RX 450H Engine Power difference

[stecko]

Hi Guys

 

I'm thinking about rx450h (2014)...but just noticed, that rx450h has 249hp from petrol engine. Same engine in gs450h has 292hp from petrol engine only. Why so big difference between this two? If this is same engine, where is difference? Is just software/ecu changes or something else?

I must admit an extra 50hp would be very handy in heavy rx450h...

 

Thanks

[olliesgrandad]

Don't forget the RX450h has 2 electric motors. 

There is ample power available in the RX450h. 

 

[stecko]

Yes, I now, but total power is 292hp in rx450h and 336hp in gs450h. Where is difference? :) Same engines...

[olliesgrandad]

I thought RX450h was 305 bhp. 

I wonder what the torque figures are? 

 

[BROUWERS]

From Wikipedia:

"For the Lexus RX 450h, the compression ratio was 12.5:1. For the Lexus GS 450h, the compression ratio was 13.0:1."

https://en.m.wikipedia.org/wiki/Toyota_GR_engine#2GR-FXE

[Britprius]

7 hours ago, BROUWERS said:

From Wikipedia:

"For the Lexus RX 450h, the compression ratio was 12.5:1. For the Lexus GS 450h, the compression ratio was 13.0:1."

https://en.m.wikipedia.org/wiki/Toyota_GR_engine#2GR-FXE

Those figure are theoretical compression ratios not actual. The hybrid holds the inlet valves open for part of the compression stroke reducing the actual compression ratio. This give short compression, and long expansion strokes as in the Atkinson cycle engines. Normal engines have the same compression, and expansion strokes "the Otto cycle"
Long expansion strokes make the engine more efficient by allowing more of the expansion of the burning gasses to push on the pistons for longer.

If the compression ratio was as high as 13:1 the engine would run on diesel.

John. 

[Britprius]

Correct me if I am wrong, but I thought the RX450H engine is the belt driven cam engine while the GS450H uses the chain driven cam engine with both direct, and indirect injection. This would explain the difference in power output.

John.

[Lager shandy]

I think your find the max power of the rx450h will be 492 bhp if set up to give max power to the motors with fully charged Battery . I would say not for very long but it's able to produce this power with a torque figure of 508 nm

engine 265 bhp

front motor 165 bhp 

rear motor 68 bhp 

But of course it set up to produce only 308bhp .would be interesting to see if some could unleash the full potential

[Britprius]

7 minutes ago, Lager shandy said:

I think your find the max power of the rx450h will be 492 bhp if set up to give max power to the motors with fully charged battery . I would say not for very long but it's able to produce this power with a torque figure of 508 nm

engine 265 bhp

front motor 165 bhp 

rear motor 68 bhp 

But of course it set up to produce only 308bhp .would be interesting to see if some could unleash the full potential

Unfortunately you cannot just add all the power sources together as the engine needs to drive the split power devise at one end to give an output at the other. In effect the power split device is like a differential. The prop is driven by the petrol engine one output shaft goes to the wheels via another diff "the axle diff". The second output goes to MG1 acting as a generator. Only when MG1 is producing electricity does first output driving the diff have any turning force. So the power from the engine is split between driving the wheels, and driving MG1. The output from MG1 can be fed to MG2 acting as a motor which is also used to power the wheels via the diff. 
The Battery can only supply a limited current as can MG1 it being about 1/3 the size of MG2.  Not enough even combined to power MG2, and the rear motor "could be called MG3" this would require a combined output of 165 HP "not BHP" plus 68 HP or 233 HP in electrical terms (746 watts = 1 HP) so power from the Battery, and MG1 would need to be 174,000 watts (174 KW). The HV Battery is rated if I remember correctly at 1.2 KWH, but even then it's rated maximum current is 100 amps giving it a maximum output of 28 KW.
Complicated I know, but this is why the figures literally do not add up to 492 HP.

John. 

[Lager shandy]

 ha ha sorry I new that would get you going lol

 

[Lager shandy]

I'm going to put a super charger on mine .the ad on eBay promised 100bhp increase from the little fan motor you put in the air box .

[Barry14UK]

10 hours ago, Britprius said:

Correct me if I am wrong, but I thought the RX450H engine is the belt driven cam engine while the GS450H uses the chain driven cam engine with both direct, and indirect injection. This would explain the difference in power output.

