How Track Friendly Are RBZ's?

[Nissan-Fan]

Hey guys, i still havent decided on what engine to invest in for my 280z, im still planning on picking up that sr20 for my car, but after seeing my friends foxbody tear down the street from my school, im wondering if the sr20 will give me enough power and torque. My main goal for the is to get into track racing, but be a mean as hell street car at the same time. The sr attracted me becuase its light and i think would do well on the track, but the sheer power of the Rb's is attracting me too. If i was to put in an Rb25, how well do you guys think i could corner with it? if im going to be puting my z on the track, should i just forget about the RB?

[stony]

My RBz weighed in at 2700lbs with a 51front and 49 rear weight distro.

 

Some suspension tweakin and that could have been over come. 400rwhp bone stock is easy but there are some internal oil feed mods that need to be done to help the rb26 survive the track.

 

Drag racing its fine.

[Gollum]

Depending on the chassis charictaristics that might be perfect though stony.

 

Take the WRX for example, subrau designed it be slightly front heavy, so that the acceleration force in a turn would bring the car close to a 50/50 distro. When is a car ever really at a natural weight distro? Coasting, that's about it. When do you want a front weight bias? Braking. When do you want a rear biased weight? Acceleration. When do you want perfect balance? When you're accelerating out of a turn. If your car is at perfect 50/50 coming out a turn that will yeild a maximum traction ability for what tire you've got. If you're natural balance is 50/50 and you accelerate out of a turn you might have a distro closer to 45/55 (depending on how stiff your suspention is).

 

The mian downside to weight distrobution in this school of though is increased understeer while braking, forcing you to brake a little earlier. But the ability to accelerate earlier and harder can be worth it. Now, in the STI this is severly important because it's AWD. If you have a rear heavy back end you can't push as hard on corner exit becuase the power distrobution is static. But the theories can still be applied to RWD cars.

 

I'm totally expecting johnc to come in here and tear my ideas to peices, wich I'm fine with. I'm always up for learning something new.

[Nissan-Fan]

Wow, stony, i had no clue the RB could give you that close to 49/51....interesting stuff.

[johnc]

I feel bad constantly correcting you...

 

When do you want a front weight bias? Braking.

 

Well... you actually want a 50/50 weight distribution under braking that way all 4 tires can contribute their maximum to slowing the car. But, its very hard to achieve that without affecting cornering balance. The Porsche 911s are outstanding braking cars precisely because they start out at 45F/55R (or somewhere around there.)

 

When do you want a rear biased weight? Acceleration.

 

True.

 

When do you want perfect balance? When you're accelerating out of a turn.

 

Doesn't hurt, but a rear bias is better for the reason you state above.

 

If your car is at perfect 50/50 coming out a turn that will yeild a maximum traction ability for what tire you've got. If you're natural balance is 50/50 and you accelerate out of a turn you might have a distro closer to 45/55 (depending on how stiff your suspention is).

 

45/55 would be nice for accelerating out of the corner. And. big misunderstanding here, suspension stiffness has no affect on load transfer or weight distribution - except when suspension stiffness affects the height of the center of gravity. The longitudinal load transfer equation is:

 

acceleration * ((weight * cg height) / wheelbase))

 

I'm totally expecting johnc to come in here and tear my ideas to peices, wich I'm fine with. I'm always up for learning something new.

 

Again, sorry. Get this book: http://www.amazon.com/gp/product/0879380713/102-0293921-4805746?v=glance&n=283155&n=507846&s=books&v=glance

[240Z_Master]

Another thing that I've noticed about SR swaps is the possibility of a lot of understeer. Most SR's swapped into the S30 chassis are a good 1-5 inches behind the crossmember, give or take. When you take weight off of the front wheels, your ability to gain traction in the front versus let's say an L-Series or RB is substantially different, and in my opinion, less traction.

 

For instance when I drive go karts with the motor out back (like they all are), I tend to stick my fat gut as far forward as possible just so I can grab more grip to the front wheels. Otherwise it just understeers really bad into a wall and then they don't like me.

 

But this is just my perspective and two cents. I hope you take it into consideration. Plus an extra two cylinders is just damn cool compared to the SR.

[Nissan-Fan]

Well, my next motor oppertunity is an rb20det from an 89Gts, the guy is putting in an rb25 and needs the motor, tranny, and ecu gone. I know the rb20 displaces the same as a 4banger, but the closer i get to the name Rb26 the more scared i get, I have this image in my head of 5000 hours of wiring and fabrication.

