Straight Six

[2strokebloke]

I just wanted to know what others think of straight 6 engines, my opinions:
PROS: Good primary balance, good secondary balance.
CONS: Engine length, crankshaft length, poor cooling, poor breathing (well with fuel injection it's really not that much of a problem)

what do you think? IMHO the best thing this class of engine has going for it is secondary balance, which is something a V-6 doesn't have (well could have with countershafts) Otherwise it doesn't seem to have many favourable qualities.

[Supra650RSP]

true and true about the engine length and crank length, but you forgot to mention one very big positive with the straight 6. The ability to place a very large single turbo on the motor with very little piping. :evillaugh

[phatdex]

Straight wins over a V anyday, much stronger and more harmonically sound. A 2JZ is stronger than a very strong thing. hehe

[Blitzen]

Agree - the RB26DETT is hella bomb proof too though .

[Supra650RSP]

Amen, Both the 2jz and Rb are incredible examples of straight 6 supremacy

[2strokebloke]

I think it's the long crankshaft that bothers me the most, it's length makes it inherently weaker and prone to wear. And again due to length, a weaker block as well.
Poor breathing - the cylinder furthest from the air filter recieves the least air, the cylinders closest to the inlet make the most power.
Uneven cooling, cylinders operate at different temperatures, again leading to different outputs from each cylinder.
Those are what it has going against it, for it is balance, it's vibration free compared to alot of engines (or at least a V6).

[Supra650RSP]

Actually,
Using both the RBxxDETT and 2JZ-GTE as examples I'm going to refute a few of your claims. First, especially in the Turbo variants the cylinder in the back of the engine farthest from the filter recieves the most air due to the manifold design. Typically a boost spike will result in the damaging of the number six cylinder in both motors. Often to avoid this problem aftermarket manifolds are necessary so the air is more evenly distributed. Secondly, the longer cranks are not quite as strong however the difference is so slight it would hardly be noticable. A forged crank would all but completly aleviate any worries here. Finally, it is not the longer crank that causes a weaker block but rather the angle of the crank. The larger the motor the more extreme the angle of the crank i.e. 3.0L has a more extreme angle than a 2.6L. It is the pressure of the crank pushing the rod against the side of the block that creates the breakdown. This is why it is easier to boost an RB26 at a little higher levels than the 2JZ. although not significantly more

[phatdex]

What other engine, besides a 2JZ can support 800HP with standard internals? Not even an RB26DETT can do that.

[2strokebloke]

"...the cylinder in the back of the engine farthest from the filter recieves the most air due to the manifold design. "

Over compensation from the engineers?

"The larger the motor the more extreme the angle of the crank i.e. 3.0L has a more extreme angle than a 2.6L. "

I fail to see this, unless the only difference between the 3 and the 2.6 is a longer stroke. The tortional strains a long engine undergoes are more than those of a short engine, I think that if there were two blocks of three cylinders, the strenght would increase, as would the cooling efficiency.

[JD@af]

Originally posted by phatdex
What other engine, besides a 2JZ can support 800HP with standard internals? Not even an RB26DETT can do that.

That's not what I've heard. I've heard that the 2JZ-GTE can support 700 with stock internals (but I am sure that 800 is also a within reach), and I've heard of an RB26DETT supporting 1,300 hp with stock internals. With precise tuning, it is possible.

[Supra650RSP]

For the 2JZ-631 in my car on stock internals is pushing it quite a bit. I've heard of around 700 hp figures but ask anyone and they'll say that over and above 650 it's time to start thinking about internals.
For the RB- I haven't heard of anyone pushing those kinds of numbers on stock internals. HKS, JUN, and a couple of other companies also reccommend replacement of the internals at or around 7-750 hp. But, if it is possible, that'll save me some money in the build
2Stroke - The air goes to the back of the manifold because of the amount of air that is being pushed into it via the Turbo(s) The air is forced into the manifold at such a high rate that it often doesn't have time to be sucked into the engine itself thus hitting the back of the manifold and going into the number six cylinder
The biggest differance between the RB and the 2JZ is indeed the longer stroke of the 3.0L.
thirdly, I'm not sure about test results on tortional strains, I must admit, here you have me. (Yes I am an AF user that will admit faults) As for cooling, I do know this the RB and 2JZ have no problems with overheating. Even with the addition of turbos which generate enourmous amounts of heat cooling is not an issue. The only cars I know that have problems with heat that are comparable to these two motors are the 300zx which is a V-6 and the RX-7 rotary. I know though that in terms of the 300Z the problem is in body design and not engine design. As for the Rotary I have no experience with this motor so I don't know why there is a problem.

[2strokebloke]

the problem is not overheating, the problem is that different cylinders operate at different temperatures, so they have different outputs (admittedly so little difference that it's not really a problem - but it still bothers me for some reason) do to uneven cooling.
In a naturally aspirated engine the number 1 cylinder will recieve the most air, but as you have pointed out in the turbocharged engine it is the #6 cylinder that recieves the most.

A rotary engine will create more heat than a 4-stroke piston engine because it is constantly burning fuel as the rotor spins, in a piston engine the combustion chamber is also subject to the intake and exhaust strokes, not so in the rotary engine.

[phatdex]

The 2JZ is supposedly much stronger than the RB26, can take much more than the GTR motor.

[Blitzen]

It is debatable (sp?), whether the Skyline block is stronger than the 2J. But then it depends on so many factors what engine will be stronger, and who would tune an engine when stock internals become an issue ? What I mean is, if 1300hp is when internals have to be uprated, the car wouldnt be drivable, and nobody will tune to that level really.

Really, Id only tune to about 800hp MAX, so both engines will be fine.

Just my 2hp

[phatdex]

The only thing I know is that an RB26DETT can NOT get 1300hp with standard internals, that is ridiculous.
The HKS GTR has 1300HP at the wheels and has aftermarket everything, its done a 7.5sec 1/4 mile. The HKS Supra has done a 7.1sec 1/4 mile. =)