Railgun

So I've searched under numerous threads using a smorgasboard of search strings over the last couple of days and didn't find squat, which would make any link to another thread a big slap in the face...so here goes...and forgive the long windedness of this. Some of us are still learning.

I have a 13B-REW that was given a half bridge. I also used S4 TII rotors...well...just because...to run a little more boost. The car is mainly a non-daily street type with more and more track time (not drag) as the months progress. Assumptions going forward with my questions are that everything else, IE fuel, exhaust, etc. are all sufficient to support anything that is suggested. Let's also say, for the sake of arguement that I'll be running 22 psi. I'm not looking for a debate by any means but rather suggestions and perhaps explanations why. The more and more I look into this, the more my brain hurts. Again, I'm just trying to get a good grasp here.

I'm not looking for certain HP numbers...at least on the surface. What I AM looking for is something that will be perfectly suited for the track. My experience with my old setup (stock REW with a 35R) was that it would come on pretty hard and tend to unsettle the car sometimes. This is very much due to inexperience as well to be sure since I wasn't rolling the throttle all that much, instead just jammed on it. However, I want to make sure that I don't screw myself in the long run here and get something that's not going to be suited well for what I'm looking for.

In my search, I came across a thread that mentioned that a stock REW needs about 30-40 lbs/min at a certain pressure. I can't remember now if it was 10 or 15 psi. Probably the former. Using some math here on the forum, and this is based on stock ports, 15 psi will require ~50 lbs/min. Now, that said, what does a half bridge do to this math. How does it change the CFM requirement? I mean, I know how, but how it is determined how much more one would need?

The two current suggestions are a 42R (4294) and a BB T04R...not the HKS. I can't find a map for the T04R. Based on 22 psi, and hopefully my math was right, it said that it would require 62 lbs/min @ 8500. I can see how the 42R may fit, but how does it fit in regards to response? What A/R would be recommended? 1.01 or 1.15? Would the 1.01, at 22 psi, let the boost build quickly enough and still allow for enough breath to maintain that up top?

I'll start with these questions as I'm sure to have follow-ups based on whatever you all respond with. Now, I know I can't have my cake and eat it too, so the best fit is all I'm asking for.

Thanks in advance!

Chrisitan

2a+RoN

I am in a similar boat to you, 1/2 bridge REW destined for the track.. One problem with a bridgeport is that it needs as little backpressure as possible in order to utilize the port. So for that reason, I have decided to use a t6 hotside. I found a diesel turbo called a gt4288 that uses the large gt42 turbine wheel and t6 hotside in conjuction with the gt4088 compressor wheel. I'm not sure how well this combo will work yet, but i got it for a great price so I figured I'd give it a shot.

So if you decide gt42 you can get it with a t6 housing (probably the 1.01) to allow for little backpressure. However, the downside is that they are beasts! The thumper hotsides alone weigh ~25lbs, which is very unsettling to go into a track car.. That lead me to a debate as to sacrifice either backpressure with a smaller t4 turbo such as a gt40 or to4r or to sacrifice weight and go with a monster turbo that will let the engine breathe a little easier.

bobybeach

Guy’s don’t be fooled into the whole big turbine housings are needed for Bridgeport’s to perform at high rpm. The turbine housings main contribution is to controlling shaft speed not flow. A turbine wheel has the biggest effect on flow. That said even with a small turbine a Bridgeport will still produce power high in the revs so long as it still has compressor flow i.e. Holding boost at peek rpm. With larger turbine you will get more overall torque at the expense of slower shaft speed acceleration (response).

The main advantage I see of using large housing with Bridgeport’s is that you are able to manage boost control better since the shaft speed does not become to much for a modest size wastegate to control. But I prefer small housings with multiple wastegates to compensate
The best thing about small a/r with street cars is that the second the throttle plate is opened from cruising... boost is rite there! Even at low engine rpm the compressor as high enough shaft speed to generate boost, and it just needs to be let in to the manifold by opening the throttle.

I run a T-64 with GT Q trim turbine and .84ar @ 24psi on my full bridge 13b. I have 5psi at 2500rpm and full boost at aprox 4000-4500rpm. But I need dual 44mm wastegate to control the boost properly.
I wouldn’t recommend larger than 1.00ar if using turbines larger than p trim, unless your ok with falling of boost during gear shifts. small turbine wheel like p trims can generate boost very quickly again so they are able to manage better with the large housing a/r but turbines like Q trim and gt42 can become flat on boost if you shift to soon or don’t carry the revs high enough even on Bridgeport’s.

In terms of compressor flow Id suggest larger something around the 70-80lbs/min to maintain compressor flow at 23psi at peek rpm.
I have customers with 65lbs/min compressors that to reach max flow at aprox 19psi 8500rpm on streetports. it will be slightly less on bridgeports.

radkins

I'm running a to4r/1.00 hotside at 25-26lbs on pump gas/AI with a half bridge. In 4rth gear I can reach 10lbs at 3500-3800rpm, and holds 25lbs to redline.

Old Slow Coach

Railgun- You said "The more I look into this, the more my brain hurts." I can appreciate these words! Your mods mention "BDC" for your port work, and I'm curious if you've asked him these questions directly and are still uncertain. If you can reach him, I'd post up his answers to your questions and see how things sort themselves out through further discussion. Sorry I can't be of any help answering your questions, but this is a subject I am very interested in and will follow this thread.

