SPS 62 in twins. Drive pressure reduction?

[RonA]

Very happy with my current setup, except for the high drive pressure. I have a 38mm Tial I can put in but I really don't care for all the added plumbing. At 60psi total boost my drive pressure gauge needle smacks the 80 peg so hard I'm afraid it's going to break. I have talked to a couple of places about modifying the gate on my 62/. 7 S300. Just not sure it would be enough . I am not sure how high it actually is, but I need to drop it at least 15 to 20 psi. Would a SPS 62 be able to do this? Or am I going to have to sacrifice my quick spooling and go to something with a larger exhaust housing?

 

[csutton7]

I think you've answered your own question--external wastegate or sacrifice--chris

 

[AK RAM]

Who have you talked to about modifying it? I'm in the same boat with my S300 on top and no external gate and have been talking to lots of people lately also.



The exhaust housings used on the stock S300, whether 12cm or 14cm, are the same exhaust housings used on the SPS turbos from II. No difference at all.



Which S300 exhaust housing do you have, 12 or 14cm?



Have you spoken to HTT about it? I think I'm going to let HTT take a crack at mine. I don’t want to go to an external gate either…. . for looks (clean install), less chance of leaks, hacking up all my existing piping…the reasons are endless. Basically I'm just lazy. Anyway, my housing is 14cm. HTT says they can enlarge the wastegate volutes a little, put on their custom stand-off wastegate cover that allows the wastegate arm full travel, and clip the exhaust wheel just a tad. Together, that will improve wastegate flow 40% and relieve most of the drive pressure issues. It sounds good in theory. If it works as they say, that should do well. I'm planning on having mine done here shortly if nothing changes between now and then.

 

[Jim Fulmer]

I run just the internal gate on my 66 without issues. Maybe a external gate would be a addition but I just really don't feel like messing with it, drive pressures aren't bad either. The last time I really got a good check on them (takes 2 people or a tell tale gauge) it was 1 to 1 at 75psi. Perhaps when the boost gets higher than 85 I should look into it.



Rod you need to talk to Brady about modifying you S300.



Jim

 

[AK RAM]

The last time I really got a good check on them (takes 2 people or a tell tale gauge) it was 1 to 1 at 75psi.

Holy efficiency Batman! Is that running it as a single or twins? If a single, that is odd as not only does II retain the same housing when they mod the S300 to make their SPS turbos, HTT is also using it on their Killer 64 and Sled Puller 66 according to them. Never measured it on a SPS66 above 40psi, but we know on the Sled Puller 66 drive starts to overtake boost above 50psi. The different wheels used will have an effect on drive pressure, but you wouldn’t think that much of an effect. I wonder if Brady is enlarging the volutes and clipping the wheel before they ship as part of his normal mods. If that is the case, then the stock S300 can be made to run just as efficiently.

Rod you need to talk to Brady about modifying you S300.

…and let us know what he says! Oo.



Anyone else measure drive pressure on a SPS66?

 

[RonA]

Jim runs twins so I imagine that's what numbers he is giving. I have heard that the turbine wheel is larger on the SPS also. I'm trying to keep my setup simple so I can run the K31 and smaller injectors for daily use, and swap the B2 in with larger injectors to dyno with. It would be great to be able to use just one top charger and no external gates.

 

[AK RAM]

Yeah, a bigger exhaust wheel would help drive pressures a good bit by itself. I have thought about that too but really don't want to loose my quick spool. I'm hoping a little clipping won't hurt spool as much as a bigger wheel with more mass. Decisions... decisions. 1:1 at 75psi would be sweet.



What size is your exhaust housing?

 

[RonA]

Little wimpy . 7 housing on mine. I like it, but have never tried a . 8. I was told there was a very noticeable difference between the two. This turbo with the 3b was a dog. Switching to the K31 made a big difference. Towing and normal driving is excellent. It does 480 to 500 easily with sub 1200 egt. But I'm not sure it will make it to 550 . Would be great if it did.



Ron

 

[Cooker]

I'm sure someone will correct me if I am wrong, but as Ron mentioned the Super Phat Shaft turbos do use a larger turbine wheel and from what I know they are only available with a . 8 housing.



With that said Ron, the SPS62 will help with your drive pressures some but going to the . 8 housing you will be giving up some spool-up.

 

[RonA]

I'm going to install my 38mm gate and see how it does. If it doesn't work I can make another hotpipe and try a different turbo.

 

[Diesel Freak]

Ron, remember that it takes a specific ammount of energy to spin a turbine to do work.



A difference in temp, and a difference in pressure.



In basic terms,



Qin=Qout+Qamb+Work



Since you fueling level is relatively constant with respect to RPM and power putput (BSFC at a pre-determined RPM) your heat input into the turbine and turbine housing is also a constant at that same RPM. If you put a bigger wastgate on, it really wont help much with respect to the turbine it is bypassing. That turbine still needs a difference in pressure to get the same energy output when heat input is a constant.



What do you want to do? lower total drive pressure, or lower drive pressure across a specific turbine stage? The two are intimately related.



Your bottom turbo turbine, housing geometry and it's wastgate have the largest effect on drive pressure at equal pressure ratios. You may be able to lower total drive pressure some with a larger top wastgate, but the top turbo will slow down as a result... thus pressure compounding will not be ballanced. and the bottom turbo will be working too hard at the same "total" boosty pressure.

 

[DRAG DIESEL]

Ron, you have Email waiting for you.

 

[Jim Fulmer]

I'm going to install my 38mm gate and see how it does. If it doesn't work I can make another hotpipe and try a different turbo.

I can't say I really like rebuilding stuff but if you already have a 38mm gate you could go that route but I would still have II do there stuff to the S300



On the SPS 66 there is nothing trick about the gate on it and I don't have it opened all the way, Brady has spacers that will allow it to open more but I don't have enough fuel for it to matter right now.



