cavemancan

There's some information on the forum but I haven't seen a single thread dedicated to the subject so I thought I would make one. I admit I am creating the thread for biased reasons. I am looking into the possibility of a motor swap but ironically the determining factor for me is handling.

I know adding too much weight to the front of the car will, to some degree, affect the handling characteristics of the car and I admit I need to be schooled on how it will be affected and how to make up for the imbalance.

So with that said I am thinking about the most controversial swap. The LSx v8 swap...Say what you want it is a great engine and I do love rotaries but the truth is...It's a relatively cheap way to add torque, power, and reliability (compared to other motor swaps).

Things I know:

- I know it's heavier (Edit: Then a Renesis)
- I know it has a taller center of gravity
- I know it will sit higher up in the engine bay

Things I don't know:

- How much weight is on the top and how much is on the bottom of the motor?
- What can be done to correct the imbalance?
- Add weight to the rear?
- Remove weight from the front?
- Would I need a staggered wheel setup?
- Suspension changes?
- Heavier rear end (no pun intended…LOL)?

I know some of you will flame me...So be it but I hope others will provide actual constructive info on the subject. It would be awesome if some of you physics nuts could chime in too (I'm a dork in disguise).

Brettus

iTrader: (2)

good idea to discuss this .
I'm firmly in the belief that it will negatively impact handling to the point that much of what we enjoy about the handling will be sacrificed - would be interested to hear what the reality is though .

cavemancan

I realize this is not fact but it's interesting to hear from a builder...

"...won't a V-8 have a higher center of gravity than a rotary ?...

Another parameter typically debated "rotary vs. V-8" is CG height. Many believe the V-8 with it's higher heads and intake manifold raise the CG height and must ruin the handling. Our response is that things are not as they may seem. The engine/trans should be considered as a package. The rotary's appx 6" higher eccentric shaft centerline and resulting higher transmission location all but eliminates any advantage the smaller rotary engine is thought to benefit from. We doubt the CG of the engine/trans package, as installed in an RX-7, is that different. An LS1, with it's aluminum block, aluminum heads, and plastic intake manifold, may even have an advantage over the rotary with regards to CG height. "

See: http://www.grannysspeedshop.com/

Half way down the page.

Brettus

iTrader: (2)

6" higher ????? sounds like BS .......

Brettus

iTrader: (2)

The dist. from the eccentric shaft to the top of the sump is less than 61/2" - so unless the LS is only 1/2" from crank centre to sump .............

cavemancan

Please note I know enough to be dangerous but I am not familiar with sump. However based on the term dry sump oil system I can assume you mean...from the eccentric shaft to the top of where the oil gets collected?

What is the sump exactly...Dont worry I learn quickly.

ASH8

The "Sump" is Oil Pan..

You could Weigh the LSx first and then the RENESIS after you remove it,,, there is a thread showing a changeover somewhere here I think...Search or Google...

Crudely, the more weight in the engine bay, then the equivalent extra weight should be put in the Trunk or over rear axle...IMO

cavemancan

I was thinking the same thing but I realize it shouldn't be that easy. As much as I hated physics (main reason I changed degrees...LOL!) in college I did understand some of it. Simply adding weight to the back may not be the right choice. You may need to add the weight in the back but at the centerline of the drivetrain.

In other words a heavier rear end? Or a bigger gas tank?

cavemancan

I thought this was also interesting...

"...Think the v-8 will forever ruin your handling? The August 2005 issue of Grassroots Motorsports Magazine will features quite a few V-8 powered RX-7s that entered their $2005 Challenge event in Florida. The premise of the event is to build the best handling, best appearing, and quickest car possible for a total budget of $2005., including the price of the car and all components. You will be surprised at the wide variety of entrants and how creative they are. Check out the August issue for a feature on this year's challenge winner, a FORD POWERED 2nd gen RX-7!!! For a free copy of the magazine or to check out this year's $2005 challenge results, go to the Grassroots Motorsports website.
In the 2004 event, of a total of 76 cars that participated, a total of 9 RX-7s took part in the event, 5 V-8 powered and 4 rotary powered. In the drag race portion, all the V-8 RX-7s finished ahead of the rotary powered cars. No surprise here. The quickest V-8 RX-7 recorded a 12.636 ET, the quickest rotary's ET was a 14.323. What DID suprise a lot of sports car people is the results of the autocross competition. The quickest RX-7, a V-8, finished nearly 4 seconds ahead of the quickest rotary version. Among the 9 RX-7s present in the autocross, V-8 power captured 4 of the top 5 spots. Don't listen to those who tell you that a big V-8 will ruin your handling!!!
Daryl Evans's ZZ4 powered RX-7 solo car was last years local, regional and Canadian Western Champion in E Mod."

