Turbos for the 660

[cj!]

Ross, Steve and I have been discussing on and off possible alternate turbos for the 660 engines. Your input on this would be appreciated.

The original turbo fitted to the F6A and some K6A engines (mine) is verrrrrry small and is an IHI RHB31FW, also known as a VZ25. The other variant fitted to the K6A is a Hitachi HT06.

The RHB31FW is also sold in a modified form by Suzuki Sport.

From what I can tell the RHB31FW has the following specs (Japanese translation)

Suzuki Sport (OEM)

Power: 100ps (with 295cc injesctors and modified ECM) (64ps)
On-diameter: 30 (25)
Outside diameter: (compressor?) 40 (37)
Outside diameter: (turbine?) 39 (36)
Out-diameter: 32 (28)
A / R: 9 (7)
Trim compressor: 74
Boost 1.3 (0.9)
Pressure relief 0.9 (0.7)

I have seen a Garrett GT1241 listed for 400cc to 1200cc and 50 - 130hp applications which has the following specs:

http://www.turbobygarrett.com/turbobyga ... 068__1.htm

Compressor
A/R: 0.33
Inducer wheel: 28.99mm
Trim: 50
Turbine
A/R: 0.43
Wheel exducer: 30.12mm
Trim: 72


A possible second hand option is a Garrett T2 as fitted to early Pulsar/EXA which put out 86kW. The T2’s compressor inlet is 45mm diameter and the discharge nozzle is flared to 52mm at the slip-on hose connection. The compressor housing is also marked with a 0.48 A/R. Exhaust gas passes through a 50 x 39mm turbine passage and the mounting flange is 63 x 93mm. The turbine and dump pipe both connect with 4 bolt flanges. The T2 turbo uses the same turbine mounting flange as some larger T25 and T28 turbochargers and there was also a water cooled version.

Other options include the Daihatsu Charade (993cc) which used a V04 trim IHI RHB32 and the early Toyota Starlet ( 1.3 77kW) which used a CT9 or possibly one of the turbos off a twin turbo Subaru or twin turbo Supra. There is also a Hitachi HT07 as used on the 1.0 K10A engines.

[gwagensteve]

Ross and I discussed the Pulsar ET Turbo as there was one at Pick-a-part and I thought it might be $150 well spent. However, apparently they will be far too inefficient for a 660 - even though the HP rating looks suitable, they were achieving that with a 1.5 litre motor so there was plenty of gas flow to spool it up.

The applicable toyota turbo is the CT12 from a 1GGTE - it's a twin turbo 2 litre 6 cylinder and I think the "hottest" version was about 210 HP, so the turbo is equivalent to a 105 HP 3 cylinder 1.0 litre at fairly low boost- probably ideal for power production in a 660 methinks.

My guess is the boost threshold would go too high with the HT07 - that's a 130hp 4 cylinder motor from memory so I think it might be a bit big, but I think you have some tech on this?

It's all too easy to get carried away with these motors and over turbo them - there's lots of guys with 5500rpm boost thresholds whch make lots of power above that, but that's no fun in the bush. (or even on the highway) based on about 4500rpm highway cruise, I think a 4000rpm boost threshold would be absolutely as high as you could go or you'll forever be in 4th.

Steve.

[mightymouse]

A .48 A/R in a T2 is still too big IMO for a 660 for all the reasons listed by Steve - not unworkable but far from satisfactory for a 4WD where low end torque and response is important.

If it was me, and an appropriate turbo wasn't forthcomming I'd be spacing the CHRA from the exhaust housing to provide greater radial vane clearance. I've done this with Starion's ( remember them ? )for racing with some sucess - well at least they didn't melt their turbos immediately......
A collection of different thickness spacer rings gives the ability to play to find whats the best compromise. In the longer term I'd be using stainless rings as mild has an annoying habit of corroding rapidly when exposed to the typical turbo environment. You would need to see how much the CHRA can be moved out of the housing before deciding on spacer ring thickness.

