Hi-flowing vs new turbos?

[Lepperfish]

What other modifications did you do at the same time as the turbo upgrade?

Wait........ Are you crediting your high-flow for the "responsive off boost"???

No, just the way the car drives off boost with that turbo on the car..

[Merli]

No, just the way the car drives off boost with that turbo on the car..

Wait... Do you have a GTS-t or a GTR? This discussion is about GTRs...

If GTR, you never said what other modifications you did at the same time as the high-flows that might boost bottom end response

[Lepperfish]

Gts-t

[Merli]

Ahhhh... I think the GTS-t will be less susceptible to changes in turbo setup, and because they're so quick to spool up anyway, a small gain or loss in turbo boost threshold will have minimal effect.

The GTR, with it's entirely too laggy standard setup would definitely be less driveable as a street car with even 500-1000rpm more lag from a bad turbo choice. Fine for track, but a 5000rpm boost threshold doesn't make a street-friendly car IMHO.

[bendertiger]

Rule of thumb, the smaller the turbo, the quicker it spools, the bigger the turbo, the more power and the longer it takes to spool, of course, there are MANY variables in this equation but rule of thumb

[Roy]

Fine for track, but a 5000rpm boost threshold doesn't make a street-friendly car IMHO.

Even on the track i think that will be too high. Im chasing a few hundred rpm improvement as i dont want to have go back to 2ng gear on tight corners like turn 8 Eastern or final turn Wakefield.

As when throwing it back to 2nd gear you tend to wash off corner speed and also makes throttle application a whole lot more important so as not to upset the chassis balance.

So my opinion only, but if it aint any good on the street then it aint going ot be a whole lot better for the track, unless by track you mean drags

[Merli]

Yeah, well I meant drags on that comment...

For circuit work, you want torque from as down low in the rev range as you can get it Peak powah means nothing

[Roy]

...Peak powah means nothing

Hey us 2L boys have to learn to love the kick in the ass and scream at high revs.... it may not be the quickest approach but is plenty of fun

[Sydneykid]

Hi Merli, I agree but with a slight clarification I finished a 20 minute race last weekend and the car never had less than 4,500 rpm on it for the whole race according to the data log. What I want is the highest average power from that 4,500 rpm to the shift point, which in my case is 8,000 rpm. I don't really care what the power band is like under 4,000 rpm, I allow the extra 500 rpm for when I get baulked in the corners by a slower car.

If I have to sacrifice 50 bhp at 3,000 rpm to pick up 25 bhp at 7,000 rpm then I would do it every time. But only as long as the average power (from 4,500 to 8,000 rpm) didn't suffer as a result. With a close ratio gearset I could narrow that down, eg; the RX7 has a close ratio Guru dog box and it never gets below 7,000 rpm with a 9,500 rpm shift point. The Primera SuperTourer is even closer, its l;ike 6,500 rpm to 8,000 rpm with its 6 speed, close ratio, sequential dog box (Xtrac). :wassup:

Its all about matching the power band to the gearbox and diff ratios, or vice versa.

[Merli]

Yep, I absolutely agree with everything you said in that post

ESPECIALLY about matching gear and diff ratios to the powerband of your engine, something I think a lot of people understand, but..........

Unfortunately for most drivers on here, [i'm guessing that] we don't have the budget or the luxury to be changing gearsets to more suitable ratios just for the occasional trip to the race track Although I love circuit racing, and will take my car to the circuit as often as my wallet allows, I have to keep in mind that at the end of the day, it is still 90% a road car... And as a road car, I'd like as much torque down low as possible, as that's where my engine will be working for literally 80-85% of it's working life. That makes the decision to sacrifice the 50hp at 3500 rpm for 25hp at 7000rpm a little harder

But for the race cars like you deal with, it's absolutely true that a nice meaty 4000/4500 -> redline powerband and suitable close-ratio gearset would be ideal

[Sydneykid]

Yep Merli I understand what you are saying, but I believe the reverse is more applicable here. If it's not a race car, then don't match the gear ratios to the engine, match the engine to the gear ratios. So many people pick an engine spec that simply does not align with the rest of the car and then they are dissappointed with the results. Hence you have cars that SHOULD run 11's, ACTUALLY running 13's. Maybe they would be better off spending less money in total, but with an engine spec that matched the rest of the car and running 12's.

My own car has a standard RB25DET gearbox with its standard ratios, a standard R32 GTST diff ratio and runs 17 X 8 wheels with 245/45/17's. So I chose an engine spec that suites those ratios. I could have easily built an engine with 150 bhp more max power, but the average power would have been screwed and it would in fact be slower. :bonk:

So getting back to the topic of this thread, it is important to choose a turbo spec that matches what you want to achieve (road, race or drag) and what the rest of the car is going to be. I happen to like the ball bearing hi flow spec (as supplied by GCG) for a combo car (lots of road, few circuit and some drag), it matches the rest of the car nicely. There are few others around, I recently tried a car with an AVO supplied turbo and it felt just as good.

Knowing what you want and matching the whole package is the trick, it separates the cars that SHOULD, from the the cars that DO.

[Merli]

Yep Merli I understand what you are saying, but I believe the reverse is more applicable here.  If it's not a race car, then don't match the gear ratios to the engine, match the engine to the gear ratios.  So many people pick an engine spec that simply does not align with the rest of the car and then they are dissappointed with the results.  Hence you have cars that SHOULD run 11's, ACTUALLY running 13's.  Maybe they would be better off spending less money in total, but with an engine spec that matched the rest of the car and running 12's.

Wow, definitely a valid point, and I wish I knew how to do that Unfortunately I don't really know how to translate gear ratios -> powerband

With the following being the ratios of the R33 GTR box, how does one calculate where you should be aiming to be making your power?