[Nismo180]

Another thing that I've noticed about SR swaps is the possibility of a lot of understeer. Most SR's swapped into the S30 chassis are a good 1-5 inches behind the crossmember' date=' give or take. When you take weight off of the front wheels, your ability to gain traction in the front versus let's say an L-Series or RB is substantially different, and in my opinion, less traction.

 

For instance when I drive go karts with the motor out back (like they all are), I tend to stick my fat gut as far forward as possible just so I can grab more grip to the front wheels. Otherwise it just understeers really bad into a wall and then they don't like me.

 

But this is just my perspective and two cents. I hope you take it into consideration. Plus an extra two cylinders is just damn cool compared to the SR.[/quote']

 

Astonishingly enough that extra weight upfront in the heavier motored cars is actually doing more for understeer than the lack of weight, the added weight brings with it added momentum, more understeer. Now, the SR poses a huge advantage track wise because it is/can be set back so much further. The less weight you have in the overhanging areas in front of and behind your tires the more willing your car will be to rotate, better turn in, better feedback, better controlability of angle.

 

NissanFan: Stay the F' away from the RB20 speaking from experience in RBs and SRs all the RB is compared to an SR is two more cylinders of weight that stick out farther forward, and less of an aftermarket support system. With simple bolt-ons you can get 300+whp out of an SR I dipped 12s in a 2900lb car with my 250lb *** in it on a stock shortblock, and turbo. RB20s have next to no aftermarket support (jsut try and find an equal length manifold) and are limited to about 280fwhp by their tiny turbos and injectors.

[johnc]

Now, the SR poses a huge advantage track wise because it is/can be set back so much further. The less weight you have in the overhanging areas in front of and behind your tires the more willing your car will be to rotate, better turn in, better feedback, better controlability of angle.

 

Well, it depends...

 

http://forums.hybridz.org/showthread.php?t=100849

 

Also, comparing a SR20DET installation (Amir's 260Z) with a NA L6 installation (mine) that has the engine set back shows identical weight distributions and a better polar moment for the L6 because of the IC and associated plumbing on the SR install.

 

Funny how the real world is different from what's though of as the truth on the Internet...

[Gollum]

Hey john... since nobody else said it about me. OWNED!!!

 

My *** feels nice man, real nice.

 

I somewhat understand what you're saying about wanting a rear bias under corner acceleration. But I guess it all comes down to weather or not turning force >= accelleration force. Since tires can only withstand so much force you want to put more weight on tires to keep from traction loss during accelleration and only need as much weight as needed to turn the car on the front tires. So i guess in most cases the acceleration force is greater than the turning force of the front tires, meaning you would need more weight in back. Correct?

 

I guess a 50/50 distro would be most important if you're worried about controlability when sliding.

 

I'll look into the book for by carroll for sure.

[crazy280]

From what I've learned, JohnC is right. The modern school of thought regarding weight distribution for road racing is to have a slight rearward weight bias to take advantage of traction during acceleration, braking and while accelerating out of a corner. Most purpose-built road-race cars (LeMans Prototypes, F1, Indy, ChampCar, etc) are midengine, rwd, and have a rearward weight distribution. However, too much rearward weight bias can make it difficult to control oversteer at the cornering limit (think Porsche 911).

 

Where I disagree with JohnC (respectfully ) is that I was taught to minimize PMOI, and to keep the car stable with suspension adjustments (toe, sway bars, etc). Hence the advantage of the mid-engine layout. Even front engined cars are optimized by moving the engine down and back as far as possible in the chassis (think: Corvette, RX7, and JohnC's 240z). The SR20DET should be the best for road racing, becuase even with IC/etc the SR is much lighter than the L6 (490 lbs with crossmember, tranny and all accessories!!). If you optimize the placement of the engine and IC, the weight distribution should be perfect, and the overall weight should be less than it would be with the L6. I don't know all the stats on Amir's car, but I would wager that it does not have optimal engine/IC placement, or that it was heavier to begin with than JohnC's car.

 

Of course, JohnC obviously has MUCH more experience in this field, so he's probably right...damnit lol

[Gollum]

Well, you could always go rotary like aux But there isn't nearly the same potential as the RB motors.

 

I think it would be best to have a motor with a low center of gravity that you can get tons of HP with NA. This would eliminate the fmic weight that's way too far forward, and would also eliminate alot of piping & turbo weight. This is why the V8 is so perfect for the Z. Personlly though, I think the weight of a V8 is a bit high. I'd much rather run a high compression V6 for optimum weight distrobution.

