New l 28 for my 72

[Diseazd]

I'm building a new L 28 for the green 72. We're using an F 54 block and a P 79 head. We bought Nissan original new .040 over size pistons.We bored the block .040 over and .080 shaved heads (shimmed cam towers). SI stainless swirl valves and an Isky Stage III cam. New rockers , springs and retainers. We'll update as we build onward. Guy

<a href="http://www.flickr.com/photos/14049800@N00/3530079948/" title="IMG_1652 by RVAE34, on Flickr"><img src="http://farm3.static.flickr.com/2323/3530079948_bd79878ae4_b.jpg" width="1024" height="683" alt="IMG_1652" /></a>

<a href="http://www.flickr.com/photos/14049800@N00/3529267621/" title="IMG_1653 by RVAE34, on Flickr"><img src="http://farm3.static.flickr.com/2133/3529267621_a017b24083_b.jpg" width="1024" height="683" alt="IMG_1653" /></a>

<a href="http://www.flickr.com/photos/14049800@N00/3529268785/" title="IMG_1654 by RVAE34, on Flickr"><img src="http://farm3.static.flickr.com/2154/3529268785_3c1e3ae0ab_b.jpg" width="1024" height="683" alt="IMG_1654" /></a>

Pistons

<a href="http://www.flickr.com/photos/14049800@N00/3532382276/" title="IMG_1664 by RVAE34, on Flickr"><img src="http://farm3.static.flickr.com/2046/3532382276_4117198b33_b.jpg" width="1024" height="683" alt="IMG_1664" /></a>

<a href="http://www.flickr.com/photos/14049800@N00/3532383308/" title="IMG_1667 by RVAE34, on Flickr"><img src="http://farm4.static.flickr.com/3104/3532383308_ef497d4d77_b.jpg" width="1024" height="683" alt="IMG_1667" /></a>

Crank

<a href="http://www.flickr.com/photos/14049800@N00/3531575271/" title="IMG_1689 by RVAE34, on Flickr"><img src="http://farm3.static.flickr.com/2266/3531575271_c91f38911f_b.jpg" width="1024" height="683" alt="IMG_1689" /></a>

<a href="http://www.flickr.com/photos/14049800@N00/3532393432/" title="IMG_1690 by RVAE34, on Flickr"><img src="http://farm3.static.flickr.com/2193/3532393432_23321a1733_b.jpg" width="1024" height="683" alt="IMG_1690" /></a>

[Carl Beck]

Hi Guy:

Looks great so far...

Please Post some pictures of the combustion chambers with the valves installed. If your machine shop cc's the combustion chambers, I'd be interested in knowing what you would up with in the end.

regards,

Carl B.

[beandip]

I'm building a new L 28 for the green 72. We're using an F 54 block and a P 79 head. We bought Nissan original new .040 over size pistons.We bored the block .040 over and .080 shaved heads (shimmed cam towers). SI stainless swirl valves and an Isky Stage III cam. New rockers , springs and retainers. We'll update as we build onward. Guy

Guy, What have you figured the .080 off the head will give you. I know .030 gave me 9.5 . Looks like you are doing a first class job.

Gary

[Diseazd]

Gary.....The Z doctor in Roanoke is building the head.......he says 10 to 1 , but with the higher duration cam it runs perfect on 93 pump gas....at least the last one I built did! Carl.....I'll get pics of the head with valves when it comes back.....I'm not sure how I could cc the head though. Guy

[Carl Beck]

Hi Guy:

I'm hoping that The Z doctor would have a Plexiglass cover to fix to the head, through which he would inject a precisely measured amount of fluid into the combustion chambers. It's a fairly simple process that most engine builders use to assure even combustion chamber volumes.

One Example - if you google "cc'ing combustion chambers"

http://www.cosworthvega.com/cc_an_engine_GEC.html

FWIW,

Carl B.

