V8 Handling question

[Guest Anonymous]

When I did my first conversion, the JTR manual/method did not exist. It wasn't until a total stranger brought the essence of the JTR concept to my attention that I found it necessary to buy this book.

Four years ago this month, a post made to another board, (not this one) which read as follows:

 

"Kim is a unique guy.

He believes that as much weight as absolutely possible should be added to the FRONT axle, as it makes the z-car more stable at speed. Kinda like a Formula 1 race car is setup. Because of this, he always does Scarab Style conversions.

 

Anyway, he has done a few conversions,(more than me), but his cars handle terribly, despite his claims.

 

He is really fast in the quarter though.

 

I still recommend the JTR conversion book if anyone is thinking of doing a V8 conversion." (end of quote)

 

Well, I think you can imagine how I felt, especially since I had never met the man in my life that I knew of. I of course never made any of the statements referenced in this post. The poster would later admit that his only involvement with my car was as a spectator who watched me race at our local drag strip on only one occasion. These statements on the Internet were made without even the slightest basis of truth or substance, or were they?

 

After reading the book it was clear to me where his ideas came from. This manual leaves the reader with only one conclusion regarding what is the correct way to do a Z V-8 conversion.

I reread my JTR manual last night (sixth edition) and I was again struck by the many and repeated optimistic superlative statements used to describe the JTR method.

Conversely, any reference to the Scarab method was badly disparaged to such a degree as to leave one wondering why the Scarab was ever attempted in the first place.

This is where this young man got his ideas. Not from good solid comparative analysis, or first hand experience. He believed without question that the author was correct.

The moral of this story lies at the heart of my concern with this book. This young man's unqualified belief that his car was vastly superior to mine almost caused him serious injury to his person.

As Paul Harvey would say: "Now for the rest of the story."

I decided to settle the issue once and for all. On a race course of his choosing.

We would eventually race each other on three occasions over a period of a year.

The results were as follows:

Race #1: Freezeout Hillclimb, Emmett, Idaho. The JTR car won by 0.062 of a second. I took second behind his first place finish. Unfortunately he wrecked his car on his last run by understeering it into the left hand guard rail which totalled the left front side of his car. Months later he would admit that it was his unwaivering BELIEF that his car could post better times than mine that led him to push the envelope beyond his previous best efforts. In his mind, a near matching time from my car was not an indication of equality among the cars, but rather a deficiency on his part as a driver. He truly believed that his car could go even faster than mine, simply because of his unreasoning belief that his car was superior in handling.

90 days later we would race the two cars against each other again.

Race #2: Bogus Basin Hillclimb, Boise Idaho

The Scarab car won first posting three back to back runs which were 1.5 seconds faster than the JTR car.

(30 days later I would take my car to Teton Hill Climb in Wyoming where it set a new hill record for OSPO by over three seconds. The JTR car did not attend this race.)

Race #3: Freezeout Hillclimb again.

The Scarab car won by a 1.0+ second margin of victory.

It was only after the third and final race that this young gentleman finally conceded that his position regarding my "terrible handling car." was in error. I know that this persons behavior was extreme and not indicative of JTR owners as a whole.

What I am trying to say here is that sometimes it can be dangerous to blindly believe everything one reads. It is true that I have issues with the nuts and bolts of the JTR conversion which I have elaborated upon prior, but more importantly I take issue with any one way of doing something being championed without question.

You simply don't hear of Scarab owners taking such an agressive position with regard to their cars on the basis of the opinions of just one writer/author/technician. Even now, solid scientific data to support these claims are still tied up in conceptual stasis.

I think that there needs to be room for continued discussion of the benefits and detriments of both conversions, without denying one or the other the right to have a respected opinion on the subject. To this board's credit and everyone who posts on it, you have not unreasonalbly closed the door to your subjective thinking mechanisms and I thank you for it.

