Ok just thought I'd clear something up, after doing some reading and research, and finding that engines with long strokes produce lots of low-down torque but don't rev well and lose torque quickly, such as the Ford 6s, and are therefore commonly known as "dogboxes", not good for high performance applications.
Well people commonly refer to the RB30 as the "long-stroke" version of the RB series, and yes they are technically right because it is esentially just a RB26 block with a longer stroke. However, "long stroke" engine suggests that the stroke is longer than the bore, and I just found on rbforum.com that the dimensions are bore x stroke: 86.0 x 85.0 mm, which means it is an over-square motor, not a "long-stroke" motor.
The reason why I am writing this is because after reading about the problems of long-stroking I was put off the RB30 in favour of the smaller RB20. Of course the SOHC 8 valve head is still a disadvantage, but knowing that the RB30 bottom end isn't a dog is very comforting.
Hope this is informative for everyone.
Yes you are exactly right.
How high in the RPM range the power peak occurs, and how much power you end up with, depends only on engine breathing capability.
It is always breathing that limits power.
Nice opinion of the ford 6, that makes a **** load more torque from zippo to revline than the RB30. In both N/A and Turbo I might add also... Some people...
OK despite my own personal opinions on Ford (I'm a Holden fan) I didn't want to start yet another Holden vs. Ford bunfight. I was just giving an example of a long stroking, torquey engine. I think the Holden 3.8 is the same, but I don't know for sure so I didn't use it as an example.
And South2, I was actually refering to the old carby ford engines, the new ones are far superiour but still you can never compare an RB30, which was designed in 1986, to a modern spec engine.
Guys please stick to the topic at hand, which is the RB30 or stroke vs. bore or whatever, no ford-bashing in this post please. Ta
Ps. vlc_31t, I like your style, its the same solution to stop snoring, just blow high pressure air down the gullet, that'll help any breathing problem
Some original photos have not been recovered yet.
I think he *might* be usin a bit of the ol sarcasm there...
I've only ever heard the term 'Dogbox' used in reference to straight cut gearboxes (i.e. dog gears), never long stroke engines...
same, me thinks someones got the wrong term going on there..... lol
We all know ho good the RB30 ET is man, glad you like them now.
99% of guys here are into street cars, not race cars, a torquey motor that is all over at 5000 - 5500RPM is not a bad thing at all on the street, you dont need much of a hi-stall etc, engine wear is lessened etc.
Quote:
Originally Posted by HSVSUX
A torquey motor that is all over at 5000 - 5500RPM is not a bad thing at all on the street, you don't need much of a hi-stall etc, engine wear is lessened etc.
This is very true for a street engine, and is definitely the best way to go.
For a race engine, you would be better to shorten the stroke, and fit shorter rear end gears. The reason being that long stroke engines suffer from very high ring friction loss at high RPM. This is the main reason the power falls so quickly after the power peak on a long stroke engine.
If you assemble a new engine without the rings fitted, it will turn over with just the flick of the wrist. Install the rings, and you need a spanner to turn it over. With a few hundred psi gas pressure pressing the rings against the bores with the engine under full load, the frictional loss is a lot more than you probably realise. Perhaps 50 BHP at 8,000 RPM for an n/a RB30. High boost makes ring friction even worse.
Shortening the stroke means less torque, and the power will peak at higher RPM, but the power will also be a bit more at those higher RPM. You can get all of that lost torque back through suitable gear ratios.
If you could build a long stroke race engine that had the same power, and peaked at a low RPM, and had no loss of BHP, everyone would be doing it.
For a street engine though size IS important (as they say).>
Technically, the rb26 block would be a destroked version of the rb30, not the other way around.
And considering the japs have kits like the OS Giken 3L, I think i'd rather slap a better breathing head on a rb30 (prepped) block, if i was going all out.
I dont know why I typed that, but I think there's a point in the somewhere
[quote=Warpspeed
Shortening the stroke means less torque, and the power will peak at higher RPM, but the power will also be a bit more at those higher RPM. You can get all of that lost torque back through suitable gear ratios.[/QUOTE]
Very true. A couple of other advantages of short stroke engines (all else being equal):
1. the rod ratio (ie conrod length/stroke) will be higher. This means that the piston will spend more time at TDC and get more work out of the combustion.
2. because the diameter of the cylinder is greater, you can fit bigger valves.
Quote:
Originally Posted by 2Bad
Ok just thought I'd clear something up, after doing some reading and research, and finding that engines with long strokes produce lots of low-down torque but don't rev well and lose torque quickly, such as the Ford 6s, and are therefore commonly known as "dogboxes", not good for high performance applications.
Well people commonly refer to the RB30 as the "long-stroke" version of the RB series, and yes they are technically right because it is esentially just a RB26 block with a longer stroke. However, "long stroke" engine suggests that the stroke is longer than the bore, and I just found on rbforum.com that the dimensions are bore x stroke: 86.0 x 85.0 mm, which means it is an over-square motor, not a "long-stroke" motor.
The reason why I am writing this is because after reading about the problems of long-stroking I was put off the RB30 in favour of the smaller RB20. Of course the SOHC 8 valve head is still a disadvantage, but knowing that the RB30 bottom end isn't a dog is very comforting.
Hope this is informative for everyone.
From what I understand, the RB20 will rev and rev and rev harder than an RB25 or RB30 (good news). However, it will only produce its potential power at high revs, so it's a PITA for normal use (bad news). The larger RB30 will produce similar power at lower revs with better low-end torque.
As you've quoted, the RB30 is only just under-square. There's stories that GMH tried to get them to produce a 3.3 litre version for the VN (prior to the adoption of the Buick boat-anchor) but I don't know whether it was to be bored or stroked to get that capacity. It's certainly not a long-stroke motor in the way that the XK Jaguar (introduced 1948) and the Alfa Romeo twin cam straight four (introducted 1955) were. In its original 3.4 litre form the Jag engine had 83mm bore and *106* mm stroke!!! That's undersquare . Even in 4.2 litre form (with the same stroke) the bore was 92 mm, so it was still way undersquare.
Interestingly both the Alfa and Jag engines had extremely successful competition careers, so for some applications having a long stroke is not the show-stopper for track use you might think. Also interesting is that in each case in the ultimate development of the engine the *bore* was increased but the stroke remained the same, yet the result was in each case an engine that was rougher and less keen to rev than its predecessor yet had more low-down torque. (1.8 vs 2litre Alfa, 3.8 vs 4.2 litre Jag XK). So in some cases (maybe severly undersquare engines) an increase in bore can have similar effects to an increase in stroke in a more "square" engine!
Note that the Jag's long stroke meant that the spark plug had to be offset to one side of the combustion chamber as it couldn't fit between the valves, and there's some evidence that because of this the XK has indifferent efficiency in burning fuel at part throttle. With the Alfa, less extremely undersquare, in standard engines the plug was between the valves, but for some racing versions they went to a twin-plug head when larger valves meant a single plug wouldn't fit and they wanted to continue to ensure good combustion. Twin-plug heads were also tried on the XK, but I'm not sure with what results.
All very interesting stuff!
Some original photos have not been recovered yet.
