Datsun Roadster Forum-311s.org

whats the biggest you have seen?
and these h20 parts what is this refering to?
the only thing i could find was forklifts.

what are the rod to crank journal size? (so maybe i can find a different rod to fit)

thanks
steve

The H20 is a R16 block with a 2L rod and crank with dished pistons for low compression also has a cast iron head. The motor was built for a forklift to run on gas or propane. A person can take that H20, press some R16 pistons on and install a aluminum R16 head and have a stroker motor. Or you can just rob a U20 crank and rods, cut the end of the crank down to fit the R16 and do the same. I am currently selling a roadster on ebay with the H20 in it and it feels like it has the torque of a U20 with the hp close the R16. I was really suprised how well it ran in a car.

Alexi

Unless I am mistaken, the R pistons need machine work to fit as the skirts would interfere. Most folks think that the H20 was only a forklift motor, that just ain't so! They were used in a lot of industrial applications (generators, welders, pumps and the like), and they also were in passenger cars in Japan as well as utility vehicles. I don't know if there are flat top pistons available from Japan, but there well could be. The heads for the forklifts are interesting. They LOOK like a roadster head, but the intake ports are TINY.

If you have a 1600 with a head that has been cut too much, it would be good to use the dished H20 pistons to get a more liveable compression ratio.

As far as cutting down the U20 crank, I have heard some folks complain about having a tough time finding someone to drill and tap the newly cut end to work...

If you check Rallye's website, you'll see that both U20 pistons and R16 flattop pistons have the same part number. I believe - but don't quote me on this - that these are all H20 pistons, as both R16 (definitely) and U20 (someone confirm this please) used domed pistons originally.

The H20 crankshaft and connecting rods will install directly into a 5-main R16 engine (engine serial number above 40,000) and give you the same displacement as a U20 engine, only with pushrods instead of an OHC. From what I've been told, you'll want to get larger carburetors, bore and hone the intake manifold and head, have larger valves installed, and have the camshaft profile reground to take full advantage of this increased displacement.

Most parts for the H20 can be purchased from www.motorpowerinc.com for prices that'll amaze you. For example, pistons are under $16 each. These aren't Nissan brand but should work fine. This is a forklift place, but a bunch of people (me included) have ordered parts for our engines from them. In my case it was to rebuild a J15 engine in my 411, and I was very impressed with the service and parts I received. Most of the parts I received were either Japanese or US mfd (the pistons were Korean). The only parts not listed there are the crankshaft and connecting rods, but you should be able to buy them from a Nissan forklift dealer for much less than from our vendors or car dealers.


Now what I'm more interested in is installing an H25 forklift engine into a Roadster...

The U20 pistons were flat tops. The R pistons are domed. The H20 pistons that I have seen are all dished (and according to the local forklift guy, that is all that he has seen and can get). U20 pistons will work in the H and the R. The skirt length on the R is longer than the U20 pistons. The H should be the same dimensions as the U20 units. To use the domed pistons in the other motors, you have to mill approximately .100 off of the bottom of the pistons. The Bob Sharp manual gives the details. I could be wrong on that dimension - I don't have the books handy...

I stand corrected on the pistons. The J15 pistons were flattop, but admittedly that's a completely different engine. The Old Datsun page www.geocities.com/olddat indicates the H19 and H20 engines had compression ratios between 8:1 and 8.5:1, much less than the 9:1 of our Roadsters. I imagine that using H20 pistons in a stroker motor would produce similarly low compression ratios, but might be good for a turbocharged H20.

I searched for pistons and found the following aftermarket piston for the R16:

http://www.piston.com.tw/product.php?mo ... 15&pid=190

Remember that an H20 is a pushrod U20, so with the flat tops, it should be back to 9.6:1. If the bore and stroke are the same, the difference in compression will be from the dish in the pistons, and the volume of the combustion chambers in the head. My U20 went from 9.6 to 10.65 by boring it .060 over. I bet if one were to build a H20 like my U20 it would be an impressive beast, lots of torque, but low reving due to the pushrods. When I say this I am assuming qutie a bit as far as head design. Also if all things are the same, one could possibly run VG30 pistons. The H20 rods with the VG30 pistons will be quite a bit lighter than the U20 setup. The VG30 pistons also have valve cutouts so one could run a higher lift cam.

Will

My J15 is bored .030 over, which I believe ups the CR to about 8.5:1 (from 8.3:1 stock) and increases displacement from 1489cc to 1511cc. I'm planning to put the old J13 head on it if the combustion chamber is smaller. If I did my math right (which is questionable) then I should have about 9.5:1 out of that engine.

Pushrod action shouldn't change much between an R16 and H20 since the distance between the valves and camshaft hasn't changed. I suppose stronger springs and larger valves might put more stress on the pushrods. One big difference between the U20 crankshaft and the R16 and H20 crankshaft is that the U20 is counterbalanced while the R16 and H20 aren't. But then again there's less rotational mass and weight with the R16 and H20.

Steve, has your car been dyno'd? I'd be curious to see what a fully prepped H20 puts out, with bigger valves, 1.75" carbs, hogged out intake... Where is the disadvantage in performance to the U20 except the OHV design, and how much performance does that actually rob?

Unfortunately I have not had my stroker on a dyno yet. I had an appointment a year or so ago but the guy running the shop never showed up. It would be interesting to see just what it is putting out. All I know is I truly enjoy driving the snot out of it when I get the chance and besides running a little rich I like it.
Steve

Well, the U20 ports are a bit better than the R ports, so there would be some improvement for the U20 at higher RPMs. The R/H20 stroker should have a bit more grunt off the line. I have not driven a well sorted stroker, nor have I driven a U20 that has been massaged, so I could be all wet...

What do you mean, the U20 ports are better? Are they larger? Is there some advantage to their shape vs. an R16 head? The R16 has enough metal to hog out the intake manifold and do some enlarging/honing in the head, if I'm correct. Would that make them equal?

The U20 ports are bigger and a bit more direct iirc. I don't have the heads side by side right now, so I can't give specifics though. Some folks have run into issues in porting the R heads - ground through to the water passages. There is not as much metal there as you may think. The U20 really does not need much work. Look at the info in the Bob Sharp manual and you can get an idea how well they regarded the ports. All that they recommended is smoothing them. The earlier manual recommended more port work.

called around to some forklift companys..they want $2300 for a short block plus $1000 core charge..kind of steep..atleast for the core charge!

i think i may just turbo the stock motor (crazy i know) if i can't find a short block for cheaper

thanks
steve

If you REALLY want to build a stroker, I have a 5 main block in the garage. Cranks and rods can be had much cheaper than the $3300 total bite you are looking at...