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Old 03-21-17, 07:09 AM
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swap opinions

I have an 85 rx7 with a 12a that I replaced a while back and runs well (put down 105 whp) with just exhaust upgrade (already on the car).

My questions are:

I can get a renesis for 500 that is running well. I was wondering what the power difference would be if I swapped the renesis in to the rx7 but, converted it to carb.

Also, how difficult of a swap would it be as, I have looked at the carb and intake swap and that part will be 1100 with new parts. I know there is more involved.

lastly, the whole reason for the swap potential was because the 12a, although running good, leaks a little oil but, very, very little.

I would like to know opinions and if this has been done. I know people have put renesis engines in FBs but, with FI. Any info would be very useful. Thanks.
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Old 03-21-17, 09:04 AM
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Someone makes a carb/intake swap for a renesis? I'd like to see that.

Mounting the renisis would require engine mounts to be fabricated because the 12A front cover
doesn't work on a renesis. Also, the headers you have won't work, have to fabricate or use
the OEM renesis exhaust manifold. Plug the injectors. Renesis requires an ECU or standalone
to run it unless you figure out how to use a dizzy with it. Lots of issues to deal with.

For that $500 you can just as easily find a 13B, swap the front cover and use it much easier.

BTW, if you are getting 105whp from the 12A with just the exhaust, you have a pretty healthy
12A and with some ignition and carb changes you easily can get another 30whp out of it.
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Old 03-21-17, 09:49 AM
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I know how it feels. I have a 12a bridgeport that I wood like to put in a 2000-2005 miata. I have seen the 13b kits but $2,400 is a lot of money. I was going to put it in my 83 rx7 but I like the miata better. Because the miata has more options as far as aftermarket parts go.
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Old 03-21-17, 10:26 AM
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Originally Posted by t_g_farrell View Post
Someone makes a carb/intake swap for a renesis? I'd like to see that.

Mounting the renisis would require engine mounts to be fabricated because the 12A front cover
doesn't work on a renesis. Also, the headers you have won't work, have to fabricate or use
the OEM renesis exhaust manifold. Plug the injectors. Renesis requires an ECU or standalone
to run it unless you figure out how to use a dizzy with it. Lots of issues to deal with.

For that $500 you can just as easily find a 13B, swap the front cover and use it much easier.

BTW, if you are getting 105whp from the 12A with just the exhaust, you have a pretty healthy
12A and with some ignition and carb changes you easily can get another 30whp out of it.
The exhaust is a long tube header from pacesetter. We put the ignition at the recommended setting for L and T based on this site for best results. The carb is a edlebrock 600 with electric choke and cannot remember what size the jets were and the rods were. With what I have, what else can be done without porting? I had it on the dyno and was running high 12s on the AFRs. We only did 3 pulls with it and put down 105 and 100 tq.

I am more into DSM cars but, I do love the rotary and like tinkering with my 7. I have an rx8 too.

The issue with the ignition is the only issue that I thought I would have. The racingbeat intake will not fit the renesis to convert to a carb? I guess I was not thinking about the difference in the side ports. good used 13b's are hard to find unless an REW.

Thanks,

Cliff
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Old 03-21-17, 10:29 AM
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Originally Posted by Scuderi View Post
I know how it feels. I have a 12a bridgeport that I wood like to put in a 2000-2005 miata. I have seen the 13b kits but $2,400 is a lot of money. I was going to put it in my 83 rx7 but I like the miata better. Because the miata has more options as far as aftermarket parts go.
Very true.

I am looking for an early model miata. They are hard to find as well. I would love to put an renesis in one with full fuel injection.
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Old 08-07-17, 10:03 PM
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Originally Posted by t_g_farrell View Post
Someone makes a carb/intake swap for a renesis? I'd like to see that.

Mounting the renisis would require engine mounts to be fabricated because the 12A front cover
doesn't work on a renesis. Also, the headers you have won't work, have to fabricate or use
the OEM renesis exhaust manifold. Plug the injectors. Renesis requires an ECU or standalone
to run it unless you figure out how to use a dizzy with it. Lots of issues to deal with.

For that $500 you can just as easily find a 13B, swap the front cover and use it much easier.

BTW, if you are getting 105whp from the 12A with just the exhaust, you have a pretty healthy
12A and with some ignition and carb changes you easily can get another 30whp out of it.


I've been thinking about getting an RX8.

Long story short can an S4 or S5 front iron bolt to an RX8 front cover?

Also, how does the RX8 engine mount? Would swapping irons disrupt the motor mounts?
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Old 08-07-17, 10:46 PM
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Front iron, not front cover? You'd deprive the front rotor an exhaust port that way.

Best to just fab some mounts to get it in the car. Stock mounts attach to the front and middle irons.

Front cover doesn't is off by one bolt, but then the water pump housing won't fit.
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Old 08-08-17, 01:23 AM
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Originally Posted by clifffyyy View Post
I have an 85 rx7 with a 12a that I replaced a while back and runs well (put down 105 whp) with just exhaust upgrade (already on the car).

My questions are:

I can get a renesis for 500 that is running well. I was wondering what the power difference would be if I swapped the renesis in to the rx7 but, converted it to carb.

Also, how difficult of a swap would it be as, I have looked at the carb and intake swap and that part will be 1100 with new parts. I know there is more involved.

lastly, the whole reason for the swap potential was because the 12a, although running good, leaks a little oil but, very, very little.

I would like to know opinions and if this has been done. I know people have put renesis engines in FBs but, with FI. Any info would be very useful. Thanks.
There are a few Rennessis first gens around, but they are entirely custom and NOT AFFORDABLE . also the BIGGEST issue would be getting a ECU to work functionally.
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Old 08-08-17, 07:07 PM
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I've thought about this swap for quite some time. Here's how I'd do it. I'd imagine you would sacrifice some low end power but you should still be able to make close to factory Renesis numbers.

Carb- use the Racing Beat 13b intake adapter and a 13b carb intake. Simple. Plug the injector holes and wire open the secondary ports. You'll lose some low end.
Ignition- use an MSD Flying Magnet crank trigger and MSD box, leading only, no trailing, direct fire.
Exhaust- fab up a custom header.
Mounting - fab up mounts to work with the Renesis mounting points.
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Old 08-08-17, 07:26 PM
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Originally Posted by j_tso View Post
Front iron, not front cover? You'd deprive the front rotor an exhaust port that way.

Best to just fab some mounts to get it in the car. Stock mounts attach to the front and middle irons.

Front cover doesn't is off by one bolt, but then the water pump housing won't fit.


I want to do a peripheral port RX8. Using the OEM RX8 front cover (using the OEM ignition and oil pump).

BUT it would be loads easier to use second or third gen RX7 housings and drill two intake holes in them; as apposed to drilling four holes in Renesis housings.

Problem there is the coolant seals. Renesis seals are in the housings. S4-S6 seals are in the irons. So I'd need to use the irons from an RX7. AND I'd like to use the front cover from the RX8 just to keep things simple or advanced or for some stupid reason.


All these ideas are spawning because of how damn cheap RX8's have gotten. I can't resist.
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Old 08-08-17, 08:11 PM
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Originally Posted by Qingdao View Post
I want to do a peripheral port RX8. Using the OEM RX8 front cover (using the OEM ignition and oil pump).

BUT it would be loads easier to use second or third gen RX7 housings and drill two intake holes in them; as apposed to drilling four holes in Renesis housings.

Problem there is the coolant seals. Renesis seals are in the housings. S4-S6 seals are in the irons. So I'd need to use the irons from an RX7. AND I'd like to use the front cover from the RX8 just to keep things simple or advanced or for some stupid reason.


All these ideas are spawning because of how damn cheap RX8's have gotten. I can't resist.
​​​​​​​Wouldn't it be easier to gut the first gen and try to put the guts of the RX-8 in ?
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Old 08-08-17, 09:19 PM
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Originally Posted by Frogman View Post
​​​​​​​Wouldn't it be easier to gut the first gen and try to put the guts of the RX-8 in ?

In essence yes that's what I'd be doing only with an FC or FD engine. But I didn't know if the front cover would bolt to an RX7 iron... apparently it won't easily.

The keg would be a normal peripheral port with RX8 rotating assembly, but i'd like to use the front cover from the 8 so I can use the 8's ignition. I mostly would like to avoid using a distributer just because I'd like to keep the 8's tac functional.
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Old 08-08-17, 09:25 PM
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Ahhhhh I just fixed my problem....