 

I don't think i've ever been more convinced of a V6 swap that I am right now.

 

I'm gonna start looking to some good V6 options.

 

JohnC, please correct me if my train of thought is wrong in this post.

 

Also, I think there are alot of other things you can look at too. I don't know of any companies off hand, but CF fenders & hood would take a good amount of weight of the front. I think that's just as important to think about as the motor option.

[johnc]

Weight distribution is important but its not "..all that and a bag of chips..." There are a lot of Actura Integra Type Rs running very fast on road race tracks to prove that a 63F 37R weight distribution is not the disadvantage the Internet experts claim it is.

 

Read up on the Chevy Cobalt/Skyline thread to get an idea. That FWD Chevy Cobalt was only 3 seconds per lap behind a 320hp, 2160lb. Datsun 240Z and it was down 50hp and was 150lbs heavier then the 240Z.

 

http://forums.hybridz.org/showthread.php?t=105093

 

And yes, reducing yaw interia (polar moment) is a good thing because it makes a car more responsive. But, again, its not "...all that and a bag of chips..." and the Porsche 911 is a perfect example.

 

It really all comes down to chassis tuning and driving. A 50/50 car with low yaw intertia theoretically might be faster then a 63/37 car with high yaw inertia, but it all comes down to the guy tuning the chassis and the guy behind the wheel. Either car can win on any given day.

[johnc]

I don't know all the stats on Amir's car, but I would wager that it does not have optimal engine/IC placement, or that it was heavier to begin with than JohnC's car.

 

Amir's car was 260Z to start with so it weighed about 220lbs. more then my early 1970. We did remove the side windows and window mechanism, removed the complete interior including the dash, replaced the bumpers with fiberglass, replaced the bumper mounts, driver's seat only, and put on a fiberglass hood. Amir's transmission was a lighter Nissan 5 speed and he was running a R200 diff. The SR20 install was as far back as possible without notching the firewall. Everything was behind the crossmmember and down as far as safe for a road race track. The IC was in front of the radiator and it was big Spearco and the radiator was the big Arizona Z-car one.

 

On my 1970 I still had a full interior, both seats, windows and window mechanisms, steel bumpers, but I did have a CF hood and CF hatch with Lexan rear window. My 240Z had a lighter wheel and tire combination and lighter brake setup. The transmission in my 240Z was heavier and I was running a R180 diff. My radiator was a small C&R with a built in oil heat exchanger.

 

Both cars run fuel cells of the same basic size mounted in exactly the same position. Both cars ran roll bars although Amir's Autopower bar probably weighed less then the Dave Kent welded in 8 point in my 240Z. Ultimately both cars were withing 10 lbs of each other and weight distribution was within 1%.

 

The comparison as far as weight and weight distribution is about as close as anyone is ever going to get.

 

Personally I don't think comparing a stock L6 install with a SR20DET install is fair. If the L6 is moved back and down then you'll find the wieght distribution numbers are remarkably similar once all the SR turbo stuff is installed. Now, a SR20DE install would end up with a more rearward weight bias.

[crazy280]

Hey, I AM "all that and a bag of chips" lol just kidding

John, I get what you're saying, but here's what I'm thinking: The sr20det weight is 490 with crossmember, transmission and ALL accessories (the stock intercooler and piping was included). So even with a bigger intercooler, the total weight should be around 500. Lets say you weighed the L6 with the crossmember, trans and all accessories. What would it weigh, around 580? Not only that, but with the SR you can put the intercooler very close to the engine (plenty of room left over in that Z engine bay!), with big hood vents to help draw the air and let it exit (like the front radiator setups on midengine exotics). That puts the weight farther back and requires less piping (saving weight). That's what I'm thinking as far as SR vs L6 anyhow. Of course, my ultimate setup would be LS1, or a tuned VQ35DE, hell yeah! Oh well, I'm stuck with the L6 for a while lol.

 

PS: that Cobalt was badass!

[Gollum]

I'm still racking my mind on how to complete this idea.

 

Get a small V6 that you can get a centrifugal blower on to get to 500HP without an intercooler, get the motor as far bas as possible modifying the firewall need be to get to the point you can't go back farther due to interior space, then modify the front end so there isn't so much nose overhang. A R230 should add some weight to the backend. Put in a cage and weld the roof to the cage to drop the roof line slightly. Rake the windshield back a bit for areo. Put in all speedglas type windows. You should have an ultra low CG with a good rear weight bias to get a really good base to tune with. Granted it would be alot of work for a small difference, it would be dang fun to do.

