Tag: compression ratio

Guesstimates about compression ratio 3 + oxidation stuff

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Before taking the cylinder head for oxidation removal, I tried (my best) to measure the head volume.

Better get some proper measuring equipment. My trusty 10cc syringe wasnt that accurate, but I got a result that was definetly over 36cc’s. I’m going to use 37cc’s until I get better tools. Next time I’ll use windscreen washer fluid or some cheap alcohol, because surface tension.

My syringe actually stopped at 38cc’s 🙂

Then measured both the deck height and stock 4A-GZE piston compression height. Deck height is 191mm and stock piston compression height 30.5mm.

Valve guides are oxided as well. Or rusted. While getting degreased for the high-tech coatings, some of the alkaline washing liquid leaked inside and made a mess.

Compression calculations:

Seems that the stock pistons are level with the deck when at TDC. Stock 4A-GZE pistons have 30.5mm compression height and Wisecos have 30.68mm. Therefore Wisecos will poke 0.18mm above deck level.

  • Bore: 81.5mm
  • Stroke: 77mm
  • HG thickness: 1mm
  • HG bore: 82mm
  • Deck clearance: -0.18mm
  • Piston volume: 5.9cc
  • Combustion chamber: 37cc

With these values the CR is 12.3:1

  • 1mm headgasket – 12.3:1 CR
  • 1.2mm headgasket – 12:1 CR
  • 1.4mm headgasket – 11.7:1 CR
  • 1.6mm headgasket – 11.4:1 CR
  • 1.8mm headgasket – 11.1:1 CR
  • 2mm headgasket – 10.8:1 CR

Well, the numbers are the same as before… and squish clearance sucks when head gasket is thicker than 1mm.

Wiseco, you suck.

Guesstimates about compression ratio 2

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Well, I might have to buy new pistons. I made a mistake when doing calculations about compression ratio.

First of all, I dont know my current deck height. Internet says it is 191mm, but Wiseco uses 192mm. That one millimeter is going to make a huge difference. We’re talking here something above 12:1 compression ratio if the deck height is 191mm.

Also, Wiseco pistons have compression height of 30.68mm and as far as I can tell, stock pistons have 30,5mm. With a small end pin, I set a stock piston next to Wiseco piston to show the slight 0.18mm height difference. Hope the photo is clear enough:

I have to find a good source for either deck height or deck clearance.

Edit: New calculation

  • Bore: 81.5mm
  • Stroke: 77mm
  • HG thickness: 1mm
  • HG bore: 82mm
  • Deck clearance: 0mm
    • (this is a rough guesstimate. Many sites give a 0.38mm deck clearance. Wiseco pistons are 0.18mm taller than stock, which means 0.2mm deck clearance. Also, my block is shaved slightly (guessing 0.2mm) so total will be 0mm)
  • Piston volume: 5.9cc (domed)
  • Combustion chamber: 36cc (not measured yet)

With these values my static compression ratio is 12.3:1, which is slightly high 😀

If I change the head gasket to 2mm thick, CR goes down to 10.8:1. Only problem then is the squish cap, which is way more than optimum.

  • 1mm headgasket – 12.3:1 CR
  • 1.2mm headgasket – 12:1 CR
  • 1.4mm headgasket – 11.7:1 CR
  • 1.6mm headgasket – 11.4:1 CR
  • 1.8mm headgasket – 11.1:1 CR
  • 2mm headgasket – 10.8:1 CR

Guesstimates about compression ratio

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This is what I came up with Wisecos calculator. Why o why is the calculator using both imperial and metric??

ok, anyhow, my guesstimates were between 10.5:1 and 11.9:1. With stock values I got 11.1:1, which sounds just perfect.

Slightly related, I just read about an aquaintance of mine who had used 135mm long conrods instead of stock 122mm in his 4A-GE. Wonder what kind of pistons he used…?

(they were custom made by Wiseco + longer conrods from auto verdi)

Oh! Edit 7.9.2017 – where did I get these numbers

Bore diameter: 81,5mm

Engine stroke: 77mm

Head volume: 36cc (stock)

Gasket bore dia: 82mm (HKS)

Compressed gasket thickness: 1mm (HKS)

Deck clearance: 0.7mm (about)

Dome volume: -5.9cc, compared to stock (Wiseco)