Mr Plow

OE Nissan pistons into Mazda BP?

An odd little project I’ve been mulling over. OE cast Nissan CA18DET pistons will go straight into a 1.8BP. Pin size is exact match, bore size is match depending on grade of Nissan piston (they have 5 std grade sizes for 83mm bore).

Why might I want to do this:

- drops my VVT to circa 8.5:1 c/r;

- OE BP pistons appear to be c.5mm thick at center of crown. The Nissan piston is 6.5-6.75mm thick as designed for higher torque std;

- the Nissan piston has oil cooling to the exhaust side of the piston;

- keeping a cast piston means less expansion, less clearance, less rattle;

- the pistons appear cheap at c.£50/piston new, potential for a cheap build challenge with China rods;

- the Nissan piston has the oil squirter reliefs and same pin offset as the Mazda piston;

- the valve cut outs align with the Mazda piston cut outs.



Why might I not want to do it:

- the squish clearance is increased. This may lead to slightly lower performance and an increased likelihood of detonation. I know people with actual experience of running less squish than this on other platforms without any measurable issue;

- The engine becomes interference if the belt lets go. I’ve measure piston/valve clearance from 0 to 40degrees cam advance for VVT and there is circa 2.5mm clearance on full rotation which should be plenty. A standard Mazda vvt clearance measured at 3.5mm for fully non interference. I also checked c.-7.5 degrees to 52.5 degrees cam advance on the Nissan piston - it doesn't hit but the clearance is immeasurably small;

- The OE Nissan piston remains a cast piston so fatigue performance should not be as good as a forged piston. Actual power rating unknown. S13 owners note 350hp safe limit but I expect this is with a humpy torque curve through simply boost control and that at least 400hp could be run ok with a flat torque curve;

It’s a lot of effort to then be limited although Mazdas are pretty drivetrain limited anyway going on people's experiences.



A few pictures of freaky experiments attached. Welcome any interesting chat.







Valve clearance - STD VVT inlet side on left - Nissan CA18DET on right.

technicalninja

Nice! you've found an inexpensive flat top
The valve pockets can be fly cut (see LS engines for ideas)

Other data I'd like to know
Deck height
Weight
Ring pack dimensions
Floating pin?

Excellent work, might work well for a super budget build.
Thank you for sharing

curly

iTrader: (25)

Honestly if you're not willing to throw this engine together and tune it knowing it might work great or might explode, I'm not sure I'd go down this path. I know I build a lot of M54s with piston issues, and if there were a drop in OE piston that could potentially solve my problems, It'd be on a dyno within a week.

Slap a head on that block and get some answers.

Frofro97

pretty interesting, I was considering coating stock pistons for a "just rods" build but ill have to keep an eye on for these

Mr Plow

Further info from my studies and measurements made where M = Mazda VVT, N = Nissan CA18DET below:

Pin diameter: M = 19.97mm, N = 19.97mm. Nissan pin goes nicely onto a standard Mazda rod as test fitted for the tests above. Both pistons have oil holes on underside for the pin/piston interface;
Minimum crown thickness: M = 5/5.3mm, N = 6.5/6.75mm
Piston weight with standard pin: M = 409g, N = 445g. Negative is that the Nissan piston is heavier - bonus is that it hopefully indicates a piston with more meat in the crown etc. I would want to be reving materially higher on these due to the weight and the fact they are cast;
Deck clearance: M = 0.4mm, N = 1.1mm. More squish clearance on Nissan piston which is anecdotally a potential negative for low airflow combustion and potential area for detonation. Experience of running larger squish clearances have not had measurable issues in a good friend's experience on a different platform.

Ring pack - not measured but looks roughly the same and same position between the pistons.

The Nissan pistons come in 5 grades of 83mm pistons. I reckon you could probably get the larger 83mm grade pistons, then only have to hone a used 83mm block to clearance.

I'll probably cross section the Nissan piston I have to double check crown thickness and also to investigate the meat at the valve cut outs to see if these can easily be machined larger without compromising something else. Could potentially take them back to non-interference.

Finally - This is investigating on a rough spare engine out of curiosity. I won't be chucking anything together and testing anytime soon but thought people might like to see this investigation. I agree entirely with Curly - only enter this with your eyes open. I think from experience reported by people on std early 1.8 pistons with uprated rods - that c.400hp with a flatter torque curve could probably be reliable on these. But - who knows.

Gee Emm

Why bother? Just do your belt changes and the 'interference' problem goes away. I ran 8k rpm BP race engines for 15 years or so, with no 'interference' issues at all.

Mr Plow

Agree but like to see what is possible - buy headroom if utterly safe and easy - it would instantly kill the budget side if you start working them IMO. I also want to see the oil cooling part around the exhaust side of the Nissan piston as I can see the 2 small holes on the underside but want to check there is not a crazy weird hollow section that would make me question the strength. This piston is used, v cheap and I wouldnt put it in a motor so whats not to like about cutting it up.

Mr Plow

Some extra comparison pictures. Double checked the piston crown thickness which is c6.75mm as previously measured. Also verified there is enough meat to open up the valve cut outs if wanted. Its about 10mm thick at those locations. Nothing odd in there like casted cavities etc.

Also comparison picture of the wrist pins. This is where the majority of the additional weight is as the CA18DET wrist pin is substantially beefier than the VVT wrist pin.

Mr Plow

Update: I tried ordering the largest grade std bore pistons from Japan as they were listed pretty cheap and this would work well with a hone of my current block - these are now discontinued. Then checked availability on +0.5mm oversize - both the original part number and replacement part numbers from Nissan are discontinued.

I'm not hot for putting in second hand pistons on a build no matter how good they look as their use and stresses would be unknown to me and so would any failure. Most likely I will revert to forged aftermarket Mazda pistons.

This was an interesting desk study but no solid outcome.

allofit

Love the idea! So unfortunate they're discontinued. Could have made for a great budget rods + pistons build.