boosting 9.5:1 compression engine
 

Hi,

I have a CA18DET engine. (Nissan 1.8l.) The turbo version has 8.5:1 compression and can take a lot of boost. I picked up an NA version of the engine really cheap. Normally you can only run about 10 lbs of boost on this engine because it has a compression ratio of 9.5:1.

I've been working on cars for a while, but this will be the first time I do my own tuning. If I used water/meth injection, how much more boost would this allow me to run? My turbo maxes out at about 14 lbs..

I kind of like the higher compression for the street, but I have some 8.5 pistons I can install if I have to. I know 8.5 is safer, but if I can have the best of both worlds...

I'm going to be using Megasquirt for engine management.

Any ideas?

Any idea how high would be your boost threshold? I'm in a similar similar situation, I run 6.5 psi on a stock 9.3:1 engine without issues, but the turbo kicks in at 3200 rpm for 3-5 and slighter higher for 1-2.

Things is, with a proper sized exhaust and intake, my dyno sheet shows improvements in both hp and torque even off boost.

If your turbo is boosting low, then I see no reason why you shouldn't install the lower comp pistons and compensate for off-boost operation with a proper sized exhaust/intake. I think water/meth should be used for improved performance on an already built engine, your stock 9.5:1 would probably need at least an upgraded gasket to handle 14 lbs safely.

Thanks for your advice.

I know the engine can take 14 lbs on the 8:5, but I would love to use 9:5. Also, while I am mechanically inclined, I've never honed a cylinder and replaced rings before.

I say take it slow. Do the setup, tune it at 6-7 psi with the stock engine, see how it runs, how you're making boost, then you can decide how to improve on it. If you don't have a definite recipe there's no telling on how it will handle.

You might be surprised on how it runs. For example, my setup resulted in two thirds increase in both hp and power from stock N/A at only 6.5 psi! Granted, I'm only boosting on the top half of the rpm range, but still. This means I have a hell of a lot more to complete before increasing the boost: clutch, suspension, brakes, better grip on the road, better fueling, they are all necessary upgrades before upping the boost, even if the engine can handle more without a rebuild.

After which I'll seriosuly become worried about how the transmission will hold :)))

Those are all good points. I want to get it Megasquirted and go from there. It's kind of fun to have an engine I don't car about, but I'd like to try to make it work.

If you do the fab work and the tune yourself and it doesn't break, you'll be even more proud of it!

There is anyway only a small improvement in torque with the 9.5:1 pistons compared to the 8.5:1 ones. So I would swap the pistons if you already have them. Let the cylinders get honed professionally, thats not very expensive.
Like that you are on the save side for boost.
I own a CA18DET as well. Its a good and powerful engine, but it has some weak spots; rod bearings for example, or sludged crankcase vent. system. So a engine cleanup and renewal of the bearings and gaskets is anyway much essential before tune up. I suppose it's not a low mileage engine, then it would be even more important.
Greetings