I was wondering what exactly makes the power differrence. Is it just the port matched exhaust, different Fuel curve ?

 

Lighter rotors, larger turbo and wastegate, better intake manifold ports, higher compression, and a few other little bits and pieces..

- Kevin

 

Lighter rotors don't add power, and the turbo isn't actually bigger, just differently configured. The wastegate won't add power either.But these will add a bit of power. However the bulk of the power comes from the fact that peak boost was raised from 6.6psi to 8.2psi. This is an 8% increase in absolute manifold pressure, and peak power is 10% higher, so most of the gain seems to have come from the extra boost.

 

The twin scroll is gone in the S5 which allowed them to make both ports in the turbine housing the same size, which probably flows a bit more..
The S5 apparently has a slightly larger a/r than the s4 turbo, which makes it a better choice for hybriding along with its larger wastegate port.
The intercooler piping is about 1/4 larger on the S5, the cores is slightly larger, the internal tubing is larger as well..
I would think everything adds up together to make the power, and do it in a manner which would still pass emmissions..Max

 

Too bad they turned it into an overweight pig.

 

Any way to Set up a S4 motor to the S5 specs, besides changing the compression ratio of course. But to rasie teh boost, shouldn't a Re-chipped ECU do that ? and of course i could port the Intake, Port match the exhaust, TID mod, and TB mod, But would this get me close to or above 200hp ? i would really like to start with 200hp before buying majors upgrades, i hope to see 340 hp (atleast) by mid next summer.

 

It mainly came from more boost...same with the FDs.

 

lighter rotors will "add" hp in a way. not really making more hp but creating a more efficient motor and allowing more of the power to get to the wheels....

Justin

 

Ohh i c, Could i install a S5 ECU into a S4 ?

Sorry for the late reply i been gone all day at work

 

not without changing the wiring harness too. its different on the 89+ cars. BTW a chip wont raise boost on the RX7. the wastegate isnt electronicaly controled by the ECU. youd need a boost controler to change boost. and boost creeps up on its own when you free up intake and exhaust.

 

The S5 IC has been measured to have only 5% less pressure drop than the S4 one, which would only be worth a couple of hp at best.

 

If your girlfriend put on 4% more weight, would you call her an overweight pig too?

 

lol

It's to my understanding that a bit of the weight was from thicker sound deadening.
The S5's generally had larger wheels than their s4 counterparts.
I know the interior material (radio surround, and vents and whatnot) where of a different material (i think a soft covering, not as brittle as s4 plastic, and I think maybe not as glossy)
But I still can't see where more of that extra weight came from. They where about 150+ lbs heavier than their s4 couterparts, right?

 

Guys, as for the HP increase, its all about the boost levels.

7,5 instead of 5,5, and fuel-cut at 8,6 instead of 6,5 (all that in psi, ain't I the gentle one ? )

2psi increase is a full 15% increase. A 0,5bar increase in CR is also a 5% increase in power output (roughly). So, here are your first 35HP right away. As for the rest 5HP, I'll let you decide what upgrade produced them

 

Read the FSM. Boost is 6.6psi for the S4 and 8.2psi for the S5. Fuel cut is at 8.6psi for all. You can't divide gauge pressures, only absolute pressures. So 6.6psig to 8.2psig is really 21.3psia to 22.9psia, or a 7.5% increase. Power went up 10%, so the rest came from the slightly better flowing components and the higher CR. CR is a ratio, not a pressure. It increased from 8.5:1 to 9.0:1. But this 6% increase doesn't mean 6% more power, because the relationship between CR and power isn't linear. The higher you go, the smaller the increase in power.

 

where do you look on the engine to find out if it's an S4 or S5 motor? where do i look to find the engine code? thanks!

 

I just couldnt let this one slide

From TeamFC2S:

5.5psi Stock Boost for 1987-1988 Turbo II (6.2psi max peak)
7.5psi Stock Boost for 1989-1991 Turbo II (8.6psi max peak)


You were correct about the universal fuel-cut point though....

Your second point is mute too, because my statement was right all along. I'll give you the fact that you have to use absolute pressures, but 1+0,4=1,4 and 1+0,6=1,6, so instead of a 50%, you actually get a 15% (which was my claim all along )

I know that a 5% increase in CR does not necessarily result in a 5% increase in HP output, but the law of gases PV=nRT still applies. And since the chemical energy does transmute to kinetic energy minus the difference of the losses due to energy turned into heat, this increase in CR pretty much equals a similar increase in HP output

 

i thought the sreies 5 came with an electronic wastegate control.

its tickling the back of my mind so im not 100% sure.

