200hp Rb25 Possible?

[Super Drager]

Its best to change gears just before redline as when you change to the next gear your revs will drop back into your peak powerband.

[mad082]

when to change gears depends on your power graph. your power drops off after it hits its peak, so you have to time the change so that you aren't reving it out to a point where at the higher rpm in the lower gear you have less power than you would in the lower gear. staying at the higher rpm when the power is dropping off can also result in you spending more time at lower power than it you change, however there is another thing to look at. in the lower gear the engine will accelerate easier thanks to the shorter gearing, so changing too early can give you slower acceleration despite the fact that you might be at a high power range in the rev range.

[R34 -_-]

Iv had my car for almost 3 years now and in that time iv played around with a lot of different driving methods etc etc but the most interesting is just the basic gear changes and throttle.. For example, when putting you put foot down in 1st and change at high rpm its really responsive but it makes 2nd gear seem more sluggish than if you were to change fairly early in 1st and then change high in 2nd. It might not make much difference but if you try what I'm talking about you'll know what i mean.

And also, full throttle from a stand still in my car seems kinda slow, almost like I'm flooding the engine but when i give say %70 throttle its responsive and seems to accelerate better (In 1st gear).

This is me just mucking around in my car lol, but everyone should give it a try and see how there car behaves.

Edited April 27, 2010 by R34 -_-

[mad082]

how far you put your foot down really depends on the RPM. flooring it at low rpm won't really do anything more than 60% throttle because at low rpm you are already letting enough air into the plenum with the lighter throttle amount.

as for changing gears at lower revs feeling like the next gear is pulling better, that may be somewhat of an illusion because you have just gone from a gear that is pulling really hard to a taller gear that simply won't pull as hard, but if you change earlier then you aren't getting as much of a rush from the lower gear so when you change gears there isn't so much of a difference in acceleration. also if you are accelerating from reasonably low in the rpm range in the higher gear you will be accelerating from lower in the torque curve so you may have sluggish acceleration to start with and then as the revs pick up it starts to pull harder so you notice the difference in performance which then gives the illusion that it is pulling harder than if you shift into that gear from higher revs in the lower gear.

[Galois]

yeah ive noticed similar things, i think its largely state of mind.

i was pretty ill last week and spent 2 days in bed without food, which meant 2 days of not driving which is prob the first time in 6 months of owning the car. im sure it was a bit rougher when warming up, but it still sounded weird for the whole trip (60 mins to pick up the gf). being a japanese car it was probably running fine, just the driver being tired and famished wasn't used to all the normal sounds...

anyways, back on topic, why didn't you look into rb30 conversion? too expensive? or didn't want to put the rb30 bottom on a car you might sell?

[R34 -_-]

The car also sounds different in the passenger seat.

Plus T would be easier than being an N/A and doing expensive mods for little gain

[TwoCents]

Yea, dont want to spend too much money on this car as i will be selling it in about 2 years. Main idea about getting the upgrades, is that they can be used in a turbo'd car

[GTS4WD]

I haven't read all of the posts in the thread but in terms of the thread question:

Short answer: Yes. 200hp is possible out of an RB25DE.

It would be even easier to reach 200hp in a hybrid RB25/30DE. Obviously by increasing engine capacty your going to be (theoretically) making more power than keeping it 2500cc.

The large question you should be asking yourself first is:

How much do you want to spend?

Will you be doing the work yourself? Expect to double the budget if your paying a workshop.

Biggest gains your going to have are from increasing compression ratio. As said before, you can safely increase CR to 11:1 without too much trouble. You can increase CR to 12:1 if you constantly run high octane fuel with a good quality ECU. Of course you could run even higher CR if you choose to run non-pump fuel and is not used as a daily driver with supporting mods.

And as all people have said above.

Reduce intake and exhaust restrictions.

I dont know why Nissan has decided to use this "over head" design, but for an NA car and intakes, you cant beat individual throttle bodies. Depending on runner leangths, trumpet diameters and head ports you can minipulate where the engines power band occours. You can move the power band higher or lower in the RPM range. So obviously you'll want to have the power band higher up in the RPM range for peak power output. ITB dimentions will also dependent on camshaft profiles (and therefore lift and duration) you have to choose from. A good healthy dose of valve overlap is necessary to get as much fresh air in the combustion chamber as possible.

To do the job properly you will need a high quality set of headers and exhaust system in the right diameter. Again, exhaust diameter and header runner length will be dependent on where you in RPM range you will be making power. You'll be looking for a slightly larger diamter to gain a higher peak output.

If you go ITB's an ECU to match. Increase fuel pump capacity.

Lighten bottom end and flywheel and balance

All of the above = $$$$$$$

Short answer = NOS.

