V8 Handling question

[Mikelly]

All the guys you are speaking to have NEVER done a V8 Conversion. Bottom line is that IF you set up the suspension right, get the right brakes on that car, the right tires on that car, and a well done V8 Conversion, you should plan for some "Fastest Time of Day" trophies. I won a regional championship in a F-prepared 260Z and that car was DOG SLOW compared to my V8Z and didn't handle nearly as well either! They will also probably tell you that the V8Z is gonna be nose heavy, and out weigh the L6 Z by 200+ pounds or some such nonsense. Trust me, you will do FAR BETTER by building a V8 and spending the proper money to do the job right with the right parts.

By the way, you need good control arms and TC rods to dial in your suspension... And I sell them!!

 

Mike Kelly

ZF Racing LLC

[blueovalz]

Mike is correct. Comparable Z cars (8 vs 6) will have the 8 run better overall. IMHO, the weight difference is not an issue at all (but that's because my Ford engine was lighter than the L24 was). They may have been steering you away from the 8 because of 1: The "purist principle"

2: It will put you in E modified (but if you enjoy self inflected pain, you may want to do this) which here in this region, has a very small group of runners (VERY small).

[SpeedRacer]

Here we go again.

 

OK, first, use light weight parts so the engine will weigh about what the L6 you take out weighs. Cool - no change there.

 

Second, if you use the JTR method of conversion, the short (four cyliders long vs. 6 cylinders long) V8 will be completely behind the front axle. This provides about 50-50% weight distribution (vs. 52-48% stock). Hmmmm... improved traction on the rear wheels. Also, they probably won't unstand it, but this improves the polar moment of the car. That's cool too because the car will turn better and be more responsive.

 

Third is the V8 is much lower than the really tall L6 engine that used to be in the car. They might understand that this lowers the center of gravity of the vehicle which will further enhance the handling.

 

Depends an the engine you install but you will have much more torque and horsepower!

 

Sounds like a winner to me. Do it and you will drive circles around them. Then they'll have something different to talk about.

[patzky1]

quote:

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Originally posted by SpeedRacer:

 

 

Second, if you use the JTR method of conversion, the short, four cyliders long vs. 6 cylinders long V8, will be completely behind the front axle. This provides about 50-50% weight distribution ,vs. 52-48% stock. Hmmmm... improved traction on the rear wheels. Also, they probably won't unstand it, but this improves the polar moment of the car. That's cool too because the car will turn better and be more responsive.

 

 

[/QB]

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SpeedRacer, do you mean the Polar Moment Of Inerita actually changes positively with addition of the sbc? > !WOW! < Please explain that to me because it sounds like a clear advantage is possible in the autoX scene with an improved ,higher I'm assuming, PMOI. Don't spare any physical details if possible.

 

TIA Patrick

[blueovalz]

While he's getting the math in order, the PMOI is dependent on the mass of the SBC in addition to the distance from the center of the car. His first statement of using light weight parts is the primary concern. And at some point the weight/distance of the SBC vs I6 will be equal. Then you have the lowered CG too, and on and on. IMHO, a small block swap is a win-win situation as far as well rounded performance is concerned.

[Mikelly]

I'll step in here again with a caviate: Those with L6 motors, please don't take offense, but physics actually do help with the argument here!

 

The V8 Small blocks of all the american manufacturers have lover decks than the L6 blocks. The majorety of the weight on a small block chevy sits at about 2-2.5 feet and below on a V8 converted Z. This gives a HUGE advantage to handling. My 383 stroker small block chevy weighed about 34# more than my L6 that had large valves and fuel injection. I moved the battery and that was about it. I also used aluminum heads and water pump/ intake.

 

These guys don't want you to "BUTCHER" your car for two reasons: They will lose another competitor from their class; You will be MUCH faster if you do a conversion properly!

 

Re-read that last part. A poorly done conversion is what has developed this MYTH of unsafe and poor handling V8 conversions. It just isn't so as long as you DON'T cut corners. Listen to those of us who have done it right, save your pennies and spend them wisely, and you will have a true "SUPER CAR!"

 

Mike Kelly

ZF Racing LLC

[blueovalz]

Amen!!

[Evan Purple240zt]

I have to say, after seeing alot of pictures and information the v8 just HAS to work better than the L6 in autocross. The SR20DET would be interesting too. I think its even lighter and its a lowly four banger. You probally need that torque for the track though.

 

I used to "frown" upon V8 conversions because i was hardcore datsun. Well im still an inliner. I have learned that the badass thing about the z is how versatle is can be. You can fit ANYTHING in that engine compartment!!!

 

I love the z for its lines, and possiblities. Not what it was when it was produced!