 

The '89-91 turbos do have simple boost control by the factory ECU - it's just a basic bleed of pressure to the wastegate diaphragm by a solenoid. The 3rd gens use a very similar method. Unfortunately, it's really only good on a stock car - as soon as you start modifying the car, it lends itself to boost creep VERY easily.

To the original poster, 200 HP to the ground in a TII is SUPER easy to do on the early or late cars. The only advantage the later cars have is -

- slightly better ECU (which could be retrofitted to an early car, but would be a MAJOR pain, and I don't think anyone's attempted it)
- Higher compression rotors
- Better castings on the iron housings, esp. around the dowel pin seats
- Far better turbine housing on the turbo (which can easily be retrofitted to an early car)
- Better intake manifold
- Marginally better stock intercooler

This is all talking about power production, BTW.

Dale

 

After reaching peak boost, a stock car will fall to the 5.5/7.5psi figures. But the peak figures from TeamFC3S are wrong. Read the FSM. S4: 6.65psi. S5: 8.25psi. And it's these figures that are more important when discussing peak power. Sorry man, but your maths is a bit off. I presume those figures are in bar? You've rounded them a lot in the conversion from psi to bar. Using the lower boost values, they should be 0.38bar and 0.52bar. Plus, atmospheric pressure isn't quite 1bar (there's a 0.2psi difference), so it's 1.01bar. (1.01+0.52)/(1.01+0.38) = 1.10, or only a 10% increase in absolute manifold pressure. I still say you should compare peak boost figures, which gives the 7.5% increase I claimed before. Where'd you get 50% from? OK. I was being a bit pedantic. I can't find it, but I have a formula somewhere that gives the relationship between CR and the amount of power that can be extracted from it. Around 8-9:1, you get a bit less percentage increase in power from the same percentage increase in CR. Over 10:1 it tapers off sharply, which is why you don't see anyone pushing past ~10.5:1. It costs heaps, but the gains are very small. And that's if you can find a suitable fuel!

 

I wont discuss the first point, because a) I forgot what we are arguing about , and b) the increase in HP comes from this increase in boost pressure levels in any case.

As for the second one: I didnt use exact numbers, cause I'm doing these calcs while I'm at the office . I got 50% from comparing 0,4 to 0,6, and 15% when comparing 1,4 to 1,6 (in order to illustrate). Same principle and formula applies to the -more accurate- boost pressure levels on S4 and S5. You are correct, but so was I, because I claimed a 15% increase from the start (without actually explaining why its 15%). I just said that 2psi is a 15% (which is correct, give or take some decimals).

As for the third point, I must admit that I havent gone that far into energy conversion/losses formulas for internal combustion engines, but the universal law of gasses is.....well, exactly that: universal . If you increase the volume ratio by reducing the final volume (9:1 instead of 8,5:1), then you get a *minor* increase in temperature, but almost 90-95% relative increase in pressure, which results in an almost direct increase of the potential of the chemical energy (O2 + carbon chains in fuel). Thats where I got my 5% (could be 4,95, could be 4,85 )

And my math is off ? That comment, for a guy who had at least 7/10 in 2nd/3rd/multiple degree Partially Differentiated functions, multiple degree Integrals, and multi-plane Algebrae while in University, can be considered an insult....luckily, I'm also a very nice guy

 

OK, your maths may be fine, but in this case your engineering isn't.
You can't divide gauge pressures to get a percentage change. Guage pressures can go below zero, so the numbers you get from dividing them are meaningless. (This applies to any measurement that can have a negative value, like degC or degF.) For calculating changes, absolute pressure is the only number that can be considered. A marketing guy will tell you boost increased 15%, because it sounds better. An engineer will tell you it increased 7.5%.

 

Luckily I'm an Electronics and IT Engineer as it says in my diploma's title, so I'm also an engineer...

And its not fair picking the initial values that suit your calculation better A 2psi increase using the 5,5/7,5 gives a totally different percentage than using the 6,6/8,2 values. Even so, using your prefered values, you arrived at a 10% increase, and not my 15% (which is based on the "normalized" pressure levels).

In any case, I'm out, going to pick up my Rex. I can continue this in order to justify my calcs tomorrow, if you'd like...