JC050's 91 Charade G102 - Road & Track


Been enjoying the car but still pondering where to go next in the quest for more NA power.

I have spare head I have been studying and looking to see where gains could be made, and my eyes are drawn to what appears to be shrouding in the combustion chamber.

The intakes have a nice 3 angle valve seat, but the transition into the combustion chamber doesn’t seem ideal - it steepens from back from 30 degrees to 45 degrees. Also the proximity of the edge of the CC near the gasket to the intake valve also appears too close.


Some hot rodder articles I have read mention de-shrouding up to 1.2 x the valve diameter - this would be 36mm for the 30mm valve in an H-Series.

I like what this guy does to a V8 head:

Love to hear from any other experts out there! Anyone seen well prepared H-Series head?


No experience with the H series. What you are proposing looks good. You can also have shrouding on the block. We used to put a small notch on Datsun L series blocks to unshroud the inlet. It would go about half way down the height to the first compression ring when it sat at TDC and the edge of this eyebrow must of course not compromise the head gasket. Don’t just think of this work as improving flow only. I’d not just focus on shrouding but also on having no sharp edges to help reduce hot spots. It is preferable that the burning mixture does not travel across sharp edges or roughness. Speaking of mixture is “squish”. Some might say I harp on about this a bit but such a focus can bring up your engine’s BMEP. So be careful with the unshrouding lest you remove much of the head that’s squishes almost against the piston. Something like 0.60mm is generally an improvement over std, but the perfect distance is engine specific depending on revs, parts…
My next step would be to blend the radius just inside the port so there is nothing sharp as air flows to the valve seat. Inside the port I attempt not to make anything bigger. Most heads flow enough. One does not want the ability to flow high amounts of air as much as one wants the air that is flowing to do so with the greatest velocity possible. Other than that and match porting I like to knock the vavle guides out and blend the guide boss casting to match the port. Sorry if I’ve covered anything you already knew. Happy porting.


Thanks Mr Gormsby, I am glad you commented and good to get some re-assurance. I was chuckling at the thought of “No cylinder head ported by Gormsby ever comes back for a second helping!”

I am busy designing a tool to do the de-shrouding job, if its works I will post it. I have done some of the smoothing you mentioned and my block has been machined to improve squish clearance - free horsepower really. And I do plan to do some sharp edge removing as you mentioned in the CC itself.

One thing I really don’t like is how the seats on the H-Series head tend to overhang on the long side of the intake port, which is not an easy thing to correct.


When doing heads for myself I’ve always made sure I had two or even three spare. They never get re-tweaked, but I do start all over again at times. I am yet to do an EJ-DE head and am looking forward to the challenge (I have no less than five spare DE heads and one VE). I’d say you are dong some high quality work there and you certainly are attending to important details. It’s exciting to be a apart of a forum to see work like yours JC!

In case you’ve not read A. Graham Bell’s book on four stroke performance here’s a link.



The de-shrouding tool is done - I will be giving it a whirl over the weekend. There is a dowel which is a snug fit in the valve guide and the cutter spins with the drill. This should give a radius and 25 degree angle next to the valve seat.



Some pics of the de-shrouding:


There is a limit to what you can do, bore size, material thicknesses and angles in various places. And trying to blend appropriate angles and radiuses etc.




I’m in awe of you guys… Lots of “real” information as well…



Great stuff mate!

Loving the time and detail you are getting into to give the old Dai H series some good justice.

I also watched your Dyno video, that sound and power delivery sounds all too familiar!! My ears enjoy that daily with mine! Similar characteristics too with the flat torque curve.

Like our earlier cams discussion on the old thread, I gave up for that elusive “y” cam with the tightest LSA and wanted my “H” cam reground for the more practical wider flatter torque it will produce with the HD, which is pretty much what I built the car for. Not jus top end engine ringing HP. I’m very happy with it, and I’m sure you are too.

Keep it up mate!


Forgot to add, the work you are doing to your heads generally with all the precise changes is essentially the REAL engine tuning, not the fuel and ignition engine tuning on a dyno. For a smaller engine generally speaking, a couple HP here and there will make for a noticeable improvement.


Cheers Mick.

I would like to get 100kw atw on an H-Series. Not sure if I ever will, but it has been fun doing mods and seeing the effects.

I may get a billet cam eventually (1143c or a 1185c) but for now I am going to push this setup as far as I can. I still have plans for throttle bodies in my head, I have often imagined the noise it could make while ripping through the gears…


For a race car - torque is your best friend. Having power is great but a nice flat-high torque curve will make it driveable and allow you to accelerate out of corners. With your attention to detail I am sure you’ll hit the 100kw.


did you see on the facebook page adam deschamps put dual throttle bodies onto his hde motor powered g102 charade ?
interesting idea to say the least


No I didn’t but I have read about a similar concept in one of A Graham Bell’s engine tuning books.


Finally got around to ordering these:


Still a long to do list until they can go on the car though!


Awesome mate can’t wait to see these on. Then i’m gunna copy you haha.


hey Jason how’s the charade going?? taken her out to any events recently? I’m in the middle of a complete re-wire on mine at the moment, fitting a Link ECU and will hopefully be tuned up on alcohol and ready for action by summer :slight_smile: … then carry on with the ‘other’ race car build… :wink:

keen to see how you’re finding the new ratios :slight_smile:



Hi Tim - No more events since the motorkhana a couple of months ago. The gearbox is great, the only change was to 2nd - but I am sure next time I am at Taupo I will notice. I do like the short G102 / Gtti final drive, glad I didn’t change that.

I have been working on a spare cylinder head, this is the first time I have spent much time playing with the combustion chamber, I have made an effort to smooth it out and to try and de-shroud the intakes. This HD head also has much bigger intake ports compared to the HE head I have on it now. This head should be going on next weekend.

CC compare

My ITB’s have arrived from the US so now I am in the process of doing some layouts in CAD - the only way I can get it to work is with curved trumpets. Fortunately an ex work mate owns a local 3D printing business, and once done I will get them printed. At least that way I get the correct tuned length and I also plan to integrate a mount for an ITG filter.


An alcohol GTti - that sounds awesome. I bet you will need some big injectors. When its running I would love to see it.


ahh I thought 3rd was different too… glad to hear your enjoying it nevetheless :slight_smile:

considering you’ve got access to a decent CAD program, might I recommend getting your own printer… they’re pretty cheap these days and man is it handy for mocking up parts :smiley:

hah yeah just waiting on a set of ID1050x injectors to arrive :sunglasses: should have plenty of squirt to support 1.7bar odd boost :smile: still looking forward to an opportunity to meet you at Taupo to have an NZ style Daihatsu mega meet… i.e. more than 1 daihatsu on track haha


Yeah lucky for me I get a home license through work for CAD - great for homers. Hadn’t actually thought of buying a 3d printer, but you are right its not that expensive anymore.

Looking forward to the Daihatsu meet at Taupo - your rocket ship will make my car look like its propeller driven!


Any luck with those ITBs yet? I love reading through your build. :grin: