Single turbo vs V8 need help
 

Hey guys I'm sure this topic is on here somewhere but I haven't found it. If I can get help an opinions that would be great.
I have a 93 fd rx7 ALL STOCK (except down pipe) and I am not sure if I want to make it into a V8 or go single turbo and port the engine.
I had a 72 nova pushing about 500 horsepower and it was a monster but 6 mpg so I no longer have it. Buuuut I love the rotary how small, balanced, raw it is...can someone shine some light..what do I consider or think of?

Sorry don't mind the part out...did that by accident.

Both have big power potential and will cost about similar. The rotary will always be less forgiving of tuning errors. It really depends on what you like.

Well I'm new to rotarys, but I fell in love with this car. But I miss the rumble and just out right brutal power from the v8. Is the v8 engine much heavier than the rotary? Does it affect it's handling if I wanted to race up a canyon?

Be true to the roots of the car! I am far from a piston hater. Love some mustangs! If you take the time and do it right you will have more to be proud of staying rotary. Only way it would make sense to me going v8 is if you have no knowledge of motors and are strictly just wanting the looks of the fd.

I was always a piston guy growing up with 2 older brothers and my dad having every type of muscle car about ever made. The rotary was different making it more interesting and more of a challenge. No better feeling than running a turbo v8 and handing there ass to them.

Just my 2 cents

Personally, if the rotary is running OK and has good compression, I'd probably just do external mods to it, and all reliability mods of course. I wouldn't rebuild or do a V8 swap until the existing rotary expires.

Like vs. like ( with a/c, p/s, etc.), an LS V8 adds about 100 lb and shifts the weight forward a smidge, 1-2%. Basically goes from being ~48F/52R - 49/51 with full fuel and driver to ~49/51 - 50/50.

Ok cool thanks. Yeah the car is running great right now I was just thinking for the future. Do u know How much it generally cost for a port and engine rebuild on a rotary?

A proper LS swap can actually come out LIGHTER than a rotary. You are loosing a lot of weight ditching turbos, the stock cast iron manifold, intercooler, etc. Handling is also no different. Its all up to you and what you like. As far as cost, it really depends on what is wrong with the motor and what you are looking for. There is a very wide range of quality when it comes to rebuilding these engines. We personally NEVER re-use any seals or gaskets. A good estimate is $3000-5000 for the motor, depending on how extreme you go.

I know there's a bunch of LS engines....I tried to read on all of them and see what's what but I'm not sure how to define each one and what the differences exactly are? Like if I do an LS of course I want low end, it's a v8 but having had a v8 before it had killer low end power but absolutely nothing up top, I want something that is all around from low to top end to keep making the power. I know you can't have it all so if I had to split it up I would say if prefer a tad bit more top end then low. Just because after launching you don't go back to that low end power, you're up in the rpm's so no point of having power down low, you know?

What do you want the car for?

Street
Drag
Road Race
AutoX

If there is nothing wrong with your car, leave it be. Maybe do some of the reliability mods. AST, radiator and such. I did all of the bolt on and single turbo stuff. I said to myself if the motor ever goes I'll do the swap. My MPG more than doubled. Peak HP stayed the same and there was a TON more TQ everywhere. (stock LS1) My RX weighed in at 3030 with full accessories, interior, tons of dynamat and a sub box. Pretty much the heaviest you could possibly make it. Small bias to the rear. Removing the box made it 50/50. The T-56 is about 50lb heavier than the RX trans so it helps a lot with moving the weight back.

The issue is that a quality rotary rebuild is roughly the same price as a used LS1 and T-56 trans. Check out No Rotors and get to reading. There are a ton of options. A rotary car is NOT a civic. You HAVE to be knowledgeable about what you are doing to the car and why you are doing it. It is not a forgiving motor to mistakes. If you love the look and feel of the RX and just want to drive without having to watch your gauges all the time the LS is the way to go hands down.

You cannot really compare an old school V8 to the LS series. Leaps and bounds better. While it is true that the power does not increase like a turbo rotary and may even feel boring(?) the car WILL be faster. (baring crazy modded rotary on meth) I ran a 12.2 with a stock LS1 on 225/50 300 tread ware sumitomos.

Yes, it *can* come out lighter than stock, if you lose some things like A/C and power steering. A similar decontented rotary build with single turbo will come out lighter still.

All things relatively equal, an LS build is going to be 50-100 lb. heavier. There are 2750 lb. V8 swaps, there are also 2650 lb. rotary builds.

My LS2 is very much a street car, and weighs ~2980 lb. with full tank (weighed 2949 with 3/4 tank). That's with some other weight-adders, though: roll bar, rear-mounted accusump installation, bigger wheels/tires/brakes, tons of dynamat, etc. Figure it'd be about 50 lb lighter without all that stuff, or ~2930 lb, with full tank. That's still 50-100 lb heavier than stock.