[simjim89]

im a 1st year greese monkey with an r34 rb25de and i have done a bit of looking and talking with people in the performance industry .....now this may sound little bit out of the norm but how about just a bigger throttle body & injectors and a adaptronic ecu ? more air more fuel ... tunned properly .... should give u that extra that u want....... ecu installed and tunned $1900....... injectors and probs fuel pump no more than mayz $800...... and top end t/b maybe $150 ? this also may lead way to cams & valve train being utilized better if u choose so latre on .... also wet pants ... would love to hear more about how & why u finaly choose and what its gains were ... great thred

[R33_Dude]

This comes up all the time but I think my current list for a 100hp per litre RB25DE is:

Intake: GT-R independant throttle bodies on adaptor plate. Trumpets. Foam filters (or sans filters if your feeling manly).

Head: Full radius cut valve seats (better than a three way job and should be the same price - of not find a different shop), shave to a compression ratio approaching 11:1.

Exhaust: Good extractors 3-2-1 design. Haven't found a set I like yet. High temp coated and wrapped in heat wrap. 2.5" straight through stainless pipe - the properties of stainless steel make it a far better choice, especially here where every bit counts. Mandrel bent of course.

High flow cat. Two resonators. Muffler. Or if your like me and live in Tassie ignore the muffler, mufflers by default are power prohibitive.

ECU: Nistune or other aftermarket system...

LAST THING: cams. I would leave them until you have discussed your planned mods with a cam specialist.

It would be pricey all in all but I see no reason to touch the bottom end. If you did feel the need, lighten everything, H-beam conrods, knife edge the crank, balance and skip the head shave, and put in higher compression lightweight forged pistons instead. CP make them at whatever compression ratio you want to order.

Problem is then after you have done all that your left with an angry car that I imagine would suck as a daily drive...

If anything sounds fvcked up or I've forgotten anything - I'm tired, leave me alone.

[ONE-VIA]

im a 1st year greese monkey with an r34 rb25de and i have done a bit of looking and talking with people in the performance industry .....now this may sound little bit out of the norm but how about just a bigger throttle body & injectors and a adaptronic ecu ? more air more fuel ... tunned properly .... should give u that extra that u want....... ecu installed and tunned $1900....... injectors and probs fuel pump no more than mayz $800...... and top end t/b maybe $150 ?

first off a larger tb will alow more air to flow how ever it will also make the throttle less responsive and and lazy in the low rpm range

injectors, what about fuel reg,lines,pump etc etc and if your gonna change all them and get a tune might aswell do a e85 conversion

[SKiT_R31]

If E85 is available for you, then that would be a great option. With the increased compression ratio with higher octane and higher oxygen content in the fuel your goal should be a lot easier to achieve.

It would be a good option for you to not shave the head at all, and if possible even use lower compression pistons (flat/dished pistons are actually better than dome anyway) Then increase the compression by shaving the block/bringing the piston height up. This way the piston could pass the head gasket so the peak of the compression would be between the head and the block, this will reduce detonation (by minimalising hot spots in cyl wall and head gasket ring) AND means you can safely decomp the engine at a later stage (using a decomp plate) without altering the factory squash or adding hot spots.

Also if a good fuel isn’t an option, there are other alternatives, like a smoothed and polished combustion chamber and smoothed and polished pistons. Running a good lean tune straight out of the box with a good fuel (my pick would be an E10 fuel, like boost 98 if E85 isn’t available) to reduce carbon deposits by having rich mixtures or using gypsy detergent fuels (carbon deposits cause hotspots and detonation). You could also ceramic coat your pistons and chamber to further cool things down.

At the end of the day, to keep the car drivable, you really want the best management you can find and the highest compression ratio practical on the fuel available. This is how you'll get usable power from your N/A, the only other way is to increase revs but pushing your peak power up (using cams and inlet runners) which will then make it a pig down low (which you may or may not care about, if you don’t care then BAM even more power).

And as cool as they are (and the beautiful sound of induction!) I would only recommend ITB's if you keep the factory GTR plenum and use an AFM. Otherwise a short runner length inlet manifold with a single throttle body would be the better option, using MAP & Air Temperature sensors for the best performance and drivability. Tuning EFI cars with ITB's and trumpets with cams/high compression at light throttle and idle is a nightmare and you would never get decent daily drivability from it, the only benefit would be high rpm response - the power difference would be negligible (infact having a sealed plenum would mean you could have a ram air CAI, which would net more power and gain response at higher speeds anyway).

In summary; pretty much what I would do is shave the block(or raise the piston) as much as possible, if more compression is required I would change the pistons, shaving the head as last resort. If funds were available (otherwise I wouldn’t touch the head at all) I would do a full port and polish (full radius cut valve seats does sound like a good option) as well as general smooth over on the head, and at least get the piston smoothed and ceramic coated (once again skip pending funds). I would match the cams, inlet runners (make customs) and exhaust runners to suit the same rpm peak power & torque (This is what will make good power), I’d probably aim for a peak of around 7000rpm with the limiter on power drop off (or within harmonic/oiling limits), ECU would be MAP based, being able to tune when the engine is in vacuum will give you great part throttle response and economy especially with a high compression motor.

