I've been all over the net. I've seen LT1 conversions with 200R4 Autos and LS1's with T-56's. I've decided that my dream car will be a 93-95 RX7 with a LS1/6 engine and the T56 to match. But here's what I want to know that no one has answered yet in the hundreds of pages I've seen...

1. Once the swap is done (LS1 or LS6 and T-56), do you or can you have traction control?

2. What's it take to make an LS1 or LS6 hit 7500-8000RPMs with reilability?

3. Are the widest tires for the 3rd gen wide enough for traction?

Thanks in advance for your help.

 

I don't have an LS1 converted car yet, but should be starting on my project at the end of the summer.

The car doesn't have a TCS to begin with, so it won't have one unless you add it. Do a search for the Racelogic TCS. It will work with the ls1/fd, and there's even a group purchase going on right now.

7500-8000 rpm with a torquey V8 is probably unnecessary, and it is definately outside the breathing range for the stock heads. So, you'll need ported heads, and upgraded internals (forged). The crankshaft will need to be balanced, and most likely lightened. You'll also need aftermarket valves and springs. It adds up pretty quickly, and like I said before it's probably unnecessary as it makes good power before 7500 RPM.
From what I have heard, you can basically write off 1st and 2nd (regardless of the width of your contact patch) unless you have a feathery touch on the accelerator. Most of us don't.

 

Do you? No. Can you? Yes. As mentioned above, you can easily add the RaceLogic traction control system to the FD. Unfortunately the group buy mentioned closed at the end of last month.

Aftermarket engine management for one, and a solid roller cam for another.

The stock computers for the LT1 and LS1 don't have the ability to control fuel past 7,000 rpm, so there is an rpm ceiling if you're using the stock computer.

There is also an rpm ceiling if you have a hydraulic roller valvetrain, which is the stock configuration for both the LT1/LT4 and LS1/LS6. The LT1 and LS1 have 6,000 rpm redlines, and the LT4 and LS6 were bumped to 6,500 rpm through the use of revised heads (better breathing), more aggressive cams, and sodium-filled valves to reduce weight. In fact, anything you can do to reduce weight in the valvetrain or rotating assembly is beneficial for high rpm use.

If you're going to turn 7,000 rpm, LT1/4 owners who stick with a hydraulic roller usually use a rev kit like the AFR setup which helps to control the lifters and keep them from "bouncing" off the tips of the cam lobes at higher rpm. The LS1/6 already has a "rev kit" of sorts, with springs that retain the lifters.

You'll also need stiffer valvesprings to control the valves and keep them from bouncing off their seats. You still run the risk of having a hydraulic lifter collapse, however, because the only thing holding tension in the valvetrain is the oil pressure in the lifter bodies. Get too much oil "upstairs" (gravity is the only thing draining the oil back to the pan) and it is possible to run low on oil at higher rpms with a stock capacity pan, which can allow too much slack in the pushrods. Once a pushrod comes loose, you're going to have damage of some kind.

A solid roller valvetrain doesn't need a rev kit because the solid lifters can be used with much higher spring pressures. They don't have the oiling concerns of a hydraulic system, and in fact, oil to the top of the engine should be limited with restrictors because it's not required. The ramps on the lobes of a solid roller cam are also the most aggressive that you'll see, so the valve stays open longer and farther than with a hydraulic cam, even with identical duration. The result is that solid roller engines make more power than hydraulic roller engines. Large solid roller cams also behave better on the street than large hydraulic roller cams.

In order to turn 7,000+ rpm, then, you'll need a solid roller cam, solid roller lifters, much stiffer valvesprings, and you'll need heavily ported heads to make sure that you can take advantage of the elevated rpm. If your heads become a restriction at 7,000 rpm, then there's no use in turning 7,500 rpm. A forged rotating assembly is also highly recommended, if not required, for increased strength. High rpm puts a lot of strain on a reciprocating assembly, and you don't want to cut corners just to end up rebuilding/replacing your short block at greater expense later.

You also have to sacrifice some low end for a higher redline, and the easiest way "around" that problem is to build a stroker engine. The increased stroke (distance from the crankshaft centerline to the centerline of the connecting rod journals) will give the pistons more mechanical advantage which produces more low end torque. Torque is horsepower, obviously. The more low end torque you make, the more low end horsepower you make, which can help make up the deficit. You'll also get a much broader powerband as a fringe benefit.