The 66's gate is not like the Holsets, it's a much better design were it vents from and exhausts too, that's why I figured it would work better. Keep in mind that this turbo wants to work, meaning if you by-pass too much trying the run the bottom charger harder you actually hurt yourself.



Jim

 

[BradyWilliams]

We would be glad to fix your problem! Some people get so worried about rotating mass that they forget some basics with turbos. Putting in larger comp. wheels slows turbine speed. I get calls all the time, they ask can you sell me a turbo with a bigger comp. wheel. A bigger comp. wheel needs to be driven with a larger turbine wheel. This increases the turbine/compressor speed which allows the comp. wheel to do it's thing (compress air). The added bennefits of this is lower drive pressures. The A/R of the turbine housing is only one part of the drive pressure puzzle. I can say this however, I would never select a . 70 turbine housing to make big or bigger hp. the smallest housing that should be selected should be a . 80. There is a lot of exhaust volume that must get through the turbine housing. The dual wastegates that we use are a nice option to help drop the drive pressure. We do use a . 70 turbine housing on a Phat Shaft 62 that runs at altitude but never on a Super Phat Shaft. The spool up is not a problem with a Super. Don't ever let anyone tell you that our turbos are the same thing that they make or sell. Thanks, Brady 1-800-955-0476

 

[paulb]

We would be glad to fix your problem! Some people get so worried about rotating mass that they forget some basics with turbos. Putting in larger comp. wheels slows turbine speed. I get calls all the time, they ask can you sell me a turbo with a bigger comp. wheel. A bigger comp. wheel needs to be driven with a larger turbine wheel. This increases the turbine/compressor speed which allows the comp. wheel to do it's thing (compress air). The added bennefits of this is lower drive pressures. The A/R of the turbine housing is only one part of the drive pressure puzzle. I can say this however, I would never select a . 70 turbine housing to make big or bigger hp. the smallest housing that should be selected should be a . 80. There is a lot of exhaust volume that must get through the turbine housing. The dual wastegates that we use are a nice option to help drop the drive pressure. We do use a . 70 turbine housing on a Phat Shaft 62 that runs at altitude but never on a Super Phat Shaft. The spool up is not a problem with a Super. Don't ever let anyone tell you that our turbos are the same thing that they make or sell. Thanks, Brady 1-800-955-0476

Thanks for the info Brett. I was beginning to wonder if I was the only one that had found that out. Lots of theory being presented by previous posters, but it's nice to see someone post that has tried things.



From what I have seen, the top turbo needs to have a large enough turbine housing, so that once the bottom turbo starts making boost, the top turbo can get the he!! out of the way. Calling twin turbos compound is really not totally correct. Sequential is probably more accurate. The amount of compounding that the top turbo does should not be fixed. What I have found works best for me (drag racing, and performance street), is to have the top turbo supply up to 35psi of boost when total boost is low, and then reduce that (I'm dropping that to 24psi when set to 60psi total) as the bottom turbo starts making more boost and drive pressures increase. The way to reduce it is to wastegate more of the exhaust to the bottom turbo. An external wastegate does not need to be used to do this, if the top turbo's wastegate is large enough. This setup has netted the most consistent 1/4 mile times with the lowest EGT's, from what I have tried so far. Testing will continue!



Just my $. 02 worth.



Paul

 

[JasonCzerak]

One thing here that always confused me about this twin turbo deal.



I fully understand the exhasut side of things bypassing the turbine wheel on the small charger to the bigger to prevent over spinning the thing,getting that extra air to the bigger turbo.



But, the big chargers is eventually going to force 60psi though a turbo that can't make much over 35psi it's own. . with no "wastegate" like deal on the compressor side, how does this work out?



What's preventing the bigger turbo from pushing the little turbo to fast and blowing it up?



Would I be correct in gussing that the little turbo is just re-compressing the same air volume some more from what the bigger turbo has already started to compress? Would PSI be at say 40psi in the cold pipe between the 2 turbos and after the little one compresses a bit more it's now 60psi, but the rotation speed doesn't change because of this re-compression?



Smack me if I'm way outa the ball park here.

 

[csutton7]

You are pretty much on the right line--I don't recall the exact multplication factor that the smaller turbo compresses the air to, but I've always heard it's more than two times--but of course that was when twins were being first put on and guys were shooting numbers out like if you had 15lbs of boost from the big turbo you will end up with 70 lbs of boost--those aren't correct numbers just an example---finally some guys started putting guages on the cold pipe to see what the big turbo was making, but this isn't done by many, so we will have to wait and hear some better specifics from guys who have the guages set up to monitor this--chris

 

[Diesel Freak]

There is definately more than one way to skin a cat. Like I wrote in the other thread, pick a power level and build for it.



Chris, 15 psi off the primary could yeild up to 45 psi off the secondary, but definately not more than that.

 

[JasonCzerak]

You are pretty much on the right line--I don't recall the exact multplication factor that the smaller turbo compresses the air to, but I've always heard it's more than two times--but of course that was when twins were being first put on and guys were shooting numbers out like if you had 15lbs of boost from the big turbo you will end up with 70 lbs of boost--those aren't correct numbers just an example---finally some guys started putting guages on the cold pipe to see what the big turbo was making, but this isn't done by many, so we will have to wait and hear some better specifics from guys who have the guages set up to monitor this--chris

wow. . I've just impressed my self just a little bit

 

[csutton7]

thanks DF I knew someone would be able to point out some #'s that would define it better--when I get my twins back on I plan to add another guage to monitor this and maybe a temp guage too--will see--first I need my top turbo to arrive----chris