Head Modification. Neo Head Vs Modded 25Det Head.

[Daboss]

Hey forum once again i call on the expert opinions of the skyline kings. You guys have been a great help so far.

I have finally saved enough money to do my final performance mod and was wondering which option would be my best option. My final mod is for the head. I was wondering would it be best to mod the stock 25det head or fit the neo det head to the 25det block?

I have searched this forum through and through and found nothing definitive as to what all has to be done to get the neo head to fit to the 25det block.

1) Would I have to change pistons in order to fit the neo head and does the greddy intake manifold bolt up to the neo head? If that has to be done then that is the deal breaker, modded 25det head it is.

I would like to retain vct along with solid lifters. 2)If I put solid lifters into the 25det will that make me lose vct?

3)Is there a way to keep vct and put in solid lifters in a 25det?

I heard the neo vct works differently than the rb25det. 4)Can the neo vct be controlled with the 25det ecu made to be switched on and off?

[discopotato03]

If it were me I'd use the Neo parts if not the complete Neo engine . Newer better rods and you'd think coming from an ultra low emission (ULEV) era a bit more detonation resistant than the R33 era RB25DET . Aside from better cam profiles and soild buckets you lose the awkward side feed injectors too and should be able to fit shortish EV14s . Also the R34 CAS is easier to get at times .

Personally I don't think the aftermarket inlet manifolds are worth it unless you are chasing more than 310 Kws and its going to be laggy anyway .

Nismo always said he made real good power ages ago and that was with a std config RB25 inlet manifold .

A .

[jangles]

Hey forum once again i call on the expert opinions of the skyline kings. You guys have been a great help so far.

I have finally saved enough money to do my final performance mod and was wondering which option would be my best option. My final mod is for the head. I was wondering would it be best to mod the stock 25det head or fit the neo det head to the 25det block?

I have searched this forum through and through and found nothing definitive as to what all has to be done to get the neo head to fit to the 25det block.

1) Would I have to change pistons in order to fit the neo head and does the greddy intake manifold bolt up to the neo head? If that has to be done then that is the deal breaker, modded 25det head it is.

I would like to retain vct along with solid lifters. 2)If I put solid lifters into the 25det will that make me lose vct?

3)Is there a way to keep vct and put in solid lifters in a 25det?

I heard the neo vct works differently than the rb25det. 4)Can the neo vct be controlled with the 25det ecu made to be switched on and off?

2) don't have to lose it

3) yes there is.

4) the Neo VCT is constantly variable so.. Better, if you're building it you'll have an aftermarket ecu anyway?

[GTSBoy]

The Neo DOES use different pistons (and has RB26 rods). The Neo pistons suit a combustion chamber that is about 10cc smaller than the older RB25 chamber. If you put the Neo head on an older block, the compression ratio will be extremely high. Not recommended except for an E85 or screaming NA build.

[GTSBoy]

4) the Neo VCT is constantly variable so.. Better, if you're building it you'll have an aftermarket ecu anyway?

Not true. Works exactly the same as older RB25. On-off. Nothing else.

[NYTSKY]

If you have a non NEO head already, just put some poncams and springs in and away you go. You could clean up the ports or do some port matching if wanted.

Will be fine for 90% of most setups.

The advantage of the NEO is solid lifters and the ability to use a bigger drop in cam profile.

Even in standard form these heads flow A LOT of air and produce the numbers.

[Joshbigt62r]

What he said ^^^

[Daboss]

If it were me I'd use the Neo parts if not the complete Neo engine . Newer better rods and you'd think coming from an ultra low emission (ULEV) era a bit more detonation resistant than the R33 era RB25DET . Aside from better cam profiles and soild buckets you lose the awkward side feed injectors too and should be able to fit shortish EV14s . Also the R34 CAS is easier to get at times .

Personally I don't think the aftermarket inlet manifolds are worth it unless you are chasing more than 310 Kws and its going to be laggy anyway .

Nismo always said he made real good power ages ago and that was with a std config RB25 inlet manifold .

A .

Thanks for the information and fast response. Sorry I didn't mention it in my earlier post but already have a built bottom end and a greddy style inlet manifold. Chasing 440rwkw as a daily and just wanted solid lifters for a bit more revs and be able to keep vct for the low end drive.

2) don't have to lose it

3) yes there is.

4) the Neo VCT is constantly variable so.. Better, if you're building it you'll have an aftermarket ecu anyway?

How is it kept. Just replace standard lifters with the solid lifter conversion and use neo camshafts to suit?

If you have a non NEO head already, just put some poncams and springs in and away you go. You could clean up the ports or do some port matching if wanted.

Will be fine for 90% of most setups.

The advantage of the NEO is solid lifters and the ability to use a bigger drop in cam profile.

Even in standard form these heads flow A LOT of air and produce the numbers.