[Diseazd]

Carl....... I've seen how it's done in my old "Modify 510,240Z Book". Doc probably knows to the cc what the volume is.......I'll ask him next time I talk to him. He did say that the standard bore L28 with .080 shaved P 79 head was 10 to 1 compression, so you might be able to plug in your other known L 28 numbers to find swept volume. Guy

[Oiluj]

I'll second the great pics comment! Looking forward to seeing more as the project progresses.

[Carl Beck]

Hi Guy:

The reason I was hoping we could verify the combustion chamber volume with an actual measure - is because when I plug the numbers in - I get a C/R of 11.6:1 - - if you are using flat top pistons and stock head gasket.

I'm not certain that milling the head 2mm (0.080") removes 11.62cc's however. The reason is that the combustion chamber walls are dished, rather than straight. The other unknown at this point is the type of cylinder head gasket Z doc plans to use..

L28 – Flat Top Pistons (79-83) & 1mm overbore (0.040")

Swept Volume of Cylinder = 480.5cc

Combustion Chamber volume = 53.6cc minus 11.62cc for 2mm (0.080") shave head.= 41.49cc

Gasket Thickness = 7.6cc

Deck Height = -3.69cc

So:

41.49 + 7.6 - 3.69 = 45.4 combustion chamber volume

480.5 + 45.4 = 525.9 total volume

525.9/45.4 = 11.58 : 1 Compression Ratio

To get to 10.0:1 you'd need a combustion chamber volume of 53cc's. So you'd have to pick up about 7.3cc's somewhere. Dished pistons increase combustion chamber volume by about 10.9 cc's. Using a 1mm thick metal head gasket, with a 91mm diameter opening, would increase combustion chamber volume by about 6.5cc. The 2mm thick metal head gasket would add 13.01cc's.

Playing with the numbers is fun, but it is better if we have verified numbers to start with.

FWIW,

Carl B.

[Diseazd]

Carl.....The first L 28 I built was standard bore, flat top pistons, F 54 block, P 79 head shaved .080, shimmed .080 with Isky Stage III cam .490 lift and 20 degrees more duration than stock L 28. I guess you could start with the CR of a stock 1983 L 28 which is standard bore, flat top pistons, standard head etc. ( what CR was that engine stock?). If it was 8.5 to 1 or so, I guess the decrease in head volume brought it up to 10 to 1. The new engine I'm building now will be bored .040 over, so I'm not sure what CR I'll be running on this engine, but I've had absolutely no problem with 93 pump gas with the first one.........It's a real joy to drive with the SU's. It really gets up and goes and has very little lope. It makes driving a ball!!! Guy

[Carl Beck]

Carl.....The first L 28 I built was standard bore, flat top pistons, F 54 block, P 79 head shaved .080, shimmed .080 with Isky Stage III cam .490 lift and 20 degrees more duration than stock L 28. I guess you could start with the CR of a stock 1983 L 28 which is standard bore, flat top pistons, standard head etc. ( what CR was that engine stock?). If it was 8.5 to 1 or so, I guess the decrease in head volume brought it up to 10 to 1.

Hi Guy:

First let me say that I have more questions at this point than answers. I've received somewhat conflicting data from different sources over the years. Sources with a high degree of creditability and years of personal experience. One reason is that the data from L24's is based on engines that ran in SCCA's "Stock" classes - and were therefore torn down and checked, time after time. So right from the beginning those engines were built to very exacting specifications.

With the data from the L28's - that is not the case. For the most part with the L28's we are getting inputs about modified engines - and the data becomes more speciifc to the engine and engine builders.

For example:

- From various engine builders we get inputs that "deck height", the amount the piston exceeds the cylinder wall in the block is either "0" or 3.69cc

- Depending upon the cylinder head gasket used, the volume added to the total volume and the combustion chamber volume can both vary between 7.6cc {stock 88mm L28 gasket} and 13.01cc {2mm thick, with 91mm dia.} for the metal gaskets.

- Then of course there is the question about the actual cc's of an altered head/combustion chamber.

So I'm hoping that as you work with Z doc - you'll be able to pin down some very specific data related to your current project. In effect ask them to cc the combustion chamber and report the exact value, and ask them specifically what cylinder head gasket they plan to use.

