Rb30 Head On 25 Block

[pf.]

Hi all what would be the go with this what would I need to mod the head or the block? Also how and what would I do to do this.

Also I do not need anyone telling me to use a 25 head there is reasons why I am doing this I could work it out myself but want to fast track the process.

Thx for helpful responses in advanced.

Edited April 1, 2013 by pf.

[mad082]

don't know if this is an april fools day joke or not. if it is, you posted it after 12pm, so it doesn't count.

why would you want to make an engine less powerful than stock?

as for what you would need to do to make it work, i wouldn't have a clue. i'm guessing that you would be one of the few people who have decided to go down the route of making a single cam rb25, given that the rb30 only made 115kw in 3L form, so dropping the capacity by 500cc will drop power down to well under 100kw at the flywheel (where as the standard rb25 makes over 140kw at the flywheel).

so sure, you may have your reasons for wanting to do this (which i'd like to hear), but the simple fact is that it is a bad idea and all of the replies you are going to get are going to say that too. you are better off using either the complete rb30 engine or a complete rb20 or rb25 engines. any of those three are going to make more power than what you are planning on doing. as well as being much cheaper.

[89CAL]

[pf.]

Well I already have a 25/30 so I was going to recycle the leftovers. A engine builder has said he can build a 30 head to flow better for alot less in fact he believes the 30 head will flow better allround.

I do not want any talk of 25/30's as I already have one being built it will be turbo.

Edit at the end of the day a 25 or 6 head could flow better particularly the 26 head I doubt the 25 head would for n/a but it will cost a lot more money buy more I mean like 3 times the cost. The engine builder I spoke to said he could get me upto 350hp or more with a 30 head that is on a 30 block though.

Edited April 1, 2013 by pf.

[pf.]

Also a advantage of using the smaller stroke of the 25 block means if I get a cam for 8k then it will spin up easier.

[mad082]

Well the most I've ever seen from a built rb30 is just over 230rwhp (and it revved up to about 8000 rpm from memory), so to get to 350 would be extremely unreliable and probably require race fuel to get there (not to mention a metric shit ton of money). Unless he is talking flywheel horsepower, which would put you back at about 250 to 270hp at the wheels. Then take into account the smaller capacity, I'm guessing you might just crack 200 if you are very lucky.

But good luck with it. I'm happy to be proven wrong. I just hope you are happy with the results and don't blow a heap of cash and get nowhere.

[pf.]

Yea I am talking flywheel hp. The engine builder I am referring to has built 2v 6cyl race engines up to 350hp fly he said a rb30 build could see me at 350 fly I trust this guy's words.

Edit here is his words quoted.

BMW E20 engine, 2.8L, 2 valve per cylinder, SOHC, E85 fuel (I did the head & intake, specced the cam & provided specs for headers etc)

260rwkw (351rwhp) @ 8000rpm.

That 120% VE @ 8000rpm.

Tis only fed with 45DCOE's with 40mm chokes as well.

I predicted it'd peak at 7800rpm, so I got it wrong by 200rpm, I was short 40hp on my estimate as well.

Another engine that made exactly the same peak power (not a BMW engine) went on a engine dyno shortly after & made a tad over 400hp - so it's a pretty good bet this little beamer is doing about the same.

PS - 2.3hp/ci f**k yeah!

Edited April 1, 2013 by pf.

[pf.]

Oh yea I don't think he told me I could make 350hp but after seeing his recent builds I think he could but I am not using this guy. I have local mates that are builders so ill look around for a good head porter and get my mates to build it.

Edited April 1, 2013 by pf.

[niZmO_Man]

Lol do it and post up the results.

[XKLABA]

ROFL, that's gold

RB30 single cam has bigger ports than any other RB ( including the 26 ) the problem is air velocity which is why 25/26 heads on 30 bottom ends work better in N/A form, loss 500cc and there would be very little air speed left

like previously stated by others, happy to be proven wrong so do it and post result

[MBS206]

The 30 may have two big valves, but the 4 valves in a RB25/RB26 head mean more valve area which = more air flow = more power.