John.

Maybe it depends on the year but I am under the impression that the later 3rd Generation RX450h cars are chain rather than belt drive. The Wiki ref seems to infer that the Lexus do their rating with 91 octane fuel whereas most of us use 95 or 97/8 fuel which should produce more power.

BHP for the 4th generation seems to have been increased along with improved petrol consumption (possibly a lower drag coefficient  could have helped the latter?) but acceleration and top speed don't seem to be much different.

With the shape and weight of an suv it would be necessary to obtain a huge increase in power to gain a really significant increase in speed and acceleration and you are looking at diminishing returns. 

[Britprius]

3 minutes ago, Barry14UK said:

Maybe it depends on the year but I am under the impression that the later 3rd Generation RX450h cars are chain rather than belt drive. The Wiki ref seems to infer that the Lexus do their rating with 91 octane fuel whereas most of us use 95 or 97/8 fuel which should produce more power.

BHP for the 4th generation seems to have been increased along with improved petrol consumption (possibly a lower drag coefficient  could have helped the latter?) but acceleration and top speed don't seem to be much different.

With the shape and weight of an suv it would be necessary to obtain a huge increase in power to gain a really significant increase in speed and acceleration and you are looking at diminishing returns. 

Hi Barry. It is unlikely that using higher octane fuels will increase engine power unless the engine is specifically tuned for them. The reverse is more likely because higher grade fuels contain less calories not more, and it is the calories that govern the energy content of fuels. Fuel companies however would have us believe the reverse is the case.
Ethanol raises the octane rating of petrol, but it also lowers the MPG.
As in my previous post I was not sure if the RX/GS engines were the same, but I had seen posts on LOC about cam belt changes on the RX, but that could be on earlier versions. Do you know if the later RX engine has dual injection as does the GS as this could well explain the difference in output power?

John.

[Barry14UK]

Hi John,

Well the RX450h has quite a high compression engine which means that with a higher RON petrol it can run with more advance without pinking, thereby producing more power.  Conversely, if you lower the RON the engine will (automatically be retarded and produce less power).  I once had a fuel injected Mercedes where you could manually retard the ignition to help cope with lower octane fuel, higher octane not being available in some countries.  I remember on a BMW forum some years ago there was an in depth  discussion on fuels and it was considered that the Shell V3 high octane gave slightly more power and ran cleaner and many members ran it from time to time due to the better ability of the additives. Clearly, there is greater advantage in using higher octane fuel in cars with higher compression engines.  I think this puts it reasonably without being technical -   https://www.moneysupermarket.com/car-insurance/articles/is-it-worth-paying-more-for-premium-unleaded/

"Higher-octane fuels suit high-performance engines where pressures and temperatures are greater and it can therefore be used to boost the amount of available horsepower and improve performance."

From what I have read the RX400 had cam belt but the RX450h chain.

Not aware of the method of fuelling the RX models but happy to learn.

[stecko]

My old rx350 ( very similar engine 3.5 v6 to 450h) has a chain, so I think all 450h (rx/gs) have a chain.
Rx450h with ~350hp wpuld be a nice toy:)

[Britprius]

Hello again Barry.

While I agree that engines with high compression ratios can benefit from high octane fuels it is also required that the ignition timing is also advanced somewhat. The ignition basic timing is set in the ECU of Lexus cars, and cannot under normal circumstances be changed. The ECU has no ability to advance the timing if different fuels are use to that recommended by the manufacturer there being no octane sensor in the fuel system. The ECU does have the ability to retard the ignition if it detects knock from low grade fuels "below specification"
We do not know what the real compression ratio of the hybrid engines is, and it is almost certain it is variable depending on the intake cam timing. I suspect the ratio is around 9:1, but have no definitive proof or figures for this.
I can say in my GS450H I get no measurable or noticeable performance improvement by using high grade fuels, but I can definitely state my MPG goes down if such fuels are used. If high grade fuels improved MPG this would also reduce pollution. The manufacturers would then specify the fuel accordingly to possibly lower road VED making the vehicle more sale-able. There would also be in the case of the GS450H the real kudos in braking the 300 HP figure for the engine my handbook for the 2007 version showing the power output for the engine to be 298 HP. So the improvement would only need to be 0.6% to achieve this.
There "may" be some cleaning advantage to using the high grade fuels with cleaning additives, but no more than adding fuel additives to lower grades and this would only require the occasional tank of fuel to be of benefit. This does depend on the engine configuration somewhat. Direct injection engines not benefiting much at all only cleaning the injectors, and exhaust valves. Port injection engine will benefit from having the inlet valves cleaned along with the injectors, and exhaust valves.

