When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Why no V8 conversions using the stock turbo 5spd transmission?
I'm doing some research on V8 swaps and I've noticed nobody seems to use the stock 5spd turbo RX7 transmission with any of their swaps. This is pretty common with other cars using adapter plates or dedicated bellhousings made to adapt one motor to another transmission but this doesn't seem to be the case in the RX7 community.
It seems like the stock 5spd can easily handle 3-400 hp/tq of a modified rotary, why doesn't anyone adapt an LS1 (for example) to the stock 5spd? This would greatly simplify a lot of the swap in my opinion but maybe I'm missing something obvious?
A couple reasons, first and foremost the rotary engines e-shaft arrangement means the "crank shaft's" output is at the center of the engine instead of the bottom like in every other engine ever made so this rules out the rx-7 transmissions with out a detachable bell housing. Now then you must ask your self if sourcing some random bell housing from a 19whatever-19whocares mazda/ford god knows what and then fabbing a bell housing adaptor is worth it to retain the original and probably beaten transmission when most V-8's have great trans options already and all you need is a custom drive shaft which is a very easy thing to source, even locally. And lastly their are the automatic transmissions, a ford C4 or GM 700R4 are strong and can be made stronger for not a lot of money, good luck showing up to your local speed/trans shop with your freaky deaky rotary auto talking all kinds of craziness like "higher/lower rpm stall converter" "reliable with 400 ft/lbs" "can you fabricate a crazy *** bell housing adaptor to make it fit?"
Thanks aa35199, so if a guy has a turbo 5spd tranny (which has a removal bell housing) and doesn't care about automatic tranny's then there's no real reason not to just use the stock 5spd tranny I guess. Sure the stock 5spd could have been abused but so could any used tranny, with used parts you're always buying an unknown, even when buying a T56 for example.
Using the stock tranny would allow for a perfect stock shifter location and feel with the stock shifter, **** and boot. Also it allows for the stock transmission mount, stock driveshaft and stock clutch lines. It's nice on a big project like this to be able to use as many OEM parts as you can, it really helps lower the overall complexity of the project as well as potentially the cost.
My next question would be will an LS1 (which is what I'd most likely use) play nice with the firewall when using the stock 5spd in it's stock location. Probably nobody will know that because I don't think anybody has tried!
You would need a rear gear change to make the car drive able with the Mazda 5 speed transmission. The gearing is wrong for an engine that makes torque. That is at minimum around $1800. That will negate any savings from reusing the stock transmission.
By keeping the Mazda trans you are actually making the swap more complex and the end result will not be as good. All the mounting options for the T56 have been perfected at this point. They drop right in. The T56 behind the LS1 lands the shifter about perfect in the car.
If you have an FC, a C4 Corvette driveshaft works perfectly with the stock rear. You just have to change the pinion flange and slip yoke.
You would need a rear gear change to make the car drive able with the Mazda 5 speed transmission. The gearing is wrong for an engine that makes torque. That is at minimum around $1800. That will negate any savings from reusing the stock transmission.
I didn't find that to be the case at all with my 420rwtq/420rwhp rotary FC.
I think the gearing doesn't suit an engine that doesn't like to rev would be a better way to say it.
People just feel like they are killing their V8s and gas mileage running them 3,500 or 4,000rpm down the freeway like the rotary does (I ended up with shortest JDM 5th in my TII topped out at ridiculously low 177mph but got there REALLY fast.)
By keeping the Mazda trans you are actually making the swap more complex and the end result will not be as good. All the mounting options for the T56 have been perfected at this point. They drop right in. The T56 behind the LS1 lands the shifter about perfect in the car.
100% true ^^
I can see the allure of keeping the stock TII trans is that its really really cheap and stronger than say an also cheap T5 and WC 621 bellhousing.
T56 cost some $$ these days.
Hopefully people keep working with the 350/370Z trans and come up with a cheap v8 bellhousing solution because that is a strong 6 speed that actually shifts quickly and nicely unlike the T56.