The bottom line though, is that there's no reason to increase rpm unless the limits of the package (naturally aspirated, for example) require it to make the power levels you want. In other words, if you're going with forced induction, you don't need to turn high rpm to make a lot of power, since the engine can ingest all the air it needs to make that power simply by changing the amount of boost. For a naturally aspirated engine, the only thing that will increase the amount of air ingested is rpm, and in that case, you may find that you need to exceed 7,000 rpm to make your target power levels.

My ~7,500 rpm solid roller 396 will produce about 650-660 horseopwer and 560-570 lb-ft. of torque when completed. No street radial available is going to be able to cope with that much power in lower gears without help, even if you were easily able to fit a P345 on the car. More on that in a second.

Unless you plan on running DOT slicks, which pretty much defeats the ability of the car to turn corners, you're not going to get much help from the tires with a lot of horsepower. Drag radials might help a little, but will wear quickly, aren't available in a wide number of sizes, and aren't really designed for cornering either. I went with Bridgestone Pole Position S-03s, because they were the best choice for dry and wet traction, handling, tread wear, and road noise in my opinion, and I was resigned to the fact that I would have to take further measures to aid in getting traction.

One, which was mentioned above, is the RaceLogic traction control system. Still, with this much power on tap, it would be pretty easy to overwhelm the system and have it constantly cutting fuel to the engine with a heavy foot.

The second was gearing. Not only was the stock 4.10 ring and pinion too much gear for a street car with this much torque, but it put the cruise rpm at 70 mph too high, and from the analysis that I ran, would actually produce slower times (more frequent shifting) in the ranges I was interested in. If I were drag racing, sure, but since the car is a street car, something had to be done. My only other choice was the 3.90 gear set from the automatic cars which isn't enough of a change to help. What I ended up with was a Cobra 8.8" differential in the back (still in progress) with 3.55:1 gearing which improved strength, reduced weight slightly, and allowed me to pick the gearing that I needed to reduce maximum torque at the axles in lower gears somewhat. If you're not willing/can't go to that extreme, then consider a set of 3.90s from an automatic car.

Back to tires... given equal tread compounds and design, a P315 tire (for example) will not increase traction significantly over a P295, and a P345 would be only very marginally better. This is contrary to what at first would seem to be logical concerning tire width... more tire on the ground = more traction. Unfortunately, it doesn't work that way. The problem is that the coefficient of friction remains a constant (or nearly so) while the increase in tread width actually reduces pressure at any given point by spreading the load of the car over a wider area. That's why a narrow tire will cut through standing water and a wider tire will tend to hydroplane. With me so far?

The only way to make a wider tire more effective is to use a softer compound, and with street radials, you reach a point of diminished returns. In other words, an S-03 Pole Position is about as good as it gets, and increasing width doesn't help past a certain point (I'll discuss this next) because of the reason mentioned above. If the tread design isn't radically changed (like using a racing slick) and the rubber compound is the same, then going wider than a P285 or P295 which will fit on the car with a little effort, you're not going to gain anything with a P315-345 that you didn't already have with the "narrower" tire. However, to some bigger is always better, and to achieve a certain look or status, you might be able to justify the expense of a widebody kit or flares and even wider tires.

That said, wider tires can enhance "traction", but not in the way you might think. In other words, it isn't the "more rubber on the road" theory, it just amounts to "more rubber" period.

Wider tires weigh more. Bigger wheels to mount them on weigh more. A larger diameter wheel weighs more even in the same width and style, simply because of the increase in material (both rim circumference and spoke length). That's where the perceived increase in "traction" comes from. Increase the weight of the tire/wheel combination and it becomes more difficult to accelerate, especially since the bulk of the weight is located at the circumference of the wheel. Push that weight farther away from the center of the wheel, and it becomes even harder to accelerate. That's why, especially since heavy cast wheels are so inexpensive and popular, Civics which were reasonably peppy with the stock 14 or 15" stamped steel rims turn into slugs after a set of 17s or 18s are installed.

Past a certain point, no increase in weight is really going to slow down an engine, especially one that makes 400+ lb-ft. of torque from 2,000 to 8,000 rpm. That's one reason why I wasn't especially concerned about going to 19s. I don't plan to track the car, and certainly wouldn't on "street" 19s if I did, and the engine has more than enough power to turn those big bastards far faster than traction will allow. Considering that street radials can only afford so much grip (and I did what I could there), and weight can only absorb so much power, I went for appearance and chose to go with 19s.

