since when would the rb30de not pass emissions, it would be alot better the the 30e and pass with flying colours..got to remember the engine only has to meet the requirements of the cars manufacture date. which is 86.
Seriously mate, dont even bother.
I'm doing it at the moment and a cheap rebuild will still be $4000+ without turbo if you decide to turbo it.
just buy a VL with a RB25 in it already.
Quote:
Originally Posted by E-Z
since when would the rb30de not pass emissions, it would be alot better the the 30e and pass with flying colours..got to remember the engine only has to meet the requirements of the cars manufacture date. which is 86.
If it was a motor offered in that model (RB30e, RB30et) then it would be 1986.
The motor legally has to be fully tested as its not a motor on offer from the manufaturer in that series.
If Nissan made a RB30DE - no worries.
But alas, they didnt.
It's a shame that this idea has recieved so many negative comments as the result would be one of the best naturally aspirated motors around...
It has been said that the std rb25 head flows as much air as the best ported RB30 head and would really wake up the 3 litre. Along with the RB25 cams, which make good power to over 6000rpm, it would free up the RB30 hugely.
The longer stroke would cap the rev limit but no where as much as the stock RB30 head/cam does. The stock rods, crank, etc are good for a 6000 - 6500 rev limit...
The only thing that makes the idea questionable is the fact that the combustion chambers in the RB25 head are larger and result in a compression ratio of approx 8.3:1 with the std RB30 pistons. This means you need a set of custom pistons to get the compression ratio back up around 10:1.
If you can find a suitable set of pistons, at a reasonable cost, then you would have a little ripper on your hands...
Actually, now that I think it through a bit further, a set of std RB25 pistons would solve this problem and give you the correct compression ratio. Relatively cheaply too.
TOBES is right, there are two main issues.
One way to fix the compression problem is to use RB25DE pistons with the RB30 crank and rods. They will certainly fit up inside the head without any valve clearance problems, and the compression will be very high. But by the time you have fitted some decent cams, you will need to have very high static compression anyway.
The biggest problem will be sufficient breathing. A standard RB25DE reaches peak power at 6,800 rpm. By increasing the stroke and engine capacity, the cylinder head will still peak at the same maximum airflow. Unfortunately the maximum power rpm falls to 6,800 x 2.5/3 = 5,667 rpm. Bigger cams will help, but don't expect it to rev as sweetly as a short stroke RB25 would.
another off hand thought. it'd only work for a high comp non turbo setup, but an RB20 head might work here. they suck for turbo setups cause they raise the compression ratio to high, but if you want to run it as an NA, it just might work.
from memory, the dish size of the head is about 7-8 ml less than the 25 head, meaning the compression rate will be up near the 10 mark again. I think it takes the turbo pistons up to 9.3, which is too high for turboing.
hey, i might be wrong
The problem with an RB20 head, apart from the unfortunate water jacket locations, is that the valves and ports are far smaller than with an RB25/RB26 head. It will severely limit the airflow capacity.
Best to stick to the RB25 head for the reasons Warpspeed said.
A couple of other points -
While the RB30 stroke is longer, the con rod is also 25-30mm odd longer so the rod/stroke ratio is much better than the RB25. Better combustion, less wear and helps it rev...
If you read the head conversion thread on SAU, SK states that the Rb25/Rb30 combo's make the same Hp as a Rb25 with 20% less revs. That is a Rb25/30 makes the same Hp at 7200rpm as a Rb25 makes at 9000rpm...!!!
