Improve Top End Without Sacrificing Bottom End.

[R34Liner]

Hey guys,

I raced my mate a while back at a track day and we both have R34 non turbo's...off the line i beat him on the launch and 1st gear i pull away easy for some reason, but as soon as I'm finishing up with 2nd and into 3rd he starts overtaking me after I'm already in the lead by a car length? and this happens consistently.

So my question is, why? and how can i improve my top end without sacrifice my already quicker bottom end?

My car's mods:

-K&N Panel Air filter

-Stock air box with direct piping from throttle body to AFM.

-extractors and 2.5inch Cat-back

- i have a slight leak in my exhaust, i need to replace the gasket between the rear muffler and the cat-back. (<- could that contribute at all? i have found that my car struggles hard without back pressure, like any car i guess.)

- i have a GTT 5spd Gearbox (not the standard non -turbo box)

His Mods:

-Pod filter (contribute to top end?)

-stock exhaust with a after market muffler/cannon

-stock manual

So it makes sense that my mods are helping my bottom end....but something is taking away my top end?

any help would be much appreciated

p.s since we dont go to that many track days i cant really play around with mods and then race him on a regular basis so that's why i need some theory help

[Touge Kyousou]

The lack of backpressure will actually help high end and not low end (really generally speaking, tonne of variables on exhaust backpressure on n/a applications).

His pod if setup well will be helping his high end but making him lose low end likely.

Your exhaust plus extractors should be helping your high end.

To be honest, with your mods i expect your high end to be strong, not low down.

Have you checked the gear ratios and final drive ratio of the gt-t box vs the gt box ? The gt-t box will likely be geared for an engine with much stronger torque so that once it's on an n/a, it becomes mismatched.

To answer your question,

Try getting some form of ecu tuning (reflash, piggyback, stand alont, interceptor etc). A good tuner should be able to unleash a few good kw's from your mid and top considering some of the mods you have. You might need to upgrade your air intake to keep up with the flow of your extractors and exhaust.

And also, weight reduction. Empty the boot out (free!), then relocate the battery to rear (if its in front from facory) to help offset all that weight gone in the back, put a dry cell battery in while you're at it. How heavy is the bonnet ? Will a CF/Fibreglass one help ? Do you ever carry back passengers (need those rear seats?). Alot of junk in the car ?

Can also look at getting ultra light weight wheels (exxy though). Items from volk, work, enkei etc come to mind.

[mad082]

the gearbox may be the reason here. they are a stronger box and probably have more drag/resistance in them with that. gear ratios will be pretty close as it is usually just the diff ratios that vary between the turbo and non turbo, but if your car was originally auto i think they ran a taller diff which will slow your acceleration down.

there are so many variables that could come into play here. his engine may be stronger than yours (yours might be tired and have lower compression), or his timing may be a bit more advanced than yours. your cat may be a bit blocked, or your knock sensors are more sensative than his and are retarding the timing a bit. his injectors may be a bit more clean than yours and giving a better spray pattern. his coils may be in better condition than yours and giving a better spark. the list is almost endless.

[R34Liner]

The lack of backpressure will actually help high end and not low end (really generally speaking, tonne of variables on exhaust backpressure on n/a applications).

His pod if setup well will be helping his high end but making him lose low end likely.

Your exhaust plus extractors should be helping your high end.

To be honest, with your mods i expect your high end to be strong, not low down.

Have you checked the gear ratios and final drive ratio of the gt-t box vs the gt box ? The gt-t box will likely be geared for an engine with much stronger torque so that once it's on an n/a, it becomes mismatched.

To answer your question,

Try getting some form of ecu tuning (reflash, piggyback, stand alont, interceptor etc). A good tuner should be able to unleash a few good kw's from your mid and top considering some of the mods you have. You might need to upgrade your air intake to keep up with the flow of your extractors and exhaust.

And also, weight reduction. Empty the boot out (free!), then relocate the battery to rear (if its in front from facory) to help offset all that weight gone in the back, put a dry cell battery in while you're at it. How heavy is the bonnet ? Will a CF/Fibreglass one help ? Do you ever carry back passengers (need those rear seats?). Alot of junk in the car ?

Can also look at getting ultra light weight wheels (exxy though). Items from volk, work, enkei etc come to mind.

Weight Reduction is important, but dont really want to sacrifice some of the more basic comforts of the car whilst I'm on the street, but for track i empty the whole thing Hmm a ECU might be the way to go, and maybe fix up my intake a little more....

Good point with the Gear ratio's GTT vs GT box... i also have a S15 Differential in the car...so not sure where that leaves we with the final drive ratio :S

the gearbox may be the reason here. they are a stronger box and probably have more drag/resistance in them with that. gear ratios will be pretty close as it is usually just the diff ratios that vary between the turbo and non turbo, but if your car was originally auto i think they ran a taller diff which will slow your acceleration down.

there are so many variables that could come into play here. his engine may be stronger than yours (yours might be tired and have lower compression), or his timing may be a bit more advanced than yours. your cat may be a bit blocked, or your knock sensors are more sensative than his and are retarding the timing a bit. his injectors may be a bit more clean than yours and giving a better spray pattern. his coils may be in better condition than yours and giving a better spark. the list is almost endless.

It is an auto conversion, but i forgot to mention i have a S15 diff....so the gear ratios are changed once again.... and acceleration isn't a problem down low, its up top where i think you are right, the Turbo box is designed to have more HP to push it through the top end, where as an N/A is struggling to keep going top end as it is...hmm i also have splitfire's so ignition isnt a problem but as you said it could be a magnitude of things.

Might have to start building a list of the most likely things....

[Birds]

May well be an underlying issue with your vehicle, but modifications wise...well I say there's no point spending excessive money on an N/A vehicle that came out so accessibly in a turbo model, but throttle bodies / camshafts / engine management will help you out in the top end.

[R34Liner]

May well be an underlying issue with your vehicle, but modifications wise...well I say there's no point spending excessive money on an N/A vehicle that came out so accessibly in a turbo model, but throttle bodies / camshafts / engine management will help you out in the top end.

I'm sure you aware of the p-plate law...hence why N/A's are now predominantly owned my us p platers - but yea it is a tad waste of money, but im planing on turbocharging this car so its all good in the end. 1+ on the engine management.

[Birds]

Yep very aware of it

I'm also aware of what it's like to have an N/A car that you want to go fast. Problem is though, that the mods I listed come to something like a 5-6k bill with you doing alot of the work. The end result will make you happy for about a month before you'll start wanting more power. Then you'll probably ditch the throttle bodies in the course of doing a turbo conversion, you'll need a remap regardless, and the camshafts will most likely not suit the lift and duration required by forced induction. I'd recommend working on that underlying issue that's sapping your power and maybe invest in some things that will make you go faster but still benefit later on when you do a turbo conversion - really good tyres, brakes, suspension etc.

[rob82]

I'm sure you aware of the p-plate law...hence why N/A's are now predominantly owned my us p platers - but yea it is a tad waste of money, but im planing on turbocharging this car so its all good in the end. 1+ on the engine management.

I just dont get this approach - why dont you just get buy a GTT once your on your opens. You will spend way too much and the resale of the car will be similar to a non turbo, not a GTT.

Why dont you try taking you cold air setup off and just leave the airbox open (with the filter in) and then see who wins.

[noely1]

dude he jus finished saying he's going to be turbo'ing THIS CAR far out man read aye