 

V8 dude.. do it - Evan

 

PS... do the transes way more than the L6 ones? Never dealt with one before.

[blueovalz]

I believe the weight was within a few pounds of each other (T-5 vs the Datsun 5 speed). I don't have the specifics here, but the weights were real close.

[pparaska]

quote:

---

Originally posted by Evan Purple240zt:

...I used to "frown" upon V8 conversions because i was hardcore datsun. Well im still an inliner. I have learned that the badass thing about the z is how versatle is can be. You can fit ANYTHING in that engine compartment!!!

 

I love the z for its lines, and possiblities. Not what it was when it was produced!

---

 

What we see here is a purist (hardcore brand guy) converted into a hotrodder! This doesn't happen easily! And only thanks to people like we have here at HybridZ does it happen. Certainly, places like that other "site" we visited lately, with idiots like Sheepman, will NOT foster this kind of free thinking and won't open any minds. I just LOVE seeing minds open!

 

Evan, the words you wrote could have been written by any "hot rodder" or "modifier" of any car, starting back in the 30s and 40s with the jallopies they built with old Fords, etc. to the guys who buy a brand spanking new Vette, Camaro, Mustang, Honda, BMW, you-name-it, and say to themselves "Now, no holds barred, how can I make this thing REALLY rock!"

 

When a person takes down the silly idea that a car should have only aftermarket or parts manufactured by the factory that produced the car, then the world of performance is wide open to them. It's almost a religious experience, no?

 

Anyway, I see no problem with a turbo 4, turbo 6, V8, etc. as long as one realizes the strengths and weaknesses of each and factor them into their desires/needs/uses.

[Guest Anonymous]

Hey everyone,

I just got a easy question. I havent been here for a while and progress is slow on my conversion. As a mater of fact it hasn't even started, got my JTR manual though. Anyways, I have been auto crossing my 72 6 still and at all the auto crosses that I have been to all the 6 guys say don't do the V8 if you want to auto cross her. I thought that 50/50 wieght distribution creates a better handling car? Why are these guys all say that? They also get hella good times runs with there 6's that always beat the 8's that are there. So my question is can I get a 8 to handle and beat these guys both at the auto cross track and at the drag track? Don't get me wrong you 6'ser out there just that I want the best of both worlds.

Thanks,

[DavyZ]

Evan, I knew you were not a purist (but an L6 guy), but I'm a little surprised to hear you say to "V8 it!" I do know that you keep an open mind and are not wedded to anything in particular but performance for performance sake, and that is very cool

 

BTW, that's what makes any hybrid Z so much frikken fun!

 

Davy

[SpeedRacer]

Actually I'm going to cheat a bit on the "Polar Moment" answer by using the Yahoo search engine. Here is a pretty good description:

 

"Rather than some scientific explanation, let’s look at an example that illustrates the concept. Picture your car as a set of barbells with 50 pounds of weights at each end. Picture trying to quickly turn and stop the bar bell while holding it. Because of momentum, it’s hard to turn, and hard to stop turning once it starts. Now, move the weights in close to the center of the bar and try it again. The bar turns, and stops turning, much more easily because the weights have less distance to travel. Reduced polar moment of inertia makes a car feel like it "wants" to change direction. The car feels better and the suspension is easier to tune."

 

BTW, while I was on that web site there was something titled "Stupid Cars" so here is the link. http://www.bryanf.com/cars/stupid.htm Seen the first one here before ut the others are worth the trip!

[pparaska]

If you don't mind a little algebra:

 

Polar moment of inertia = radius*radius*mass

 

Thiss is the effect on total PMOI due to a point mass (all objects are assumed to have all their mass concentrated at their center of mass).

 

So moving a 525 lb engine (rough estimate of a SBC) from 3 ft (my wild ass guess) from the CG of the car to 2 ft 8 inches (a move of 4 inches) means a difference of:

 

PMOI (Scarab) = 36inches * 36inches * 525lbs = 680400 lb*in^2

 

PMOI (JTR) = 32inches * 32inches *525lbs = 537600 lb*in^2

 

or a factor of :

 

PMOI (JTR)

----------- = 0.79

PMOI (Scarab)

 

Now, mind you, the moving of the engine will move the CG of the car, but I left that effect out.

 

Interesting though, the contribution of the engines weight on PMOI has a pretty health influence on the PMOI. But my numbers are guesses here.

 

I mainly ran these numbers to show that the distance that an object is from the overall CG is a SQUARED factor, and this is not insignificant.

 

If I only knew what the PMOI of the entire Z was, I could get a feel for what the real effect of the Scarab vs JTR placement was.

