To4z And Alternatives .

[discopotato03]

Hi all , people are starting to ask the power potential of the TO4Z and its worthwile discussing some of the available alternatives .

It no secret that the TO4Z cartridge is an evolution of the Garrett/HKS TO4R turbo and now has a modified GT40R/GT42R/T51R style ball bearing centre section . It also uses the TO4 P trim turbine which is getting pretty long in the tooth . Its surprising that they chose that turbine given that the ball bearing GT40R was being developed though to be fair it was not then being tested in its final form (Garrett were still playing with the 84T GT40 turbine) .

Garrett is starting to change their ideas about turbine trims for petrol engines and moving down from the agricultural 84T to lower sizes such as the 78T in the final release version of the GT40R (GT4088R) . The old P trim measures about 74.2mm OD and is 76 trim , its rather heavy and uses I think 11 blades compared to the 10 Garrett uses on the UHP family ie GT35/37/40/42 . Many people are saying that the 68mm GT35 turbine can pretty much do the same job while being more compact and have less innertia to overcome at the spool phase . It sounds good to me though The 68mm turbine compared to the 84mm TO4R compressor wheel makes me think hmm are the turbine blades long enough to get good easy low gas speed shaft power , did the TO4Z use the P for this reason ? I think Garrett should have looked at using their 72.5mm GT37 turbine in an appropriate trim to replace the aging P when it grew balls .

The fact that the GT40 ball bearing cartridges turbine is 78 trim rather than 84T sent me after its turbine map to see how it weighed up compared to the GT35R's turbine map . The smallest .85AR turbine housing for the GT4088R comes out at a similar ~ 32lbs of corrected flow to the GT35R with its largest 1.06AR turbine housing thought the 40R reaches this point at lower pressure ratio than the 35R .

Then I started to find mention of a hybrid GT40R 67 (67 is what the Americans call the TO4R compressor) which is the GT40R hotside and the TO4Z compressor end combined .

A company called Precision Turbo and Engine get this combination made up and market it in the US as the GT4067R .

The as sold GT4088R is no slouch either though it has gone to a new 7/14 blade GT compressor of the C117 family . It uses a huge .72AR GT40 port shrouded cover which looks like a carry over from the TA45 series turbos . The debate over GT4067R/GT4088R is ongoing in the US but the power developed is easily in the 7-800Hp and beyond with the best optomised housings and engine setup . The Honda/Lancer/Supra people are developing all sorts of things ATM and much of it surrounds these turbos or the even larger GT42R/HKS T51R . Just on these last two take note that HKS's T51R gets the 76T 82mm turbine while the Garrett GT42R gets fobbed of with the 84Trim 82mm turbine - Power and Response by High Kost Spec .....

So anyway the TO4Z or GT4067R or GT4088R are all vying for the 650-750Hp arena with the US performance crowd pushing the two GT40R based turbos . I have a feeling that the Precision GT4067R will be the best all rounder and very tunable with turbine and compressor housings . Its unfortunatly going to be the most expensive of the non HKS options because it has to be disassembled and balanced plus its unique backplate machined up and fitted . Garrett could do a lot worse than offer it themselves .

Any of these turbos are not for the faint hearted and probably need a high reving RB26 or preferably an RB30DET to do them justice .

Cheers A .