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Cosmo or series 6
Im building a second motor for my 94 series 6 3rd gen rx7. I have an option to get a cosmo engine or a standard series 6 for my rebuild. Both are complete units for same price. Which one should i go for. Im putting a gt35r single into the new motor.
Greg |
COSMO!!! But it does require some slight modifications to work properly. Well worth it though in my opinion.
-J |
The rear iron is definitely much different between the 2 blocks. The 3rd gen motor mounts do not bolt up to the cosmos block in any way, shape, or form. There are also very restrictive exhaust diffusers in the cosmo block which will need to be swapped out for turbo diffusers. Also, the series 6 rotor housings are the best out of all the blocks. Things that have to do with the slightly modified water jackets near the spark plugs for better cooling in that area, as well as the actual chrome plated surface itself. (basically had better wear characteristics).
If this were for a 2nd gen or earlier, well than the cosmo block by far (due to less modifications for mounting). In your case, I would use the Cosmo upper and lower intake manifolds, but use your 3rd gen throttle body. That'll pretty much give you the best of both worlds, as well as having a better block. If you want to modify for motor mounts......well.......have fun. |
S6 and cosmo housings are the same with the exception of the exhaust diffusers.
The cosmo rear IRON can be drilled/tapped for mounting into an FD, but this is not a trivial process. Get a series 6 if the price is the same. |
2lucky2tha7
bar the engine mounts and the turbo diffuser are all the other parts interchangeable?such as water pump, alternator, starter etc. What is the main advantage of the cosmo over series 6?-power capability/limit...is this relevant for my medium gt35r setup...im looking for streeatable 450rwhp on a ported motor with necessary other mods....who knows if in the future i will want bigger hp.... ......confused...... |
No advantage, the port runners are bigger, thats it, and the S6 engine can be ported to match the cosmo runners (same casting thickness)
The rest of the components are not as good (rotor bearings, stat gears etc), or the same (eshaft). In the states a JDM cosmo engine goes for about 40% less than a JDM S6 that is the main advantage here
Originally Posted by Custard
(Post 7751253)
2lucky2tha7
bar the engine mounts and the turbo diffuser are all the other parts interchangeable?such as water pump, alternator, starter etc. What is the main advantage of the cosmo over series 6?-power capability/limit...is this relevant for my medium gt35r setup...im looking for streeatable 450rwhp on a ported motor with necessary other mods....who knows if in the future i will want bigger hp.... ......confused...... |
Originally Posted by 2Lucky2tha7
(Post 7750977)
The rear iron is definitely much different between the 2 blocks. The 3rd gen motor mounts do not bolt up to the cosmos block in any way, shape, or form. There are also very restrictive exhaust diffusers in the cosmo block which will need to be swapped out for turbo diffusers. Also, the series 6 rotor housings are the best out of all the blocks. Things that have to do with the slightly modified water jackets near the spark plugs for better cooling in that area, as well as the actual chrome plated surface itself. (basically had better wear characteristics).
If this were for a 2nd gen or earlier, well than the cosmo block by far (due to less modifications for mounting). In your case, I would use the Cosmo upper and lower intake manifolds, but use your 3rd gen throttle body. That'll pretty much give you the best of both worlds, as well as having a better block. If you want to modify for motor mounts......well.......have fun. Also the other big difference is the front cover..... The front cover on the RE has one less bolt in it than the REW. This means when you change the RE front cover to the REW front cover for the OMP to to work, you need to drill and tap the front iron for the extra bolt. -J |
Originally Posted by slo
(Post 7751262)
No advantage, the port runners are bigger, thats it, and the S6 engine can be ported to match the cosmo runners (same casting thickness)
The rest of the components are not as good (rotor bearings, stat gears etc), or the same (eshaft). In the states a JDM cosmo engine goes for about 40% less than a JDM S6 that is the main advantage here |
I have both engines fully disassembled in my garage.
The only "advantage" is the runner size, I didn't say that was the only difference. The difference between the manifolds is trivial, The actual internal ports on the RE are identical for the secondaries and smaller for the primaries. What you say about the front cover is not correct, (or I misunderstand), I have been using an rew front cover for a long time, I never tapped the missing bolt hole and never had a problem. If using an RE in an FD I would have to assume that one would be tapping out the mounts in the rear iron, and use an REW oilpan, the oil pans do not swap. The casting difference for the RE starter is a non issue and makes no difference.
Originally Posted by internal comsucktion engi
(Post 7751377)
This is not true....there are way more differences than runner size.
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I too have both apart in my garage.... You need to look closer at your secondary
ports on your RE. They ARE different in more than one way. And yes using an RE in an FD does require these changes. But it also requires you to run the front cover of the REW so the OMP work. In this case you DO need to drill and tap the front iron to except the extra bolt on the REW. On a side note: Its basically better to just run an s6 engine with RE plates and intake manifolds. :) -J |
I made a plexiglass template of all four ports for both engines, the rew and re port openings (not the runners) for the secondaries are the same.
the runners are bigger, but the rew runners can be ported out to match the re runners (the casting is the same in that section) infact 20B guys do this all the time, And I'll say it again, I have put many many miles on the engine, without the extra bolt hole tapped, there is one less bolt in the front cover, it makes no difference what so ever. All of the previous engines, including S5, S4, and the re had one less bolt in the front cover, so what. And finally, you would have to show conclusive proof (back to back dyno's) to prove to me that the larger manifold runners for the primaries only make any difference what so ever. The manifold runners on the secondaires of the rew are the same.
Originally Posted by internal comsucktion engi
(Post 7751460)
I too have both apart in my garage.... You need to look closer at your secondary
ports on your RE. They ARE different in more than one way. And yes using an RE in an FD does require these changes. But it also requires you to run the front cover of the REW so the OMP work. In this case you DO need to drill and tap the front iron to except the extra bolt on the REW On a side note: Its basically better to just run an s6 engine with RE plates and intake manifolds. :) -J |
Oh well I'm not saying it would be the down fall of your engine if you don't run the
bolt, Im just saying there IS an extra bolt hole and you SHOULD drill and tap it. Also the "ramping" in the port design of the RE is a lot less abrupt than that in the REW. Look again. Besides your absolutely right you CAN port the REW runners etc. to be just as good as the RE. -J |
thanks guys for the feedback.
sounds like there isnt much advantage of using the cosmo over the series 6, if i already have plans to port. probably wont be porting the runners now though, since that can be done at any stage afterwards without having to pull the engine and open it up. At least with the series 6, you get all the parts and can ultimately have two fully built motors to swap in and out as you wish. |
no, they mean the port runners in the irons. I remember about a year and a half ago when I had a cosmo iron next to the rew iron for comparison. The RE has larger/ taller port runners. If you port the runners larger on the REW, then just match your manifold ports to your new porting.
If for you plan on eventually using the RE manifolds for some reason, then you'll need to keep in mind that you will need to port your runners in your irons large enough for the RE manifold. If not, you'll have a "ledge" that "steps up" where the manifold meets the block. Or, I guess you could fill the upper and lower parts of the manifold ports with something and then port it to match the irons. |
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