

Ray

Mon Aug 22, 2016 4:56 pm

Boolean wrote: Deck height is the closest linear distance from piston to head. Nothing excluded.
Try to get it close to 1mm (.040")

Which part of the head? Where the arrows are in this photo? This is below the 0.030" lip in the new head. If that is the case I should add the 0.030" to my deck height and I have plenty of room. I could even use a smaller shim..

Mon Aug 22, 2016 5:36 pm

Ok, so this is what I gather I'm being told I should do:

1) Increase deck height to 0.040" +/- 0.005" (this is measured from top of piston head to top of jug)
2) Fly cut 0.030" lip out of the heads so I can increase the compression.

What is the compression ratio range I should be shooting for a type 4?
I need to know this to figure out how much of the 0.030" I should fly cut.

I'm wondering where this 0.040" came from though.

Mon Aug 22, 2016 5:42 pm

where did .040 come from?
over 100 years of trial and error.

When CFD became advanced enough to model quench it was discovered the squish velocity diminishes rapidly above .040 clearance, which, everybody already knew. Hooray for computers :roll:

Mon Aug 22, 2016 5:47 pm

modok wrote: where did .040 come from?
over 100 years of trial and error.

When CFD became advanced enough to model quench it was discovered the squish velocity diminishes rapidly above .040 clearance, which, everybody already knew. Hooray for computers :roll:

haha thanks. Is there a portion in the bentley or something that agrees with these numbers? I've literally only seen people write those numbers. I haven't been able to find an actual spec.

Mon Aug 22, 2016 6:00 pm

No, I do not believe Bentley ever published blueprints of of the engine in great enough detail to figure it out, but if you do measure the parts you will find general evidence that all of the aircooled engines 40 horse and newer were initially designed to have .040-.050 quench clearance, as the case deck height, cylinder length, stroke, and rod length are even MM sizes, and the deck height was controlled by the piston pin height which ends up an odd size, which we DO have, through mahle.
Around 1970 the clearance was doubled in an effort to reduce HC emissions, but prior to that it appears they were aiming for 1mm. By the early to mid 80's cats were advanced enough that there was no real need to do that anymore, and the engines should have returned to a tight quench clearance, but by that time the engine was only used in third world applications(didn't give a crap), and they never did return to the original dimensions, but IMo they should have. Most all other engines did.

I think you can trace most combustion chamber design back to 1921, research by Harry Ricardo.

The step in the head you have was added to replacement heads to replace the head gasket, as it was found they seal better without a gasket. If the piston fits within the step then you could remove the .010 shim under the cylinders and get that much closer to ideal, I would, but if even the the CR is too low for your liking then I suppose the heads will need to be cut.

Mon Aug 22, 2016 6:20 pm

mrcool wrote: Ok, so this is what I gather I'm being told I should do:

1) Increase deck height to 0.040" +/- 0.005" (this is measured from top of piston head to top of jug)
2) Fly cut 0.030" lip out of the heads so I can increase the compression.

What is the compression ratio range I should be shooting for a type 4?
I need to know this to figure out how much of the 0.030" I should fly cut.

I'm wondering where this 0.040" came from though.

Modok answered that right on.

As forcwhat you should be shooting for.....is a huge range of opinion. Bear in mind that even thoug its a vanagon.....its a bus either way. What CR you should have is based on loads (heavy bus, poor aerodynamics, low gear ratios and pissibly carrying lots of stuff) , how you drive...etc.

But since you are keeping it roughly stock with stock injection.....right?....ad assuming stock gearing snd tire sizes....right?

Even the Porsche 914 2.0 had 7.6:1 compression for all but t2o years....but with a different head, cam, gear ratios and weight.

I would suspect that for stock.....about 7.8:1 or 8.0:1 tops would be the safest bet.

Right of the bat....a 72cc chamber volume is HUGE. And I am sure you measured that with the plate on top of the step. Removing the step volume from the calculation gives you a volume of 66.71cc.

You may be able to use a bit higher compression. I do not know what your gearing is like.. ..and just like a bus I am assuming vanagon engines were configured for torque.

Take a look in the shoptalk forums. Lots of vanagon work there. Typically with a CU series vanagon.....upgrading compression to 8.2.1 or 8.3:1....is considered a performance modification...requires a cam similar to a Web 73, Raby 9550 or 9590......and better exhaust.....and is usually twin carbs or aftermarket injection and not stock L-jet or digifant.

Some have used a 1.7L from 411/412/914....with 8.2:1 and 82hp......but thats very risky in hot weather in that heavy of a vehicles.....as it typically lived in 2200 lb cars.

I dont know what the rest of your build looks like....but if you are keeping it stock....keep the compression rather stock......about 7.8:1.

A cam improvement and larger valves?....maybe 8.0:1. Adding exhaust and some ignition work....8.2:1 max. Ray

Mon Aug 22, 2016 6:26 pm

Also, may want to CC the pistons. I found some are 1cc larger dish than claimed.

Mon Aug 22, 2016 8:35 pm

Thanks for the insight guys! This is all helping me grasp the concepts that are at hand here.

Modok,
I did CC the pistons and all the heads, the pistons were actually 15ml.

Ray,
I should have been more specific. Everything is stock and I want to keep it that way. The cam, the crank, the wheels and trans gearing. I will be driving this engine as a stock engine. I have no problems using 91 oct gas if i need to pay for it. OK awesome, now I have a target number for the CR. Is there a CR that is too low?