Also from http://www.grannysspeedshop.com/

cavemancan

Grannys Speed Shop also claims that a SB Ford v8 weighs even less. Any idea what motor this is? Could it be this one?

FORD 289/302/5.0/351W V-8

I checked but there appears to be different types. I wonder how it compares to the LS blocks.

luv4eternity

in my opinion , never add weight ....weight ruins everything ( handling&performance )......

i suggest :
1 ) lose some front weight ....
2 ) lighter hood , lighter fender
3 ) staggered wheels ( bigger rear for traction, smaller front for handling )

if the engine is heavier , there's nothing that can be done....hope the POWER makes up for all the weight

WTBRotary!

iTrader: (6)

^^^ Go rear the staggered wheel thread discussion and why some people are for it and others against it.

dmitrik4

iTrader: (5)

the SBF is an iron block, and is much heavier than the aluminum LS engines.

from what i can tell, the LS is significantly heavier than the Renesis...200lbs or so, IIRC. given the differences in geometry, i have no idea what the net result in weight distribution or handling would be. i would expect that you would need to upgrade the driveshaft and diff to cope with an LS engine. but it's not just the engine you need to take into consideration...other parts would need to be redesigned, and can be designed to be lighter if needed.

FWIW, LS swaps into Miatas end up gaining a little less than 200lbs, with 1/3 of that over the rear axle (keep in mind that the Miata engine is an iron block). the end result is about the same as adding a turbo kit, and i wouldn't be surprised if that was the case with the RX-8 as well. the Miata V8 swaps don't appear to inflict much, if any, damage to the Miata's handling.

http://www.flyinmiata.com/V8/

shadycrew31

iTrader: (6)

The LSX is about 200 lbs heavier and comes with 200 more horsepower so yea Id say your power to weight ratio is good at that point.

When you consider the LS6 weighs about 700 lbs dressed up and the 20b weighs about 770lbs dressed up the ls6 puts down 100 more hp.

Speed source runs track with the 20b just fine.

soooooo

yea

im just sayin.

quazmosis

iTrader: (2)

Im in subscribed.

cavemancan

I'm glad you posted this. Ironically enough I actually wanted to disprove the v8 swap being a good one but the more I research the more I find evidence (not fact) to the contrary.

I read that the weight of the 13b with all the trimmings = 388.4 lbs. See post from "jimlab" for details.
http://www.rx7club.com/showthread.php?t=250486 - Rx7 forum

- I am confused though at what exactly is included in that weight cause the guy was a little erratic is his explanation of what he weighed. Perhaps someone could explain it better.

Now some guy on the Rx7 forum claims the following for the LS1 with all the trimmings...

"Got the LS-1 motor weighed today with all the accesories attached (A/C, P/S, Alt, wiring harness, ECM; etc. Believe it or not it weighed in at 481-LBS !!! I believe a T56 (6 speed) weighs around 140lbs."
http://www.rx7club.com/showthread.php?t=255423 - from "gnrx7"

So total is = 621 lbs?


This is engine and tranny compared but I realized the turbo and intercooler on the Rx7 were not taken into account which I read weigh like 180 to 200lbs. Sounds like both setups practically weigh the same...Give or take like 30 lbs (aka battery).

EDIT:

I reread the post and it seems the Tranny was not included in the figure for the 13B. The tranny = 112lbs which brings the total to 500.4lbs. For a gran total difference of 120.6lbs? Is that right? Or am I reading this wrong?

cavemancan

A quote from the guy on the Rx7 forum...

