# High compression pistons 1.6 and 1.7L?



## chickenfriend (Jan 31, 2005)

I was just wondering if there were, or still are, pistons that were made for the 1.6 and 1.7 engines that turned them into high compression engines?


----------



## chickenfriend (Jan 31, 2005)

*Re: High compression pistons 1.6 and 1.7L? (chickenfriend)*

The 1.6 Euro GTI Heron pistons will fit the 1.7 block, according to the book by Greg Raven, Water-Cooled Volkswagen Performance Handbook (0760304912 isbn). He says this boosts the compression to 9.2:1.



_Modified by chickenfriend at 6:39 AM 9-11-2006_


----------



## ABA Scirocco (May 30, 2001)

*Re: High compression pistons 1.6 and 1.7L? (chickenfriend)*

If that's what Raven's book says, it's wrong, under a conventional head, the Heron head pistons would substantially reduce the compression ratio of a 1.7L engine. Back in the day, 1.6 and 1.7L high compression pistons were available, nowaday, those engine have fallen out of favour so it might be tough to find piston "off the shelf", custom piston are of course always available.


----------



## chickenfriend (Jan 31, 2005)

*Re: High compression pistons 1.6 and 1.7L? (ABA Scirocco)*

The book says that, page 45, under a picture of the top of a 1.6 Heron piston compared to a 1.7 piston, is the caption, "The 1.7 pistons (left) can be replaced with Euro 1.6 Heron pistons for higher compression."
On page 55, he states, "In most case, the pistons that mate with this head [Heron] cannot be interchanged with those from an American head without changing the head too. The exception is that the pistons from the 1.6 liter GTi bolt into the 1.7 liter motor, raising the compression ratio to 9.2:1. Other than this, you will normally use flat-top (or shallow-dished) pistons with American-style heads and the deep-dished pistons with the Heron heads."
From his picture, it looks like the Heron piston dished deeper than the 1.7 piston, and the Heron's dish is a slightly smaller diameter.




_Modified by chickenfriend at 6:41 AM 9-11-2006_


----------



## ABA Scirocco (May 30, 2001)

*Re: High compression pistons 1.6 and 1.7L? (chickenfriend)*

Unless I reading it wrong, that just doesn't make any sense, the Heron head has a zero volume combustion chamber in the head as a result the matching pistons have a much larger volume dish to make up for it.


----------



## chickenfriend (Jan 31, 2005)

*Re: High compression pistons 1.6 and 1.7L? (ABA Scirocco)*

Yes, it does seem the other way around, as you state.
For the Heron piston to increase the compression ratio under a 1.7l head, the dished-out area of the Heron piston must be less volume than the 1.7l piston.
Although the Heron has thicker walls around the dish than the 1.7 pistons, it does not seem that would be enough reduction in volume to offset the deeper dish of the Heron, unless the Heron piston is "taller" than the 1.7L pistons, travelling higher in the block. I don't know. I just emailed Greg. I'll see what he says.


----------



## ABA Scirocco (May 30, 2001)

*Re: High compression pistons 1.6 and 1.7L? (chickenfriend)*

Let's do the math, the euro GTi 1.6L with the Heron head displaced 1588cc and had a compression ratio of something like 10:1, that means it had a total chamber volume of 44cc per cylinder and allowing 8cc for the gasket volume, that gives a piston dish volume of 36cc. 
Now doing the same calculations for a North American 1715cc engine with a compression ration of 8.2:1 and a head volume of 28cc per cylinder you get a dish volume of 23.5cc


----------



## Shrttrackr (Oct 13, 2004)

From what i understand, the 1.6 pistons will fit in 1.7; however, the top of the 1.6 pistons will need to be altered so that the piston does not stick out above the block. i have been told that you would need to take approximately 3/32-1/8" off the top of the 1.6 piston.
the top of the 1.6 piston has more material than the top of the 1.7. i compared them side by side when i rebuilt my 1.7 and turned it into a 1.6.
it is VERY difficult to find stock replacement pistons. i was lucky enough to find a set of 1.6 w/ .5mm.
this method is supposed to raise your compression ratio quite a bit (not sure exactly how much).
craig


----------



## ABA Scirocco (May 30, 2001)

*Re: (dirtoval.com)*

Okay, that makes more sense now. I don't really have enough information to do completely accurate calculations but you'd have to shave 3.2mm off the top of the 1.6L pistons to make them work with a 1.7L crank, this would reduce the size of the dish by maybe as much as 14 or 15 cc which would result in a very modest increase in the compression ratio. Doing the same sort of thing to North American spec 1.6L piston, assuming the piston ring spacing allows for that, would likely result in a bigger increase because the dish is smaller to begin with.