I'm just gonna get some old 1985 or before 13B housings... and shove them in the renesis build. Keep the front cover and front irons no swaping nessary just the pre 85 housings.
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Old 08-12-17, 07:35 PM
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Originally Posted by Qingdao View Post
I want to do a peripheral port RX8. Using the OEM RX8 front cover (using the OEM ignition and oil pump).

BUT it would be loads easier to use second or third gen RX7 housings and drill two intake holes in them; as apposed to drilling four holes in Renesis housings.

Problem there is the coolant seals. Renesis seals are in the housings. S4-S6 seals are in the irons. So I'd need to use the irons from an RX7. AND I'd like to use the front cover from the RX8 just to keep things simple or advanced or for some stupid reason.


All these ideas are spawning because of how damn cheap RX8's have gotten. I can't resist.
Imagine using the RX8 factory ports, PLUS P-Ported 13b housings. You could have more air and fuel available for combustion than you could ever use. Even on extremely low boost (6psi?) you would have unlimited air and fuel and plenty of exhaust holes to move it out of.

Also, thinking about the problem with the Renesis- the usual problem revolves around the center exhaust port creating too much heat. What if you used a 13b center iron, RX8 ends and 13b housings (even p-ported ones). You would have 4 exhaust ports which should be plenty, plus 8 intake ports. I imagine this would be a monster, even n/a.
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Old 08-12-17, 10:22 PM
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Originally Posted by TheRX7Project View Post
Imagine using the RX8 factory ports, PLUS P-Ported 13b housings. You could have more air and fuel available for combustion than you could ever use. Even on extremely low boost (6psi?) you would have unlimited air and fuel and plenty of exhaust holes to move it out of.

Also, thinking about the problem with the Renesis- the usual problem revolves around the center exhaust port creating too much heat. What if you used a 13b center iron, RX8 ends and 13b housings (even p-ported ones). You would have 4 exhaust ports which should be plenty, plus 8 intake ports. I imagine this would be a monster, even n/a.



No I plan on blocking off the side ports... Just a plain jane PP engine with high compression rotors, high energy ignition, and a top notch lubrication system. Not to mention a cheap yet well designed body/suspension.

As for using both the side ports and the housing ports. I don't think that would work as well as you'd think. But who knows you might be on to something.



All that being said I still think the RX8 is a vomit worthy ugly car, but mine will be loud and strange.

Last edited by Qingdao; 08-12-17 at 10:27 PM.
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Old 08-25-17, 09:52 AM
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Originally Posted by clifffyyy View Post
The issue with the ignition is the only issue that I thought I would have.
You are somewhat correct here, ignition would be a problem. The RX-8 has four coils, each of which is fired independently according to rotor position in the motor. This runs off of the timing wheel, similar to a trigger kit. You'd need a RX-8 ECU to run the timing correctly, or go aftermarket which would be way more expensive.

Originally Posted by clifffyyy View Post
The racingbeat intake will not fit the renesis to convert to a carb?
It absolutely will not fit without their additional $316.00 adapter plate to use their own manifold. So you'll need the adapter plate for $316.00 plus the lower intake manifold for the FC's which is an additional $298.00. You're talking $614.00 without tax or shipping for just the manifolds to adapt the Reni to a carb setup. Then you'll need an IDA carb to work with that setup.

Originally Posted by TheRX7Project View Post
I've thought about this swap for quite some time. Here's how I'd do it. I'd imagine you would sacrifice some low end power but you should still be able to make close to factory Renesis numbers.

Carb- use the Racing Beat 13b intake adapter and a 13b carb intake. Simple. Plug the injector holes and wire open the secondary ports. You'll lose some low end.
Ignition- use an MSD Flying Magnet crank trigger and MSD box, leading only, no trailing, direct fire.
Exhaust- fab up a custom header.
Mounting - fab up mounts to work with the Renesis mounting points.
This is the best explanation I've heard here yet. Still ungodly expensive to want to run a Reni in my opinion, but it would work.

Only issue is mounting the motor. The 8's mount their engines sideways with aluminum motor mounts going towards the subframe. FB's mount engines on the front cover. The motor mounting situation would be sketchy at best, really bad and scary at worst.

I own an RX-8 that I've rebuilt and redone almost everything on to this point, and have had over 10 first gens so I know both chassis setups very well.

Personally, I'd never put a Reni in an FB unless I totalled my 8 and had a spare FB chassis sitting around. It's fun and all, but my carb'ed S5 NA FC 13b motor on stock ports in the FB feels faster than the Reni in my RX-8.
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