Turbo Vs Gearbox

[Trip]

Since started racing i always considered the gearbox's i used are too high ratio. After a chicane i was ending up exiting in 2nd gear and just wait for the turbo to spool . The other option is to put it in first but that needs more precise(syncronized) gear change and if not done right, time can be lost.

So i was looking into a GT2860RS turbo to help reduce the spool when exiting in second gear. Since then I managed to get hold on a Close ratio gearbox with similar gears ratios of an RB box. This "should" help me select that missing gear i always craved for between 1st and 2nd. It should also shift my usable rpm higher up the rev range.

Now my question is, should i still consider a GT2860RS or get a bigger turbo to shift power band in the top RPM range ? I am not after BHP numbers, I am mainly after response and area unde the torque curve where i need it most.

 

[skiddusmarkus]

Try with just the new gearbox alone 1st and see how you feel.If you change 2 things at once you won't know which made a difference.

 

[campbellju]

I agree

 

[whytie]

I agree also I just fitted my rb box last week and on standard turbo standard boost I have virtually no lag.

 

[Fast Guy]

After a chicane i was ending up exiting in 2nd gear and just wait for the turbo to spool .

If your that low down the revs in 2nd, why aren't you changing to 1st?

 

[Trip]

I will do as advised but i am scared that my standard turbo will not hold until i get time to fit the gearbox. Which will break first.. Gearbox or Turbo


I prefer not change in first cause of two reasons.

1) Putting it in first while moving i get a gear crunch and it doesn't get in very easly.. Even when i rev match (heel toe braking) .
2) Every time i did it and go WOT after, i get on the revlimter soon after. And when i hit the revlimter the engine will back/missfire badly.

http://www.youtube.com/watch?v=MCTUbeIL3_0 @ 04min 37sec . Just before the turn you can hear the rev matching part (heal towbraking) and hearing a gearbox crunch a split second after. Also you can hear the backfires/misfires while exiting the corner.

 

[BabyGodzillaGTi-R]

Have you tried downgrading the tyre size of your car?

What size are you currently running? 225/45 R17s right?
How about dropping it to 195/50 R15s?

Maybe the lower unsprung weight and better final drive gearing might overcome the "extra grip" offered by the 225s?

Just my 0.000000000001 Banana Currency.....

 

[Trip]

If I could I would run smaller wheels but with 310mm disks all round , it's kind of hard to find a wheel in 15" which fits. I am running 225/45 R16

 

[campbellju]

You could try leaving it in second and accelerate earlier so that it comes on boost at the exit. Driving around the car's weakness.

Assuming you are running an OEM T28 then between an RB box and a better turbo I'd go for the turbo. Aside from the reduced lag you will get more direct pedal feel from a fast responding turbo.

However, given your 1st gear is getting questionable and an RB box is suited to the hill climbs you do from the vids I've seen then I think I'll switch my answer and say change both.

For turbo choice, my opinion is a T2860rs would be a better match for an RB box.

My 3071 .64 a/r was fast responding and with a lazy torque curve that worked well with the longer first and second gear on the quaife box. This was good for street and race track but on the tight chicanes you have then even in 2nd gear on an RB box it would probably overwhelm the tyres.

As you don't drive the car outside of a race and both the box and turbo are dodgy, on refelction if you have the cash then change both as they do different things and they should both be more fit for purpose.

 

[Trip]

You could try leaving it in second and accelerate earlier so that it comes on boost at the exit. Driving around the car's weakness.

Assuming you are running an OEM T28 then between an RB box and a better turbo I'd go for the turbo. Aside from the reduced lag you will get more direct pedal feel from a fast responding turbo.

However, given your 1st gear is getting questionable and an RB box is suited to the hill climbs you do from the vids I've seen then I think I'll switch my answer and say change both.

For turbo choice, my opinion is a T2860rs would be a better match for an RB box.

