Big bore rebuild Options

[Damo]

Hi all and happy new year. I’m new to the forum but have owned my 914 for around six years now. I’m doing a full strip down and rebuild of my stock 1.7 engine but have chosen to add a Biral big bore to the standard case. I have noticed that I don’t have any main bearing dowel pins in my case ? Are these fitted to all engines or just the later 1.8 and 2.0, just need to confirm if I need them. Also would like to keep my stock FI system so would need some advise on how to tweak the injection to run the bigger engine, should I fit 2.0 injectors or just rotate the mixture on the ecu ? Any advice will be appreciated. Thanks.

[Superhawk996]

I have noticed that I don’t have any main bearing dowel pins in my case ?

You absolutely need the main bearing dowel pins. They can be made by any competent machinist if need be. Post on classifieds WTB and I'm pretty sure someone can find a spare set.

Recommend that you check this case very carefully to make sure the bearings haven't been spinning already leading to case wear of the main bearing bore. Sounds like it was built by someone that was truly neglegent.

Have the case bearing bores measured by a competent machinist and compare to factory manual specification.

[BeatNavy]

Also would like to keep my stock FI system so would need some advise on how to tweak the injection to run the bigger engine, should I fit 2.0 injectors or just rotate the mixture on the ecu ? Any advice will be appreciated. Thanks.

The knob on the ECU controls idle mixture only. It won't have any effect under acceleration / load.

Conventional wisdom here is generally that the biggest displacement stock D-Jet FI can reliably and effectively handle is 2056 (96 mm pistons/cylinders, 71mm crank). To tune it to that you need to adjust your Manifold Pressure Sensor (MPS). Others have tried with 2258 (2270) and I'm not sure they've had great results. Usually go to carbs or aftermarket FI at that point.

This is good reading: https://members.rennlist.com/pbanders/manif...sure_sensor.htm

Happy New Year and (IMG:style_emoticons/default/welcome.png)

[VaccaRabite]

(IMG:style_emoticons/default/welcome.png)

The lack of dowel pins is troubling. Have the case measured for sure before buying anything. I think bearing now are more available then the were a few years ago, but its still easier to get bearings in standard then plus sizes.

Since you have a 1.7, your easiest "bog bore" that will run on DJet is a 1911. That means your stock crank and 96mm pistons. This will give you about 110-120 crank hp.

I do not think that Biral is needed with 96mm and djet. Standard cast iron will be fine. If you go over 96mm, then you will need the better cylinders (and you won't be running Djet.)

Good luck!
Zach

[Damo]

Thanks guys. I’ll check the case but when I first stripped the engine down I was surprised at how clean it all looked, bearing wear, pin wear, bores etc. I wasn’t sure that it had been rebuilt as all parts looked original. I’ve had the car for about 6 years but done very little mileage in her. was blowing oil at the head/cylinder so always knew a tear down was needed. I’ve rebuilt a coupe of 911 engines in the past so I know my way around air cooled but wasn’t sure about the dowel pins. I could see where they should be but the lack of all of them left me puzzled. Thanks guys.