----------



## Mk1Racer (Apr 16, 1999)

*Re: (ABA Scirocco)*

You should check w/ the guys that race VWs in the SCCA. There are guys running limited-prep HProd cars @ 11:1 on 1.6 motors. The GProd guys are running whatever they want, CR-wise.


----------



## xjronx (Oct 28, 2001)

*Re: High compression pistons 1.6 and 1.7L? (chickenfriend)*

ebay
oversize 1.6 pistons , $15 buxs a set of 4
High comps on there from time to time, or just get them made


----------



## chickenfriend (Jan 31, 2005)

*Re: High compression pistons 1.6 and 1.7L? (xjronx)*

Interesting comments.
Still no word back from Greg Raven about the the quoted material, above, regarding the Heron pistons.
If you have to take the Heron pistons and saw off the top, and if that would somehow to fit in a 1.7L block and head, I don't think that qualifies as an swap.
Does not make sense.
At any rate, since the Heron pistons seem to be nearly impossible to find, I suppose the discussion drops in the trivia bucket; nevertheless, it should be noted if the book is in error, and if so, proper credit to ABA for catching it.
The Heron set-up is very interesting. I wonder why it was not pursued or retained by VW? Was it too polluting? Was the interference head too much trouble? Were there detonation problems? Supposedly it had a 9.5 to 1 compression ratio. That was before the time of Knock sensors, I think. I can't find out much about it on the internet.



_Modified by chickenfriend at 6:45 AM 9-11-2006_


----------



## Shrttrackr (Oct 13, 2004)

don't quote me on how much you have to take off the top of the 1.6 piston in a 1.7 assembly. you should really assemble one entire assembly and measure BEFORE you cut anything.
btw...i am referring to US 1.6 and 1.7 pistons. i know nothing about the Euro stuff.
craig


_Modified by dirtoval.com at 10:34 AM 9-9-2006_


----------



## ABA Scirocco (May 30, 2001)

*Re: High compression pistons 1.6 and 1.7L? (chickenfriend)*

Up until very recently at least, Eurospec was selling Heron heads (reproductions I think). As for the genuine article, very few of them made it to North America, I know of only one locally, anybody looking for one would probably has to source one in Europe.


----------



## Butcher (Jan 31, 2001)

*Re: High compression pistons 1.6 and 1.7L? (chickenfriend)*

Many years ago I had a 1.7 crank in a 1.6 block. I used the 1.6 pistons and had them shaved .060". This allowed a lot of compression. [about 12-1]. I modified the combustion chambers [bigger] so the compression was much better. With 2 DCOE's and a big valve head the engine ran great. This was in the early 80's and I know it works. Cheap to do with today's prices. I am certain you can shave the pistons more than what I did but I know I only had them done to .060.


----------



## grigoris (Oct 19, 2004)

*Re: High compression pistons 1.6 and 1.7L? (Butcher)*

sorry to bust in like that but in order to increase compression ratio, shouldnt you also change the crankshaft? otherwise you might be stealing cc's from the combustion chamber....


----------



## chickenfriend (Jan 31, 2005)

*Re: High compression pistons 1.6 and 1.7L? (grigoris)*

Others have questioned the statement in Raven's book regarding the swapping of 1.6 Heron pistons into the 1.7L block. I just ran across this thread, in which the poster asks, 
"How in the heck does a deep dished piston increase the C/R when it replaces a shallow-dished piston? Can anyone explain this, or am I reading the above paragraph incorrectly?"

http://www.audifans.com/piperm....html
The first responder to the question stated that, "Non flat-bottom heads with the heron pistons would increase the combustion chamber size in a big way, *decreasing* CR." 
Just for reference, I also came across this information:
US / Euro GTi
Engine Codes FN / EG
Stroke 80.0 / 80.0
Bore 79.5 / 79.5
Hp 75 / 110
Torque 88 / 103
Compression 8.2:1 / 9.5:1


_Modified by chickenfriend at 8:02 AM 9-11-2006_


----------



## RoccHead (Dec 22, 2003)

*Re: High compression pistons 1.6 and 1.7L? (Butcher)*

I second that. I haven't done the 1.6 piston in a 1.7 block myself, but I know people who have. How much compression do you want? The 1.7 crank throw reaches .126 inches higher in the bore, so unless you cut that much and re-dish the piston, you'll be raising the compression. You can run the piston a little above the deck, if you want.