Will it be fine for a 440rwkw car? Was getting head ported and polished, but also wanted to retain vct as it will be my daily driver. I also wanted solid lifters for a bit more rev. That is why I was thinking the neo head to kill a few birds and spend less money as many of the parts I think I need are already in that head, so I figure it will be as simple as get neo head, port and polish it, bigger camshafts and bolt on neo head to my built non neo block. If the neo head is a simple bolt on with a few minor mods I can handle that but, from a response in this post sounds like I am gonna need new pistons which I am not changing as I have forged pistons and changing them for the sake of the head is not worth the effort to me and it will raise my compression ratio. I forgot to mention that I am on methanol injection if that will help with the higher compression ratio.

Was thinking of the tomei 264 drop in camshafts as I read this is the biggest you can go and retain the vct with non neo head. What is the biggest cam profile you can use with neo head and retain vct?

Was also thinking of oversized valves intake and exhaust to help with flow no matter which head I end up with. I am a bit weary of the oversized valves as I read they can actually reduce spool up and low end power when installed.

What are your thoughts and suggestions?

[GTSBoy]

Thanks for the information and fast response.

What are your thoughts and suggestions?

Did you read my post? You really can't choose the Neo head unless you use a Neo specific bottom end. Given you have a built bottom end and want solids, you need a solid lifter conversion kit. Poncams are certainly big enough for your power aim. And if you want the head done, get someone who really knows what they're doing to port and prep it. Decent valve seat job and shaping of the ports is worth more to you than bigger valves anyway.

Edited February 16, 2013 by GTSBoy

[Daboss]

Did you read my post? You really can't choose the Neo head unless you use a Neo specific bottom end. Given you have abuilt bottom end and want solids, you need a solid lifter conversion kit. Poncams are certainly big enough for your power aim. And if you want the head done, get someone who really knows what they're doing to port and prep it. Decent valve seat job and shaping of the ports is worth more to you than bigger valves anyway.

Yes I did and was not ignoring your advice was seeing if anyone else had thoughts on it or had done the conversion successfully, to try and reduce the price that will be added with the solid lifter kit. If you read my re-post you would see were I mentioned that changing the pistons was not worth it for the head.

Question for you, If I get the solid lifter conversion kit will I retain vct and will I now be using neo spec cams or does tomei make solid cams for a non neo with solid lifters and the star pattern cas and the non neo vct intake cam?

Won't I have to change the valves to to suit the solid cams anyway? I think the only valves they have available for the solid lifters are 1mm oversized.

[NYTSKY]

Eg: Non NEO head with VCT, no porting, Tomei springs, poncams, 514rwkw (currently 563rwkw) 8000rpm redline.

Eg: Non NEO head with VCT, ported exhaust ports, Tomei springs, HKS step 1 cams 546rwkw 8500rpm redline.

Both heads have standard size valves.

[Daboss]

Eg: Non NEO head with VCT, no porting, Tomei springs, poncams, 514rwkw (currently 563rwkw) 8000rpm redline.

Eg: Non NEO head with VCT, ported exhaust ports, Tomei springs, HKS step 1 cams 546rwkw 8500rpm redline.

Both heads have standard size valves.

WOW!!!! Thats impressive, they are both 25/30,s though. So the displacement is there to spool up a bigger turbo for high horsepower. Do you think i will be able to get to 440rwkw with a head tidy, up standard valves, upgraded springs, poncams and a built block? What turbo do you suggest for this I had a precision bb 6765 in mind plus I only want to run 35 psi of boost max.. What do you think spool will be like with the mods I listed?

[NYTSKY]

At 35psi a 6765 will see you well into the 500s. I would suggest a 3788 or similar. Are you running E85 or 98?

That VL had a standard head on it, just poncams and springs. 440rwkw wont be a drama.

I was making 420rwkw with a 35R on a built RB25, same head.

[Daboss]

At 35psi a 6765 will see you well into the 500s. I would suggest a 3788 or similar. Are you running E85 or 98?

That VL had a standard head on it, just poncams and springs. 440rwkw wont be a drama.

I was making 420rwkw with a 35R on a built RB25, same head.

98 with meth injection. So a precision 6265 bb with 35 psi should meet my horsepower goals?

[discopotato03]

440 Kw is around 585Hp and if you wanted it "nice" for a daily driver it should have had an RB30 bottom end . The whole point of the extra capacity is that you don't have to rev it to make the power . Five sixths of 8000 revs is 6666 and I'd rather be there with an RB30 that at 8K with an RB25 .

I really don't think the inlet timing change is going to pull the bottom end power up on an RB25 with a bigish turbocharger on it .

IMO the nicest overall result would have been an RB26 head and six throttle inlet system on top of an RB30 block .

A .

[Daboss]

440 Kw is around 585Hp and if you wanted it "nice" for a daily driver it should have had an RB30 bottom end . The whole point of the extra capacity is that you don't have to rev it to make the power . Five sixths of 8000 revs is 6666 and I'd rather be there with an RB30 that at 8K with an RB25 .

