soulezoo

Piers and Tom worked together on the "mix and match" of the EH's. The EH's are both proprietary to Tom and are custom jobs matched to this application. The primary is expected to be able to push from 35-40 psi dependent on fueling. I can push my BHT3B (with 26cm EH) to 35 fairly easily now. The secondary chokes it quite a bit as it is still just a single wastegate... the new secondary EH will be a double wastegate... (more precisely, one wastegate actuator opening two ports so all cylinders are evacuated)

HOHN

My thoughts exactly.

Aside from simplicity, I'm not sure I see the merit in a huge internal gate as many seem to want to do. A large external imo is the way to go. Especially if you are running a smallish top charger (or tight housing) that will require bypassing a lot of exhaust flow. The 60mm Tial flows 330cfm @ 1psi pressure drop! That's negligible restriction imo when talking about elevated pressures. You can never have too much gate if you have a good control setup.


I'm also starting to think that a larger primary is the way to go-- larger than one might expect. I see this because a larger turbo not only has more ultimate flow capacity, but it has a broader operating range. For example, going from a GT42 to a GT45 gives you not only more ultimate flow capacity, but each of the efficiency islands gets larger as well.

IMO if you are pushing your bottom charger past 30psi, then the top charger is too small. The secondary compressor should be big enough to "swallow" enough air from the primary that boost stays under 30psi.

The other possible thing here (apart from an undersized secondary) is that the turbine housing on the primary is too small and it's overboosting.

Hence, a gated primary can be really great in regulating boost from the primary and keeping TIP under control as well.

Ideally, you'd have to two external gates-- but that's pretty expensive.

Thus far, I'm looking at a 44-60mm gate on top, and a smaller 38mm external on the primary.


I'm also considering the GT4708 as a primary-- similar to a GT4508 in flow, but has a larger turbine to keep DP down and improve efficiency.

Fitment of a turbo that size could be challenging, as the hot side is pretty large from what I understand.

We're off to go househunting, so perhaps I'll be able to get started on my twins by year's end. I found a nice house with a shop, but we'll see if we can swing the $$.

Justin

Idaho CTD

The compressor size is the problem with the GT47's not the exhaust housing size. They have a 6" inlet and are about as big as you can fit between the frame, manifold, and motor.

Mike Holmen

Hohn, if you go that large, go with the smaller exhaust housing. I'm not sold on the larger CFM wastegate. The best way is to balance out the exhaust flow, using both turbos to keep building up the pressure curve and working together. If you dump to much exhaust by the secondary turbo turbine, it will start to loss pressure dP. I'm still on side with your original idea of using the GT4202R, just use a medium sized turbine housing. 100lbs/min of air is tons for us daily haulers.

soulezoo

Well the parts are starting to come in now for the twins and so are the questions...

The part number for the top turbo is 751473-5013. This is for Garrett BB turbo... I thought I was getting a Gt3788r stage 3... this appears to be more like GT4088r, except this part number doesn't show on any of the garrett listings. Anyone have an idea?

Mike Holmen

Are you gonna dump in some fuel? If you have fuel it would work for a secondary. Its kinda small for a primary unless your not much than 450-500 rwhp. It would be wicked fast spooling with a small GT37 or smaller. I would just run it as a single and forget the twins idea. To bad your so far away, I would like to see how it runs regardless. Awesome turbo.

Idaho_CTD nice rides like to see them. How fast is the 06? How did you get the transmission to work?

turbos10

I think you might want to be careful on the gate size. Too much and you will not be able to fine tune it. Same theory as valve sizing in a hydraulic system; If you go too large the system will hunt no matter how fine tuned it is. For reference sake I use a 50mm tial with my TV71 on my turbo gasser. I regulate it at 11psi with no problem. As deltaP rises the ability to control boost will increase if you vent it to atmosphere instead of recirculating. I built a muffler for mine using 2" pipe, two pipe reducers, some steel wool and a 2" turn out. If you dont do the muffler it is a bit noisey when it opens.