 

That oil pan clearance issue is not to be dismissed. For that very reason, I bought a now NO LONGER AVAILABLE 6.5" deep 60's Corvette 6 qt pan to put on my engine, so it would be at the same level as the crossmember. I too dread hitting the oil pan on a speed bump. At least my blowproof bellhousing will hang down lower than the oil pan now! That MIGHT help.

 

[ October 13, 2001: Message edited by: pparaska ]

[blueovalz]

Just a comment about the oil pan clearance issue. My front sump ford pan sits just slightly behind the axle, thus the speedbumps are not really a concern (pan pretty much follows the travel of the wheels at reasonable speeds), unless I start running parallel over them between the wheels.

[Guest Anonymous]

The total weight shift fore to aft shouldn't be that difficult to figure.

I plugged in what givens I could find and based these on a first generation chassis.

Wheel base: @91 inches = Z

Total drivetrain weight = W

Assume a roller chassis ready to accept the drive train. Mounting 100% of the drivetrain weight over front axel would equal 100% of "W" over the front axel and vice versa for the rear axel.

Balancing "W" equidistant from front to back would theoretically result in equal weight distribution of "W" or 1/2"W" on each axel.

Assuming a linear progression of weight change per inch of movement from either axel towards the other we get 1/2"Z" = 1/2"W"

If I plug in 525 pounds for total drivetrain weight, then 1/2 "W" would be 262.5 pounds. 1/2 "Z" would be 45.5 inches.

Making a simple ratio comparison, I calculate that a 3.5 inch change (Scarab vs. JTR)in the location of 525 pounds of total weight comes to 20.19 pounds.

Total drivetrain weight is porbably closer to 675 to 725 pounds.

Plugging in the 725 pound figure comes to a total weight shift of 27.88 pounds.

Even if this simple calculation is in error by 100% in its accuracy (by virtue of some nonlinear progression of weight shift factor)

this still only equates to a total weight shift of approx. 55 pounds.

Simply moving the battery to the rear of the car would acheive almost the same weight shift as a 3.5 inch change in motor position.

As for offsetting the weight of the driver this is also true to some degree, but when one considers the diversity in driver weights this fixed weight shifting factor can only offset a part of driver weight at best. I weigh 175 pounds, my brother weighs almost 290. Any discussion of handling is only as accurate as the actual driver/wet weight of any particular car.

There are several other non drivetrain weight factors which change static corner weights. Some of these are rim width/material, tire size, vented vs. nonvented rotors (or modified brake systems for that matter), size and volume of high capacity cooling systems. Transmission weight can vary as much a 100 pounds. Single vs. dual exhaust, fiberglass body panels etc etc.

My point is that the location of the drivetrain weight is only one of many factors which determine final axel weight distribution.

To make a blanket statement of fact regarding handling vs engine location is simply not fair.

IMHO it appears that few have actually done the before and after conversion weight measurements to such a degree as to be able to factually support the claim that one can count on greatly enhanced handling characteristics based soley on engine position.

The JTR manual is consistent with my findings regarding the total amount of weight change.

Page 1-1: "Positioning the engine 4 inches further back than the typical (Scarab) conversion will change the weight distribution about 1-1/2%; it's about the same change as relocating the battery to the back of the car. The engine is also positioned 1/1/2" lower the the more typical conversions."

"1-1/2" pecent of our car's weight is as much as 45 pounds.

Page 1-5: "The (JTR) car gained 140 lbs from the V8 conversion: 100 lbs on the front, and 40 lbs on the rear."

Page 1-10: "The increased weight(non JTR conversion) from the above conversion(150 lbs) is ALL on the front wheels."

Comparison of page 1-5 to 1-10 would tend to indicate that page 1-10 is somewhat misleading. Page 1-5 admits that even with the JTR kit, that "100 lbs" (is) on the front." Simple subtraction reveals that the actual total weight change between JTR and Scarab is 150 lbs. minus 100 lbs. or again 50 lbs total change. A Scarab conversion DOES NOT put 150 additional pounds on the front axel as compared to JTR!

The language used in the JTR manual is clearly biased against the Scarab but offers no real tangible proof that the claims made are accurate and meritorious.

I simply do not see how a weight shift variable of 50 lbs can justify the claims made in this manual regarding "heavy steering" "overheating" and other supposedly serious detriments that Scarab cars are allegedly afflicted with.

I have built them all, driven them all and raced against them.

I know that my position on this subject will probably not endear me to many on this board, but all I ask you to do is verify for yourselves as I believe I have done, whether or not a the claims made in this manual have merit.

Equal consideration should be given the positives of the Scarab as well as the JTR. The dispensation of advice to anyone who is trying to make an informed decision as to what their options are should include all aspects of safety, required body modifications, degree of difficulty as well as subjective intangibles like better handling.

