JC050's 91 Charade G102 - Road & Track


I had someone say similar things about the head - but I ignored them! Perhaps I have been lucky.

Going back to the earlier question about CR vs duration, may I suggest you read up on static and dynamic compression ratios. Generally speaking you want a higher CR with more duration, as the intake valve closes later and leaves less time for compression to take place.

As for piston to valve clearance issues, choosing a low lift cam based on clearance is probably going to work against the objective of making power.


JCO5, thanks for that info. I’ll have a read up on that now. Cams and the relationship between CAR, valves and such has always confused me a little, I think mainly because of the thought of closing a valve with a piston. However what you’ve said makes sense. I’ll have a read up on the things you’ve mentioned. Cheers.

As for the softness of the head, perhaps I’ll just have to wing it and hope for the best. I do have a spare if need be. :sweat_smile:


Just some thoughts here on piston top and combustion chamber shapes.

With normal fuels domed piston solutions to higher compression mean, during combustion, that the flame has to travel a longer distance than, high compression sought through a flat top piston (with the area in the head near it’s perimeter welded to give squish). The best explanation of when and how this was first understood is in the now out of print book https://www.amazon.com/Classic-Motorcycle-Race-Engines-Technical/dp/1844259943
Basically Honda and Cosworth independently at about the same time shunned the then popular huge valves allowed by canting the v train way over and subsequent big domes on pistons. Combustion swirl was good and head flow fantastic, but early timing requirements got out of hand and no more power could be found. The better path, now copied by most manufacturer, was narrow valve angles to bring combustion chamber roof down with flat top pistons for high compression. They also found that very vertical inlet ports helped with tumble (instead of swirl). This forced the ignition moment into a small area. The flame front would only need to travel a short distance, timing could be advanced and the force of the flame spent more time pushing down on the piston rather than burning across the long distance of a domed piston. A cross section of an EJ-DE (though not a flat top piston does have good squish at the edges and central burn) when compared to early Cosworth and Honda race motorcycles shows a striking similarity. Note how far things are taken with how flat the combustion chamber area is within the v10 f1 motor belowHere is Mazda’s take on it with “squish” nearly everywhere and a deliberate small pocket in the center of the piston.

To improve resistance to knocking, shortening of combustion duration was also attempted. The faster the combustion, the shorter amount of time the unburned air-fuel mixture is exposed to high temperatures, allowing for normal combustion to conclude before knocking occurs. Specifically, aside from creating a more homogeneous mixture by means of intensifying air flow, increasing injection pressure, and using multi-hole injectors to enhance fuel spray characteristics, a piston cavity is used to prevent the initial combustion flame from hitting the piston and interfering with the flame’s growth.

As a side note in the late '80s I was involved in running (not driving) a rally car at state level. I thought it cool that our engine person had gone with Yamaha XT 250 dome topped forged pistons in a Nissan L series to bring the compressin right up. Bored and stroked to nearly 2.4 litres, a head that flowed like the best , running avgas and it had much dyno work. Though Murray Coote (whom we came second to) had an engine that seemed exactly the same on paper and looked the same externally our driver couldn’t match him. It could have been power, driver skill or superior car handling. However, years latter a friend purchased Murray’s engine that “beat” us. I helped pull it out of the “ground effects 1200” and when seeing the L20 with the head off I was shocked at his “inferior” flat top pistons. There was nothing wrong with them at all, they were a much better solution than our wonder XT domes. We definitely had been going in the wrong direction.


Thanks for that Mr Gormsby, I love the F1 pics - I think a Honda K-Series is probably the nearest thing we mere mortals could get our hands on, they are an amazing bit of NA kit.

I find it a bit sad that BMW and Honda have abandoned thier magnificent NA masterpeices for turbo setups. A turbo may deliver more power, but IMO will never sound as good as a ITB NA setup. I think the current V6 F1 turbo vacuum cleaners illustrate this point very well, with many missing the sound of the old NA V8s, V10s & V12s.

As for my car, I was never going make a F1 motor out of my H-Series, but I like to read & research what works and see what I can apply to what I have.

Most people when they build a high comp 1.6 use 1.3 pistons to get a CR of around 11:1. A CR of 11:1 was what my goal was too. However I knew there was some wasted potential, as simply putting in taller 1.3 domes does nothing to improve the squish, which on the stock H-Series is around 1.5mm.

So I did it the hard way, kept the stock flat top 1.6 pistons, skimmed 0.4mm off my block, and 1.5mm off my head. This leaves nice small combustion chambers (35cc), a squish of 1mm.

With my regrind camshaft though, this also left me with valves that “just” interfered with the pistons. While it turned over fine, as soon as it started a strange metallic melody emanated from the intake manifold.

Clay revealed that I only had 1mm of clearance, most of what I read suggested 2mm was needed. So I ended up doing some backyard flycutting of my pistons to get the required 2mm of clearance, this was from a method I borrowed from an online V8 article.

I had to open these up a bit more with a die grinder (I used a template to maintain the same shape on all pistons) to get the required 2mm axial and radial clearance.

Fortunately it all worked, and the car runs really well, alot of work though. Between the squish, high CR and ignition upgrades, if I take it easy I can still get the same fuel consumption as when I had the stock 1.3 - which suggests I got something right.