Railgun

2a...I was thinking the same lines as far as some one off hybrid like that to better suit the application. How long before you get that up and running. I'd like to know how it works. I need to corner weight the car. I have no PS or AC so I'm sure with any setup I'm heavy on the right side but the battery is in the bin on the driver's side.

Radkins...you run IRP a lot IIRC, don't you? How would you describe your experience with that setup on track?

Gen X...I've tried to hit BDC up via IM a couple of times...perhaps he was just away at the time. I'll try calling him over the weekend to get some better specs on the port, but he knew what I was looking to do, though I don't recall if any turbo ideas were discussed so...

Boby...I'll definitely take that into consideration, but how much of a difference in turbo selection is there between a full and half bridge? Needless to say the full would flow more and I would think would change the characteristics of how a turbo responds. Would that be a logical statement?

bobybeach

I wouldn’t think there would be much difference.

The other thing to mention with turbines is that size and trim are two different things

A small trim gt42 like the 74 trim found in hks t51 is not much bigger than a t04 Q trim exducer. Allthough it is a much bigger turbine altogether it has a much more smaller(aggressive) trim giving it gd leverage for response.
But with larger trims like 84 trim a gt42 will become a lot less streetable and I doubt you could justify or measure any gain in peek power due to increased turbine flow.

I guess its debatable but I would think large trim to4 or small trim gt42 with 1.00ar would be practical limit for compromise on flow and response on large port 13b whether its full or half bridge.

Railgun

I've chatted with BDC and got some good input from him. Any more input from anyone?

Old Slow Coach

All this talk about intake ports and turbo response, but no mention of exhaust porting, which has a huge effect on spool-up. I assume you enlarged the exhaust ports a bit?

What did BDC advise?

radkins

I have not had the car at IRP on this setup, but I am a little scared to find out. I should be entering turn one at 150+

Turblown

iTrader: (12)

Gt42R is a drag race turbo.

I'm curious as to what advice Brian gave also, after all he is the one who cut the bridge and built the motor..

Slammedblk7

iTrader: (7)

You guys give me a headache reading this. I run the MP GT45 1.05a/r turbine housing. Normal take off, 12psi by 6600rpm in 1st gear and that is because I let off. Its on a 13bt Full bridge BTW.

Howard Coleman

iTrader: (6)

road racing w a turbo'd engine requires as linear a power curve as possible. i can just see you in the middle of turn 1 at IRP and all of a sudden the turbo starts to really crank. you will be in the grass real fast.

let's start w the pounds per minute thing.

the rotary makes approx one rear wheel hp for each 1.92 CFM. 14.471 CFM make a pound per minute.

so let's talk ROTARY (different from piston as to airflow) HP.

what size wheels and tires are you running? are they race tires or street/race tires? the reason i ask is because a turbo'd FD making more than 475 rwhp just goes sideways when you get on the gas.

the turbos you are talking about.... the gt4294 makes 85 pounds per minute. 85 X 14.471 = 1230 CFM/ 1.92 = 640 rwhp. unless you are runnning approx 10,000 dollars of well thought out suspension mods you aren't going to do anything but go sideways and melt your tires.

the T04R makes around 63 pounds per minute which works out to be approx 475 rwhp.
you'll need a minimum of 10 inch rear wheels and 285 on up sticky tires to hook up 475.

you'll need water or alcohol injection to run the above hp levels on a road course.

you'll need 13 inch front brake rotors and you should have 4 piston rear calipers w a proportioning valve.

OTOH, your GT35 depending on wheel size will make around 400. life gets easier. you can whomp lots and lots of cars w a 400 hp FD.

it seems that you state your problem is the non linearity of the boost curve. generally that is a question of either tune, driving or can be fixed by switching hotsides etc.

can you tell us more about your turbo and related systems?

BTW, i am very familiar w BDC and his ports. i run Brian's ports on my motor and they will work fine on a road course.

lets have some more info,

howard coleman

kabooski

good info HC!

No_Rotor_RX7

damn, i need to find out the cfm of a master power T70! haha

Railgun

I was hoping that you'd chime in. In answer to your questions...

At the moment, Toyo RA-1s at 275 out back. It's a work in progress so I'll keep that in mind.

Something I'll think about, but is this going to be necessary if I run, say 100 octane? And were talking about ~20 psi or so.

Fronts are good to go. Rears are stock calipers with sloted rotors and Hawk HP+ pads. My intention was to go with the RZ rears.

Since sold and needed a rebuild.

Well, that's what I'm shopping for. As far as everything else, it's all in my sig save for the item in question. The fuel system will change a little too in terms of the rail and primary injectors.

Brian has suggested pretty much the same thing as far as going with the T04R. Bobybeach was who he pointed to as I guess they've worked together. It's starting to sound like a good option.

As far as my suspension. Well...that was something that wasn't thought of at the time is was purchased. When opportunity allows, I'll be offing those (Tein RA) in favor of something a little more...reasonable.

As far as more info...I'm not looking to get this car into competition. This is more for fun and what not. I suppose that I may be attempting to make this a little too well rounded in terms of performance, but I'm liking street to road course performance as I can see the similarities there more than I can comparing any other two. Basically I started this thread as I wanted to make the best decision here as I [hopfully] won't be changing this out anytime soon.

But I thank all of you for your input.

Railgun

My bad. I misquoted BDC. It was a T66 or 70 with a .96 a/r he had suggested, not the above.

bobybeach

so im guessing your happy with the dicision to change?
Have you got that thing dynoed yet?
what sort of boost are you putting in to it?