Hello!
I have an S4 RX7 that has a bad motor. I think I found one here on this board I can use. However, it is an S3 6 port motor. That got me thinking about something else. I have access to an S5 motor that is in okay shape.
I have searched for this for awhile on teh interwebs, but didn't come up with anything definitive.
Can you bolt an S4 upper intake manifold to a S5 lower intake manifold (on an S5 motor)? I am aware (from looking at it) that one bolt hole is in the wrong location. I can fix this with a little grinding.
Is there any reason this wouldn't work?
I do not have any interest in getting the S5 VDI and intake to work. (It seems like a lot of trouble for small gains.)
Second topic: To eliminate the OMP on an S5 motor, can I just remove the OMP and put on a block off plate? OR do I have to remove the little driveshaft and everything?
Thanks,
Rob R.
the gaskets don't look drastically different on Mazdatrix website, but whitout having the two pieces in front of me I can't answer that question. However why would you want to do this anyway? Why not just use the S5 motor with your S4 intake system? I know that works,and I can't imagine that the S5 made all that big of a difference in the real world like you said. Blocking off the OMP is a common mod that a lot of people do,and just run pre-mix. I don't think you need to remove the driveshaft, or at least we didn't on my friends 87 race car.
The S5 motor has a port on teh block that appears to be EGr or something. This rectangular port is left uncovered by the S4 intake. I guess I could JB weld it or something.
If the car is an S5 with S5 wiring, removing the OMP will put the ECU in 'limp mode'. It has to 'see' the OMP. 'Limp mode' is retarding the timing and cutting the injectors, it's designed to allow you to get to the side of the road only.
I have heard of just plugging the OMP in and tie strapping it somewhere in the engine compartment.
If you want to block off the OMP, the driveshaft does not have to be removed.
On my setup, I used a complete S5 intake with an S4 front cover and mechanical OMP, then made a cable to operate the lever. I have heard of making a hybrid S4/S5 intake like you mention (S4 lower with S5 upper to get the VDC), but honestly don't understand why you would. I'd just swap the whole S4 intake onto the S5 and be done with it.
I know my friend has an s5 engine in his race car with the s4 intake system. I will have to ask him what was involved but my guess is it wasn't too bad.
Curmudgeon wrote:
If the car is an S5 with S5 wiring, removing the OMP will put the ECU in 'limp mode'. It has to 'see' the OMP. 'Limp mode' is retarding the timing and cutting the injectors, it's designed to allow you to get to the side of the road only.
I have heard of just plugging the OMP in and tie strapping it somewhere in the engine compartment.
If you want to block off the OMP, the driveshaft does not have to be removed.
On my setup, I used a complete S5 intake with an S4 front cover and mechanical OMP, then made a cable to operate the lever. I have heard of making a hybrid S4/S5 intake like you mention (S4 lower with S5 upper to get the VDC), but honestly don't understand why you would. I'd just swap the whole S4 intake onto the S5 and be done with it.
I run premix, so I don't need the OMP. Nothing on this car is S5 except the new engine.
How did you get the VDC to work with S4 electronics?
Why would you want to use the S4 intake over the S5 intake? The S5 intake is slightly better.
It's been a while since I've been around the RX-7 boards, but if I'm reading this correctly you're wanting to run an S4 computer, injectors, and sensors on an S5 motor. I think if that's the case then I don't think you'll have to worry about the OMP causing the computer to go into "limp mode" if you remove it.
But I was curious, didn't the S4 motor have a lower compression ratio than the S5? Something like 9.0:1 versus 9.5:1? With the S4 computer and injectors expecting the lower compression ratio of the S4 motor, would that be a cause to worry about detonation issues?
The S5 motor has higher compression rotors.
You can run an S5 block in an S4 car if you change the front cover and use the mechanical oil pump; that is what I did in my Turbo S5 in my user avatar.
If you've got an S4 computer, spending money on a RealTek chip is worth it.
If you're using a S4 ECU on a S5 N/A engine, what do you plan to do with the #5 and #6 intake ports? On the S4 they were operated by vacuum, on the S5 they were electrically operated. Are you just going to leave them open all the time?
I safety wired mine open on my S4, and my butt dyno never knew the difference. (new exhaust)
Okay, to reiterate, the questions are: Can I run an S4 upper intake manifold on an S5 lower? Do I need to do anything other than put a block-off plate where the S5 OMP was to remove it?
I am running premix. I am running S4 computer, injectors, sensors, everything. I don't care about emissions (because racecar).
The 5th and 6th ports will be wired open.
The reason for not running the S5 upper intake is the control mechanism to make it work. I am not spending money on rpm chips, air compressors, etc. I don't know how to make it work without some type of rube goldburgian method. Therefore, I will stick with the S4 upper intake.
In reply to Brett Murphy: I run an rtek computer in my TII swapped GXL. I am not sure if it would help in this situation (everything is stock components with no porting).
No worries about running the higher compression engine with the S4 electronics. These things run really rich anyway.
wvumtnbkr wrote:
Curmudgeon wrote:
If the car is an S5 with S5 wiring, removing the OMP will put the ECU in 'limp mode'. It has to 'see' the OMP. 'Limp mode' is retarding the timing and cutting the injectors, it's designed to allow you to get to the side of the road only.
I have heard of just plugging the OMP in and tie strapping it somewhere in the engine compartment.
If you want to block off the OMP, the driveshaft does not have to be removed.
On my setup, I used a complete S5 intake with an S4 front cover and mechanical OMP, then made a cable to operate the lever. I have heard of making a hybrid S4/S5 intake like you mention (S4 lower with S5 upper to get the VDC), but honestly don't understand why you would. I'd just swap the whole S4 intake onto the S5 and be done with it.
I run premix, so I don't need the OMP. Nothing on this car is S5 except the new engine.
How did you get the VDC to work with S4 electronics?
I didn't. I used a cheapie compressor and an RPM switch to supply pressure to the 6 port actuators and stuck the VDC open in the high RPM position. Works OK that way. The 6 port does have a bigger effect on low RPM torque than the VDC does, I tried them wired open/shut in all different combos till I settled on the one I use now. With the 6 port wired open the engine lost a good bit of bottom end and idled poorly.
wvumtnbkr wrote:
Okay, to reiterate, the questions are: Can I run an S4 upper intake manifold on an S5 lower? Do I need to do anything other than put a block-off plate where the S5 OMP was to remove it?
Since you're running an S4 ignition, ECU, etc. that's all you should have to do.
I'm really not sure about the s4/s5 intake question... I messed with turbo stuff and kept my N/A stuff pretty stock.
My take is if the bolts line up and the gaskets will work, it should be fine.
Bolted it up last night. Everything fits just fine.
Thanks for your help guys!
Rob R.