Some impressive work there @JC050, even for a “backyard” job. It is a darn shame BMW left their NA ways. My father owns an E46 M3 and my god the induction sound that thing makes is beyond compare. A straight six with ITBs is absolutely one of the best engines I’ve heard. I actually developwd a cold air intake for his car that he sells now and much to our surprise it actually increased power on a factory setup, dyno results and all to prove it. Our main aim was to increase the induction sound, and boy did we ever, the power was just a luck benefit. Excuse the crappy phone video.

As for your compression ratio, what would you consider it is now? I’m just curious as I will be following a similar path to what you have. I have a 1.6 and two 1.3s so I’m unsure as to if I should put the domes in and call it a day, put some flats in and shave the head and block or something else. Your thoughts?

Love your build so far though. Some real do it yourself work and that’s the best kind in my opinion.:+1:


It produced 220 psi on all cylinders. I actually don’t know what a stock motor is! As for the CR I do recall calculating it to be very close to 11:1.

Just be aware of the risks of doing what I did:

  1. Some say that skimming a H-Series head isn’t a good idea (although I have put at least 20000km on mine, first on my old 1.5 block and now on the 1.6).
  2. Flycutting of pistons - these have only done around 2000km. The area where I cut into is near the thickest part, it is something I have seen others do hopefully its ok.

I love the sound of the older six cylinder M3’s - as much a musical instrument as a performance car.


Awesome work. Im about to order my cam, I am running a 1.6 block with 1.3 pistons, it would be interesting to compare the compression tests on the cylinders to your results.


Today I finally got my gearbox back. :grin: Rebuilt by a gearbox specialist with new bearings, seals, and with 1st, 2nd, 3rd, 4th, and final drive from a Gtti.

Below is the offending 2nd gear that kicked this process off:

Fingers crossed it all goes well over the next few days, I have really missed driving the car.


Happy to report that the rebuilt gearbox went in and works fine. Took it easy for around 200km, but have since had some good wot runs in the lower gears. New slightly longer 2nd from the Gtti box definitely better with the HD motor.

Need to get it to the dyno now…


Might have to look into that 2nd gear for mine.


The change seems to add around 5km/h to 2nd gear, it just helps close up 2nd to 3rd.

On the road the the gearbox ratios are a bit short with the modified HD, but it will be great on a track where you want good acceleration.

I hope to take part in a motorkhana (first time) next weekend, and have a dyno run planned for the following week.


Today was dyno day for the 1.6, it took a bit longer than I thought, thanks to slipping clutches, broken gears, and needing surgery to re-attach my hamstrings after a disastrous attempt at water-skiing.

I got 112.5 hp, picked up 7hp and quite a bit of torque (up to 14N.m in places) below 5000rpm over the 1.5. I think I might take a break from engine mods, its already cost a bit to get this much, and with NA it just gets more expensive the deeper you get into it.


Torque is your friend and that is a nice flat line


Thanks Mr Gormsby.

I do love how I can go up a ridiculously steep hill near where I live in 5th gear at 2000rpm. The original 1.3 motor couldn’t even get out of 3rd gear!

Here is the dyno video - red line is set at 7000 rpm.

This time round it was a hub dyno (instead of a rolling road), as my tuner has spent some coin upgrading his gear. It gives very accurate results, the only downside being that dyno time now costs a bit more!


Most people out there don’t get the importance of torque when it comes to performance. Power figures and big (unusable) hp is something they chase. How many out there just want to win bragging wars about how much max power they have? And I’ve seen many big hp cars humiliated by wells sorted driveable ones or the big hp engines detonate on a track (or even hlllclimb) when WOT occurs repeatedly. With the main hillclimb car I am associated with the chase is massive torque from 2500rpm up ward, even if it means loosing 15hp top end as that bigger number should never be at the expense of not being able to pull out of a corner at lower reves. You’ve got a really exciting car that most would never appreciated unless they got to go for a ride.


The whole reason I want the turbo version of the K3 is for the low end tourqe and the manual states 170nm@2800rpm (@engine) which to me sounds epic, what do you think old wise one @Mr_Gormsby?


170nm down that low is going to be an epic revelation. It won’t be (just) a “wow” thrill, rather make for a whole new mindset on what you know performance to be (a bit like running on soft race radials for the first time). The thing will be fast, instantaneous fast. The facebook talk of low compression for more boost is farcical. I remember driving some big boost race cars before there was access to good electronics where/when low compression was essential. Well find me a race series (other than drag racing) that go the low compression route anymore. Modern electronics and a thorough understanding of combustion means you can have your cake and eat it.

I am close to dropping all Daihatsu Facebook links (other than that excellent Sirion rally one that 601to602 just made known to me. There is much poor information out there, nonsense discusion (that’s fine for some but not my thing) and living in the hyper real world of imagery/coolness is a drag. We are a community here that has a strong side that I respect and the work in JC050’s Charade is of a hundred times more interest to me than any JDM coolness or stories on the latest hypercar. This guy really is living the dream and enjoying his car.


Looks like a nice result mate, i’d be happy with that.



Sorry @JC050 for going off topic.
I agree with you stop moding now as enjoy what your have built


I love this thread. Love the first hand info/facts on engine differences. Been searching for a while.
I feel it belongs in “Wiki” section with a few pictures for reference! :grin: