[Mk2] [Turbo] Information request - Rev 2 vs Rev 3 head - Real world advantage?

[Danbob]

Hello,

The plan for next year is to megasquirt my Rev 2 and run a (Lag assist only ) direct port, wet Nitrous kit....

My question is, before I go ahead investing time in machining the rev 2 plenum for the Nitrous and boring out the fuel rail making it twin feed etc. Is there any fundamental advantage in using a Rev 3 head instead (I want to find out now as manifold/fuel rail is not interchangeable)?

When my stock Rev 2 (but only 17k miles of use) head gasket eventually goes (I predict at some point next summer) I'll consider doing some headwork when the car comes off the road. aswell as swapping the rebuilt CT26 to a CT20B - So by fundamental advantage I mean one that a rev 2 head could not achieve with retrofitted Rev 3 parts.

I heard the Rev 3 cams are 'better', can anyone tell me what is different about the profile? And can they be retrofitted to a Rev 2 head?

I know Rev 3 loses T-VIS and this may help peak power figures, but as the car is used for Sprinting I am quite keen to keep TVIS to attempt to maintain low RPM drive-ability (being able to stay in gear can save time).

In Summary:
If I bore out the Rev 2 fuel rail and use rev 3 injectors, would prefer to keep TVIS (may go for a larger plenum in the future like the ATS manifold), will be using the Megasquirt map sensor and rev 3 headgasket anyway and will have all winter to port inlets etc. of my rev 2 head and convert to Rev 3 Shim-Under-Bucket or 1ZZ shimless buckets
- Is there any advantage at all that a rev 3 head would have over this - other than the cam profiles IF the cams are not interchangeable?


Sorry for the long winded question, another consideration is that I already have the rev 2 head and all mating parts AND have a spare rev 2 head/engine, so if there is no significant real world advantage, then it won't be worth me considering.


Thanks in advance

Dan

[Super_red]

Cams are interchangable, you can swap the followers to eliminate the cam lobe causing the shim to pop out at high revs. You might also want to consider N/A cams as these are better still for lift and duration, a rev 3 inlet cam is the best stock cam from memory and you can fit one for the exhaust aswell.

With the MS you might want to reconsider the fuel injector swap as it only has 2 injector drivers so will run the car in batched mode and not fully sequentil like stock. You might find you need smaller injectors not larger.

What are your power goals? I beleive a rev 2 head is capable of everything a rev 3 is up to a certain level of power then one is better (which I dont know, rev 2 should flow more air peak I beleive).

[Danbob]

Thanks for the info on the cams, are you saying you can use thr rev 3 inlet cam for both inlet and exhaust? Thats an interesting idea! Has it been done with good results?

I'm building a Megasquirt 3 with ms3x so it will be more than capable of supporting full sequential and give me lots of other toys to play with. I'm not really chasing a specific power figure anymore, just want to keep the car competitive and satisfy my need to keep tuning. I just like the idea of future proofing, but it sounds like the rev2 head will be up to the job with a few tweaks!
Cheers

[Danbob]

Thanks for the info on the cams, are you saying you can use thr rev 3 inlet cam for both inlet and exhaust? Thats an interesting idea! Has it been done with good results?

I'm building a Megasquirt 3 with ms3x so it will be more than capable of supporting full sequential and give me lots of other toys to play with. I'm not really chasing a specific power figure anymore, just want to keep the car competitive and satisfy my need to keep tuning. I just like the idea of future proofing, but it sounds like the rev2 head will be up to the job with a few tweaks!
Cheers

[Super_red]

Yes you can use a rev 3 inlet for the exhaust as the cams themselfs are the same. The most aggressive OEM cam is the REV3 N/A inlet cam. but even this is not required if your goals are modest. I think on a CT20b there is not a lot of gain to be had swapping cams but this is not experience just my thoughts.

[Danbob]

My car will continue to constantly evolve so while the mid term plan is to run a ct20b, who knows what it might end up with, also with the ct20b I think running the more aggressive rev 3 cam will be more significant as I wont have a big turbo running big boost to make up the power.
So when I have the head off to replace the hg in the future, I may aswell swap to different 3 cams at the same time. Maybe I'll be able to pick up some NA cams pretty cheap from a breaker, I imagine na parts dont hold so much of a premium as the turbo bits?

Cheers for the advice, I think keeping the rev 2 head and swapping in bits as and when required is going to be the best route for me!

[RyanRs]

The rev3 head is superior to the rev 2. It flows far better due to better designs in the port angles and iirc valves. Once one has a rev3 head on there engine, there is not really much machining wise that can be done to improve its flow design (porting / polish etc). Big 800-900 bhp + 3sgte engines literally only go as far as fitting oversized valves and smoothing the combustion chambers, port shapes etc are more or less kept the same.

Also if you get a complete rev3 head, you will have the better cams, better valves, fitting holes for the superior rev3 fuel rail and shim under bucket design. Also the Rev3 head can accommodate a higher lift camshaft without requiring any machining work.