Same vs. same, the LS swap does add weight even relative to the stock rotary (which has those heavy turbos and manifolds). But it's not a huge amount and doesn't really affect the handling balance of the car.

I want the car mostly for street but still want it be fast on the rare occasion I go to the track. Because at the moment I am thinking of going with 6266 precision turbo, all the supporting mods of course and hopefully getting roughly 450 hp out of it. Numbers aren't too important to me but I want it to be fast and yes I would like to be able to cruise this car everywhere with great mpg and be reliable like a v8 so I'm still in the rough about exactly what I want.

Down low only power - sounds like youve driven alot of trucks and low-po V8 engines. try driving a camaro, gto, corvette, cts-v, etc. LSx engines arent down low power and dead up top. Power pulls all the way to redline. This differs DRAMATICALLY to the first V8 car I ever drove, a mid 90s Tbird where after 3500rpm's it was crap.

I had a 1972 nova with a 406 small block that ran a 10.27 at 142mph. My dad built it for me...I got rid of it because it only got 6 miles to the gallon...I regret getting rid of it every day. But the only thing was it was wicked in a quarter mile, amazing low end and mid range but it red lined at about 6k rpm. So drivability on the freeway was horrible, you couldn't take it up to 100 and keep it there because it just revved too high. That's my impression on the v8.....I don't know too much on the LS engines but it seems like they're pretty awesome from what I'm reading. I'm just not sure what my deciding factor is? I'm trying to get pros and cons on both ends of the rotary and LS.

Here's the dyno for my LS2 w/ L92 heads, LS3 intake, 222/230 .597" cam:
Attachment 650722

A little optimistic! Later run confirmed power at more like 463rwhp. But the curve is worth noting. Stock cylinder heads, mildish cam, and it breathes very well to 7000rpm, peak power at 6400.

It is noticeably soft down low relative to a stock LS2, but really brings it home in the higher revs :)

Nice...looks good. How's it do on mpg? Because I want it to be a street monster but one that I can drive everyday...I know they'll be some sacrifices to get good mpg though.
One thing I notice and motivates me to make this rx7 a street monster is everyday on my way to work and home some corvette, mustang, evo etc is always revving and egging me on and I'd like to show them my car can move....but it's all stock lol 😣

Gets 25 on the highway. On the previous leaner tune, it actually did 29mpg on one tank!
In town, much worse. Like 15.

I think that's really good considering the power and it being a v8. The 15 mpg is pretty low though, you would probably have to baby it a lot to see better numbers. But that's no fun.

MPG and go fast are the complete antithesis of eachother. You get one or the other. Having fun in the car will never net good fuel economy. How the motor/car act when you aren't on it is what really matters. The V8 getting 15 around town is still better than a rotary gets around town. In hawaii with stupid traffic and a 2000ft altitude change to and from work I usually averaged about 21MPG but my heads and cam were far from ideal for power and economy.

On the freeway you'll get ~double the MPG of the rotary. Your V8 build for reasonable power and MPG is all in the details. 0 or - overlap on the cam, small port heads like stock or the AFR's that have great port velocity and rear gears among a few other things. A 4.10 gear is not ideal for a street car. 3.55 is better suited but a diff from another car is required to pull that off.

If you have ANY concerns about MPG and want more than 400whp the rotary simply isn't even an option as it cannot be done currently.

If you took an LS1/6 with 243 heads and a stock cam you'd be at over 400bhp and have a motor that would do 100k miles and not even break a sweat.

Yeah I hear you. What I am thinking is (and I'm not to sure just an idea) is picking a LS engine with some power of course maybe in the 350ish range and turbo it....how do you think that would turn out? Not a huge, just a turbo to push me into the mid 400's. that way mpg is good until I start to boost. Maybe an LS engine tht revs a little higher. What do you think?

It seems like you are going to overcomplicating things. Just do a H/C/I LS1 like everybody says and you will pretty much get exactly what you want.

If the rotary in it now is OK, it is madness to initiate a swap. Mod it, run it, when/if it expires, *then* consider the swap.

That's the thing, is it worth modding then later on replacing to a v8 or is it better just to save money and jump into it now?
What are your experiences with having the rotary and then a v8 was it worth it or how did you go about things?

A friend of mine bought the car with blown engine and did the swap. I bought it from him already swapped.

Personally, if I *had* an FD with a functioning rotary, I would do research on all the reliability/durability mods and also on modding for more power while INcreasing reliability, and enjoy it while it lasted! If the engine blew, I'd go into LS swap mode. It's a risk, but then again it's also risky and expensive to do a V8 swap. Cars have gone down for years and years and YEARS undergoing engine swaps! Enjoy what you have now while it's working, I say!

You know what...you're right. I'm going to focus on the rotary and when she blows I'd see if she's worth it to me to keep her going or swap. Thanks you guys! I wish I was rich so I can get two fd's one rotary and the other ls! Lol