25DET head in stock condition VS 30ET Head in stock condition

[Guilt-Toy]

I keep hearing conflicting storys.

One is that that RB30et head flows more then the RB25DET head.

[Alf]

The SOHC heads can be ported out more.

With only one intake and exhaust valve for each cylinder, larger valves can be fitted than on twin cam heads and area in the port can be opened up more. It has less moving parts.

But then again the SOHC heads are older than twin cam heads and are proned to cracking. The twin cam head is made from better alloy.

If you compare a bare 25 and 26 head theres not alot of difference in the size of the ports etc.. so it's obvious that twin cam is better. Correct me if I'm wrong but a stock 20det head out flows a 30et head.

Yes it seems that there is more R&D here in oz with the SOHC, it's alot cheaper to buy and easier to work with esp when there are so many VL's out there with SOHC heads.

[Abo Bob]

I think I remember SK saying that stock for stock the RB25 head was worth about 25 rwkw more.

[Warpspeed]

The DET head completely standard will flow about 30% more, but fitting it will reduce your compression ratio slightly too, so the power increase is not quite that much. As a straight swap on an RB30 block it is a very worthwhile modification.

Saying that the two valve E head can be ported to reach the same flow is probably true, if you want to spend the money. Getting all of that 30% would not be a cheap job. A quick port clean up and match will only get you typically about 5%. Extensive porting done properly with larger valves is going to cost you far more than the DOHC conversion.

Best bang for your buck would be a DET head with aftermarket camshafts. If you still want more, get that ported.

If it is n/a a set of RB25 pistons will increase the compression of that RB30DE to about 10.5:1 which is ideal with big cams fitted as well. It is probably too much compression for the stock cams.

If turbo, the 8.5:1 compression is ideal with the standard RB30 pistons.

[MrSkylineRB30ET]

Hey, this whole DOHC, SOHC thing, I don't know... SOHC making 504kW at the wheels isnt so bad, to my way of thinking.

RB30E heads are prone to cracking mainly in the VL's. VL's standard were released with small radiators, Aircon models have a thicker core, not to mention if you bleed the airpockets from the head you should be fine.

I find, much like a point made earlier, that the SOHC is a cheaper, easier and to me the smarter way to go, especially if we are talking drag application, I mean, they make the big power. You can make the head bolts bigger if you like, build it strong, spew boost down it and hold on. These engines are really not given the credit they deserve. Much like the heads.

Im not here to tread on anyones toes, nor can I really say I have the "real world" experience to argue, but when the results are there to be seen, why argue? hehe. I admit it is a pity head work costs so much, but $4 flapper wheel is all ill need for my polish and as for porting tools, I have my fair access to those.

I have a stock rb30e atm, Im experimenting with a td04l from a 2L wrx engine bolted straight on, I feel safe the injectors, AFM and ECU etc will cope, im more concerned about chocking my exhaust. Small boost, standard compression, running Premium Unleaded with a real nice polish.

Any views on this idea are appreciated.

[Alf]

Off topic:

$4 flapper wheel is all ill need for my polish and as for porting tools, I have my fair access to those.

I have been searching all over the gold coast, none of the tool shops I've been to have the flapper tool, anyone know who sells them?.

[Warpspeed]

Mr Skyline,

Saying someone has made 504Kw is one thing, but you cannot make that sort of power with a totally stock engine, no way.

Highly modified Skyline GTR engines with the four valve DOHC head are reputed to be now capable of over 1,000Kw, so what ?

The fact is, the DOHC head is a much better basis to begin from. From there you can spend insane amounts of money, but the DOHC will always beat the two valve for any given budget.

I have never heard of anyone with a GTR fitting the VL cylinder head because it is somehow better. Have you ?

[R31Nismoid]

 

Best bang for your buck would be a DET head with aftermarket camshafts. If you still want more, get that ported.

meh, dont bother porting the 25 head.

just dial in 1-2psi more boost and thats free, not $500-$600

[R31Nismoid]

Hey, this whole DOHC, SOHC thing, I don't know... SOHC making 504kW at the wheels isnt so bad, to my way of thinking.  

RB30E heads are prone to cracking mainly in the VL's. VL's standard were released with small radiators, Aircon models have a thicker core, not to mention if you bleed the airpockets from the head you should be fine.  

I find, much like a point made earlier, that the SOHC is a cheaper, easier and to me the smarter way to go, especially if we are talking drag application, I mean, they make the big power. You can make the head bolts bigger if you like, build it strong, spew boost down it and hold on. These engines are really not given the credit they deserve. Much like the heads.

Here are my views/bits of info

1) Of topic a bit, the VL heads cracked due to the mounting position of the radiator, not the size. The radiator sat lower than in the R31 skyline... something holden overlooked.

2) Anything can make big power with... big money.

