Thinnest performace head gasket

[ward00]

Any one know what the thinnest "performance" head gasket one can get for the 2 liter engine.

AutoRicambi has one that is 1.2 mm thick. Any negative experiences with it on a higher compression engine 9.5 -9.8 compression?

Any other candidates that are thinner? I currently am building an 2l engine with 2mm domed Venolia pistons (block came that way, otherwise would have gotten something taller) and 2liter head and would like to increase compression over what the 2mm will get me.

[fiatfactory]

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[ward00]

Ok ... so your question has gone from "how do I lower my static compression ratio" using a thick head gasket in an earlier thread, to now it's "how do I raise my static compression ratio" by using a thinner head gasket..

I thought you were convinced that the manufacturers figure of your static compression ratio of 10.4:1 was correct?

2mm dome... it depends on how wide the base of the dome is to determine it's actual volume and if the flycuts intrude into the dome and reduce it's volume.... but out of the Fiat parts bin there is a piston with a 1.6mm dome that comes from some "pedestrian" models with the 1800 engine, if these are used in a stock 2 litre engine the resulting CR is approx 9.5:1 depending on h/g thickness / valve position in the head / any material removed from the head face... so it sounds like you have something similar but in a forged piston.

post a picture of your pistons... and post the results of your head combustion chamber volume measurements ... with some math we can get "close" to figuring what you have as far as static CR goes.

SteveC

So after a whole lot of back and forth with the seller who stated that Venolia (who just went out of business) had represented my pistons as being 10:4 compression, I have determined they must have used something less than a .040in head gasket to arrive at the 10.4 number. The online calculator at https://goodcalculators.com/compression ... alculator/ gives a compression of 10.2 with a .040 head gasket and my engine specs. Since all I want to do is make sure that I don't go to higher than 10.4, a .040 in thick head gasket seemed like it would/will work. I would post the pictures of the pistons, but this site makes it too painful to do so. The 1 and 4 pistons have offset valve reliefs that can accomodate up to 47mm Intake 40 mm Exhaust valve. I have a feeling that with such big valve reliefs the compression will be even lower than 10.2, which is ok by me. Hence my original desire for lower and now my desire for higher compression. Any feedback/comments will be appreciated, particularly with regard to wron assumptions on my part and what size valves make sense if I am going to use a stock exhaust cam and a Delta A16 regrind intake cam (40 degree duration, 10.8mm lift, 106 degree lobe center).

My block specs are these and are what I used in the calculator
bore 85.6 mm
stroke 90mm
head chamber volume 53cc
gasket thickness .040in or TBD
gasket bore 86mm
piston to deck clearance -005in
dome height 2mm

[fiatfactory]

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[fiatfactory]

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[TX82FIAT]

With all the technical talk about measurements/calculators and what type of pistons, I'm wondering what it is you are trying to accomplish with the engine. Is there a specific goal or compression ratio that really matters given the intended use of the car. My point, there are various head gaskets from 1.2 and up including some of the fancy multi layer gaskets on the market and you can easily buy a thicker gasket with very little performance loss. Yes, you will sacrifice some compression with the slightly taller space. But, what are you after? From a guy running 10:1 compression and blowing two head gaskets out over the last 8 years, I've found little difference in performance and some comfort in a thicker head gasket. In fact, next time I replace the timing belt, I will seriously considering a multi-layer head gasket for the long haul.

[fiatfactory]

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[RRoller123]

Great explanation. Thanks for sharing that.

[ward00]

I appreciate all the advice of this topic.

So I got about to cc'ing my piston dome height/volume for my .6 overbore 2 liter pistons (85.6mm bore 90mm stroke)

At TDC with dome and cutouts for valves they take away 4.6 cc from my 53 cc head combustion chambers.

My outer diameter of the pistons is .6 mm below the top of the block

Using a 1 mm head gasket looks like I can expect about 10:1 CR

With a 1.6 mm- 06 in. head gasket the CR will be about 9.5

Bottom line, within a range of values I can live with and that the manufacturer advertised the pistons to provide.

[fiatfactory]

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[ward00]

0.6 mm overbore is 84.6, not 85.6mm as you've specified.

small numbers make a difference in CR calculations.

there are a couple of things I notice...

Above the piston top ring, the piston is always a smaller diameter, and there is a space between the piston and the bore above the top ring, this volume should be calculated and added to the CR calculations.

With the CH of the piston positioning it at 0.6mm MINUS deck, a simple bump in both CR and the effectiveness of the SQ could be had by simply decking the block so the piston sits a ZERO deck... or even slightly proud.

In a DOHC keeping the SQ to under 1.5mm makes it most effective, beyond 2mm the effect diminishes quickly.

If you want to share the volume calculations you did and I can help with / double check your math... I do this sort of thing at least twice a week when I sell pistons / engine kits / heads... so I'm quite practiced at it.

My disbelief of the PO's / manufacturers quoted CR is because the 125TC / 130TC uses a small 2mm dome, and small flycuts and it's CR ends up in the mid 9's (9.45:1 is quoted) with the stock chamber CC's / 1.65mm gasket and the stock CH piston sitting about 0.15mm minus deck

SteveC

Yes, the 85.6 vs 84.6 was a brain fart and did change the calculations. I also remeasured the dome volume measurements. Here's what I have.

bore is 84.6mm
stroke 90mm
head gasket diameter 86mm
head gasket thickness assumed to be 1mm
combustion chamber 53mm
positive dome volume 6.25mm
piston deck .55mm below top of block

online calculator gives 10.1 compression

The only thing that I don't have is the distance of the top ring from the piston deck. Venollia is the piston company, but it just recently closed shop, and without removing the piston I don't have a way to know this dimension/volume. From your experience, what's a ball park figure for the amount of compression loss the volume above the top ring represents?

[ward00]

One thing still strikes me as being odd and which is the reason I started this thread.

I assumed that my Venollia pistons that only have a 2.1 mm dome height were not going to give me the 10:1 compression I was hoping for, yet if my measurements are correct, I will be in the ball park.

The reason I thought this was that if the online retailers pistons are advertised with an 8 mm dome to get 10.2 compression my 2.1mm domes were going to give something in the low 9:1 compression range.

It must be because of the shape of my domes? Or perhaps the retailers pistons are used with a much thicker head gasket than mine? Somethong special about my domes?

[fiatfactory]

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[ward00]

I'm happy with this result because I know I have option of increasing the CR by decking my block or decreasing it by increasing the gasket thickness. 9.8 ish is just right so that I don't need to worry to much about octane booster. Thanks for your help

[fiatfactory]

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