Response VS restriction are two sides of the same coin - improve one and its very difficult not to hurt the other. A well designed, equal lenght exhaust manifold can do wonders to improve responese and make up for larger A/R housings however as the 660 exhaust housing isn't a split pulse design some of the potential is lost. At one stage I was running a 1.52 A/R TO4 on my RX5 and with a single entry exhaust housing its was 1,2,3,4,5,6....... Away you go......... . Split pulse was not perfect but a noticible improvement.

Now if you want to see a white hot turbo a rotary is the way to go. Exhaust was still a dull red where the pipe passed over the rear axle. At constant load you could see the standing waves in the exhaust as darker bands.....

Machining the housing is also possible but thats a bit permanaent if you aren't exactly sure how much metal to remove - and should you have a "fatality" then you have to do it all over again.

[cj!]

Thanks Ross. My manifold could do with a redesign anyway as it is pretty awful. Steve's is better but still not great. Will have to investigate this CHRA spacing idea further. Any useful links that you could suggest to learn more about this? What sort of A/R do you think we should be looking for?

[mightymouse]

A/R is a ratio so it depends on the turbocharger... a .48 A/R on a T25 is vastly different from a .48 T04.

There are also variations of wheels ( both compressor and exhaust ), different exhaust housing designs ( split pulse vs single entry ), different compressor covers etc etc - let alone the brand variations.........you get the picture ?

All of these affect the suitability of the turbo for an application, and applications are all different as well - so at the very best turbo applications are initially a "best guess" by people who know particular brands of turbos well and can read the turbos datasheets and then fine tuned by experience with the particular application - not always sucessfull at first go.

And then there's your expectations to consider - ask an "expert" what's suitable and you'll get their view based on their interpretation of your needs - whether that translates to what you want on the car is an unknown.

Its a bit like buying an off road tire sight unseen and with no one who's run them before. Everyone will have an opinion, you'll be able to make some gerneral assumptions based of the supplied information - but till you actually get them on the car and drive in the range of situatons you are interested in, you won't real be able to judge.

And yes many turbo exhaust manifolds are usually pretty crap designs ( matching the N/A design quality in many cases... ). I often wonder exactly what book they read before they started designing.

Even the "D" manifold is average... and you would expect better for a homologation special - the actuall rally cars used a decent, extractor style, equal lenght fabricated setup so they definately had more power than the 2600 roadies made.
Its probably a lifespan concern that stopped Mazda fiting then to the roadies or perhpas noise ( pipe resonates... )

I'd play with the stock system first, learn its characteristics and limitation and then you'll be in a better position to move to the next step.

As for CHRA spacing - I've never searched as I had no need - working in the field bypassed the "everyones_an_expert_NET......"

[cj!]

Here are a couple of pics. The VZ24 is the stock 660 turbo and the VZ25 is the SuzukiSport modified version.

Apparently according to someone who has spent sometime with these engines and turbos the VZ25 is ideal for gymkhana and daily driving since it develops power lower down and delivers the torque smoothly through the midrange. The HT07 was better suited for the track situation as the effect is "explosive" when the power arrives all in one burst which is above 3500rpm. The HT07 is supposed to be good for around 95kW and the VZ25 for 85kW. The VZ25 runs out of puff higher in the rev range where the HT07 is still flowing and obviously the VZ24 is a bit worse still.

[mightymouse]

No pics of the exhaust side ?

[cj!]

Not yet but I'm hunting I figure the more I can find out what has been used and how it works the better an idea I may have of what I'm trying to end up with as this is all new to me. I'm trying to find compressor maps but being OEM type stuff I'm not holding my breath.

[cj!]

Here's pics comparing the stock VZ24 with the HT07-4B

[cj!]

The twin turbo MK3 Toyota Supras are also a possible turbo candidate with the CT12 turbos. The 1998cc 6cyl 1GGTE (CT12) developed 153kW and the 2491cc 1JZGTE (CT12A) developed 209kW

Here are the sizes:

1G turbine inlet = 25mm
1J turbine inlet = 30mm
1G turbine exhaust outlet = 42mm
1J turbine exhaust outlet = 44mm
1G compressor inlet = 31mm
1J compressor inlet = 38mm
1G compressor outlet (to intake manifold) = 29mm
1J compressor outlet (to intake manifold) = 29mm