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Old 09-30-2010, 11:04 AM   #1
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FD3S RX7 Engine into An rx8

i have an RX8 2004 6 Speed manual in Pakistan , The water seals of the engine are gone and the mechainc says the we need to redo the engine .

Here in Pakistan people are putting in Supras 1jz and 2jz in rx8's and rx7's after their rotary engines are blown up .

I , Myself am a rotary fanatic , Either i will build up my rx8 engine or I was thinking of putting in FD3S RX7 Single turbo engine into my rx8 as it prodces more power .

I just want to know if anyone has done this before , If yes then i want to know all the positives and negatives of this conversion .

Thanks all ,

Faraz Sheikh
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Old 09-30-2010, 11:26 AM   #2
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It can be done, has been done. The people who've done it have not felt it necessary to give us any details about their experiences, so it is still largely unknown at this point.

The obstacles mainly involve motor mounts, intake to firewall clearance (there is about a 6 inch discrepancy between the two engines), as well as the twin turbos interfering with the frame rail in the rx8.

Then you have all of the electronics issues to resolve. Some functions of the car will be lost in the swap and you will almost certainly have one or more warning lights on the dash as a result.

A custom gas pedal and throttle cable would also have to be made.

Here's a more comprehensive list of things I've considered about this swap in the past, an excerpt from an email I sent to someone else who inquired about this.

Quote:
There are a few issues I can think of offhand:

-rx-8 uses drive by wire throttle (electric pedal with sensor, and electric
throttlebody with motor, and the computer controls the throttle opening)
while the rx7 engines use a standard cable driven throttle.
-rx-8 power steering is electronic controlled (there is no mechanical PS
pump) and requires the rx8 stock engine computer to work
-modern features such as cruise, ABS, traction control, stability control,
tach, speedometer, etc. are all run through the rx8 stock engine computer.
Doing an engine swap might leave one or more of these systems non
functional, and warning lights on the cluster as a result.
-the upper intake manifold on the rx8 motor is "stepped" to clear the
firewall, which hangs over the engine slightly. The intake manifold on the
rx7 engine, as well as the intake pipe for the rear twin turbo, might hit
the firewall and require modification/cutting, since they are taller.
-the rx7 engine mounts totally different so custom mounts would have to be
fabbed. This would not be a really big deal but is still a challenge.
-the rx7 engine would require a custom front mount intercooler, and possibly
battery relocation.
-the rx7 engine would require an upgraded fuel pump, not a big deal.
-the oil cooler lines would have to be modified/remade as they connect in
different locations on the 2 engines.
-an upgraded radiator might be necessary due to fitment or cooling needs
-the front half of the exhaust would no longer line up, so something would
have to be fabbed. The car would never be emissions legal because you
probably could not keep the stock cat convertor...and backwards engine swaps
to older engines are not allowed in emissions tests anyway.
-the rx8 uses a returnless fuel system, meaning there is no fuel
return/drain back from the engine to the tank, fuel just gets pumped to the
engine and stops. the older engines use a return fuel system where unused
fuel is returned to the tank, so a new fuel line would probably have to be
run to the tank and plumbed in.
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Old 09-30-2010, 11:36 AM   #3
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I dont see why you need a RX7 engine. just rebuild and turbo it. much cheaper than doing a swap.
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Old 09-30-2010, 11:42 AM   #4
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^and the headache it causes.
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Old 09-30-2010, 11:42 AM   #5
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Quote:
Originally Posted by jasonrxeight View Post
I dont see why you need a RX7 engine. just rebuild and turbo it. much cheaper than doing a swap.
See man, I told you. EVERY THREAD. lol.
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Old 09-30-2010, 11:47 AM   #6
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Quote:
Originally Posted by jasonrxeight View Post
I dont see why you need a RX7 engine. just rebuild and turbo it. much cheaper than doing a swap.
Quote:
Originally Posted by nycgps View Post
^and the headache it causes.
Also, I'm not sure I can agree with that. In theory, doing the work yourself, you could acquire and install an rx7 engine for under 5 grand and make around 300 "fairly reliable" turbo hp.

If you rebuild the renesis and buy a turbo kit and everything needed to support that, you're easily, EASILY going to have 10 grand into it. And, let's be honest here...the turbo'd renesis engines I've been seeing have a much shorter lifespan and make less power than earlier turbo rotaries which were intended as such.