Secondly, 120% VE? BWAHAHAHA... You know this guy is trying to tell you that each time your 2.5L engine completes a full cycle, it's really taking in 3L of air... Or in a very simple terms, running 3 - 4 PSi of boost?

It's nigh on impossible to make an NA engine 100% VE, yet alone 120%!

Edit: I did some light digging, and it appears the RB30E runs a 42mm valve, while the RB25 runs two 35mm valves... (WOAH! The RB25 is smaller... Wait... We knew that)

What this works out to is the RB30E has roughly a 130mm^2 valve area (I have not subtracted the very tiny amount for valve part going back up to the head), whilst the RB25 retains a 219mm^2 valve area...

Now what does this mean... The RB25 for the exact same air speed, can actually draw in MORE air then the RB30... Or, to make this simpler, to get the same amount of air in, to make the same power, the RB25 has a lower air speed (The opposite of what you've said)

Also, if valve sizing was idential, an the RB25 had a high air speed (Like you've claimed) what you're actually saying is the RB25 head allows more air into the cylinder. This is good. Why is this good? Because you can shove more fuel into that cylinder, to keep the AFR identical. More fuel and air in the cylinder when it comes to ignition, means a bigger BANG... A bigger bang means more power.

You've provided yourself with all of the evidence as to why an RB30 head on a RB25 bottom end will be completely terrible.

Not to mention, there is nothing majorly different between porting an RB30E head, as to an RB25DE/DET head. Which begs to question, why is your engine builder charging you three times as much to port your RB25 head over what he says he'll do for the RB30 head?

[Birds]

PF = performance forums?

[Captain Natro]

People make life difficult sometimes. Just build it, put it in a vl and chuck skids...

[89CAL]

If you want to work with leftovers, why not just buy a second hand RB25 Head. I've seen plenty on here for less than $500

[pf.]

The 30 may have two big valves, but the 4 valves in a RB25/RB26 head mean more valve area which = more air flow = more power.

Secondly, 120% VE? BWAHAHAHA... You know this guy is trying to tell you that each time your 2.5L engine completes a full cycle, it's really taking in 3L of air... Or in a very simple terms, running 3 - 4 PSi of boost?

It's nigh on impossible to make an NA engine 100% VE, yet alone 120%!

Edit: I did some light digging, and it appears the RB30E runs a 42mm valve, while the RB25 runs two 35mm valves... (WOAH! The RB25 is smaller... Wait... We knew that)

What this works out to is the RB30E has roughly a 130mm^2 valve area (I have not subtracted the very tiny amount for valve part going back up to the head), whilst the RB25 retains a 219mm^2 valve area...

Now what does this mean... The RB25 for the exact same air speed, can actually draw in MORE air then the RB30... Or, to make this simpler, to get the same amount of air in, to make the same power, the RB25 has a lower air speed (The opposite of what you've said)

Also, if valve sizing was idential, an the RB25 had a high air speed (Like you've claimed) what you're actually saying is the RB25 head allows more air into the cylinder. This is good. Why is this good? Because you can shove more fuel into that cylinder, to keep the AFR identical. More fuel and air in the cylinder when it comes to ignition, means a bigger BANG... A bigger bang means more power.

You've provided yourself with all of the evidence as to why an RB30 head on a RB25 bottom end will be completely terrible.

Not to mention, there is nothing majorly different between porting an RB30E head, as to an RB25DE/DET head. Which begs to question, why is your engine builder charging you three times as much to port your RB25 head over what he says he'll do for the RB30 head?

You are new to engine dynamics by the sounds of this there are many factors that give a two valve head a performance advantage at a cost ratio to four valve head. Yes four valve heads can flow higher numbers but cost a whole lot more to build think about it I am going to use bigger valves so I only need half as many and so on down the valve chain. I'll edit in some other facts soon.