All this is something I wish I had the presents of mind to accurately measure and record years ago when I swapped in my first, second and third L28's. My present engine uses Nissan's Flat Tops with a 2cc pop-up and 0.5mm overbore, a 72 E88 head with increased valve size, unshrouded valve seats and the Nissan Slalom Cam Kit {0.475" lift & 275 degrees duration}. Triple Webers and UniLite distributor w/o vacuum advance. At the time we built the engine, we calculated the C/R at about 10.13:1. Runs fine on 93 octane pump gas, not quite so well on 91 octane as the timing has to be retarded a couple of degrees.

For the sake of discussion, below are three different ways of calculating the C/R, depending on what was done, and/or what parts were used, and using a "0" deck height.

Holding everything else the same - it would seem that the 0.040" overbore raises compression ratio from 10.78:1 to 11.58:1 .

Z doc may well be doing other things that will lower that to something closer to the 10:1 your looking for.

STOCK 8.5:1 C/R

L28 with Flat Tops and P79 Head

Swept Volume of Cylinder = 458.9cc

Combustion Chamber volume = 53.6cc

Gasket Thickness = 7.6cc

Deck Height = 0 cc

So:

53.3 + 7.6 = 60.9 combustion chamber volume

458.9 + 60.9 = 519.8 total volume

519.8/60.9 = 8.5 : 1 Compression Ratio

= = = = = = = = = = = = = = = = = = = = = = = = = =

MODIFIED #1 10.78:1

1mm Overbore and 2mm Milled Head:

L28 – Flat Top Pistons (79-83) & 1mm overbore (0.040")

Swept Volume of Cylinder = 480.5cc

Combustion Chamber volume = 53.6cc minus 11.62cc for 2mm (0.080") shave head.= 41.49cc

Gasket Thickness = 7.6cc

Deck Height = 0 cc

So:

41.49 + 7.6 = 49.09 combustion chamber volume

480.5 +49.09 = 529.59 total volume

529.59 /49.09 = 10.78 : 1 Compression Ratio

= = = == == = = = = = = = = = = = = = = = = = = =

MODIFIED #2 11.58:1

Same as Mod #1 except the block has been decked by 0.020 to assure flatness, or it may be true that the stock L28's pistons do exceed the block deck height by 0.020" to begin with.

L28 – Flat Top Pistons (79-83) & 1mm overbore (0.040")

Swept Volume of Cylinder = 480.5cc

Combustion Chamber volume = 53.6cc minus 11.62cc for 2mm (0.080") shave head.= 41.49cc

Gasket Thickness = 7.6cc

Deck Height = - 3.69 cc

So:

41.49 + 7.6 - 3.69 = 45.4 combustion chamber volume

480.5 + 45.4 = 525.9 total volume

525.9/45.4 = 11.58 : 1 Compression Ratio

So if you get a chance to talk to the people at Z doc - see if you can find out what the measured cc's of the combustion chambers are and what head gasket they will use. Also see if you do have pistons with a positive deck height or not, you'll be able to tell once the pistons are installed.

I'd also suggest that if you can get the specific data - unlike me, write it down and keep the records.

FWIW,

Carl B.

[Diseazd]

Carl......I've got your answer. Go to www.datsunzgarage.com click performance tip, then under heads, click the underlined P 79. This guy worked with the Z Doctor and has built and discusses the identical engine to my first build. He mentioned that he cc'd that identical P 79 .080 cut and shimmed head and got a reduction to 46cc chamber volume. Now you can tell me what my 1mm overbore will give me as a CR. I appreciate your help. If I did my numbers right, with the stock gasket that would be 9.9645 to 1 on the 1mm overbore. Guy

Edited May 17, 2009 by Diseazd

[Carl Beck]

Hi Guy:

Yes if the combustion chambers are 46cc's that is correct.

On the other hand that also means that the first engine was not 10:1 but rather 9.56:1

Thanks for the input - I'll add it to the C/R data base... Be sure to Post some pictures of the combustion chambers when you get the head back..

FWIW,

Carl B.