**Also must add.. If you do intend for more power later on, you will have to loose the TVIS . I am 85% certain the rev3 inlet manifold flows much better than the rev1/2 and it has no tvis plate to worry about. It also uses the larger TB.

[Danbob]

Thanks Ryan, that is a good point to consider aswell, it will probably be less work to just swap the head while doing the HG rather than faffing on fitting cams and buckets etc.

The only thing that was holding me back was I didn't want to spend time and effort machining the inlet for the nitrous and boring out the fuel rail only then to change it all to rev 3 stuff a year or a few months later, but I suppose I can always sell them on.

I'll start keeping an eye out for a Rev 3 head, but in the meantime will start work on my spare rev 2 inlet mani and fuel rail.


One last question, Can a NA rev 3+ head be used to the same effect? Is the head the same as the GTE only with the more aggressive cams? I know manifolds and injectors will be different, but does the head itself have all the same benefits of the Rev 3 turbo head?

Cheers
Dan

[gavinda]

Actually intake port angle is worse on the rev3 than rev2. Rev2 head can be made to outflow the rev3 considerably.
Standard intake ports theres not much in it, better velocity in rev3.
Rev2 is let down by its manifolds.

[gavinda]

Rev3 head is more side draught hence needing more wasted stem valves. this showed no advantage when i tested it in a rev2 head if i remember correctly. In fact the valves in the rev2 were better for the rev2.

[Danbob]

Interesting, Does anyone have any data to prove either way which is better?

Does anyone know if the Rev 3 NA head can be bolted up with no downsides? As I think I can get an NA head considerably cheaper than a Turbo head.


If a Rev 2 head flows better with rev 3 cams fitted then that's great for me though!

[gavinda]

Rev3 turbo exhaust valves are different to na , to withstand the heat

[bolton]

Rev2 will out flow the rev3!
The intake ports on the rev2 are massive!!!

[RyanRs]

Interesting Gav.. do you remember who did the testing?

Bolton.. its not down to the Flow alone, its also velocity and having big chunky ports is not good for velocity! Think of the intake plenum... the larger it is, the longer the air will take before it finds a path into the runners. Have a plenum too small and it becomes restrictive, too big and you loose velocity.. you need the happy medium. From what i have always understood, the rev3 head was better tuned for optimal flow/velocity over the rev2 and not much needs be done to the rev3 to produce serious power (800 whp onward). i guess if you was aiming for over 1000whp then perhaps a rev2 head would be the better candidate for some port butchering, but until then the rev3 is better.

Plus.. look at the celica that won the hillclimb at goodwood.. twincharged rev3 with something like over 1000 fwhp!

[gavinda]

Yes ryan i remember as it was from my own testing.
I believe jonnys twincharged celica is at around 800hp.
Top power builds i can think of run a rev2 head.

Like i have stated rev2 manifolds are the main problem on rev2 setup/optimisation.

The rev2 intake port tapers down quite a bit bolton so overall difference in flow is not much.

I have a modified head package that i am bringing out to market

[JAP BOY]

Yes ryan i remember as it was from my own testing.
I believe jonnys twincharged celica is at around 800hp.
Top power builds i can think of run a rev2 head.

Like i have stated rev2 manifolds are the main problem on rev2 setup/optimisation.

The rev2 intake port tapers down quite a bit bolton so overall difference in flow is not much.

I have a modified head package that i am bringing out to market

Interesting be nice to know some rough prices

[ashley]

Yes ryan i remember as it was from my own testing.

Would you be prepared to share the results of your tests? Flow data etc?

Would be extremely interested to see, even if just by PM...

[Danbob]

All interesting stuff seems like there is still quite a lot of debate! As for 800hp this would be completly irrelevant for my build. I think an eventual 500 would be my max and this would be several evolutions on from now

Does anyone on here have a rev 2 running a ct20b, rev3 cams and injectors and an aftermarket ecu deleting maf? Would be good to compare dyno results against a similar spec rev 3! Not just for peak power but to see the torque curve!

[JAP BOY]

Does anyone on here have a rev 2 running a ct20b, rev3 cams and injectors and an aftermarket ecu deleting maf? Would be good to compare dyno results against a similar spec rev 3!

Think most do the above but not swap the cams out it would defo be interesting not to hijack the thread but pretty much was under the impression that the american boys were frequently running big power with stock internals also i though they only got the very early editions of the Mk2 turbo so rev1/2 and there is quite alot of them making the power... Maybe some swapped out the head with cams would be interesting to see what they did around the cylinder head

[gavinda]

I have a modified head package that i am bringing out to market [/quote]

Interesting be nice to know some rough prices [/quote]

I am still working out the package and price would be dependent on exact spec.

need to test a rev3 head with oversized valves and throat correction for comparison. when i have finished the fully ported heads at stock valve size and oversize then i will dig out all the data ashley and tabulate it, il let you see some data then..but basically i have put together what i believe is the best head and have the data to back it up.