 

I have asked an engineer friend of mine and fellow Datsun driver at NASA to look into the PMOI equation and give us his qualified opinion as to how to predictably quantify the results of any given set of conversion parameters.

He has agreed to do so and I will post the results. I hope this will allow future builders to make a more informed decision with regards to componentry, and a greater degree of predictablility as to final performance results.

(When this engineer was 17 years old he built his own turbo kit and installed it along with custom rack and pinion steering into his 1966 SPL311 Roadster. He is currently working on a custom 3.8 Buick turbo into one of his 1967 SPL311's)

[Mikelly]

OK, here is a problem with that test you are running. One of you may be a much better driver than the other. Best way to judge the merits of both is to have an unbiased third party drive both cars. I'd find someone who has Zcar experience and turn him loose in both cars on the same course. I've seen professional drivers take cars of less ability and drive circles around those with much more HP and handling...

 

Mike Kelly

[Guest Aaron]

In order for the comparison to be completely unbiased, wouldn't the two cars have to identically prepared (spring rates, sway bars, roll cage, brakes, etc.) except for the engine position?

 

I have no doubt that each of the mounting positions have their pros and cons; however, the notion of a "good handling" car is completely subjective to the driver. I have long been a fan of NASCAR, and one of the best stories that illustrates this point was in 1994 when Ernie Ervan took over after Davy Allison died in 1993, they were returning to a track where Davy had run well the year before. Initially the crew set the car up as Davy had run it, but when Ernie ran in the car, he said it was so loose that he could not drive the car.

 

Based on my understanding of the way most NASCAR teams set up their cars, I would assume that the scarab position should allow someone to maintain more speed through the middle of a turn, but not be able to accelerate out of the corner as well. The jtr position should create a car that would get into and out of the corners a little better but would not be as fast through the middle of the corners.

 

[ October 16, 2001: Message edited by: Aaron ]

[BLKMGK]

Sport Compact had an article not long ago that I found interesting and is somewhat related. They took a professional race car driver, a pile of wheeltires, and some sacks of concrete to the racetrack. They blindfolded the driver and put him in the car after swapping wheelstires and in some cases putting sacks of concrete in the car for ballast. In each case the driver was able to pretty much figure out what had been done! It was interesting that thin sidewalled wheel combos weren't always his favorite BTW.

 

Anyway, my point is that a talented driver CAN discern minor differences. Things like 50lbs of weight moved around can really change how a car handles. That might only be 1% but it could be enough to change things. I know in the case of my RX7 that folks report they can tell the difference when a lighter BATTERY is installed - it sits way out front just past the front axle FWIW. Mine weighs a ton

 

However, I'm no "talented driver" and the minor difference in weight, while possibly making the steering lighter, wasn't really my big reason for doing the JTR swap. I wanted the trans to line up and any added handling benefits were simply icing on the cake I I really want to go around corners, at this point, my RX7 would probably make my Z look pretty silly

 

P.S. Adding weight to the front of a car in order to keep it on the ground at speed just feels "wrong" to me. Obviously you're racing the car and have experience I don't but it seems counterintuitive to do that. If the added weight is as little as 50lbs at what speed does the lift overcome that advantage? Wouldn't a spoiler provide greater than 50lbs advantage? I honestly don't know and am curious. Hrm, and it's pretty pathetic that someone would claim your car handled badly without some sort of knowledge about it. I'd never ASSume that out of hand without some sort of direct knowledge. What a jerk!

 

[ October 16, 2001: Message edited by: BLKMGK ]

[Guest Anonymous]

Mikelly and Aaron, your observations are spot on. I couldn't agree with you more.

Any truly accurate statement and conclusion of fact should be made with the input of an unbiased third party (or two or three). My post involves only two cars with three different drivers over a period of a year and three races, and I STILL DO NOT feel that the results of these races proved anything except that all factors of car and driver in this instance allowed one specific car to win over another specific car. The fact that both cars were converted using different methods did not translate into an odds on advantage for one over the other. Statements made to that effect prior to these contests were premature and simply not accurate in this case.