My 3071 .64 a/r was fast responding and with a lazy torque curve that worked well with the longer first and second gear on the quaife box. This was good for street and race track but on the tight chicanes you have then even in 2nd gear on an RB box it would probably overwhelm the tyres.

As you don't drive the car outside of a race and both the box and turbo are dodgy, on refelction if you have the cash then change both as they do different things and they should both be more fit for purpose.

This is my driving style. If my right foot is not on the brake, its on the throttle pedal fethering it (controlling understeer) until i can WOT in exit. By the time I WOT in second I loose valuable revs. I have asked other drivers who race with similar cars and from all which do not have a close ratio box have similar problem. Toyota GT4's, EVO's and STI's..

I am currently using an OE box. When i had to urgently (2 days before a race) replace the engine i didn't have time to split the quaife and swap gearboxes. So i simply installed a standard engine which was already mated to a standard gearbox. I have my doubts how long will the gearbox live with my abuse.:lol:

The standard turbo I currently have was probably never rebuild and on one occasion i was told i got a puff of smoke on gearchange. Using a very mild launch control although not too aggrasive does not help with its health either.

Before I bought the gearbox i was looking into getting a GT2860RS with 0.86A/R but since i managed to find a close ratio box, i had ?? in my head if the GT2860rs was too small for the combination and get the GT2871R 48 or 52trim with 0.86A/R

I would ask another question regarding turbos. Would it be an overkill on a GT28RS to get the new turbine housing T25flanged with a 2.5" discharge non gated in 0.63A/R ? According to the ATP "Turbine housing, we call it "T25 Plus", T25 inlet flanged, T31-V-Band outlet, Externally wastegated, flows like full T3. Available for full size GT3071R/GT3076R turbine wheel. Allows full T3 flow but on T25 flanged manifold. Turbine housing available in .63 A/R and .82 A/R." You would still need to install an external wastegate and mod the elbow to complete the system.

 

[Fast Guy]

If I could I would run smaller wheels but with 310mm disks all round , it's kind of hard to find a wheel in 15" which fits. I am running 225/45 R16

You could fit smaller tyres. I'm running 215/35/16s (315mm front brakes) which is 556.9mm diammeter compared to your 608.9mm diammeter

 

[Trip]

You could fit smaller tyres. I'm running 215/35/16s (315mm front brakes) which is 556.9mm diammeter compared to your 608.9mm diammeter

I have a sort of deal with the Toyo dealer in Malta to race with Toyo's. I choose the smallest diameter R888 in 16's i could find. although there was the 195 which had smaller dimeter but they would be too thin to race with and my 8inch width rim would need changing.

I read somewhere that Rota Slipstreams in 15" would fit under 310mm brakes, but I do have slipstreams in 16 and i don't see how half an inch less would clear the calipers..

 

[campbellju]

Before I bought the gearbox i was looking into getting a GT2860RS with 0.86A/R but since i managed to find a close ratio box, i had ?? in my head if the GT2860rs was too small for the combination and get the GT2871R 48 or 52trim with 0.86A/R

Depends what your target HP is and at what boost level. There are more knowledgable turbo people on the forum but if you are running an RB box on a tight course I would have thought your priority was response over hp.

 

[Fast Guy]

I read somewhere that Rota Slipstreams in 15" would fit under 310mm brakes, but I do have slipstreams in 16 and i don't see how half an inch less would clear the calipers..

Markturbo has 330mm discs under 16" Compmotive MOs(I think) so maybe a 15" of them would clear your 310s?

Depends what your target HP is and at what boost level. There are more knowledgable turbo people on the forum but if you are running an RB box on a tight course I would have thought your priority was response over hp.

You also need to consider what top speed you need with the RB box. If it's anywhere near 120mph then ideally you want max power to be around the 7500rpm mark instead of the standard 6400rpm ish. As it stands I'm making max power at 104mph in 5th. I'm crossing the line at 112mph on the strip so after 104mph I aren't accelerating as hard as power drops off. A set of cams and max power at 7500rpm (123mph) would make alot of difference to my times.