[crazy280]

Wow, sounds like a whole different car. I don't think you have to go that far with mods. Sounds cool though

[Gollum]

Isn't that nirvana? Complete hybrid.

 

For me, half the apeal of the Z is that half of those idiot car people out there don't know what they are unless they have a badge.

 

My brother liked getting looks at his cobra, and it gots looks because it is a cobra. I want people to look at my car and say "what is that?"

 

Imagine walking up to a car, that looks totally unique, and realising there isn't a single thinig on the outside to tell what it is. That's my goal with my projects. I can't stand peole who just put body kits on thier cars. It just looks so unatural. Mody work should either enhance the stock lines, or recreate the whole look altogether. Most kits just try to make the stock lines look like something they're not, without actaully changing them.

 

I'd still love the idea of a mid engine Z, just becuase it would be so different.

[Nismo180]

Well' date=' it depends...

 

http://forums.hybridz.org/showthread.php?t=100849

 

Also, comparing a SR20DET installation (Amir's 260Z) with a NA L6 installation (mine) that has the engine set back shows identical weight distributions and a better polar moment for the L6 because of the IC and associated plumbing on the SR install.

 

Funny how the real world is different from what's though of as the truth on the Internet...

 

Don't see how you could acuse my statement as being supossed truth taken from the internet, it's hard to argue that in an all things being equal, enviroment, the longer engine would protrude further forward. Besides, I noticed he was talking about RB20 swapping it so he would still have the I/C piping and other turbo accesories out front that your I6 car lacks. Besides that in the example your using for how between the two different engines the weight balance is near identical the setup wasn't optimized in the SR20 car. If your main goal was indeed preserving overhanging weight why in the world is the Intercooler all the way out in front? My radiator in my 240sx sits roughly 3inches from the front of the crank pulley, just enough room to squeeze a fan in, and the I/C sits directly in front of that. I've moved a 20lb radiator back 9 inches, and a near 30lb I/C back more than a foot, not to mention saved a number of pounds in the I/C pipping and spool up time in the lower volume of intercooler piping. If those strategies had been used in your example a different result would have occured undoubtedly.

 

What I'm getting at is that it is indeed dependant of setup and where you put everything, but if you have a 2 foot long 400lb motor, and a 3foot long 500lb motor and have no plans of cutting the firewall that 3foot long motor will have more weight closer to the front of the car than the 2footer, period. The SR can be mounted further back than a motor that is longer than it. Yes, if you throw a bunch of weight out front it'll change the balance/distribution. But, as far as the basics of it, I was correct.

[johnc]

Don't see how you could acuse my statement as being supossed truth taken from the internet

 

I wasn't really focusing on your statement or anyone else's in particular. There just seems to be this basic assumption that putting an SR20DET into a 240Z automatically results in some ideal weight distribution and a super lightweight car. That basic assumption is wrong because so much more is involved as evidenced by your statement below:

 

I've moved a 20lb radiator back 9 inches, and a near 30lb I/C back more than a foot, not to mention saved a number of pounds in the I/C pipping and spool up time in the lower volume of intercooler piping. If those strategies had been used in your example a different result would have occured undoubtedly.

 

Absolutely and I agree 100% but the difference won't be as great as expected. Remember, both the radiator and IC will still be in front of the wheel centerlines.

 

My example above was meant to show that just moving the L6 engine back 4" and down 2" will get you right where a typical SR20DET install is as far as weight distribution is concerned. It also shows that chassis choice (1970 vs. 1974 260Z) has a big affect on overall weight and can even negate the supposed weight savings of an SR20DET install.

 

I'm not knocking the SR20DET engine, not making fun of those doing the install, not saying the L6 is the best, etc. I'm just saying that the mythology that's sprung up around this engine swap in a 240Z is overblown. A perfect example is a customer that I'm working with now who is putting a SR20DET that makes a gajillion horsepower into a 240Z. He was convinced that just this swap into an ex-ITS 240Z would make his car a track killer, until I spent a hour on the phone explaining things like: handling, balance, traction, all those little subtle things that have nothing to do with the powerplant.

 

A RBZ or a SRZ can be a very fast and track friendly car, but being fast and track friendly has much less to do with horsepower then most people think.