This poster isn't alone in making such statements.

If I may I would like to quote a post from this forum dated February 22, 2000:

"You should N-E-V-E-R put the motor three inches further forward. Driving a Scarab conversion, then climbing into a JTR conversion, well there is no comparison."

 

As I said earlier, both of your replies are spot on. Definitive statements regarding the differences between any two cars, much less all dissimilar cars have no real accuracy or correctness without the element of unbiased opinion to help point the way.

My position is that definitive statements like these are found in many places and retold in many ways in the JTR manual, giving rise to what has now become an almost gospel belief in the superiority of JTR cars over any other.

Your replies truly make my case for levity. Unbiased third parties are needed to lend credence to one claim over another.

What is truly missing is an unbiased voice to balance out the claims made in the JTR manual.

When a new person asks what he or she should do, would it be possible to slow down the use of definitives to describe one conversion over another?

I think the overall consensus at this time is that no one person has all the answers to the handling question, and this rule should also apply to the author of this book.

This book was written to sell books and conversion parts. I have no problem with salesmanship just so long as we recognize that is merely salemanship. The responsibility for each reader to question the accuracy of any statement made in this book is well served. Such observations make for wise decision making as well as improvements in the breed.

Please don't turn off your objective headlights simply because something is put in writing.

Your replies make it clear to me that the sword of scrutiny should be wielded equally

when a question of fact is raised, no matter who raised the question.

Thank you.

[Guest Anonymous]

Hey, over whelming response. Thats why I keep coming back here. I think you guys really convinced me now. For a while I started turning away from my initial plans on the JTR V8 conversion but now I'm back on track. I love my 6 thats in there now but if I want the car to be my Super Car as my daughter says about daddies Z then it looks like I need to go with the V8.

Thanks Guys,

[ZROSSA]

Howdy all,

If you make mounts that attach to the original x-member and angle back like a parallelagram (sort off) you can fit the mech fule pump and have the engine set back.

 

As for handling. I really believe its all up to tuning your ride to how you drive it. That i know off there are only two cars that come out of the factory with a 50/50 weight split. Bmw 3 series and the current vette.

 

Cars with a very low polar moment can be very twitchy and difficult to control on the edge. Cars with higher polar moment although not as quick to react to you imput are easier to control when getting lose. Cars that you see on the race track with a rear weight bais usually have larger rear tyres to help with the extra weight. Dont forget that with 50/50 weight dist. you can have perfect balance mid corner (same size tyres all round) but when you begine to accelerate this all changes. There are far more people here that know more that I on the specifics.

 

Build it, tune it, drive it - hard

 

You will like it.

 

Douglas

[SpeedRacer]

I find the comment "Kim is a unique guy.

He believes that as much weight as absolutely possible should be added to the FRONT axle, as it makes the z-car more stable at speed. Kinda like a Formula 1 race car is setup. Because of this, he always does Scarab Style conversions." Maybe the old Formula 1 cars but they switched to mid-engine years ago. Hmmmm... why would they put the engine in the middle of all places?

 

BTW, those F1 guys are so nuts that some teams are considering designing a new V-10 (the rules now require a V-10) with a wider V angle so it will lower the CG of the car! Some of those 3.0 litre engines are rumored to weigh just over 100 lbs., produce almost 800 HP @ 19,000 RPM !!!

 

Thanks Pete, we can always rely on you for a level headed analytical response.

[Guest Anonymous]

The lightest F1 engines weigh in at just over 90 kilos, which is about 200lbs... Still pretty awesome! Last Year's BMW was rumored to be making 850bhp and revved up to 20000!!!

[patzky1]

WOW, guys, gracias for the thought-out responses! Well, I knew what PMOI was before reading in to this discussion, but now I even know about how much of a difference is inherent between JTR and SCARAB. APPARENTLY NOT MUCH.