He subtracted the weight of the tranny so 500.4lbs sounds legit.

cavemancan

I wish we could have some hard evidence. I hate relying on what others say the engines weigh. Regardless, this is another good point.

Granted Speed Source is dealing with a tube frame chassy and can relocate weight anywhere they please with little to no effort. With that said if the weights mentioned above are accurate how can you go wrong?

Let me guess...Center of gravity? Food for thought...The LS is all aluminum with the crank being the center of gravity which is located in the bottom half of the motor effectively keeping the center of gravity of the motor at the bottom...Not the top. Wouldn't that be like adding a heavy Strut tower brace? Or metal air box accesories? Or front mounted intercoolers and turbo's? Or bigger radiators and oil catch cans? You dont hear those people crying about the balance of there rotary Rx8 being ruined? Do we? What about superchargers like Pettit's, which I love. I am sure thats system would add 150lbs or so but those cars are being raced and owners are happy.

What about the 20B? It's a longer block then the 13 B...Anyone know how far forward and up, if implanted in the Rx8, would the 20B sit? I'm guessing the center of gravity on both motors are very very close in position. What about a turbo...most install one...Ding fries are done...more weight.

I would guess you can make an LSx weigh less then a 20B turbo. With internal work on the LSx it could also keep up in power and definately have more torque.

Someone prove me wrong...

shadycrew31

iTrader: (6)

http://www.turborx7.com/20bbasics.htm

shadycrew31

iTrader: (6)

20B-REW "Production" Engine specifications
Origin Closely based on 3rd generation (FD3S) RX7's 13B-REW
Special 3 rotor parts based on 13G design
Capacity 654cc x 3 rotors = 1962cc
Compression ratio 9.0:1
Turbo Boost 0.7 Bar (=10.29 PSI)
Induction Turbocharged (twin sequential)/intercooled (intercooler mounted
near car's radiator), electronic fuel injection (2 injectors/rotor)
Exhaust Peripheral Exhaust Port
Ignition Distributorless electronic ignition (2 plugs/rotor)
Power/RPM 280ps@6500rpm
Torque/RPM 41kgm@3000rpm
Max RPM Cosmo Tacho redline at 7000rpm (scale ends at 8,000)
Dimensions Length 672mm Width 549mm Height 520mm (with accessories)
Weight 350kg With all accessories & manifolds
Special Features Ignition knock control uses one sensor per rotor (on rotor
housing above trailing spark plug)

cavemancan

770LBS!!!

Not to mention the turbo, piping, and intercooler are located at the front/top of the car...even modified ones.

shadycrew31

iTrader: (6)

it comes with the turbo. Thats part of the 20b.

cavemancan

That's what I mean...I was more pointing out the location of those items. In order to contrast the argument that a v8 swap would be top heavy. The point is...so would a 20B Turbo swap. We could argue the weight disadvantage is relatively identical for both a v8 NA swap and a 20B Turbo swap.

Either swap adds weight to the front and upsets the balance to some degree but no one complains about it on the track from what I am reading. Many basically relocate some weight to the back to resolve the issue.

A spare tire and a battery in the back and your in business...LOL! I know this is over simplification at its best...I kid I kid.

cavemancan

Now Wikipedia says the Renesis weighs "122 kg(247 lbs)" but does not include tranny (120 to 150 lbs) and oil coolers (weight? 30lbs?).

So maybe 427 lbs total? Compared to 621 lbs LS1 tranny combo...So a difference of 194lbs?

So if you relocate the battery...35+ lbs?
Lighter/stronger subframe...I heard somewhere it could be a difference of 30+lbs?

Let's say you could save 100lbs in replacing parts...then place the 35 lbs battery plus some weight in the back. Sounds like we could achieve the 50/50 weight distribution without much effort...or get very close.

Racing Brake also makes a light weight caliper and rotor combo for the front which could save another 5 to 10 lbs.

shadycrew31

iTrader: (6)

the 13b core is around 200 lbs fully dressed is 250.

the point is you could make the engine work. the plus side to the 20b is that you can sit it father back than a LS.