3) The stock RB25DET head can flow enough for 300rwkw with no cams or porting. It can be better with cams and stuff of course, but for a stock head thats much better. Most VL's you'll find at least have had to put a cam in to hunt for more than 250rwkw as the head simply does not flow like the 25 one stock for stock.

4) The RB20DET/RB30et heads flow roughly the same

5) RB25/25 heads flow roughly the same (as stated about 30% more that point 4)

And to answer your question Guilt-Toy about the times run by VL's etc.

Remember yor comparing VL racing against GTR/GTS-t racing.

The cars are very much different, and most Skylines you'll find are manual. Not the point and shoot Auto's the VL boys use

cheer - ash

[Guilt-Toy]

anyone else want to tell MrSkylineRB30ET that he has no idea and that he is an idiot ?

he gets his info from a commodore workshop manual...

LOL

hahahahahahahahahaa

and various websites

Things a Friend said about of MrSkylineRB30ET

LOL funny shit. he has no idea what he is on about.

[DoughBoy]

1) You will never get the same amount of valve area in a 2V head vs 4V - 4V heads will always have a larger total of valve area compared to 2V, with lighter valves (better valvetrain dynamics, higher RPM and better sealing possible), better combustion chamber shape (and a more ideal quench area) and alot better flow.

2) 2 ports will produce more power than 1 port. If you want the single port to flow as much volume as 2, runner velocity is going to be up the shit. Runner velocity is more important than total flow figures, but in both cases a 4V head is going to be better than a 2V. Even if your application demands flow>velocity you are still going to get more from 2 ports. There are a multitude of tricks you can do to the 4V head, not many are done since they are not necessary to produce the flow figures needed.

3) You can enlarge the head studs with 4V heads as well, don't think it's a 2V only mod.

You'll also notice that with alot of the "big power" single cam VL's they are running less power than capable to run quicker times, they are making too much power as it is and can't hook it up. Then again, 30+PSI with a 140lb/min turbo is going to make a ton of power on any moter....

[MrSkylineRB30ET]

I get my information from alot more reliable sources than just websites and books, effy, mr i have two cams so that means i have double the duration and lift. You want to talk about me know nothing yet you argue octane, boost and compression levels have nothing to do with detonation, if you wanna take the word of a spastic little child who throws a tanty over how he didnt get mcdonalds, be my guest.

As for the other thing, you can only learn from trying.

[R31Nismoid]

dont take it personally dude. Not everyone is an expert

[Alf]

anyone else want to tell MrSkylineRB30ET that he has no idea and that he is an idiot ?

he gets his info from a commodore workshop manual...

LOL

hahahahahahahahahaa

and various websites

Things a Friend said about of MrSkylineRB30ET

LOL funny shit.  he has no idea what he is on about.

Why havent the mods stepped in? this kind of childish behavour doesnt belong here esp from a 26 yr old.

Mr skyline has a Valid point and is entitled to his opinion.

[R31Nismoid]

Mods aint stepped in (me) cause for gods sake.

If i went around editing things everyone someone has a bit of a stir... i'd never get a chance to read the forum myself.

He is entitled to an opinion, and he has given it. As with anything, there are other points too.

[RB26zcar]

Mods aint stepped in (me) cause for gods sake.

If i went around editing things everyone someone has a bit of a stir... i'd never get a chance to read the forum myself.

He is entitled to an opinion, and he has given it. As with anything, there are other points too.

Well spoken.... I drop in quite often to try and learn from you guys, and a little humor is nice once and awhile :wassup:

Please keep this thread going.... :headspin:

[Guilt-Toy]

Thanks Nismoid.

This guy has been trying to convince me to take the twin cam head off my RB30DET and put a single cam one on there and run a $4 flapper with a drill over it to make up for the single cam.

He needed to be put into his place. He has no idea that a RB30DET is far superior to a RB30ET any day of the week no matter what the modification is.

Now we all know that running a flapper wheel over the combustion chamber and exaust ports will increase flow & allow more agressive ignition maps which will give you a small increase in power wether it be a twin cam engine or single cam engine. But more importantly we know that is it not nesessary to reach 400bhp on an RB30DET with compatible support systems in place. OR even a RB25DET OR RB20DET.

Correct me if i am wrong but isnt the $4 flapper wheel a "OLD SCHOOL" technique ??? with the power gaines in other area's for the same money as a retail port job and flow be no way near the power increase as a bigger turbo and bigger injectors with a proper ecu to controll the Ignition & fuel maps ?

We all love nissan engines and we dont really care if it has two cams or one. But luke. get a clue.

Ive had my say.

[R31Nismoid]

also a DET motor will rev harder for less

Well spoken....  I drop in quite often to try and learn from you guys, and a little humor is nice once and awhile  :wassup:  

Please keep this thread going....   :headspin:

thanks for the support.