Oh, for the front downforce of an F1 racer we are really talking about the front spoiler, correct? They are pretty aggressive in terms of brute downforce at speed from what I've seen. Remember, they DO turn some pretty-dang-nuts corners and the front wheels need to be in good contact.

As a side note, where can I get me one of those 200lb 850 horse engines?? Make a hella dragster if you can afford it($$$$$$$$$ I'm sure). But one would have to mount the engine almost entirely past the front Xmember on the Z to be safe at high speed!!!LOL

[Modern Motorsports Ltd]

Enjoy your planning zeezee, my 280ZXV8 has:

a slight rear weight bias

is lighter than stock

daily driver (ie. not a stripped out race car by any means)

, and this is without any exotic mods.

 

Idaho Z makes a good point, part of the more pointed replies is due IMO to the fact that are archives/search contain 95% of the answers to any newbie q's. Someone suggested a 'have you searched the forums yet' tag to come up before you post a new topic which seemed like a good idea. Their's often updates to that info obviously, but an informed reply from archive reading can stimulate even more detailed discussion. Just an ideer.....

[pparaska]

I try to be a critical thinker in all aspects of my technical and personal endeavors. Open mind, try not to pre-judge an answer, etc. Sometimes I succeed.

 

And I fully agree that a blind test of the same car with the JTR and the Scarab position mounting, all other things kept the same, would be needed to be done, by a competitent Z driver to make any real numerical comparisons as far as lap times, etc.

 

Reading the JTR manual, I did see the overt slamming of the Scarab position. Whether it was totally salesmanship, or Mike Knell's belief, I can not say.

 

But one thing I keep coming back to is the engineering gut feel that placing the engine even 3.5 or 4" closer to the CG and also midpoint between the front and rear axle, along with putting it lower in the car, puts it ahead as far as PMOI, F/R weight distribution, etc. These issues, all others kept the same, would seem to make the JTR setup better handling, from the standpoint of quicker turn-in, less understeer, and a more balanced feel to the driver. Whether they are significant enough to be of substance to a daily driven car by amatuer drivers is an issue. I like a car that is tiwtchy, turns in quickly, etc., so the JTR system would seem to suite me better. I DO feel like I can feel the difference when the tank in my car is full, half full, empty, so I believe that I could notice the difference between the two setups. And that gets to Aaron's issue of what a driver likes - that's just as important, if not more important than lap times, in my case.

 

Next, I'm going to address Kim's Scarab vs JTR issues, as I see them in a much different light. Some conjecture and opinion follows, granted. But I think they are based in some fact as well.

 

Jim's discussion of shifter placement is also an important one to me. 3.5 or 4 inches more forward and my shifter (Tremec TR-3550 5spd) would come out where the top or middle of the fuse box is. Trying to straighten that out would not be worth going to the Scarab position, in my case.

For me, JTR wins for a manual internal linkage transmission. Automatic, makes no difference, for an external linkage manual like the Muncie, it's a matter of fabrication of the shifter mount and/ or extended linkage.

 

But Kim's issue with the oil pan sump placement is quite important to me. For this reason, I've put a shallow oil pan (6.5" vs the stock 7.5" deep sump). I have a buddy with a JTR 240Z and OE oil pan who took his pan out on a raised manhole cover (road was in the midst of a resurfacing operation), and I saw that the sump on my car was just behind the tires, where a speed bump would hit it if the car rolled to quickly off of one and compressed the suspension too much. I'd hate to have to put a dry sump system on the car just to make the JTR system work. Although getting a custom pan with a center sump and the required extended pickup may be an alternative. I say: Advantage Scarab position on this point.

 

I would think if one plans mostly on straight line use, and is using an automatic, a Scarab position might be prudent, but having that weight back 3.5 to 4" with the JTR setup may be worthwhile as well. Not sure if either has an advantage on this point alone.

 

To me, the hood latch issue is a non-issue, as it's what I feel is a minor mod.