----------



## grigoris (Oct 19, 2004)

*Re: High compression pistons 1.6 and 1.7L? (chickenfriend)*

the US Gti has a 8.2:1 CR...i guess its due to lower octane petrol used in the States, right?


----------



## chickenfriend (Jan 31, 2005)

*Re: High compression pistons 1.6 and 1.7L? (grigoris)*

If the 1.6 heron pistons were swapped in a 1.7L, would the piston deck height change?


----------



## Mk1Racer (Apr 16, 1999)

*Re: High compression pistons 1.6 and 1.7L? (grigoris)*


_Quote, originally posted by *grigoris* »_the US Gti has a 8.2:1 CR...i guess its due to lower octane petrol used in the States, right?

Pretty sure that the GTI CR was 8.5:1 and the 1.7 FI motor was 8.2:1.


----------



## Mk1Racer (Apr 16, 1999)

*Re: High compression pistons 1.6 and 1.7L? (chickenfriend)*


_Quote, originally posted by *chickenfriend* »_Others have questioned the statement in Raven's book regarding the swapping of 1.6 Heron pistons into the 1.7L block. I just ran across this thread, in which the poster asks, 
"*How in the heck does a deep dished piston increase the C/R when it replaces a shallow-dished piston? Can anyone explain this, or am I reading the above paragraph incorrectly?*"

http://www.audifans.com/piperm....html
The first responder to the question stated that, "Non flat-bottom heads with the heron pistons would increase the combustion chamber size in a big way, *decreasing* CR." 
Just for reference, I also came across this information:
US / Euro GTi
Engine Codes FN / EG
Stroke 80.0 / 80.0
Bore 79.5 / 79.5
Hp 75 / 110
Torque 88 / 103
Compression 8.2:1 / 9.5:1

_Modified by chickenfriend at 8:02 AM 9-11-2006_

I don't have any of the data on this, so this is pure speculation. Is it possible that the pin height on the 1.6 Heron pistons is lower (distance between top of piston and centerline of pin is great) than that of a stock 1.7 piston? Is so, I can see where you could actually gain compression w/ a piston w/ more dish.


----------



## chickenfriend (Jan 31, 2005)

*Re: High compression pistons 1.6 and 1.7L? (Mk1Racer)*

I am not sure we are going to get an answer to this question unless there is someone out there who has installed the Heron pistons in a 1.7L block and head, and can tell us what the piston deck height is.
If it is true the 1.6 non-heron pistons will stick out of the block on a 1.7 L engine, is it reasonable to assume the Heron pistons would protude by the same distance?
Does anyone know what the piston deck height is for the 1.7?


_Modified by chickenfriend at 11:26 AM 9-14-2006_


----------



## rhussjr (Aug 7, 2000)

*Re: High compression pistons 1.6 and 1.7L? (chickenfriend)*

The compression height on a 1.6 liter piston is ~1.73"
The compression height on a 1.7 liter piston is ~1.60"
So, it you install 1.7 liter piston in a 1.6, they will set 0.13" lower in the bore and if you install 1.6 liter piston in a 1.7, they will set 0.13" above the deck. You can make the 1.6 piston work in a 1.7, but it will require machining the pistons. Not worth the time, as the ring land will be closer to the top of the pistin and posing a greater risk to land failure.


----------



## Butcher (Jan 31, 2001)

*Re: High compression pistons 1.6 and 1.7L? (RoccHead)*


_Quote, originally posted by *RoccHead* »_I second that. I haven't done the 1.6 piston in a 1.7 block myself, but I know people who have. How much compression do you want? The 1.7 crank throw reaches .126 inches higher in the bore, so unless you cut that much and re-dish the piston, you'll be raising the compression. You can run the piston a little above the deck, if you want. 

