T3/T4 turbo housing problem

[CHB]

guys i just got myself a T3/T4 turbo from my local turbo dealer. it has hotside A/R0.63 with 56mm exducer diameter and 58mm compressor wheel. my engine is 3T-C 1800cc and fitted with low comp forged pistons running on Megasquirt 3.0.
when i "drive" it, the engine feels very flat and the boost comes on very late and when i reached 7000RPM only 12psi is built up.
after discuss with the dealer, he recommended me to change to 50mm exducer and same A/R0.63, which i did. the boost now comes on a lot faster and drive great!
but lots of my other friends says better stick with 56mm exducer and change to lower A/R (ie 0.48) will have better high revv power. so i am confused now.. any input guys?

[3jcelica]

What is your compression ratio? what pistons are you using?

[CHB]

i never calculate the static compression ratio but i guess it is around 8.0. its from 2JZGTE.

[3jcelica]

I will calculate your static compression ratio shortly, but from my brief look I think you may be at 7 or lower unless you have shaved your head and decked you block significantly??

this could explain the boost coming on late and not hitting your expectation. Standard compression for a 3tgteu is 7.9 I think, the 2jzgte pin height is lower (~1mm resulting in ~5.8cc of extra space in the compressed volume) and the piston crown cc is significantly more i.e. -2cc(3tgteu) compared to -14cc (2jzgte).

all up you have added ~18cc per cylinder more to the compressed volume and therfore lowering the compression ratio from the standard one

Have you done anything to the engine to bring the compression back up?

I have done the calcs and make your compression ratio out to be ~6.4, which doesn't sound great

Roger

[CHB]

ok basically it is 3T-C with 63cc combustion chamber volume. i did not done anything on the head except dual performance valve springs, that all on the head, still stock head, stock valve etc.
the 2JZGTE pistons were mated to the stock 3T-C conrods. at TDC, the top of the pistons is exactly same heights with block deck height. bare in mind that stock 3T-C pistons has a dome top and this 2JZGTE pistons is bowl, so the highest of the 2JZ-GTE pistons is same height with the block deck.
previously i am using a stock CT26A from 7MGTE and it works great but it flat out at about 14psi@5000RPM and i struggle to get the car any faster than [email protected] 0-400m. ignition timing was set to 23*BTDC in boosted region and this is the estimation only as the nearest dyno is 900km away from my home. so all i have is butt dyno, wideband 02 and my Megasquirt.

[CHB]

another question,
does using smaller A/R turbine housing and bore out the exducer hole and fitted a bigger exhaust wheel really better?
for example, get a T3 AR 0.48, bore the exducer hole to allow a 2.2" exhaust wheel to be fitted really makes the turbo breath better at high boost high RPM?

[3jcelica]

CHB,

My calcs are on a standard 2jzgte piston with a compression height of 34mm and a piston dome with 14.8cc. The standard 3tc/3tg piston has a compression height of 35mm, and the 3tg piston has a 2cc piston (mainly for the exhaust valve relief I think). Hence you have a significantly lower compression height, this will affect the spool time and the amount of boost that may be achieved.

my 3tgt with the ct26 will spool by 3200 and can reach 20psi without to many problems, a t3/t4 with a .6 a/r should be ok. Mine has been on a dyno and my ignition at that boost is lower, I think this is mainly due to the fact that with that compression ratio, you need more advance. Such a low compression ration, I am supprised you car can run 15 secs

Roger

[CHB]

is there any remedy for this combo? maybe rise the boost higher?

[3jcelica]

Remedy would be to shave the head as much as possible (you should be able to take 1mm of the head without hitting the pistons, but I have no idea how this affects the cam), I have heard of people using pistons such as this i.e. 3sgte etc, and they seem to be welding up the head to reduce the dome capacity i.e. 63cc down to 50cc. I can't comment on this appraoch either. Your only other alternative is forged 3tgt piston or cast 3tgt pistons.

The effect of such low compression will be longer to come onto boost and boost achieved higher in the rev range, timing requires more advance.

Yes you could run higher boost to overcome the problem, but you will find your car boggy untill high in the rev range when a large amount of boost comes on.

Roger

[CHB]

thanks for the analysis mate.. its true that it is too boggy at no boost but once the boost comes its really turns into a monsters.. pretty scary to drive in the town..