Help With Engine Setup?

[dano]

Hi Folks,

I've tried searching the archives but have not found anything relating to this particular setup. As it stands I have a freshly rebuilt L28ET (F54 block, stock dished pistons, and P90A head) installed in my car minus the E and T parts (running with fresh ztherapy SU carbs). For a variety of reasons I won't be able to get the E and T parts installed. Needless to say the car doesn't run great. The goal here is to have something approaching the stock power level so that the car is fun to drive again.

To fix it, I figure I have three options:

1. Swap in working-but-worn L26 (from a 11/74 260Z) that I have. It would need a new clutch, but that's it.

2. Swap the head from the L26 (E88 I believe) onto the F54 block that's already in the car.

3. Sell it to someone who has the time to install the E and T parts.

I'm leaning towards option 2 because it's the easiest and won't require much time or money (both of which I don't have an excess of). Also, I'd like to get some use out of the fresh motor if at all possible.

Any advice would be greatly appreciated!

[Arne]

Two problems with the current setup - low compression ratio and turbo-grind cam.

I don't think you'll get much if any boost from the 260Z head - while the cam will be better, the compression will still be quite low.

Best set would be flat-top pistons and a non-turbo cam in the current L28. (Cam swap is assuming your P90A has normal lifters, if you've got one of the hydraulic lifter heads, that probably won't work.) If that is beyond what you can deal with now, I'd swap the L26 back in.

Edited May 16, 2011 by Arne

[240260280z]

Maxima N47 head will work nicely.

[dano]

Arne, thanks for the information. I do, unfortunately, have the hydraulic P90A head. When you say low compression, what is too low on these motors? I've been reading threads and have seen everything from 11:1 to 8-something:1 with little information on the minimum acceptable number. If it means anything I did run the F54 block-L26 head combo through the engine calculators and came up with about 8.3:1 compression.

Blue, thanks for the input. Unfortunately living in Hawaii shipping in a cylinder head is really costly . Btw are you the same Blue that runs the excellent tech tips site?

[Zed Head]

For 1981 the FSM shows a CR of 8.8 for the NA engine versus 7.4 for the turbo engine. The earlier N42 blocks (with stock pistons), and N42 or N47 heads, ran 8.3 CR, no turbos, EFI.

[Arne]

P90 with dished pistons is a Turbo setup - seems to me the compression w/o boost is less than 8:1, maybe 7.5:1? Add to that the turbo cam grind which doesn't allow the cylinders to fill properly w/o boost and you've got a bit of a slug.

Worse, because it's the hydraulic lifter version, you can't just use a NA cam - the hydraulic lifters require a different lobe profile and won't work properly if the cam wasn't built specifically for hydraulic lifters, which were only used on a few late turbo motors.

The 260Z head (late E88) will help some, but those are a large chamber head designed for flat-top pistons as well. I doubt the compression with the dished pistons would be much above 8:1, if that.

If the fresh motor had solid lifters, I'd say swap in some flat-top pistons and a different cam and you'd be set. But with the hydraulic lifters, you really need the turbo for that motor.

[dano]

Zed Head, thanks!

Arne, thanks for the additional information. Looks like I'll swap back in the original engine and try and sell off the turbo one.

Thanks all for the help!

[Patcon]

One other option is to take Arnes advice but convert the head to solid lifter there are a number of threads at hybrid z about this because the hydraulic lifters are NLA and sometimes collapse when dirty or pushed too hard. The guys on HybridZ sometimes push the limits on these engines. If you do decide to convert the head the old lifters can probably be Ebayed. The P90 and P90a heads are good heads and flow pretty well. So that would be another way to get where you want to go.

Charles

[dano]

Charles, Thanks! The way I understand it though I'd also have to swap to flat-top pistons to bring the compression level back up to a reasonable level? I've also read good things about the P90 heads and was hoping this one would "just work" for me .

[Arne]

Yeah the P79/P90/P90A heads only give 8.8 with flat top pistons. Which is only a moderate ratio. That's a fair amount of expense and effort for something that still would require the hydraulic lifters replaced and a new cam.

[dano]

Hi Folks,

Wanted to share some additional information regarding this in the off chance it changes something.

I used the http://www.ozdat.com/ozdatonline/enginedesign/ engine calculator to determine the specs on the L26 engine I have. Turns out from the factory it had a compression ratio of about 8.2:1. I didn't realize it but the L26 shipped with dished pistons (7cc in case anyone was wondering).

Using that same calculator I got a compression ratio of about 8.245:1 for the E88/F54 combo.

Is this one of those cases where not all compression ratios are created equal?

Thank you so much to everyone (esp Arne) for helping me to understand all this stuff!

Edited May 19, 2011 by dano
changed 7mm to 7cc for dish size.

[240260280z]

You may also consider trying to source an N42 or N47 (from z/zx) locally if shipping is a problem. Just get 2mm shaved off the bottom and away you go 32cc chamber. Slap it on and move the timing chain 1 tooth closer to take up the change in height.

32cc N47 shaved 2mm (0.080")

Ref. http://www.atlanticz.ca/zclub/techtips/head/n47_2mm_shave/