As for the 72cc that is correct, it included the 0.030" lip in the volume calc. But then when I use one of the online calcs I need to take into account the 0.030 in the total DH?

With that 0.030" lip on the head, what would the piston hit first if it over extended? The lip on the head? Or the portion the red arrows are pointing to in the picture above?

Mon Aug 22, 2016 10:21 pm

Both actually......depending on the piston. The flat areas that the red arrow points to are technically the quench areas if you had a,flat top or domed piston they would hit the areas,that the red arrows point to.

However you have a dished piston. Usually they have rim around the dish of 12-14mm. Thats what will hit the quench area on your pistons. The .030" step sits right on top of the cylinder wall. Its in the same position as the original head gasket. The 0.030" ring will never contact the piston.

I do not use an online calculator. I just use the formula and a calculator. You can use that .030" step either way......you can count it as part of the chamber... .which is what's responsible for giving you the large chamber volume. ....or you can count it as part of the deck height. Meaning....if you true deck is 0.040"......to that rim arond the dish in your piston......you calculate your deck like you have a flat top piston. That means you are findijg the volume for a cylinder that is .040" in height. Find that volume.

Then add your dish volume. That is your total deck height volume. The ....since your plexiglass plate has to sit on the 0.030" step.....you include that in your combustion chamber volume.
So......you can count that 0.030" step as EITHER part of the chamber volume......or part of the deck heigjt volume ... .but not both. It calculates the same either way. Ray

Tue Aug 23, 2016 2:26 am

mrcool wrote:

Modok,
I did CC the pistons and all the heads, the pistons were actually 15ml.

R
good job, you're sharp. :D

Tue Aug 23, 2016 9:29 am

OK, well if the step is right on top of the cylinder wall and I need 0.040" to 0.060" from the piston to quench surface (not from the piston top to the top of the jug) I have plenty of room. Technically I only need a deck height (from piston to top of jug) of 0.010" with the 0.030" lip on there. Or am I missing something again?

raygreenwood wrote: Both actually......depending on the piston. The flat areas that the red arrow points to are technically the quench areas if you had a,flat top or domed piston they would hit the areas,that the red arrows point to.

However you have a dished piston. Usually they have rim around the dish of 12-14mm. Thats what will hit the quench area on your pistons. The .030" step sits right on top of the cylinder wall. Its in the same position as the original head gasket. The 0.030" ring will never contact the piston.

I do not use an online calculator. I just use the formula and a calculator. You can use that .030" step either way......you can count it as part of the chamber... .which is what's responsible for giving you the large chamber volume. ....or you can count it as part of the deck height. Meaning....if you true deck is 0.040"......to that rim arond the dish in your piston......you calculate your deck like you have a flat top piston. That means you are findijg the volume for a cylinder that is .040" in height. Find that volume.

Then add your dish volume. That is your total deck height volume. The ....since your plexiglass plate has to sit on the 0.030" step.....you include that in your combustion chamber volume.
So......you can count that 0.030" step as EITHER part of the chamber volume......or part of the deck heigjt volume ... .but not both. It calculates the same either way. Ray

haha thanks Modok, I can pretend to be sharp every now and then..

Tue Aug 23, 2016 9:44 am

" OK, well if the step is right on top of the cylinder wall and I need 0.040" to 0.060" from the piston to quench surface (not from the piston top to the top of the jug) I have plenty of room. Technically I only need a deck height (from piston to top of jug) of 0.010" with the 0.030" lip on there. Or am I missing something again? "

That description sounds right to me , simple to understand for us simple folk , I always enjoy the way our thinking works . Some very complex situations can be better understood with a little help from others . Lets wait to see if anyone has more ..... 8) but I think you've nailed it .

Tue Aug 23, 2016 10:26 am

Keep your deck on the tight side. I have 2.0's running .028" for years.
When you said stock cam.. what do you mean by that? Reground or NOS? Have a look at the CB 2199

Tue Aug 23, 2016 10:31 am

jberger wrote: Keep your deck on the tight side. I have 2.0's running .028" for years.
When you said stock cam.. what do you mean by that? Reground or NOS? Have a look at the CB 2199

What is the 0.028" you're measuring? Is that piston to jug head? Do you have the lip on your heads as well?

By stock cam I mean factory.

Surfwagon,
Youre totally right. I've never done this before so talking through everything helps a lot. There should be diagrams next to the calc that tell you what you are measuring. But I guess once I figure this all out I'll never need a diagram since it will seem so obvious.

Tue Aug 23, 2016 10:35 am

mrcool wrote: jberger wrote: Keep your deck on the tight side. I have 2.0's running .028" for years.
When you said stock cam.. what do you mean by that? Reground or NOS? Have a look at the CB 2199

What is the 0.028" you're measuring? Is that piston to jug head? Do you have the lip on your heads as well?

By stock cam I mean factory.

Surfwagon,
Youre totally right. I've never done this before so talking through everything helps a lot. There should be diagrams next to the calc that tell you what you are measuring. But I guess once I figure this all out I'll never need a diagram since it will seem so obvious.

I mean .028" deck height. From the piston top to head plane. If you have a step you always calculate that with your deck height.

Are you reusing the factory used cam? I have not been able to obtain a new factory cam in quite some time. And I have not seen good reground cams either.