Sure. We are talking semantics here, but a v8 can run down the highway at 1500 RPM.. So why wouldn't you? An LS can be built to rev to 7k relatively easy, and can rev to 6500 with a couple cheap parts. If you have 350+ WHP out of your V8 the 4.10 stock rear gear starts feeling too short, even with the wide ratio T56 gearing. I run a 3.73 in my car, and with the wide ratio trans it is awesome for track use. For a pure street car, or an NA V8 car with a lot of power 3.55 gears could be a better choice behind the T56.
The 350z trans has the same problem. It needs a rear gear change so you don't spend all of your time shifting through gears. We figured the 350z would need a 3.08 rear gear to achieve a final drive ratio that suits the V8. The rear gear change eats up any savings from using a cheaper trans.
Last edited by LargeOrangeFont; 06-02-15 at 01:44 PM.
Sure. We are talking semantics here, but a v8 can run down the highway at 1500 RPM.. So why wouldn't you? An LS can be built to rev to 7k relatively easy, and can rev to 6500 with a couple cheap parts. If you have 350+ WHP out of your V8 the 4.10 stock rear gear starts feeling too short, even with the wide ratio T56 gearing. I run a 3.73 in my car, and with the wide ratio trans it is awesome for track use. For a pure street car, or an NA V8 car with a lot of power 3.55 gears could be a better choice behind the T56.
The 350z trans has the same problem. It needs a rear gear change so you don't spend all of your time shifting through gears. We figured the 350z would need a 3.08 rear gear to achieve a final drive ratio that suits the V8. The rear gear change eats up any savings from using a cheaper trans.
Performance is why you wouldn't gear tall with wide ratio trans.
You think real race cars with V8s have wide spread gears with a theoretical top speed far above what the car can actually achieve due to aero drag?
No, they are competing against other V8 race cars with the same power and if when they have the wrong gearing they lose.
For PRACTICAL reasons you want a tall rear end ratio and wide spread gears for the LS V8- you can't pretend it is for performance.
Practical reason is a good reason to do something, I am not knocking it. It is the whole reason LS V8 swaps appeal to us, it is so practical versus making the same torque/power on a rotary or swapping in another motor.
I also agree that at some point constantly shifting is going to become slower than holding a gear- this is exacerbated by a balky shifting T56 and it would be greatly improved with sequential dog engaged trans. Again, practical vs $$$ and performance.
I found this same thing with my torquey rotary TII. In some situations it was faster to shift at 6,500rpm to land me back at the meat of my torque, in some situations it was faster to hold the gear to 8,000rpm and drive up to and just past peak hp.
I am not disagreeing with what you say per say, just pointing out that once again you are misrepresenting why we want tall, wide spread gears with an LS V8 swap.
Point taken on 350/370z trans rear end ratios for wanting to achieve practical LS V8 gearing, but you are saying a T56 plus low ratio rear end is ideal; so, you would still could save $$ with the theoretical 350/370z trans and a rear end and get nicer shifting.
I keep stressing LS V8 and not V8 because there are non giant piston/non pushrod V8s that don't mind revving. For instance the Coyote 7,000rpm redline is set for drivetrain reasons, not engine longevity. The Voodoo is 8,200rpm redline. That is just American crap. Will they even fit in our cars? Probably not (practicality).
Europeans have been revving V8s for a long time (Ferrari much? Man I want to make my RX-8 a Mazdaratti!) and even the Japanese V8s can rev or you can swap OHC heads onto an LS and even with the big ol pistons they rev to 8,000rpm.
Just pointing out we put the pushrod LS in our cars for PRACTICALITY.
I don't think you should try to justify your engine of choice's flaws its strength whether you drive a rotary or a V8 or anything else.
Im going to have to step in and tell you that in practice - ALL the LS powered V8 RX7 guys that race, time attack, etc. run between 3.55 and 4.10 gear ratios with T56 transmissions. Most run 3.73s, some 3.90s and some 4.10s, We all do this for the same reason.. it works best with this particular drivetrain.
The close ratio T56 used in the heavier GTO, CTSv and z06 is not as useful until 5th gear and above. 1nd and 2rd gear are too close, and the jump to 4th is too great in the close ratio t56
My car is set up as a track car. I have done the work, the math and have the experience with the setup. If I ran the Mazda 5 speed (or the Nissan trans) trans with 4:10s I would run out of gear at some of the tracks I run.