1st 3.214

2nd 1.925

3rd 1.302

4th 1.000

5th 0.752

Final drive 4.111

[chops]

http://www.quaifeamerica.com/

Select "downloads"

Then download QSpeedCalc.exe

Will show rev drops on gear change and a whole lot of other useful stuff.

[Merli]

Sydneykid?

I'm actually very interested in learning how to calculate rev drops and powerbands from gear ratios

I like to know the theory and mechanics behind things, not just plug numbers into a "magical calculator", but thanks chops

[Sydneykid]

Sydneykid?  

I'm actually very interested in learning how to calculate rev drops and powerbands from gear ratios

I like to know the theory and mechanics behind things, not just plug numbers into a "magical calculator", but thanks chops

I have had a few PM’s about this topic, so I hope this thread can be easily referred to later on. The basic problem seems to be a number of people are disappointed with their results, I quite often get asked stuff like, ”my car has 300 rwkw and yet I can’t do the times that a 250 rwkw car is doing”. When I dig deeper I find that no consideration was given to matching the power characteristics of the engine with the rest of the car, most particularly its gearing. :thumbdwn:

The principle of matching engine power curves to gearbox ratios is based on ensuring that you don’t end up with an engine that has a power band that does not match the gearing. The most common limiter is usually the first and second gear ratios. ie; the other ratios in the gearbox are usually closer together than 1st and 2nd. :idea:

The basic formula is pretty simple;

Engine rpm

divided by

the gear ratio

= gearbox output (or tailshaft) rpm

divided by

the diff ratio

= diff output (or driveshaft/axle) rpm

multiplied by

the circumference of the tyre

multiplied by

60 (minutes in an hour)

divided by

1,000 (metres in a kilometre)

= kph

Let’s try a simple one………….

7,000 rpm engine

divided by

1st gear ratio 3.4

= 2,059 rpm gearbox output (or tailshaft) rpm

divided by

4.11 diff ratio

= 501 rpm diff output (or driveshaft/axle) rpm

multiplied by

2.0 m (circumference of a 245/45/17 tyre)

multiplied by

60 (minutes in an hour)

divided by

1,000 (metres in a kilometre)

= 60 kph

So in this particular car you are doing 60 kph at 7,000 rpm in first gear. At the time you change into 2nd gear the speed is the same. So what rpm does the engine drop down to? :confused: Basically, we just use the formula in reverse;

60 kph

Multiplied by 1,000 (metres in a kilometre)

Divided by 60 (minutes in an hour)

Divided by 2 (circumference of a 245/45/17 tyre)

Multiplied by 4.11 (diff ratio)

Multiplied by 2.2 (2nd gear ratio)

= 4,250 rpm

This means you have to have an engine that has a power band at least 2,750 rpm wide ie; has good average power from 4,250 to 7,000 rpm.

Changing the diff ratio does not help this, nor does changing tyres sizes, regardless of KPH, the gap is always 2,750 rpm. This is because the diff ratio is the same for 1st and 2nd gears, ditto the tyre diameter. The only way to make a difference is to change the gearbox ratios by making 1st gear ratio higher (numerically) and/or second gear lower ie; make the ratios closer together.. Hence the term “close ratio transmission”, or in Janglish “cross mission”. :headspin:

Hope that answered the questions.

[Cubes]

hehehe

Gary,

What about when you run more boost?? doesn't that give you a higher speed in each gear

Lol the bloke who started that old thread was definitely strong headed.

[Merli]

That seems simple enough... Cheers!

But after a bit of simple maths, I've worked out the revs drop for each gearchange for an R33 GTR

Gear Change Rev Drops (rounded for simplicity)

1st-2nd 3410rpm (8500rpm -> 5090rpm)

2nd-3rd 2750rpm (8500rpm -> 5750rpm)

3rd-4th 1970rpm (8500rpm -> 6530rpm)

4th-5th 2110rpm (8500rpm -> 6390rpm)

So R33 GTR owners should be aiming for a powerband between 4500rpm -> redline (taking into account poor drivers holding you up)... Is that right?

Makes sense... I can understand why people consider GT2530s perfect track turbos for the GTR, since that pretty much fits the required powerband prefectly!

Very interesting, thanks!

[Sydneykid]

That seems simple enough... Cheers!

But after a bit of simple maths, I've worked out the revs drop for each gearchange for an R33 GTR

Gear Change Rev Drops (rounded for simplicity)

1st-2nd 3410rpm (8500rpm -> 5090rpm)

2nd-3rd 2750rpm (8500rpm -> 5750rpm)

3rd-4th 1970rpm (8500rpm -> 6530rpm)

4th-5th 2110rpm (8500rpm -> 6390rpm)

So R33 GTR owners should be aiming for a powerband between 4500rpm -> redline (taking into account poor drivers holding you up)... Is that right?

Makes sense... I can understand why people consider GT2530s perfect track turbos for the GTR, since that pretty much fits the required powerband prefectly! :D

Very interesting, thanks!

You got it

[Roy]

So Merli, are we looking for a new set of turbos now ...if you are makign the power you need lower in the rev range then thats cool, you get to look after those bearings etc etc by not usign so many revs...he 7,500rpm is still plenty

[Merli]

Nah... I'll stick with the GT-SS for now and see what I can get them to do... If I later decide that I want to move the GTR into more of a track car, I'll sacrifice bottom end response for that perfect track powerband and bolt on some GT2530s

Notice I said "Makes sense... I can understand why people consider GT2530s perfect track turbos for the GTR, since that pretty much fits the required powerband prefectly!"

I still stand by my claims that the standard GTR is too laggy for street driving, and that if the GT-SS can reduce the boost threshold/lag/whatever ppl are referring to it as today down to 3000-3500rpm, that's a better setup FOR STREET than GT2530s