Not to mention there is somewhere in the neighborhood of 10 times the support for a turbo FD engine making 400rwhp than there is a renesis attempting to make such. The path has already been laid down and we know exactly what to do for those FD builds...I've done many of them myself. There's not much guesswork involved...you buy a power FC computer for $700-1000 and you put a tune on it and you're mostly done. And you don't have to go through a certain rx8-specific tuner and hope you kiss his *** enough to get him to give you what you paid for (aka carbonrx8) either. That alone to me would be "worth the headache" of such a swap.
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Old 09-30-2010, 12:58 PM   #7
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well, 5 K is just "assuming" you can do most of the work yourself, including to make all the brackets to support the engine and source all the related parts cheaply.

very few people can do that/willing to do that themselves. but most of the people here just can't do that.

For this group of people, the shortest path to more power is turbo/SC their current setup.
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Last edited by nycgps; 09-30-2010 at 01:00 PM.
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Old 09-30-2010, 01:08 PM   #8
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Quote:
Originally Posted by nycgps View Post
well, 5 K is just "assuming" you can do most of the work yourself, including to make all the brackets to support the engine and source all the related parts cheaply.

very few people can do that/willing to do that themselves. but most of the people here just can't do that.

For this group of people, the shortest path to more power is turbo/SC their current setup.
Right...and 10k to rebuild, turbocharge and tune their existing renesis also assumes they are doing the work themselves (in terms of remove/install engine block after rebuild, install turbo kit, etc.). IF we're adding in labor for a shop to do a turnkey job, both jobs are probably going to increase 3-5k more.

The important part is that it is likely to cost significantly more to rebuild and FI a renesis than to rebuild and swap an rx7 turbo engine, by several grand. And you will end up with most likely less power and definitely less reliability. Doesn't sound like such a great idea to me.

I'm sorry, I like the rx8 and I think it's a good entry level modern sportscar. But I have zero faith in FI'd renesis engines, considering the cost of the parts to modify the cars, and the longevity (lack thereof) of them in FI form.

I mean hell, if you look at it objectively and put your emotional attatchment aside, these things are doing well to hold together 50-75k miles in bone stock form in a lot of cases (not all, but a sizeable percentage). The 93-95 rx7 models that made more hp and torque, 10 years earlier, could manage 50-75k. And they got arguably better gas mileage doing it.

Last edited by RotaryResurrection; 09-30-2010 at 01:17 PM.
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Old 09-30-2010, 10:26 PM   #9
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Ive seen this swap done before in a couple of Rx8's and everyone chooses a different route when doing the swap. They also dont provide very much information on their setups. One other way that you could consider to help retain some of the functions that you may otherwise lose would be to go to an aftermarket EMS like Haltek, MicroTech, or Motec which would allow you to customize the harness to retain the Rx8 throttelbody and drive by wire as well as the powersteering pump. Which Ive seen an exapmple of this before but the owner keep the details of how he accomplished all this to himself. In addition if you have motor mounts made that mount the motor as low as possible this will help with any potential clearance problems.
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No...I never saw those pics. I tend to stay away from the big bad threads that confuse me with terms like...camber and toe...and such....



I stay away from the turbo thread too....that one's scary!
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Old 09-30-2010, 10:48 PM   #10
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I've done measuring and mock up using example parts. Even if the FD engine were able to be mounted exactly as low as the renesis, the FD intake manifold is still going to cause a major problem with the rx8 firewall. To the tune of 6 inches. The rx8 intake sits further forward, is rounded and also stepped to clear the firewall.

I actually think working out the electronics would be the easy part...the physical placement of the engine and trans would be more difficult. You'd want to use the FD's 5 speed trans to hold the power, as the rx8 trans is glass and isn't really geared to suit most people. The shifter locations are different, and if you take the approach of moving the engine and trans as a unit, then you require a custom driveshaft and PPF.
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Old 10-01-2010, 12:21 AM   #11
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Yea I knew the intake would still be an issue as nothings ever easy, but if possible to minimize some massaging that would be needed then its worth examining. An Ive seen several options used for the transmission but using the FD trans would simplify the whole situation, and like you said it may make things easier by moveing things forward a few inches as getting a custom drive shaft is pretty straight forward.
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No...I never saw those pics. I tend to stay away from the big bad threads that confuse me with terms like...camber and toe...and such....



I stay away from the turbo thread too....that one's scary!
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Old 10-01-2010, 01:16 AM   #12
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Quote:
Originally Posted by JustinsFDpoweredFC View Post
Yea I knew the intake would still be an issue as nothings ever easy, but if possible to minimize some massaging that would be needed then its worth examining. An Ive seen several options used for the transmission but using the FD trans would simplify the whole situation, and like you said it may make things easier by moveing things forward a few inches as getting a custom drive shaft is pretty straight forward.
To move the engine/trans forward, means the engine would have to go up about 6 inches to clear the subframe and PS rack. A custom oil pan may be required.