HOHN

I'm still trying to figure the optimal gate size. As you mentioned, too large and it will oscillate, while too small leaves you with no control.

jh

turbos10

Yup. I started with a 35mm gate thinking with the large turbine housing I would not need to bypass alot of air. After initial tuning and slow runs I started going 1/2 throttle to test the system. It rocketed to 20psi in a split second. The 50mm, once installed, was rock solid at the set pressure.

The up side is that it is not hard to change the gate if you mount it with the contention that you may have to.

soulezoo

This is the secondary and is a hybrid between the gt3788r and 4088r... the stage 3 gt3788r supports 550hp by itself, so I am guessing this will do that and a tad more... It is 64.5 mm inducer x 88mm exducer. That is not a small turbo by any stretch. The primary is a hybrid gt4202r-- it has a gt45r compressor wheel (81mm x 108mm) in the 60 a/r housing. The turbine is still 82mm with 1.15 a/r. Airflow purportedly 112-113 lb/min. That is the same as the s480 superdave.

What is interesting so far to me is the wastegate is set at 40 psi... most twin setups are set between 20-25psi.

As far as fuel goes... potentially 700 rwhp+--- we'll see.

Mike Holmen

Depends on tuning and when you want some help from the primary. I personally would lite the primary earlier and use lower wastegate pressure. You're SOP meter will help here to define the wastegate pressure. You'll have a wicked twins set-up. You went tighter on the turbine housing which will help spool-up. I'm curious how the 4088R will lite by itself as a single. Its great to have the air, but without fuel, you wont have the power. I'll bet you'll be over 800rwhp on turbos. I just went the cheap way into twins. If you balance the exhaust flow and use the right size turbine housing to keep egt's down you might have a great set-up. You planning on use this set-up on a daily driver or fun truck. My garrett will support not much more than a HX-40 would so the 550rwhp might be high for a 3788 but that depends what someone defines as support. I like a turbo that can run low egt's and clear the smoke, as useable. I towed last weekend. The garrett survive and the egt's wasn't too bad. My head is toast so, my set-up might be better than I think. Take some pics and let us drool on them.

Mike Holmen

You don't want to totally bypass the exhaust flow by openning the wastegate. This will occur when you use to a big/large of wastegate. Once the large wastegate opens, you unload the secondary. The trick is too find the balance. I finding that the GT37r turbo is about right for size as once the open the pressure gain is smooooth and fast. Originally I thought the opposite. The larger Hx-40 that I ran prior seemed that the pressure gained not as fast and it choked off the air flow/exhaust flow

soulezoo

Asking the questions, it appears that this is the theory behind the high wastegate setting (if I can repeat this correctly): The high pressure turbo is large and can best support a very wide range of HP with best throttle response. As the low pressure turbo is already pressure sensitive by nature, it will already by virtue of exhaust passing through the turbine be supplying a substantial amount of air to the secondary. Thus, when the wastegate does open to provide more direct flow, the primary will already be, in essence, "on line" and have a faster spool rate than if left on its own very early in the pressure stage. The secondary design is as such that over spool or dangerous drive pressures will not be seen. Estimates are 70-75 lbs of boost at 1:1 pressure ratios... more important is the lbs/min airflow which should be significant. Bottom line is the airflow of the super dave at a faster spool rate. I know Tim Barber made his mid-high 900's (rwhp) with the super dave (s480). So I ought to be able to "support" mid-high 800's. I have no desire to go that far, but it is nice to know I can...

soulezoo

Again, they are just going in and they are the first of their kind so I am a guinea pig and "we'll see"... for now we'll have to settle for the shop bench racing theories....

soulezoo

Oh, the one thing I'm not excited about is the outlet on the primary... it is 4 1/2".... couldn't be 4, couldn't be 5... had to be 4 1/2. So I have a 4" down pipe to a 5" exhaust.