I have a 94 wrx CDB engine with omega pistons running 9:1 CR. I am assuming that the higher compression ratio with give me a better Volumetric Efficiency, does anyone know the std VE at various rpm ie:-

2000
3000
4000
5000
6000
7000

how does the higher CR effect the VE and does anyone know of a rough way to work out increase in VE for 9:1 cr

cheers

 

At high boost, higher VE will give you a lower VE but a higher TE.

VE varies with boost as well as RPM, and is dependant on a lot of things.

I don't think anyone will have the answers to your question, but the way to find out is hours of time on a dyno with a MAF sensor and your engine tested in both configurations.

What exactly do you want to know? Is this a question about how much more/less fuel your new engine will need? The biggest changes in mapping will be the need to reduce the ignition advance at high loads, or run higher octane fuel.

Paul

 

Pavlo

I am trying to figure out how much torque/power benifit I have got using a higher compression ratio. Maybe I should have just ask if anyone has experinced any gains with higher CR. Would just like to know a rough increase in torque/power if any.

does the higher compression shift the power band lower down the rev range.

cheers

 

The VE isn't the thing that's really affected by CR changes. What you're doing is burning roughly the same mass of air and fuel in a smaller space, resulting in a higher cylinder pressure. So you will see noticeable gains in off boost and low boost performance. However, if you're considering running say 1.5 bar of boost on a 2.0 engine, you will have to reduce the ignition advance to stave off the detonation that higher compression will bring, the net result is an engine that is low on torque because you either can't run the boost or the ignition advance (relative to the ideal rather than absolute numbers) or both. Peak power may be different as enignes tend to be less prone to det at high RPM

If you were able to run high octane fuel and/or water injection, you would be looking at a different scenario, since you would be less limited but the constraints of boost and timing.

How much boost have you been running or would like to run?

Paul

 

The engine has just been run In and mapped on GEMS,

At the moment I am running 1.4/1.5 bar midrange and 1 bar at 6000 on optimax, Im going back on thursday for a remap. At this boost level the ignition advance was only a couple of degrees less than a std CR engine according to the mapper. I think the laptop showed 30 degrees advance unless I read it wrong. We took it to slight det then pulled it back 2 degrees.

I May use

1.4 bar @ 3000
1.5 bar @ 4000
1.6 bar @ 5000
1.5 bar @ 6000
1.1 bar @ 7000

This should give me a nice torque curve. The turbo has done over 130000 miles tho, maybe I should get it rebuilt and FE mod done. The last thing I want is the turbo to blow because I feel that the FMIC wont catch the bits of broken compressor blade.

What do you think.

 

Sounds like Steve's usual method, and he seems to like high compression himself. I would however say thay 6000rpm seems to be a bit of a sore spot when it comes to det resistance, sometimes a little lower RPM on the older engines, so you may not be able to just increase from 1 bar to 1.5 bar at 6000rpm. Comparing engines directly doesn't always mean a great deal, and to put those 2 degrees into perspective, you may find that costs you 15 to 20ft-lb in itself, which may be all you gain from the high compression. Cruise, off boost and low speed running will all benefit from the CR though.

The only person I know running 9:1 (9.35 I think) was Stan S and he dropped it back down to 8.5 to allow more power.

Paul

 

Thanks Pavlo

We did manage to run 1.7 bar all the way across the rev range, we will see what hapens when I get a remap, might see what advance we can get with a fullbottle of NF.

How much power did Stan S manage to get from his high compression before he had to start lowering it, I ask because I want to aim for 400 bhp maybe changing the turbo.

how am I limited with CR when it comes to turbo selection can I add a bigger turbo

 

Of course you can get a larger turbo, in fact your higher compression will allow better spool up. You may just be limited in the amount of boost you can run. A larger turbo will allow a better breathing engine, and your VE will improve aswell as the density of your inlet charge (depending on what parts of the turbo you enlarge). Stan was using a td05/06 20g turbo, and I think he made about 380 on the high compression engine, and 425 on the lower CR one. however he also improved the heads and cams between, and I'm not sure he even used the 20g turbo on the high compression engine.

Paul

 

I was thinking about using a td05/06 20g because I have the tdo5 which I can modify into td05/06 20g, was also thinking about the APS SR40 turbo, can you think of any other turbo that might work well in this situation.

cheers

 

td05/06 20g is your best value bet for 400hp. I wouldn't use one myself on the 2.0 engine though due to surge, some get better results than others, and I certainly wouldn't let my experiences alone deter you. The APS SR40 has a long history of not actually coming up with the results on customer cars.

Paul

 

what about the PE1820 who makes it, is this a good turbo, is it roller bearing

 

It's made by Power Enterprise, yes it's roller bearing, but it's not really much cop and is expensive. A td05/06 20g will spool up faster and give a higher power ceiling.

Paul

 

I dont favor the td05/06 20g because of surge problems you mentioned, It seams to be proving difficult to find a turbo to take my upto and aroud 400 bhp but still want to run a good amount of boost to get good torque figures. What about the ion p450?

