Performance advice please - STD 2T vs STD 4AC

[sneaky pete]

We race a RWD Toyota in a 1600 standard class and we have a choice between using the 2T and the 4AC engines but in pretty std state. Now we know the 2T pretty well by now but I just want an experienced opinion on the 4AC. Is it maybe worth it ? Have we maybe missed something? All we may do is an exhaust branch and a 36 or 38 Weber (2T just loves that 38!), overbore to max specified by manufacturer and bump up the C/R to max and that is about it!.

Here guys say the 4AC heads are a problem and rather stick to the reliable old 2T. Your comments please.

[AE3SGTE]

Never had a 2T of any description, so can't comment there....
I had a decent 4A-C with a 32/36 Webber & Cam regrind in an AE86 many many years ago.
It wasn't the slowest thing on earth, but got dusted by a stock AE92 with a 4AFE at the lights one night....pretty embarrassing really.
Could you use a 7AFE block with a 4AC head and Mitsubishi colt timing belt (7AC P plater spec) and get away with it?
That would definitely be sneaky!

[sneaky pete]

Yeah it is tempting!!!! Unfortunately as soon as you start doing well (and the 2T is going well - points leader at moment so very much in spotlight) then they dismantle your engine and you loose your points and can even be banned if you have been naughty! Come now please guys give us your opinion - how does a std 2T compare to a std 4AC performance wise ?

[ctrain]

stick with the 2T they come out with 105hp stock at the flywheel, if its a 5 speed you got a winner, the 4ac only comes with 78hp at the flywheel plus most 4ac's are FWD (gay)

(these figures are based on australian versions)

[sneaky pete]

Thanks for the reply. The model we are building for our new car came out with the 2T and then later the 4AC - thus my questions about the 4AC. The motors we are racing against are largely SOHC. Based on the lack of reaction, 4AC rumours here of an unreliable cylinder head, our success with the 2T so far, etc., we have pretty well made up our minds to stay with the 2T as you suggested.

[Hen]

I have fairly limited experience with the two motors, but I'd lean towards 2T due to crossflow head. The 4AC ports and head in general are apparently sub-standard at best.

[oldeskewltoy]

stick with the 2T... the 4AC head has pretty small ports, and it is not cross flow. Do to it not being a cross flow head, the exhaust ports are not shaped well for performance.

[MorGo]

4A is a nice torque engine but not a first choice for performance.. Properly ported and cam timed the 5'th gear comes useable passing gear and generally nice to drive but match the 2T for power.. never.

[sneaky pete]

Thanks again guys. We have received some local support from different sources (engineering works, fuel, etc) so things are looking up.
Well the new cars engine is at the engineering works being bored to max o/s (1mm and not 1.5 as I thought originally) spec according to Toyota. Eventually got some new 46mm pistons. Regretably the pistons have 2mm instead of 1.5mm rings. I wonder how much of a difference the 2mm ring width will make? - any comments? I have sourced some 2mm chrome top /1st rings as I was worried about cast iron rings here- the new car has a 4.3:1 diff vs 3.9:1 in the old car - so it will be revving higher and general feelings is that cast iron rings do not like to be revved - comments?
The head has been done with new std valves & guides. Just got to work out the c/r and skim the head accordingly.
Please feel free to comment on your experience.

[oldeskewltoy]

Hmmm, I have no specific comment on the rings... for that I'd ask the ring manufacturer what they would suggest for your intended rpm range.

Are you allowed any port work??