Bigger pistons

[Kam]

I am now looking at rebuilding the t1 engine thats been sitting in my shed for 6months now.  For those who don't know I have a Gen1 civic with a t2 engine which has the usual simptoms of an old engine etc.

For my new motor I want at least 8.5:1 compression(maybe even 9:1).  The reason is that the city turbo has no power until the boost comes in and I want throttle response.  i don't want to shave the head cause there starting to get a bit rare now!  

My question is how much bigger in diameter can I go before I get problems?

And how much bigger do I need to go to reach this compression?

I don't give a shit about drag racing etc.  only an entertaining ride to get to work.  So top end isn't too much of a concern.

Also I can get custom made head gaskets to suit the bigger bore.

[Colza]

This is all a bit beyond the scope of the regular posters here i think. Unless you can track down Charles Hatcher who used to post here but hasnt since he moved to NZ or Turbo3 who also hasnt posted here in a while, then I think youre best bet is just to take the block in to an engine rebuilder and have a good long chat to them about what you are trying to do. You could try sending Bigelboe a PM, he has a habit of remembering all sorts of random details that were posted decades ago. And if youre lucky and do some searching, you may even turn up a thread or two on here...

[John_S.]

I'm going to go out on a limb here, but if it was me, and by the way, I AM following this approach on the Turbo 1600 I am assembling the pieces for, I would concentrate on the combustion chamber design rather that change the pistons. They are flattops right? If so they are ideal for Turbo applications already. But the head is where the work is needed, as increaseing the compression ratio will increase any tendency to detonate, therefore a better combustion chamber   design with increased Quench is the best way to go, even if is the long way around. Try to source some info on Quench and the effects it has on Turbo applications , and you will see what I mean. By building up metal in the appropriate areas and then shaping each chamber for maximum effect , you can both gain comp. ratio, and at the same time improve the chamber design to enable it to handle the added compression without any negative effects. Also important is that the valves are shrouded to the minimum,(also dealt with using a die grinder of some form). And on Turbo applications properly sized slightly larger exhaust valves will show more gain than larger valves on the intake side.
It you are talking rebuild...then a little homework to catch up on all the tricks which have been gained in the last 20 years...(don't forget that these old Hondas ARE 20+ year old designs), will be found to be more than worthwhile. Besides, heres a chance to be a sculptor...in a practical way.

[Colza]

Hehe, I forgot to mention John up there in the list of people to get in touch with ::)

[Charles]

Hi Kam,

A 68mm piston is as much as you will ever fit in an ER turbo. But the walls at this point will be so very thin and as the block is a long stroke one anyway I thoroughly would not recommend it.

John is correct about the head. The trouble is though there is no room for bigger valves in the ER turbo. As I remember they just about butt up next to each other.

The exhaust valve in a city turbo is about the size of a 5c piece.

So what to do?

Shave that head! The stock 10:1 carbied ER motors made 70 hp. Trying to get 70hp out of a stock 1200EB motor which when looking at it has comparatively HUGE valves takes a little bit of work (the hot RS motor did it with twin carbs and the same compression ratio).

The ER's motor strength is it's strength (sounds dumb). They are strong little tractor motors. The pistons are flattops. Use turbo 2 pistons to bring up compression slightly if you are getting new pistons. Generally the pistons suffer surprisingly little wear (suprising because of the stroke and relative sideways thrust pressures). If you can get forgies or explore motorbike forgies (I looked at Suzuki GXSR1000? pistons which I think would have done the business). The stockies have an oil slot cut in them rather than oil holes which make them more prone to the top coming off, and reduces their cooling capability.

Now a healthy ER turbo should be able to run at 20 psi. They do go bloody well at this level of boost provided all fuel and ignition is taken care of.

For what you want I would recommend running 13-14 psi but higher compression. This would reduce the wear and tear on the turbo and associated bits and it would not be spinning off the charts, you should be able to get the boost to come up to just under boost cut so no electronic trickery, you can wind up the fuel pressure about 10psi (replace your pump if you didn't fit a VL turb pump before now is as good a time as ever). Get it on a dyno with O2 sensor disconected, tune on light then full throttle using the fuel pressure as your adjuster. Given the small bore, a significant amount of material has to come off the head to make any significant gain in compression. There is a compression calculator on the net somewhere that allows you to enter all your details in to let you calculate compression increases. From memory the ER combustion chamber was 36cc's

The thing will have excellent pick up, be much more responsive and come on boost faster and harder. The top end will remain unchanged. For cut and thrust daily driving it is a better way to go.

The other option is just to swap your gearbox for a closer ratio unit.

[Kam]

Thanks for your help people.  Appreciate the feed back  After reading the 2 massive posts I have decided to shave the head.  I won't try to modify the combustion chambers simply because it's too risky for me.  (maybe after a bit of research)

Can anyone recomend a good adjustable fuel pressure regulator that they have used?

And where can I buy t2 pistons?

Just to fill you guys in heres a list of mods already done:
(conversion done by previous owner)
t1 turbo with much bigger compressor wheel (not fitted)
21/2inch mandral bent exhaust from turbo (not fitted)
front mounted rx7 intercooler
mandral bent HPC coated pipes with BOV
pod filter
lift pump, surge tank, vl turbo fuel pump, bigger lines
close ratio civic gearbox (not fitted)
heavy duty clutch (not fitted)
4x100 brake conversion
15inch wheels
lowered springs

new custom retrimed seats, big sound system etc....

What I'm trying to create is the ultimate street thrasher  that will beat my mates Reno Cleo Sport.  And I don't think I'm too fare off.

[Smithy]

"4x100 brake conversion"

please explain?!?!?   brakes are good.

You'll beat your mates Clio easy soon! stop better too hopefully.
(Renault by the way..hehehe)

[Kam]

This was actually done by the previous owner and was one of the reasons why i bought the car (originally was going to thrash it and use it for parts for my project but it ended up being pretty good car).  

This is how to brake conversion
FOR DUMMIES ;D
front
1-  get brakes off city turbo
2-  press city hub into civic 'nuckle' (hub carrier)
3-  need to make bracket for the caliper (its not as tricky as I thought)
4-  find the right brake line (Accord maybe)
rear
1-  get the whole city/city turbo rear drum assembly
2-  it will fit on to the 'spindle' but the bolt holes won't line up
3-  weld up bolt holes
4-  drill new bolt holes

easy!

[Colza]

The 4x100 conversion is usually done using parts from the 1980-1983 EN1 Civics... and if you use a caliper adapter you may as well put on MUCH bigger brakes that the little City ones.

[Kam]

I don't have a problem with the city turbo brakes.  They do brake very hard with decent brake pads and are lighter then the other brakes.  But if I need to I got crx brakes -new rotors and reco. calipers just sitting in my garage.  They cost me $50.