I will do some research on the RX engine regarding the type of injection used.

John.

[Jaystar77]

Just looked at (what I hope are the correct) engine specs and you can see whilst both engines are based on the 2GR, the GS uses the 2GR-FSE and the RX uses a variation of it, the 2GR-FXE.  Most likely that the characteristics of both engines have played a part in their selection.  Probably find that the higher compression RX unit delivers more usable power across the rev range compared to the GS which has been tuned for a higher overall output.

Looking at the cubic capacities, bores and strokes I'd guess the pistons are the only physical difference between both units.  Anyone had both apart to know for sure?

I've no hybrid experience but the electric motors will also play a large part in power delivery.  GS has 1 and the RX has 2.  

Would be nice if we could find some dyno-graphs to show how the engines perform on the rollers 🙂

Here's the specs I was running off:

 

https://media.toyota.co.uk/wp-content/files_mf/1372844679LEXUSRX450hTECHNICALSPECIFICATIONS130211M.pdf  (RX450H)

https://media.toyota.co.uk/wp-content/files_mf/1319280368tech_spec.pdf (GS450H)

[Britprius]

Hello Jay.

Thanks for trying to find the differences between the two engines.
I did note only the GS is listed as having dual injection the RX does not. Whilst the compression ratios are listed as 12.5:1 & 13:1 these are the theoretical calculated compression ratios "bore times stroke". This is rather than the actual where compression starts with the valves held open on part of the compression stroke reducing the figure significantly. It is likely however that the RX does have a lower compression ratio. 
The GS also has maximum power at 6500 RPM against the RX at 6000 RPM.

Although only listed as generators in those specifications all of the electrical units are motor generators meaning they perform both operations. This means the GS has 2 motor generators, and the RX has 3. The "generators" in question also act as starter motors.
The GS also has a two speed reduction in the transmission to reduce the speed of MG2 not listed in the RX. This enables the use of lower RPM in MG2 from around 70 MPH increasing it's torque output. The torque in electric motors falls off as it's speed increases. Maximum torque is at zero revs. Somewhat opposite to the petrol engine.

I also noted the towing capacity of both vehicles is the same at 2000 KG.

John.

[stecko]

Hello Jay.
Thanks for trying to find the differences between the two engines.
I did note only the GS is listed as having dual injection the RX does not. Whilst the compression ratios are listed as 12.5:1 & 13:1 these are the theoretical calculated compression ratios "bore times stroke". This is rather than the actual where compression starts with the valves held open on part of the compression stroke reducing the figure significantly. It is likely however that the RX does have a lower compression ratio. 
The GS also has maximum power at 6500 RPM against the RX at 6000 RPM.
Although only listed as generators in those specifications all of the electrical units are motor generators meaning they perform both operations. This means the GS has 2 motor generators, and the RX has 3. The "generators" in question also act as starter motors.
The GS also has a two speed reduction in the transmission to reduce the speed of MG2 not listed in the RX. This enables the use of lower RPM in MG2 from around 70 MPH increasing it's torque output. The torque in electric motors falls off as it's speed increases. Maximum torque is at zero revs. Somewhat opposite to the petrol engine.
I also noted the towing capacity of both vehicles is the same at 2000 KG.
John.

[emoji106]

[Barry14UK]

Thanks to those who have contributed and researched. The electric motors and Atkinson Cycle where employed add further possibilities to the variables that enable an engineer to tailor a basically similar engine/transmission system for different models. I appreciate that even with all the refinements that enable modern engineers to optimise performance, the timing is normally set at maximum advance and only retarded where circumstances require as lower grade fuel would be an example. 

Something that was not available years ago before management systems is the ability to gain more performance by having you car 'chipped' .  I wonder if anybody will admit to having this done and if so what difference has it made?