I have read many times here that the JTR mounts are simple. The fact remains that Scarab mounts are far simpler and on some models using 350 turbo transmissions, no removal of the factory trans mount is necessary. It doesn't get any simpler.

There are very real positives embodied in the Scarab mounting position which seem to largely go unheralded. The JTR causes the loss of the manual fuel pump, hood latch mechanism, and some ground clearance all of which need to be discussed and considered before deciding which way to go.

IMHO it is irresponsible to push one kit over another strictly on the basis of handling. In my experience the hype has not translated into any real world advantage in handling for the average Z owner. As a whole, our cars are street driven and as such the conditions found on the street should weigh heavily in the conversion decision.

I think when the facts about corner weights come in, we will find that Scarab cars equipped with all light weight engine components do indeed enjoy very nearly the same weight distribution as the JTR cars.

I think my Scarab car combines the best of all worlds: Ground clearance, and high speed front end stability based on the fact that virtually all Z cars are subject to loss of front end weight at speed (aerodynamically speaking) and that above 100 mph my car has better balance due to the 50 lb weight over the nose by retaining the pressure per square inch on each front tire longer and at higher speeds than cars without the additonal front weight.

The fact the most of us cannot fit the same size tires under the front that we do on the rear also dictates that a 50/50 weight car actually has disproportionate psi on the front to rear tires. The larger contact patches of the larger rear tires dilute rear axel weight in both conversions, while the Scarab enjoys the advantage of better front end bite from a shear coefficient of traction caused by more weight over the front end.

Especially at high speed!

For these reasons and others I believe it was no fluke that various Scarab cars including my own have been able to not only keep up with JTR cars, but win a disproportionate amount of the time in the race venues I have observed.

Ok, I've had my 3.5 cents worth, I am ready to get flamed.

[SleeperZ]

No flames here

I don't run a V8, but IMHO, this discussion is what the board's about. You have some strong and well-considered points - the Z rocks from the myriad of possible options - what other car has so many???

[Modern Motorsports Ltd]

 

hehe, another fun one I tossed out on a camaro board where it took a bit of convincing that a mid mount battery was superior to a trunk mount in a camaro for roadracing was.....(using a fun board members name as well)....

picture Craig in a tutu...once you've got past that he's doing a pirouette with his arms spread out...spinning slow........now he pulls them in and spins faster.....simple effect of PMOI

 

a battery couldn't be much better placed than custom sunken in the passenger tool well behind the passenger seat IMO....an optima placed their and a JTR mounted V8 got miles to improving performance....$$$$ on aluminum isn't mandatory but can be nicely added as budget permits.

 

My last few weight changes made quite a difference in my low speed steering effort and handling did improve but the steering effort was most appreciated by myself (w/ my 280ZX).

[SpeedRacer]

Idaho Z Car - No flames here but a couple of comments. I happen to be one of the few that tried the Scarab conversion first and did not like it's effect on the handling or ride of the car so I went through the trouble of switching to the JTR position. You should drive a JTR car sometime. If you drive both hard (and all other things being equal) you will notice a significant difference in the handling of the car. Believe me, there is enough of a difference that you can actually feel it. Sorry, I never ran my car on a track so I can not provide comparison times, etc.

 

Oh, BTW, you don't "lose" the hood latch mechanism - you just have to make a different bracket for it. Also, with a SBC, there is no ground clearence problem with if you stock oil pan.

 

Also, the reason the battery makes such a difference is that it's a heavy sucker and, if you mounted it in the rear, you moved it about 8 feet compared to about 6 inches!

[BLKMGK]

Hrm, moving the battery is the same as moving the weight of the battery and then some. Remember that it's taking weight from th eback and adding it to the rear. Not the same as simply removing it from the front.

 

IMO 50lbs can make a BIG difference. I once drove a small station wagon around an offramp at speed forgetting the tempseted printer that had been placed in the FAR back. It got EXCITING in a real hurry! The difference of adding a 75+lb metal encased printer to the far rear (way behind the rear axle) was enough to make a huge difference on the handling of that particular vehicle.

 

Ya', it's possible that the JTR setback doesn't help "that much" but it does help. Add to that aluminum heads, water pump, battery in the back (mine over the axle BTW), and the use of things like an aluminum radiator - it adds up. I wanted a stick shift too - it fits better. My reasons for using the JTR setback had less to do with cooling and weight than they did transmission position

 

I'm not a good enough driver to see the difference on the track but one trip around an offramp with a pile of weight in the far back was enough to demonstrate to me that I do NOT want weight at the far ends of my vehicle - I want it all within the confines of my axles I'll take everything I can get to that end - the JTR setback doesn't cost much more to do if anything does it? True it's less easily reversed though...

 

P.S. No flames here either - this is a healthy discussion IMO.