Sonic Testing The1.8 Engine Block - Forced Induction & N/A Power Mods - MX5Nutz Forum

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Sonic Testing The1.8 Engine Block

miata sonic testing cylinder wall bp engine building wall thickness

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#1 na8cgee


    spending too much money

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Posted 30 November 2019 - 07:08 PM

I thought I'd show you my results from sonic checking an engine block for my long rod N/A build.

The reason I needed to do this was I wanted to understand how big I can make my custom pistons, the only way to know this was to check the cylinder wall thickness of each cylinder - from this I can work out how much I can safely overbore the engine for the build.

The block itself is from a 95 1.8, standard 83mm bores and overall in good condition. only even ran naturally aspirated and done approximately 70,000 miles.

The things I used:

- Ultrasonic thickness gauge
- KY jelly
- Blue workshop towels
- Degreaser

The first step - clean the cylinder bores with degreaser and blue workshop towels.


Second step - turn on the ultrasonic thickness gauge and calibrate it.

To calibrate the gauge, first we need to set the sound velocity to suit the material we are measuring. In this case the engine block is Iron, so I set the velocity to 5900m/s. The second step, is to calibrate the gauge on an item of known thickness. In this case, the tester itself as a calibration disc on the front (Below the buttons), this material is a fixed 4mm, you first have to apply KY jelly to the probe then press the probe onto the disc for 10 seconds, check what it reads and adjust accordingly to 4mm.


Third step - Test your cylinder bores

The first thing to do is apply some KY jelly to the probe and start measuring from the top of the bore to the bottom in roughly 5mm increments. the first test area should be inline with the inlet valve side of the bore, then you do 3 additional test points which are at 90 degrees from the first test (You end up with 4 results per bore, if you imagine the top of the bore as a clock face your testing at 3,6,9,12)


Once you've finished testing one of the sides of a bore, you end up with it looking a bit messy but it shows you a roadmap of where you have tested


Fourth step - collate results and review

In my case, I took various measurements and I'm only showing the lowest reading I got for the whole length of the bore for each side as this is the minimum thickness measured. I have a nice little spreadsheet which makes life easy for data input and the output looks like this:


In my case, building a high RPM NA engine, the thickness issues on cylinder 3 & 4 (between the cylinders) means I have to be very careful as to what overbore I can go to. originally I wanted to go to 85mm pistons, but this would leave me with only 2.5mm thickness which is borderline. I'm planning to discuss this issue with my machinist to see if we can offset bore the cylinders towards the rear of the engine where the bores are slightly thicker, if not I will have to live with 84.5mm bores!
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Trying to achieve 220+bhp and 180+ftlb naturally aspirated

#2 Zed.



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Posted 30 November 2019 - 08:37 PM

I've been reading up on overbore options for the 1.6, one of the things I've seen reference to it using Honda pistons & conrods (sorta ghetto cheapo mod) and on one thread it's suggested to consider a 'block-fill' meduim as used in drag-engines as this can lessen the bore-wall flex 

I might be looking into this in the future....

as to ut, used to do that when I worked in pipework engineering so tested a few ford xfow & vauxhall xe blocks although it was only the xflow that would get a +3mm bore...
also used mpi & gamma on some parts :whistle: 

keep up the good work :thumb-up: 


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#3 dadbif


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Posted 01 December 2019 - 11:41 AM

I loved the old ford x-flow, it revved like mad, only got rid of mine because leaded petrol became unavailable and there was no room on my modified head to get hardened seats in.... then I moved onto the XE, yet another great engine, another story.

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