To be fair I am looking at swapping in the shorter 5th and 6th gear from the close ratio T56 box into my T56 wide ratio box. I do want the .8 5th gear, and it would help me. But the 1-4 of the wide ratio box is really well suited to the car.
This information does not apply to every V8, but the LS is the most popular option. This information would be applicable for MOST of the v8 swaps that actually would fit and work in an Rx7. The car is so light, it does not need ultra short gearing to be fast.
I would not call the RPM capability of the LS series of engine a flaw... It is something that just is. If I make the same amount of power at 8000 RPM with a smaller OHC V8 vs 6000 RPM in my OHV V8, I don't really care as long as the powerband is wide and flat.
Last edited by LargeOrangeFont; 06-02-15 at 04:32 PM.
I feel like if I'm using the stock 5speed with the stock rear end but only adding the extra torque of the V8 then this would end up being a car that drives more or less like any rotary powered RX7 FD tuned up to about 350hp/350tq.
Yes the power will come on sooner due to all that torque of the V8 but on the street during regular driving I rarely take the Wankel up past 6k RPM anyway. So imagine regular driving around town, shifting at say 4-5k but having twice the torque getting there, sounds pretty good to me.
My FD cruises at 70mph at about 2600rpm. Ya that's a bit high for the V8 to be cruising at so fuel economy will suffer a bit vs. a setup with different gearing but that's not a huge deal to me.
To be honest I think all the gearing talk is way over analyzing the situation, in other words I don't think it's that big of a deal for the average street car one way or the other. If you're competitively racing or earning a living with your RX7 then ya, get it perfect by all means.
Using an 8000 RPM redline, 25 inch diameter tire, and the FD trans ratios with the taller 5th gear top speed per gear is: (note that these are similar to my setup)
And at 6500 RPM for a typical V8 redline
1st 34
2nd 59
3rd 85
4th 118
5th 166
Keep in mind this is at a 6500 redline.. An all stock engine would likely have a lower redline. Shifting twice to get to 90 is slowing you down in a lightweight car with decent power. Could you just drive it like that... Sure. Will it be blowing the tires off all the time when you get on it? Yes.
At 6500 RPM to get the shift speed MPH where they were with the stock rotary engine, you'd need a 3.31 rear gear. All that said, from a gearing perspective the RX7 trans is a better option than the 350z trans.
Last edited by LargeOrangeFont; 06-02-15 at 06:04 PM.
I would not call the RPM capability of the LS series of engine a flaw... It is something that just is. If I make the same amount of power at 8000 RPM with a smaller OHC V8 vs 6000 RPM in my OHV V8, I don't really care as long as the powerband is wide and flat.
I don't consider the poor reliability of turbo rotaries a flaw, its just something that just is. *not!*
Not a valid arguement for your engine of choice nor mine. Its a limitation whether pushrods limiting rpm on the LS V8 or flexi engine parts limiting combustion/detonation pressure on the rotary.
You present a false choice. You make the same power at 6,000rpm and get to rev to 8,000rpm+ without pushrods holding the engine back. Even the big bore 7liter LS bottom ends are good to 8,000rpm when you put OHC conversion on it, its the valvetrain that eats itself.
Chevy made the pushrod LS more compact with pushrods- ! Now they stack the coils on the valvecover so its about the same height as a OHC engine- ?
I would not call the RPM capability of the LS series of engine a flaw... It is something that just is. If I make the same amount of power at 8000 RPM with a smaller OHC V8 vs 6000 RPM in my OHV V8, I don't really care as long as the powerband is wide and flat.
I don't consider the poor reliability of turbo rotaries a flaw, its just something that just is. *not!*
Not a valid arguement for your engine of choice nor mine. Its a limitation whether pushrods limiting rpm on the LS V8 or flexi engine parts limiting combustion/detonation pressure on the rotary.
You present a false choice. You make the same power at 6,000rpm and get to rev to 8,000rpm+ without pushrods holding the engine back. Even the big bore 7liter LS bottom ends are good to 8,000rpm when you put OHC conversion on it, its the valvetrain that eats itself.