[R33_Dude]

And as cool as they are (and the beautiful sound of induction!) I would only recommend ITB's if you keep the factory GTR plenum and use an AFM. Otherwise a short runner length inlet manifold with a single throttle body would be the better option, using MAP & Air Temperature sensors for the best performance and drivability. Tuning EFI cars with ITB's and trumpets with cams/high compression at light throttle and idle is a nightmare and you would never get decent daily drivability from it, the only benefit would be high rpm response - the power difference would be negligible (infact having a sealed plenum would mean you could have a ram air CAI, which would net more power and gain response at higher speeds anyway).

The way I have sorted out trumpet ITB's on my dads race car (mondeo V6 in a mark II escort) was to have a MAP sensor per throttle and instead of joining them for a single signal, had them seperated as individual inputs per cylinder if that makes sense. When tuned there was still a slight loss of drivability but when we compared dyno graphs from before and after mid to top end changed fairly drastically. On the ram air front we fabbed up an aluminium shroud that bolts underneath the trumpets and around them to the front of the car as a kind of air dam so that we did get a ram effect at higher speeds. Wasn't hard to do but it helps to have a laser cutting machine on your side

Idle does suffer with any of the mods we have mentioned though. Unless you have an ingenious system of getting more air and fuel while adjusting cam size at a particular RPM (VTEC, VVTi etc) theres no way around that. I think for a daily drive kind of deal the average person could handle 180HP and the drawbacks associated easily, and then once we get to 200->250 the drawbacks start to outweigh the positives. I mean I would still drive it daily but I am told I have a hearing problem and that I am vibration proof .

Added note: I'm not a tuner - I just swing spanners - so I can't comment on how hard it is to tune such a setup, but our tuner has never complained and as above the only differences in graphs were mid to top end when the restrictive effect of the plenum we had outweighed the air drawn by ITB's.

EDIT: I also find it astounding that people find it so difficult to get decent naturally aspirated horsepower out of a modern engine design like a RB25DE. The V6 in my Alfa had 160 RWHP stock (actually 158.2 something). With bolt ons (cams, head work, slight modifications, changing the AFM, replacing of worn out parts etc), a piston change and an aftermarket ecu such as Mega Squirt people see 200 HP pretty easily. And thats from a engine with its roots in the dinosaur era. Sure it's mostly that people with Alfas are willing to spend that money in the search of power - they are true enthusiasts - but surely there is something else going on here, whether it be a will to go through with it or that NA skylines are mostly owned by P platers who just get the turbo version once their off their P's, who knows. One day once I finish screwing around with this Italian crap I'll have a go at the NA route.

Edited August 20, 2010 by R33_Dude

[iseekool]

"If" you are going down the turbo path you could keep it nearly stock. Maybe slightly thinner head gasket (if they are available) and a low boost setup, and you can still cap it around the 200hp range but have mountain loads of torque.

[zebra]

Im surprised no-one has really mentioned head work...the factory 25de ports are fkn shit...and give next to no swirl in the combustion chamber...which means upping the compession much more than standard is going to mean bulk det with any meaninful timing advances.

It wouldnt be hard to raise and reshape the ports to give a better entry angle to the chambers, Also Long runner ITB's will help high rpm cylinder filling, short ones might mean the engine will free rev quicker but wont help power or torque on a small motor.

And on a short stroke motor short large diameter exhaust runners should help with high rpm breathing.

Then get cams made to suit, and rev to 9000+

As others have said aiming for 100hp/l will mean it wont be much fun at low revs/street speeds, but find a set of 4.7:1 r200 diff gears and rev the crap out of the thing.

[mad082]

that still makes it a pig as a daily.

[zebra]

that still makes it a pig as a daily.

Yeha...thats why I would never do it and just stick either a standard turbo motor or an alloy chev bent 8 in the thing

[thatr33kid]

kool

[Pal]

kool

warning handed out. if you have no useful information for the OP, please refrain from posting

[simjim89]

first off a larger tb will alow more air to flow how ever it will also make the throttle less responsive and and lazy in the low rpm range

injectors, what about fuel reg,lines,pump etc etc and if your gonna change all them and get a tune might aswell do a e85 conversion

this is very true hole fuel system would need ot be done and about the t/b the loss in the low end is probly not as much of an issue if hes going for hp and not respnse ..... if u have it tunned right shouldnt the use of more air and more fuel with t/b give u more response in the low end if done right ?

Thankyou for replying with something constructive instead of idiocy

Pump Reg rail injectors .... hmmm