APS no good
td05/06 20g surge problems
pe1820 no good
hks ?
blitz ?
IHI ?

VF range ? I hear they are too week for things like antilag

Do you know of any good turbo specialists who would be able to come up with a good turbo match.

 

Depends where in the rev range you want your boost and torque. I would think about the TD05H-18G as others have also suggested and a few are using - but with little published data.

You are going to need a compressor wheel/housing which gives a wide surge free operating range, mated to a turbine wheel/housing/bearing design that allows quick and early spool up to allow you genuine midrange grunt in any gear.

The TD05H-20G is slightly undersized on the turbine side and oversized on the compressor side. This means that you end up with surge, and a loss of top end power, but it does spool up early for a 400 BHP turbo. The TMI-141S tried to put in a different compressor wheel to avoid the surge which it did, but in so doing there were reliability problems, the compressor map wasn't rated for high boost, and it seemed to make less power than the 20G, and this was made by a turbo specialist.

The VF hybrids (that still use a VF core and turbine wheel) I've experienced seemed to not have the balance quite right either. The turbine side is more restrictive than the TD05H, and there seemed to be no gain in spool up. A plain TD05H flowed at least as much top end and spooled up noticeably better on the same car with crossover tests on the same day.

Some people prefer the iON P450 or similar sized Garrett/P20 hybrids on a 2.0. The published torque curves show torque peaks quite high up the rev range, so you need to decide if this is for you. I prefer full boost in 2nd gear by half of redline RPM if possible, and the iON approximately manages this, but on a 2.5 engine.

If I was doing a 2.0 now, I would go back to the TD05H-16G and run decent midrange boost with a strong gearbox and clutch to get the torque. Alternatively, the JDM twin scroll stuff (if you get all the bits = expensive) seems to spool up well and give good torque.

Interestingly, Evo's review of the FQ400 stated that they thought they would go faster across country with an FQ320 or 340 that spools up 1500 RPM earlier. That is on a car with far shorter pipework than most of us are using, and famed for its flexible power band.

You can of course consider a smaller turbo and prop it up using increased octane, or less practically for sustained road use, nitrous.

 

If you don't want the lag of a VF, or the surge of the 20g, then there is another combo I think would be worth trying

 

Thanks John,

I like torque and lots of it, I want to run high boost to give lots of torque from 3000 to 5500/6000, I would like to have torque in the reagion of 400 lbft+, but im not interested in top end power but would like somewhere upto 400bhp

I would quite happily run 1.8 bar with my engine internals. My higher compression helps with lag, and also have anti lag when I need to use it.

I want a higher torque figure than power.

 

Pavlo

Whats the combo you have in mind?

 

Paul's suggestion will be good I'm sure, but I think you're asking a lot to get c.400lbft from 3000 to 5252 RPM (where it would make 400 BHP) on a 2.0. A 20G on a 2.5 will just manage this. I would take 350 BHP and 400 lbft on a 16G on a road car myself. Maybe Paul can come up with a Mitsubishi or Garrett turbo that will have an edge over the 16G.

 

I would like peek torque at about 4000-5000. Maybe 400lbft was a bit over the top. 350+lbft might be more resonable. The lag on my td05 is acceptable, something with similar lag would ge fine.

how much torque can I get out of my TD05H-16G, what gains could I expect if I had it converted to front entry.

Can you tell me more about the TD05H-18G, is this the same as td05 but with bigger compressor wheel, will it take more boost? and will it give me more torque that im after

 

No need to stop at 350 lbft if your internals and gearbox can take it It is where you'll get your torque in the rev range. Front entry gains are small, I think you could run a nice inlet path whilst retaining it.

18G is a bigger compressor wheel, not sure if the 18G will or should shoehorn into the 16G housing, I think the diameter is similar to the 20G so probably best in the bigger housing. In terms of performance at boost levels, there are no public domain 18G compressor maps available on the internet.

The other one to think about is the 16G-large compressor wheel. Have a look at the compressor map compared to the small, could be quite good for very high boost.

 

Im getting confused with all these turbo sizes, lets get this straight

Is my std td05 a TD05H-16G?

is the 16G-large compressor wheel different from my std if so then

my STD TD05 has a 16G small compressor wheel?

so what your saying is put a 16G large compressor wheel into my std TD05?

 

Now you're getting the idea. I can't really make a specific suggestion as I have a vested interest. But if you are interested drop me a mail and we can discuss some options.

Paul

 

pavlo

YHM

 

The big 16G is good for midrange torque but its efficiency drops off sharply at the top end which will limit power.
For 400lb-ft on a 2.0 I wouldn't use any of the TD series as the compressors are just not designed to be efficient at the boost pressures required.

There is now no problem whatsoever with surge on the latest 20g's. You can run circa 1.4 bar from 3500rpm on a 2.0, this will allow around 400/420bhp on a good breathing set up with a splash of octane booster or 390 without.

Andy