Quoted " You can't beat the quench & flame travel characteristics of a good 2V head, nor can you beat the pressure recovery characteristics & efficient discharge coefficient than can be achieved.

4V only have the curtain area advantage, other than that they are inferior in every way.

That curtain area advantage is a big one tho & makes up for the other shortcomings at higher rpm.

Bet most people don't realise the curtain area advantage is not as big as it looks on paper tho - valve to valve shrouding reduces the effective curtain quite a lot & the necessary placement of the valves requires more valve/bore shrouding as well, also direct acting cam on bucket setups are significantly lift limited compared to rocker arm setups.

A canted 2V head can place the valves away from the cylinder wall so that the curtain area available can be almost fully utilised with fairly even discharge around the whole circumfrence of the valve - that makes for a very efficient intake tract with little or no 'wasted' volume. Compare that to a 4V head with it's shrouded valves, which must have port/bowl area above them even in areas that are innactive - resulting in less efficient use of the port volume, lower pulse tuning 'signal' & lower velocity ram effect.

In short - a well developed 2V head can outperform a 4V head up to the point where curtain area becomes the restriction in the 2V head, from there the 4V will outperform.

Oh yeah, you also have excessive pullover & reversion on 4V heads - by their very nature low lift flow is good, too good in many cases, something that flows well in one direction usually flows quite well in the other direction, so at lower rpm 4V engines experience higher rates of reversion (that's why they are doughy down low, got nothing to do with big ports).

They also waste more potential trapped VE out the exhaust as that high low lift flow comes into effect at higher rpm during the overlap period."

Also with the ve-volumetric efficiency you do realise that the scavenge effect can draw air through the intake faster it is called induced exhaust sometimes. This is the whole Idea of using tuned extractors so the crate a scavenge which will induce air flow.

Do you even know that compression increases with rpm it is called dynamic compression this is what I mean by you don't understand the dynamics of a engine, you just quote paper figures.

Edited April 2, 2013 by pf.

[pf.]

PF = performance forums?

Performance forums????

[pf.]

Also a point I want to make is that making a proper tuned exhaust is so much cheaper and easier with a 30 over a 25 head yes this is not of concern with turbos but n/a it is. To make the correct exhaust for a 4v head you need some very good metal skills as a oval port just doesn't cut it for a high power tuned n/a exhaust, round ports are so much easier to cater for.

Edited April 2, 2013 by pf.

[pf.]

. Which begs to question, why is your engine builder charging you three times as much to port your RB25 head over what he says he'll do for the RB30 head?

Also I never said he was my engine builder I would not send any of my parts to him, not due to his workmanship just because I think he is a cock. But I have my engine builder mates that are well and truly capable of building a donk I just need to send the head away for porting.

[MBS206]

Well Al, you and your 1500HP GTR seem to know everything, so how about you f**k off and waste your money making no power?

You seem to like quoting a lot of stuff yourself, like quoting paper without actually knowing what you're on about yourself.

You claim in one post that the 25 or 26 head will flow more, then you go on to claim the RB30 head will. (It has to flow more to make more power, think about it for a minute)

[pf.]

Well Al, you and your 1500HP GTR seem to know everything, so how about you f**k off and waste your money making no power?

You seem to like quoting a lot of stuff yourself, like quoting paper without actually knowing what you're on about yourself.

You claim in one post that the 25 or 26 head will flow more, then you go on to claim the RB30 head will. (It has to flow more to make more power, think about it for a minute)

I never said that a 30 head would outflow a 26 head I did say that it might outflow a 25 head. Now what I am saying is yes I can use a 26 head but this would put the cost up very high for the small gain it gives. Remember this is a leftovers engine I will build it right but I wont spend big on it.

My name is not Al I did not want anyone to know my name so I lied but I will be truthful my name is Pat Famington and I do not own a 1500hp gtr I just thought that would be funny to write

The reason I thought saying I had a 1500hp gtr would be funny is of course we all know here that it is nigh on impossible.

Edited April 2, 2013 by pf.