Slight, but insiginicant (to me) advantage to the Scarab location. Not enough to sway me.

 

I also think the mount complexity issue is minor for both installs. Especially if you buy them . Even if you make them, it's a minor project in both cases. Neither "kit" has an advantage here, IMO.

 

The issue of the manual fuel pump is a matter of preference IMO. Yes, it'd be easier to use a manual pump, but the installation of an electric one for a carb is not a big project either, and needed anyway if you go EFI. Slight, but insigniicant advantage to the Scarab, IMO.

 

I'd also rather use front downforce to deal with high speed stability than to move the engine forward. I see no real useful advantage here for street speeds, so no advantage either way for me.

 

Well, that's my view. Take it for what you paid for it .

[Guest Anonymous]

BLKMGK, I dug up my old NHRA weight slips and found the following. NHRA weighed the car twice over a period of 2 years and the weights were within 15 lbs of each other. Fuel differences probably attributed to the change.

The exhaust system accept for the headers (long tube Hookers and two 18" torque tubes) was not on the car. I have never weighed the car with full exhaust on it. This would add I am guessing 25 to 30 lbs to the rear axle.

The lighter of the two weights was 2440#

The OEM advertised curb weight for a 10/70 240-Z was 2355#

If these figures are to be believed, then the V-8 conversion added 95# to the car's total weight.

On page 1-5 of the sixth edition JTR manual it states as follows:

"The car gained 140 lbs fronm the V8 conversion; 100 lbs on the front, and 40 lbs on the rear.

On page 1-10, an air pump equipped car is described as follows:

"The increased weight from the above conversion (150 lbs) is ALL on the front wheels"

Assuming that the two conversions would weigh the same if the latter was not equipped with an A.I.R. Pump and lines, it would appear that the actual weight change between the two conversions would be (40 lbs).

This engine on page 1-10 appears to be mounted in the same position as mine, which is with the center bolt of the Chevy motor mount aligned with the center of the Z crossmember.

Scarab mounts that I have seen are offset 1.25 inches to the rear of this position, while the MSA and JTR mounts are 2.5 and 3.5 inches respectively.

The entire top end of my engine is aluminum, which not only lightens up the engine by some 50 lbs. but also lowers the CG a tad.

I will take some editorial license here and suggest that approx. 70% of a cast iron engine conversions weight is apportioned to the front axle. (100 of 140 total)

As the total weight gain in my car was reduced by the use of aluminum parts, this would tend to suggest that the total weight gain over the front axle in my car would be (66 lbs) (66 of 95 total)

My point here is that these weights suggest that one can achieve a slightly better front axle weight using aluminum parts in a FULL forward position as a 3.5 inch cast iron set back position.

It is interesting to note here that the general consensus among us is that the OEM 240-Z weight distribution was 52/48. Which I would calculate to be approx. (47 lbs)assuming a 2355# curb weight of this vehicle.

The original post question dealt with the belief by certain L6ers,that the OEM cars were more nimble and handled better than V-8 cars.

Considering that ZEEZEE is looking for to IMPROVE on the OEM weight balance, I would recommend he use the JTR mounting point simply from the standpoint that he is looking for fairly low speed cornering and handling improvements. Strictly from a weight shift standpoint, the JTR mounting point is a must for achieving the desired result in this instance.

I also believe that good ground effects should be able to negate the major portion of the front end lift tendencies at speed.

BLKMGK, as far as extra weight over the front end, the JTR manual makes it clear that at as much as 100 lbs is added to the front axle by a cast iron conversion.

My car actually has a third less front axle weight than this with what I calculate to be

approx. (66 lbs).

If you aren't asleep by now, I hope this answered your "extra front end weight" question.

The obvious extension of this weight discussion is that even better weight shift can be achieved with the combination of light weight engine components AND a JTR setback position. I think that a 50/50 weight distribution, which is BETTER than stock can be had.