I really don't think the inlet timing change is going to pull the bottom end power up on an RB25 with a bigish turbocharger on it .

IMO the nicest overall result would have been an RB26 head and six throttle inlet system on top of an RB30 block .

A .

Yea I know and I am pissed at myself for doing all these mods when I could have just saved and bought a rb30det one time. I really want 600rwhp. Knowledge really is power and a time saver, but at the time of these mods I was green and totally oblivious.

That is spilled milk now and eventually I will get a 30 bottom end, but I just can't afford it at this time and will have to get there with what I have.

Hopefully it will last long enough for me to save for the 30 bottom end or just lower my rwkw goal, which I really do not want to do cause I will still want around 500 to 550rwhp, but I know for the weight of the car I have being a R33 and the type of rwkw these guys have and low weight of their cars being evos, silvias, hondas and big hp supras that is the type of rwkw I will need to be competitive for the street import drag racing nights we have on Fridays.

Edited February 16, 2013 by Daboss

[NYTSKY]

Well firstly you are not going to run 35psi on 98, even with meth injection.

Realistically 25psi would be the highest you would go sensibly. So to make your target goal of 600 at the wheels I would go for an 800hp rated turbo which not matter what is going to be laggy.

IMO if want a mad streeter with good power and response dont shoot for a number. Pick the best turbo setup you can to get the most power while hitting peak torque at about 4000rpm.

I have had a few turbo setups over the years and by far the best for the street was the GT3076 on E85, made great power (enough for the street) and was all on song just under 4000rpm, could still bake 3rd gear

My 2c

[discopotato03]

I can see you throwing good money after bad , a head set up for an RB25 may not suit an RB30 chamber and CR wise . Can you sell your RB25 bottom end and finance a dirty 30 ?

Yes and I wouldn't even think of not running E85 or E70 at that sort of power level . I'm just putting my first full tank of E70 through and the consumption is looking like being ~ 100K per 1/4 tank . My tune needs a bit of redoing in a few places and with better injectors it can only get better .

If in the Gong where is your closest Eflex servo , Heathcote ? If so its not that far away . If you had three jerrys you could fill up and take the other tanks worth home , 800 odd Ks between fuel runs .

Don't need dual maps with a PFC , just have two and changeover with a laptop .

A .

[Daboss]

I can see you throwing good money after bad , a head set up for an RB25 may not suit an RB30 chamber and CR wise . Can you sell your RB25 bottom end and finance a dirty 30 ?

Yes and I wouldn't even think of not running E85 or E70 at that sort of power level . I'm just putting my first full tank of E70 through and the consumption is looking like being ~ 100K per 1/4 tank . My tune needs a bit of redoing in a few places and with better injectors it can only get better .

If in the Gong where is your closest Eflex servo , Heathcote ? If so its not that far away . If you had three jerrys you could fill up and take the other tanks worth home , 800 odd Ks between fuel runs .

Don't need dual maps with a PFC , just have two and changeover with a laptop .

A .

Well firstly you are not going to run 35psi on 98, even with meth injection.

Realistically 25psi would be the highest you would go sensibly. So to make your target goal of 600 at the wheels I would go for an 800hp rated turbo which not matter what is going to be laggy.

IMO if want a mad streeter with good power and response dont shoot for a number. Pick the best turbo setup you can to get the most power while hitting peak torque at about 4000rpm.

I have had a few turbo setups over the years and by far the best for the street was the GT3076 on E85, made great power (enough for the street) and was all on song just under 4000rpm, could still bake 3rd gear

My 2c

Will be driven on the streets and daily but not really a street car. Really a drag fan and response on the street is not what I am after. Do not want a pig on the street, but full throttle all out power is what I am into can deal with full spool at 4000/4500 rpm with a redline of 8000. The street/autocross/track type race is not what I want. That setup you speak of does sound great but I only do 1/4 mile and more highway pulls on the street.

I can see you throwing good money after bad , a head set up for an RB25 may not suit an RB30 chamber and CR wise . Can you sell your RB25 bottom end and finance a dirty 30 ?

Yes and I wouldn't even think of not running E85 or E70 at that sort of power level . I'm just putting my first full tank of E70 through and the consumption is looking like being ~ 100K per 1/4 tank . My tune needs a bit of redoing in a few places and with better injectors it can only get better .

If in the Gong where is your closest Eflex servo , Heathcote ? If so its not that far away . If you had three jerrys you could fill up and take the other tanks worth home , 800 odd Ks between fuel runs .

Don't need dual maps with a PFC , just have two and changeover with a laptop .

A .

Well the thing is were I am from there is no e85 or e70 as yet just 98 pump. Thats why I am on the methanol injection, plus don't you have to have the fuel system to support e85 or 70? Selling the built 25 end will be hassle as people over here have tendency to down play things and will want to purchase at little or nothing. Have read about some dsm guys making some serious hp on pump gas and meth injection.