Lock & Load

According to this tread getting more than 50hp of extra power from the renesis will be limited because of the fuel pumps and size of the injectors irrespective of what type of system of supercharging or turbocharging we use .

rotarygod:
The issue with more than about 50 hp is in the fact that the RX-8 fuel injectors can't go any higher. Even if we had larger injectors, we'd still need a larger fuel pump. There are dual pumps on the RX-8 and no return line. To add even more complexity, when you are getting gas, one pump reverses it's direction and sends fuel over to the other side of the tank. This is necessary because you gas tank sits on both sides of the transmission hump.

If you can tune it for 50hp, you can tune it for more. If you can't get any more fuel for more than this, now you've got a problem. This is why everyone is only claiming about a 50 hp gain at this point. Fix the fuel delivery issue and we'll see more.

Ajax:
So we need new injectors and 2 new fuel pumps to get an real power out of the engine? Great. We ought to redo the whole gas tank design anyway and throw away the transmission in exchange for something stronger while we're at it.

rotarygod:
Nope you've got 330 cc injectors. It least I think they are 330. If I'm wrong, I'm really close. It is 3XX cc something. The standard has 6 of them and the auto has 4.

Assuming my number is correct this would only put the total at 1320 cc for the auto an 1980 cc for the standard. As a contrast, the 2nd generation RX-7 Turbo II had 4- 550 cc injectors for a total of 2200 cc and the 3rd gen RX-7 had 2- 550 cc and 2- 850 cc injectors for a total of 2800 cc. Let's go farther...

On the Turbo II RX-7, if you were to get 85% duty cycle out of the injectors you'd only get about 269 fwhp. This number is according to the Rotary Performance fuel injector calculator. You can go higher than 85% duty cycle but it is really starting to work the injectors too hard and you risk getting one stuck open. If we take and plug in 6- 330 cc injectors we arrive at a total of about 242 fwhp. If we try this same number in the 3rd gen RX-7 fuel calculator it comes out at 254 fwhp. While it may not be exact for the RX-8, it is very close. Let's average it and just say our power potential with our stock fuel injectors at 85% duty cycle is around 250 fwhp.

Most people believe the RX-8 to be around 220 fwhp or so. This means we only have about 30 hp or so more safe potential for the fuel injectors for the RX-8. Since each of the RX-7 calculators gave me different readings and the Renesis is a little more efficient, we probably have more than this. Now we are getting close to that 50 hp more power mark that both Pettit Racing and Blitz are talking about. See ths issue now?!

The problem isn't so much a tuning issue anymore as it is a fuel issue. Now you know why!

rotarygod:
One of them would have to be modified to flow backwards when you are getting gas so that the other side of the gas tank fills up. It's not as easy as just swapping them out.

My solution to the whole problem would be to use a crossover tube (or 2) underneath the driveshaft that connects both sides of the tank at the bottom. This way fuel could flow across to the other side without the use of the pump. It would have to be removable in the event that the exhaust or driveshaft need to come out so some special attention would have to be made here. I don't think it would be that hard as long as AN lines were used and there was a shield around it. We could then replace each pump with new ones. I'd modify the fuel system to include a return line and use a conventional regulator. This would be alot of work but about the only way I can see that would make it possible unless someone designs a fuel pump that can duplicate the way the factory ones work.

Cheers
Michael

Zaku-8

I'm not sure if this is the right thread to continue rotarygod and ajax's thread, but


1) is the rx-8 tank a single tank with a high dividing wall (due to transmission tunnel) or is it effectively two separate tanks?

2) if single tank, then physics/chem/engineering majors feel free to counter-argue, but why not just use multiple narrow-diameter glass (for high surface energy) tubes to straddle the transmission tunnel? Would gasoline on either side of the tunnel then equilibrate by capillary action?

By glass I mean tempered or separate tubes connected by flexible tubular joints, because I'm not sure how much the fuel tank flexes. Hopefully not significantly.

Just as with Michael's suggestion, any fuel pumps could be used to replace stock

RXE16T

Too much boost + not enough fuel =

I think for any bolt on forced induction upgrade, 50hp gain is enough since any more than that and you run into serious problems.

If you really are chasing more than 50hp, you really should not only be thinking about solving the fuel problem, but also your upcoming drivetrain, cooling and engine problems.

I mucked about on my S14 200SX and got it to churn out 219kw (294hp) at the rear wheels.... which was fun to say the least, but your car does spend its time on the road, not on a dyno.

What wasn't fun was replacing 2 gearboxes, 3 diffs, 1 tailshaft and 1 melted piston, and that's on top of the other upgrades such as front mount intercooler, upgraded fuel delivery system, etc, etc..... the list goes on.....

Close to $20K on performance mods (and repairs) later, you're left with a car that runs the quarter in 12.8sec, but has fuel consumption bordering on 27-30L per 100km and was an absolute bitch to drive daily.

So, would I add forced induction to the 8?

Yes of course I would, I'll take a stress free 50hp gain any day over a ***** out 150hp gain simply due to reliablity and vehicle longevity.

So the moral of the story is, if you want to drive your 8 more then towing it, forget about anything more than 50hp gain.