On page 1-1, the JTR manual uses the words, "Near stock weight distribution" which would be a correct statement when using a "cast iron" engine. Considering the weight discussion on page 1-5, perhaps a more accurate reflection of the weight shift benefits of a JTR kit would have been to replace the word "near" with the phrase: "slightly heavier than stock" weight distribution.

This weight distribution topic reminds me of a very dear old lady, who sent me a U.S. Navy wool coat. In order to save weight in the shipping cost (in her mind) she cut off all the buttons and put them in one of the pockets to "save weight".

There are two lessons in this story. 1. ENJOY YOUR Z CAR WHILE YOU CAN! 2. Weight is weight, nothing is for free.

Perhaps this post will explain why my car was able to "keep up" with the JTR owner whom I have so much enjoyed spanking.

His car is a cast iron headed engine, and actually weighs more on the front axle than mine!

If he had simply taken the time to have really read the JTR manual, he would have been able to calculate that my car with all aluminum parts would actually enjoy a lighter front end weight than his REGARDLESS of engine position.

For lots of good reasons, I still like my worse than Scarab position car, but I concede here that I could get another 50 lbs off the nose if I went to JTR mounts.

Would it be worth the effort now? No. Too much work.

Too bad they quit making the 6.5 inch oil pan. I wasn't aware it even existed and appologize for suggesting that there was no oil pan clearance improving option available to the JTR guys.

Kim

[pparaska]

Kim, thanks for the thoughtful discussion!

 

BTW, the old Corvette 6qt, 6.5" deep pan is NLA, but they even come up for sale used on ebay from time to time. Another option is the 6.5" deep road race pan from Canton. Expensive piece, but it's the best one out there, from everything I've heard. Exhaust routing is a bit of a problem if you come straight down from block huggers. But if you angled out from the collector, it ought to work.

[Mikelly]

Kim,

Superdan, Owner of this site had a Scarab conversion V8Zcar. He was eventually convinced to do the JTR swap... His response is somewhere here in the thousands of posts on this site.

Also, remember that the cost to swap over isn't much, as all you need is the mounts themselves, and then re-doing the drive shaft and sorting out the hood latch. I'm biased, but I'd bet that you might change your mind once you pushed that motor back and lower. Dan realy was amazed at how much better his car tracked and steered, not to mention the traction he gained.

 

It is preference, and it depends on three things: Money, time, and intended purpose!

 

Good luck!

Mike Kelly

ZF Racing LLC

[Guest Anonymous]

Dam, this is all good stuff here. Guess we need some more of the V8 guys to show off thier cars. We should get a organized autocross going to compare all the sixers with the eighters. I guess it really would come down to the drivers abilities but it would definitely set things straight. Even being able to snitch rides from one another so after been in both one could make their own decision as to what they prefer. I'm mainly looking at it from a handling point cuz I no the 8 will beat a 6 stock anyday. Besides we all love the curves of the car, at least we could enjoy each others creation.

[pparaska]

Some of us just have "vapor" cars though .

 

Good idea, I'd like to have a test drive in similarly set up Scarab and JTR conversion Zs.

[Guest Anonymous]

I think it depends on the club that is setting up the cones, a tight track IMO would not be an advantage for the V8Z, its high torque from almost idle is going to be a bit explosive for a tight track, a inliner might just have the edge here.

 

Now on the other hand, if the Viper/Vette guys get to set up cones, well then... It becomes a bit more of an advantage for the V8Z as they'll inevitably set them up wider for they're larger cars. Give it a straight or two and I think all the better for the V8Z. Can I prove it? Not wit my car yet. But I know some of our members have cars of the ability to back it up I think.

 

I think really its a mute point, only one company that I know uses the scarab position anymore (John's cars ), and if anyone wants to deal with that guy, or fabricate mounts just to get a setup that may or may not handle as good, can be my guest to do so. IMHO.

 

Regards,

 

Lone

[fl327]

i will only race a hachi-roku drift match......

[Owen]

Shall we call you Initial Z then?