Hey boys dont know which way to go. I either want to use my old rb30e and put the 25 twin cam head on it or buy a RB30et and rebuild it. Anyone got any info on this topic and thoughts on which way to go? It will be going into a calais being street driven and raced at the track. Would be looking at a 10 or 11 second engine. What would be the best way to go. Cheers.

What is your budget?

its a tough one hey personally, im all for the twin cam head but do your own maths. add the costs of the twin cam conversion itself and the little work you need to do to the head to reach your target and then add the costs of working the sohc to reach the same thing. i ''think'' in the end, the twin cam head will get you that power for cheaper. Remember, simply adding the DOHC gives you 35% power increase and think of how much you would have to work the SOHC to reach a 35% increase aswell. Just my opinion tho.

I would imagine that you could have less agressive cams in the twincam headed motor because its more efficient, they should help to retain better low down torque, better idle but still be able to allow it to breath good at the top end of the powerband too. Where if you want the SOHC to flow the numbers you will need a fairly lumpy cam, which may give a crappy idle and loss of low down torque. That may or may not be a problem, depending on your application and the results you want to achieve. Mick

I actually have the same dillema, cost isn't really an issue for me as it's a long term project. I'll be spending more time on the street and the circuit. So i'll probably end up going for the twin cam head due to less fuel consumption, more low down torque, smooth idle and expandability options.

Buy a RB30ET work it with the SOHC! It will be original looking and still you can get easy 11 & 10 sec time's...

go the single cam head hav any of u guys that say use the twin cam head actually been in a twin cam headed vl before when making big hp u will still need bigger cams with a rough idle and there will b no extra low down torque u forget that the rb25 is a rever its cams are not made for low down torque as the rb30 cams are the rb30 will make the same power with less revs and there is no way u will get 35% more power from a 25 head that is just an old myth lol as for the rb26 head thats in its own league best by far u will get huge results with that just my opinion cheers brendan

go the rb30 - Im not a great fan of the engine conversions etc Im ya traditional old vlt lover.... If you want power, got rb26

Quote: Originally Posted by vl30psi go the single cam head and there is no way u will get 35% more power from a 25 head that is just an old myth lol just my opinion cheers brendan what is the actual power gain from the DOHC then?

As far as i know, JET88C is still running standard cams in his RB25/30. And it cuts 10's easy. Mick

Buy my RB25/30 car and do it up....PLEASE

theres a R.I.P.S skyline over here in kiwiland that has: -Stock? rb30 block -stock rb25 head -FACTORY rb20det exhaust manifold -big turbo does 10 sec 1/4s!!!!!!!!!!!!!!!!!! considering that the rb30's in vl's always have electrical problems and suck the gas hard then wouldnt a twin cam head be the best for reliability, fuel consumption etc???

Again in the "I have Heard" pile..... Standard RB30 bottom ends do not like big revs and tend to fly apart when they do i.e RB25 twin cam head conversion on RB30 and new found 8500rpm red line!, however they can handle big doses of boost OK. A serious bottom end rebuild would be on the cards for any serious Twin Cam head conversion i.e $$$$ And who gives a 'F' about fuel consumption when chasing 10 second qtrs Speed costs fuel...get used to it Some original photos have not been recovered yet.

Walkinshaw Wagon; thats Rob's car, does a 10.4 1/4 with a 5 speed box in it. The head and bottom end are stock. The intake and exhaust manifolds are stock but have been modified. To get the 10.4 he also used a 60hp shot of NO2, otherwise it runs low 11s. And afaik, the turbo is a T3/4 hiflo.

Quote: Standard RB30 bottom ends do not like big revs and tend to fly apart when they do i.e RB25 twin cam head conversion on RB30 and new found 8500rpm red line!, 7500rpm is where harmoic problems come into play

Depends on what mods you would do to the SOHC. If you are going to do the ecu then I would use the twin cam head as with the twin cam head you have to do the ecu anyway. Then you have to work out if its worth the extra $750-900 for just the head or $1300 for a complete rb25de. Just the heads are hard to find unless a jap wrecker has been sitting on a rb25de complete motor for a while and simply was to get rid of it. The twin cam RB30 gives you a much wider power band and a lot more torque every where. Also.. I don't know of any RB25's with stock cams or even mild cams that make peak power at 8500rpm. They all tend to change gears at around 7500rpm which by then they are making from 350-400rwkw anyway. The twin cam head doesn't drop torque as rapidly so you could rev the motor to 8500rpm but why would you when you can change gear and accelerate at a slightly quicker rate. The RB20's tend to rev up to 8000-8500rpm but this is because of their smaller baby valves and cubes. Hence they need to rev to get the airflow to make power.

why do you have to do the ecu when you put an rb25 head on??? think about this one.... not as stupid as it sounds. Surely you can change the cas trigger and ignition module to suit direct fire coils, run them in a batch sequence...... Surely not the greatest way of doing it, but i do believe it is possible

personally id go the twincam head... twin cam have always had there advantages....nothing wrong with single, but i know if i had the cash and the option which way id be going good luck,hope it all turns out well

HYPED6, You could do that. You would also then have to try and adapt all of the RB30 sensors/hardware. Some easy, some not. Coolant temp sensor, Airflow Meter, Oxygen Sensor, Injectors, Throttle position sensor. Anymore?!?! I think thats it. Wouldn't be too much of a problem. So I assume the RB30 stock ECU uses batch ignition fire? Does the VL ECU use sequential Injection? From a performance/economy point of view batch ignition doesn't cause any negatives however batch injection does cause a loss in performance and economy due the fuel sitting around in the ports waiting for the valves to open, in turn a loss of atomization.

Quote: Originally Posted by spooln Hey boys dont know which way to go. I either want to use my old rb30e and put the 25 twin cam head on it or buy a RB30et and rebuild it. Anyone got any info on this topic and thoughts on which way to go? It will be going into a calais being street driven and raced at the track. Would be looking at a 10 or 11 second engine. What would be the best way to go. Cheers. dane put a wrx motor in it. i heard theyre sick!!!!!!