Chevy made the pushrod LS more compact with pushrods- ! Now they stack the coils on the valvecover so its about the same height as a OHC engine- ?
I'm not sure what you are arguing. No one that runs an LS is saying "Man I need this thing to rev to 8 grand!" It's like saying why don't you rev your rotary rev to 12k? You simply don't need to.
Can a Ford 5.0 coyote rev to 8000? Yes in Boss 302 trim. Does it make any more power than an LS3? Not really. Is the powerband any wider? No.
BTW you can make a small block Ford rev to 8000. You can make an LS do it too.. There is just really no need.
Also notice that our shift points are in the same ball park between your rotary cars and my V8 car... That is the point I have been trying to make here. I am jealous of your .8 5th gear though. Did you swap that gear or is that the stock 5th gear ratio? Mazdatrix said it was .76 for the TurboII trans.
Last edited by LargeOrangeFont; 06-02-15 at 09:01 PM.
Here is a small block Ford long block next to a Ford modular DOHC 4.6 long block. The mod motors are dimensionally similar to the Coyote 5.0. The small block ford is dimensionally similar to an LS engine.
A DOHC V8 barely fits in an FC engine bay.
Last edited by LargeOrangeFont; 06-02-15 at 08:54 PM.
Did you swap that gear or is that the stock 5th gear ratio? Mazdatrix said it was .76 for the TurboII trans.
That is the short 5th from most JDM FC and FD transmissions. Makes it a pain to find good transmissions for my ASP FD where I have to have the stock USDM 0.719 ratio 5th.
0.803, 0.76, 0.719 are all R type trans 5ths.
As an aside.. How do you like the Mazzis RC1 tires now that you've ran them
I like them a whole lot. Even though they have no real tread pattern they are the most streetable R-comps I have tried yet.
4 sets RA-1s (daily)
3 sets NT01s (daily)
2 sets Ventus TD (wore out *cruising*)
1 set R888 (everywhere tires on RX-8, but not daily)
1 set V710 (race only, scary street moments babying to track)
RC-1 has really good forward traction which amazed me. My FC was completely hooked up in 4th and 5th on them in a straight line. They don't need heat, they are really quiet cruising, progressive breakaway and the sidewall is OK.
Ultimate cornering grip is so so, but I still love them. Its like Maxis made a slick out of the newest 200UTQG street tire compounds.
I put them on my RX-8 for a bit after I blew up the FC and RC-1 were really nice on that too. Probably faster than the 295 R888 I put on the 108rwhp RX-8, but wide wheels/tires look cooler.
IDK what you normally run, but NT01 are popular so I would say- RC-1 has slightly less ultimate grip than NT01, better sidewall, better cold grip, much better road manners/daily driveability. A more *refined* tire than NT01, kinda like NT01 when you wear them down to slicks except not easy to shock into spinning like that. Very forgiving.
I'm doing some research on V8 swaps and I've noticed nobody seems to use the stock 5spd turbo RX7 transmission with any of their swaps. This is pretty common with other cars using adapter plates or dedicated bellhousings made to adapt one motor to another transmission but this doesn't seem to be the case in the RX7 community.
It seems like the stock 5spd can easily handle 3-400 hp/tq of a modified rotary, why doesn't anyone adapt an LS1 (for example) to the stock 5spd? This would greatly simplify a lot of the swap in my opinion but maybe I'm missing something obvious?
Thanks!
P.S. I did search!
The numbers I found way back when were that the TII could handle around 550-ft/lbs and that the thing that killed them (like any trans) was high shock load. I'll be putting this too the test.
The reason you haven't heard of anyone doing it is because I've only recently, on a different forum, said that I've done it. On this forum there is a year old (or so) thread that heavily implied what I was doing; actually, it might have said it outright, I cannot recall.
The reason you don't see people doing it is several fold.
1. "no one" has done it before and provided a road map.
Most of the automotive world is not inventive or that clever when it comes to modding their car or that rich. So if it hasn't been done, most people aren't willing to take the risk.