Even moving the engine forward several inches, it will still be difficult to clear the firewall. A custom lower intake manifold would greatly help...this of course just increases the costs involved.

It's also 90% likely that the stock twin turbos (or any variant thereof) and their side exit exhaust would not fit with the rx8 frame rail in the way. So a single setup would be in order. Good thing they are plentiful and relatively cheap especially if you fab your own kit.
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Old 10-01-2010, 06:49 AM   #13
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hmmmmm ..... thank you all for for providing valuable info ... but am still confused ...

which option should i go for ? !!
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Old 10-01-2010, 08:57 AM   #14
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^ How much money do you have and what kind of knowledge do your local shops have?
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Old 10-01-2010, 10:40 AM   #15
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hmmmmm ..... thank you all for for providing valuable info ... but am still confused ...

which option should i go for ? !!
Let me dumb it down some. This is one of those times when, if you have to ask, you can't do it yourself and probably can't afford to have someone else do it either.

Thus, the reasonable conclusion is to work with what you've already got, which fits perfectly and is plug-and-play.
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Old 10-01-2010, 11:53 AM   #16
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20B sounds good to me.
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Old 10-01-2010, 12:42 PM   #17
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20B sounds good to me.
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Old 10-01-2010, 01:59 PM   #18
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Yea, 20B is the most cost effective solution....... (insert sarcasm here)
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Old 10-01-2010, 05:05 PM   #19
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Quote:
Originally Posted by RotaryResurrection View Post
To move the engine/trans forward, means the engine would have to go up about 6 inches to clear the subframe and PS rack. A custom oil pan may be required.

Even moving the engine forward several inches, it will still be difficult to clear the firewall. A custom lower intake manifold would greatly help...this of course just increases the costs involved.

It's also 90% likely that the stock twin turbos (or any variant thereof) and their side exit exhaust would not fit with the rx8 frame rail in the way. So a single setup would be in order. Good thing they are plentiful and relatively cheap especially if you fab your own kit.
Very true on the turbos being a problem as well. But the only real way to see what will have to be done to make a swap like this work is to have the engine and trans there for mock ups and see what will ultimately work best.

Out of sure simplicity I would probably just keep the 13b-msp and spend my money on making it a reliable turbo block as best as possible.
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No...I never saw those pics. I tend to stay away from the big bad threads that confuse me with terms like...camber and toe...and such....



I stay away from the turbo thread too....that one's scary!
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Old 10-01-2010, 05:07 PM   #20
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20B is cool and has loads of potential but very expensive.
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Quote:
Originally Posted by sephyobsessed View Post
No...I never saw those pics. I tend to stay away from the big bad threads that confuse me with terms like...camber and toe...and such....



I stay away from the turbo thread too....that one's scary!
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Old 10-01-2010, 05:13 PM   #21
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Very true on the turbos being a problem as well. But the only real way to see what will have to be done to make a swap like this work is to have the engine and trans there for mock ups and see what will ultimately work best.

Out of sure simplicity I would probably just keep the 13b-msp and spend my money on making it a reliable turbo block as best as possible.
I guess this is the point where I state that during a rebuild/install on an rx8, I once grabbed a rear iron and an upper/lower intake manifold from an FD engine and attempted to mock it up. With the rx8 transmission in it's normal position in the car, and the intake touching the firewall, the rear iron was 6 inches or more from meeting the transmission. The $450 custom groundzero intake manifold for the FD would gain you maybe 2, 2.5 inches. A one-off custom welded intake manifold may be required, kind of like what mazsport was trying to rig up on that infamous 20b rx8 install. In this case the twin turbos would be out of the question, although that's likely the case regardless.

I've analyzed this dilemma for the past two years (at least) and my own inaction with my personal rx8 highlights how challenging I feel it would be to properly and reliably execute either project. Not worth the trouble for a car worth 8-10 grand on a good day, especially when a stock renesis rebuild with premix can approach bulletproof reliability.
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Old 10-01-2010, 05:21 PM   #22
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2 years is a long time to be looking into this, you must have considered tons of variations. I personaly dont have an 8 but if I did I would just keep the 13b-msp rather than swap. I did swap a 13b-rew into my 88 Fc Rx7 which proved to be challenging, but I wanted to be different and a few years new as the Fc is slowly losing aftermarket support from some vendors.
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No...I never saw those pics. I tend to stay away from the big bad threads that confuse me with terms like...camber and toe...and such....



I stay away from the turbo thread too....that one's scary!
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Old 10-01-2010, 05:21 PM
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