 

[Trip]

Depends what your target HP is and at what boost level. There are more knowledgable turbo people on the forum but if you are running an RB box on a tight course I would have thought your priority was response over hp.

My ultimate priority is response but i wouldn't mind having response and somewhere close to 380bhp.

 

[Trip]

Markturbo has 330mm discs under 16" Compmotive MOs(I think) so maybe a 15" of them would clear your 310s?

A 15" wheel will reduce its size to 12.7mm from each size. I have stuck a cardboard tube 16mm diameter on the caliper to see clearance. It got squashed and reduced to size about 13mm. that just leaves 0.3 of a millimeter clearance . Wheel was Rota sliptream 16x8 with 35offset and using a 5mm spacer.

You also need to consider what top speed you need with the RB box. If it's anywhere near 120mph then ideally you want max power to be around the 7500rpm mark instead of the standard 6400rpm ish. As it stands I'm making max power at 104mph in 5th. I'm crossing the line at 112mph on the strip so after 104mph I aren't accelerating as hard as power drops off. A set of cams and max power at 7500rpm (123mph) would make alot of difference to my times.

My top speed. I wouldn't know my top speed. But looking at my competitor's onboard video which is a Subaru build up with with no money spared, and has a close box, he never seem to go beyond 4th gear which is about a 100mph. I do not know his ratios but as a ball park figure they should be roughly the same as our RB.

 

[whytie]

I've seen some of your vids an I think an rb box or similar would help. I think you will be surprised the difference and then it will give you a better idea of what turbo to fit. I was shocked when I fitted mine.

 

[MarkTurbo]

I prefer not change in first cause of two reasons.

1) Putting it in first while moving i get a gear crunch and it doesn't get in very easly.. Even when i rev match (heel toe braking) .
2) Every time i did it and go WOT after, i get on the revlimter soon after. And when i hit the revlimter the engine will back/missfire badly.

http://www.youtube.com/watch?v=MCTUbeIL3_0 @ 04min 37sec . Just before the turn you can hear the rev matching part (heal towbraking) and hearing a gearbox crunch a split second after. Also you can hear the backfires/misfires while exiting the corner.

Looking at that video i'd say you'd benefit from the rb box on that corner as it would probably mean you could stay in second. But thinking about it another way would having the rb box mean having to make more gearchanges elsewhere? If it did could the time you make up in one place from not having to go down into 1st be lost in other places due to extra gearchanges?

At Wiscombe hillclimb theres 2 corners where i need to use 1st gear, our gearboxes never like selecting 1st whilst moving but you just need to force it in. It never sounds nice though :lol: You can just about hear it in this clip as my car goes out of view.

http://www.youtube.com/watch?v=0v795EDtCE4

 

[Trip]

Mark, so that crunch sound isn't only on mine

We have lots of slow corners here.. next sunday's race is even worse (if its not postponed again)..It going to be held the same location I done back in 2006 just 2 days after my pulsar landed from the UK . Car was fully standard with just seats removed. I barely knew the car
http://www.youtube.com/watch?v=g3cXV8jB_88
This is another example where a lower gear could help. I took the chicane wide but you can see i exit with 0 boost. You can hear me press the clutch to get the rev up just after the exit. Both the evo before me and the one after put it in first gear on exit.
http://www.youtube.com/watch?v=3DJbiE_tOFk @ 00:49sec


The time wasted changing is minimal compared to the times i wait for some positive pressure.

 

[Fast Guy]

Transmission Gear Ratios:
1st - 3.285 (RB: 3.067)
2nd - 1.850 (RB: 2.095)
3rd - 1.272 (RB: 1.653)
4th - 0.954 (RB: 1.272)
5th - 0.740 (RB: 0.911)
Reverse - 3.266 (RB: 3.153)