2. T-56
This is, IMO, a very good reason, except for the fact that they command nearly $2k now. It is an extremely strong and reliable trans, no/few mods required to fit it depending on which car you pulled it from and has pretty good ratio's for the engine it's attached too.
3. It takes a lot of work
While people are willing to spend 100+ hours researching, designing, and building a bracket to located a power steering pump or A/C they're not willing to do that same thing for a trans. Largely because T-56.
Looking at the gearing and tire selection on RX-7's, the TII trans isn't that bad a fit. Assuming 25" tire, 6500rpm redline, and USDM TII trans gears, you're looking at:
1st - 34
2nd - 59
3rd - 85
4th - 118
5th - 164
If you bump up the redline to 7000rpm 5th goes to ~180mph. If you use a JDM TII 5th then it drops it back down. With good tires on a track oriented build you should never have to drop to 1st gear and the rest of the ratio's are decently spread. It gets even better if you can rev higher than 7000rpm. I wish I could rev to 8000rpm.
Attached are pictures of my TII trans to LS1. You'll notice a trans support piece in addition to a trans mount. I didn't like the huge moment created where the engine and trans connect so I made that. I might change it again and only use that support piece in conjunction with a few of the trans pan bolts. I'm not sure yet and this setup works. You might notice a large chunk of my firewall was cut out and new pieces welded in place. Technically speaking my car is right around where I can call it a FMR. My engine sits lower and further back than any other LS1 swap I've seen. If I hadn't moved the firewall I could have likely used a modified stock trans crossmember.
At the end of the day doing the adapters (trans and flywheel) cost me ~150 hours of my time and ~$500 in parts. This includes end mills, lathe bits, drill bits, and the metal. This is across 3 iterations of the plate and 4 iterations of the flywheel adapter. Half of that 150 hours was spent in my buddies shed running his mill and lathe to build the parts. Most of my swap has been less "get it pretty" and more "get it done". As it probably very evident. A caveat that's worth mentioning is the car has not been on the road again yet. That should happen in the next 2 weeks once I figure out what I want to do about the dashboard.
BTW you can make a small block Ford rev to 8000. You can make an LS do it too.. There is just really no need.
HP is the reason racers rev pushrod motors to 10,000rpm, but it cost a lot of $$,$$$ and they aren't super reliable.
People want to rev LS V8s so bad they make aftermarket OHC conversions and do crazy VK35 head swaps.
There is a need.... a need for speed.
Those conversions do exist, but not one is really doing them en masse, and certainly not on cars driven in anger.
Thanks for the info on the RC1. I normally run NT01 255/40/17s all around, but am running the RC1 in 275/35/17, so I suspect (hope) I'll get more ultimate grip out of that setup. I like the NT01s.. I just want a bit more grip to lean on as the car pretty much is driven with the throttle. Plus I have another 50 or so WHP to add sitting in the garage.
Oh and by the way.. Here is your LS2 (6.0) based 8200 RPM pushrod engine. NASCAR tested and approved... 9 years ago. You can replicate this for less than half of the $22k cost if you know where to get the parts . It is based off OEM head and block castings with upgraded internals and a dry sump.
It makes 625 HP and 500 lb ft of torque. NASCAR's New Motor - Circle Track Magazine
Last edited by LargeOrangeFont; 06-02-15 at 11:12 PM.
You are right, the Turbo trans gear spread does not look horrible,. It's borderline where it sits, but it will be a handful as the power level increases.
Last edited by LargeOrangeFont; 06-02-15 at 11:16 PM.
Thanks, LOF. The TII trans certainly doesn't have ideal ratio's, especially when you can't rev it high, but it'll do and I won't feel too bad if I have to replace a $250 trans a time or two. Frankly, I expect I'll be doing a lot of skip-shifts. And probably roasting a lot of street tires in 1st-3rd, maybe 4th too.
Looking at those pics I posted makes me feel like they could be used in an eye spy book. Automotive edition.
06-01-15, 09:00 PM
! Now they stack the coils on the valvecover so its about the same height as a OHC engine- 
?
. It is based off OEM head and block castings with upgraded internals and a dry sump.