As mentioned, beyond what reasonably fits on the car, you're not going to gain much. A P285 is the reasonable limit without having tire hanging out of the quarter panel or absolutely requiring coil-over shocks for inside clearance, so that's what I got. It's more for looks than anything else, given all the reasons above. It fills out the wheel well and looks "better", even if a P265 would have given the same level of performance as far as traction is concerned, and weighed a bit less, reducing unsprung weight and improving handling slightly. Like I said, I don't plan to track the car, and certainly wouldn't on the tires and wheels I will be running on the street.

At any rate, I hope this helps, and if you have any questions, just ask and I'll write you another novel.

 

Stock LS1 rev limiter is 6250

 

Close enough.

 

Damn Jim! Thanks for that very professional and detailed reply. The more posts I read from you the more I learn.

Chances are I'll be going with a stock 405hp LS6 engine and keep its 6600rpm redline. So that solves the RPM issue.

As for traction, I'll probably get aftermarket TCS like that Racelogic. I'm not too keen on the idea of a computer leaning out my engine if I lose traction but it seems to work.

One thing I plan on doing is a 99 Spec body conversion. I prefer the look and the front end has 33% better air flow through the front of the car. I will also get the 17"X7" sized front and 17"X8" rear tires from the 99 car as well. I'll look into those S-03 tires, but does Dunlop make a competitive tire?

PS... I have tried to keep up with your threads and everyting concerning the LS series engine swap, but I have heard that there is a clearance issue in the front of the engine concerning the hood. Obvisously, this isn't an issue now. But I was wondering how that problem was resolved. Was it a modification made to the engine cradle?

 

It doesn't actually lean out the engine, it cuts fuel completely to one cylinder at a time and prevents a combustion event for one full cycle of that cylinder. It took me awhile to get past the "leaning out" concern also... I have a lot riding on not arbitrarily screwing with the air/fuel ratio of my engine.

The hood clearance is resolved by lowering the steering rack in order to lower the engine. The bump steer elimination kit that Brian/Lane sells resolves the problem of lowering the steering rack which would normally introduce bump steer if left uncorrected.

 

You may want to look into a bit wider wheel for the rear of the car, as an 8" wheel will leave you with little tread on the road. 9" will let you run a 255 or maybe a 265 and 10' a 275 or 285 and keep the contact patch wide.

 

Sweet. Thanks for the info Jim. I can't wait to get the car and start on it. The plan is for a 100% street legal hotrod with good reliability, fuel economy (for a sports car), driveability, and razor sharp handling. I figure a light FD3S body with a nearly stock LS6 and T-56 tranny will fit the bill. Aside from traction issues, the car will meet my needs.

The '99 Spec wheels wear 235/45R17 front and 255/40R17s in the rear. If I get that Racelogic traction control I should be ok with those tire. That combined with a 3.90 or smaller rear diff shouldn't make traction for acceleration an issue. They aren't massive so the unsprung weight will be ok. And it has a certain factory look that I want to preserve.

Jim, with that lowered steering rack, is there enough room to mount (with a custom bracket of course) a supercharger? I'm just curious, not actually planning on forced induction.

 

Ok. So I got an itch to lookup the number on the Z06. Some of this stuff I can't believe!

1999 RX7 Wheels = 17x7 and 17x8 wearing 235/45R17 and 255/40R17.
2003 Corvette = 17x9.5 and 18x10.5 wearing 265/40R17 and 295/35R18.

So it looks like I might have to get wider tires to handle the power and provide grip. I wonder what is the widest rim you can fit, front and back, in the 3rd gen.??

1993 RX7 rearend is either a 4.10 rear end or 3.90 for Auto.
2003 Corvette is a 3.42.

Jim, this is for you buddy:
Can you use the Z06 rearend on the RX7? I heard you have a Ford 3.55 on yours.

 

cdk managed it...

 

There are people running 10" wide wheels front and rear, although I wouldn't personally recommend it. There is plenty of information in the suspension/wheel/tire forum on the amount of back space and front space available on the FD. Look for posts from SleepR1, or just send him a PM.

That'd be a negative... not without a lot of work and custom fabrication to close the front of the differential. It's intended to be bolted to the rear of the C5's rear mounted T56, so in that sense, it's not a complete or separate differential.