When I installed the 1.7 crank and the 1.6 pistons they do pop out of the top of the block by a little. Remember when I did this I was only 19 years old and had no brains about automotive stuff. If I remember right the 1.6 pistons [and 1.6 crank]did not come to the top of the block. They actually sat lower than the top of the block. When I had the 1.6 pistons with the 1.7 crank the pistons were too high [duh]. With only .060 cut the pistons were slightly lower than the top of the block. I did not do drugs so my memory is clear but there was a lot of the old type carb. cleaner around so I am willing to say I am wrong. Measuring the compression ratio was well over 12 to 1 and since I could not afford to have the pistons cut again I just increased the cc's of the head so I could get the compression lower [about 10 to 1].


----------



## RoccHead (Dec 22, 2003)

*Re: High compression pistons 1.6 and 1.7L? (Butcher)*

Both the 1.6 and 1.7 liter pistons sit significantly below the deck at TDC. So, you don't have to cut all of the difference in crank-throw piston position. The best I can come up with says that the Heron piston won't change the CR significantly, I'll post it anyway, 'cause maybe someone can find the error. The assumptions are:
1.7 liter swept volume 428 cc
1.6 liter swept volume 397 cc
Bore for both 79.5
1.7 liter stroke 86.4
1.6 liter stroke 80
Euro GTI compression ratio 9.5
US 1.7L compression ratio 8.2
Euro GTI head volume 0
US 1.6/1.7L head (combustion chamber) volume 28cc
So the compression ratio come from the swept volume, and the TDC volume. The TDC volume comes from the head volume+gasket+bore depth to the piston+piston dish. 
The Euro GTI should have a bore+gasket+dish volume=46.7cc
So the Euro GTI CR=(46.7+397)/46.7=9.5
The US 1.7L will put that piston 3.2mm higher in the bore at TDC, removing 15.9cc from the compressed volume, but it adds 28cc for the head volume. So for the 1.7 L with a Heron piston I get:
(46.7-15.9+28+428)/(46.7-15.9+28)=8.28, which isn't worth doing. 
I'll post this anyway, to see if someone can find an error. 
What are you trying to achieve? You haven't said if you are building a race motor with limits on valve size, and changes, or if you are trying to mildly hop up a street motor. Or is this a mental exercise? If this is a street motor, you'd get a lot more if you lost the 1.7 completely. If it's a race motor, putting in a cut US 1.6 piston should work. Both the 1.7 and 1.6 pistons sit nearly 3mm below the deck. You can make a flat top with a 1.6 piston cut. This might give an appropriate "race" compression.


----------



## chickenfriend (Jan 31, 2005)

*Re: High compression pistons 1.6 and 1.7L? (RoccHead)*

Thanks for that wealth of information

Let's hope no one has Heron pistons custom made for their 1.7 thinking that is going to magically take them to a 9.2:1 compression ratio.


----------



## RoccHead (Dec 22, 2003)

*Re: High compression pistons 1.6 and 1.7L? (chickenfriend)*

A friend of mine is building a 78 scirocco with a 1.5 with, I think, a 45mpg target. The issue of a high efficiency motor is an interesting one. One idea behind the 1.5 is that engines are more efficient running with higher throttle opening, less pumping losses on the intake, higher combustion pressures. I was thinking it might be interesting for the 1.7, with 1.6 pistons, to dish the center of the piston and make a double squish motor. You might be able to run 11:1 CR or more. That's what VW has done on the later 2 liters. The 1.7 configuration doesn't help the fuel efficiency effort IMO. I would think 1.8 is a better starting point, mainly because you can get the motors and parts easily. The small displacement of the 1.5 would probably be even better. They're getting rare.


----------



## chickenfriend (Jan 31, 2005)

*Re: High compression pistons 1.6 and 1.7L? (RoccHead)*

I think that is an interesting idea.


----------



## vinziboy (Oct 16, 2008)

Reviving this thread as I stumbled over it - here is the alien you are all looking for. A 1.7l block, a euro head and dished pistons.... but it's no longer for sale :laugh:

https://forums.vwvortex.com/showthr...RON-engine-complete-and-assembled-(in-service)


----------



## vinziboy (Oct 16, 2008)

Oh and I did not measure pistons but the markings on top are still present as you can see in the pictures so these were not decked / machined. So, tuner pistons? Stock 1.6 pistons. I can confirm these result in high compression though. This engine has NOTHING to do with the stock one that was in the car when I bought it...


----------