I'm using an '03 Cobra 8.8" IRS differential, and the sky is the limit on the available gear ratios. I chose a 3.55:1 gear set to go with my M29 T56; 2.97, 2.07, 1.43, 1.00, 0.80, 0.62. The "standard" T56 is 2.66, 1.78, 1.30, 1.00, 0.74, 0.50.

 

That's pretty sweet. I'll probably go for the "standard" gearing on the T-56 but I'll want to compute the RPM Vs. Speed for the gearing with the tires sizes and all before I solidify anything.

Here's a question for ya (Trying to make you think hard). What do you do to the rear suspension to combat excessive squat under heavy acceleration?
(Providing you get enough traction to make the rear end sit down)

 

You're all killers and rapists - this is supposed to be a "rotary love" forum. What a waste of a beautiful car with a brilliant engine...in fact just go play with other team you traitors.

 

Ya know, if it were any other car people would be in awe of the V8 conversion. But just because it's a Wankel motor, people get a piece of salt up their butt if you put a better engine in the darn thing.

Did you hear Toyota enthusiasts screaming when the GT Race Supra dropped the 2JZ-GTE engine for the 3S-GTE? Hell no.

Are V8 Miatas bashed because they got a 5.0 and not a 1.8?

The V8 RX7 is a lot like the Shelby Cobra. Take a light great handling foreign car and give it the pride of American V8 power.

You like the 13B-REW, fine. You like burritos with mild hot sause, fine. You like the 13B and it's weaknesses, fine. But don't be a ***** and think that your way is the ONLY WAY!

 

No.

It sounds like an absolute dream and yes what a wicked combo...but surely it would be heavier?
Surely any power you can get from a LS-1 you can get from a 13B? Is it just about torque?
We have a dude in New Zealand who drives a 454 FD!!!

But its still not cricket... as much as it would make me think of it at night I could never shake your hand.
I am a staunch rotor enthusiast.

 

I'm not even going to try and explain this to you. You need to learn more about engines.

 

as much as it would make me think of it at night I could never shake your hand.
Why are you thinking of him at night? Is it some sort of love hate relationship? Interesting

 

I agree with Jim and CDK's comments on the above questions. Hopefully the below information will help with your last question.

I run 245/50/ZR16 Sumitomo All Season tires on the back of our LS1 FD RX7. The only modification to our rear suspension is a tested tubular torque arm that we built and sell to help transfer the new found power through the stock Mazda rear. FYI, our car is a 6spd car with the Mazda 3.90 rear gear.

In complete street trim at 30psi in the rear tires, I cut a 1.86s 60' time at our local 1/8th mile track. Ironicly, the car bogged on the launch. If the line was shorter, I would have made another pass to try to get the short time in th 1.77-1.82s range.

On the ET Streets, I have cut a 1.52s 60' time. With a little more effort, I feel the car is quite capable of a 1.4X time. Remember this is on a stock Mazda rear with the addition of our tubular torque arm to help transplant power.

Below is a video of a spinning launch at Huntsville Speedway. The short time was a slow 1.62s 60'. Video [i](Copy and Paste link if not working for you.)

My point: 1st and 2nd gear is very usable and very very fun.

Good luck with your project.

 

EDIT: double post

 

That would be an awsome combination when you guys get done would like some track numbers

 

Hinson is running 11.4's with a mild cam and bolt ons. he has added a little n2o lately and thinks he is capable of 10's but hasnt been to the track.

Mike
Less than 2 weeks away from my ls1 fd being finished!!

 

Ok. Here's a good question for all you V8 lovers. Which is cheaper to buy (crate engine new) and build to about 415rwhp with equal torque. The LS1 or LS6?

 

It isnt cost effective to buy a crate engine, because of all of the little parts you will need to complete the swap. A complete used takeout will be the only way to go, unless you like to step over a dollar to pick up a dime. 415 rwhp will take extra cubes and cam head swap, forced induction, or nitrous, as no factory offering will get you that number, be it an LS1 or 6. The LS1 will be cheaper to modify, because it will be cheaper to begin with, but it wouldnt be cost effective to but a used LS6 because you would have to also buy an Fbody T56 and all the supporting hardware.

 

Ok. So here's a question (Looking in Jim's direction). What would the cost be to build up an LS1 to 396ci with a 7500RPM redline and a flat torque curve with 450hp and 450lbsft?