Ok heres the question to anybody thats got this combo.
The twin combo using a HT3B on the bottom and the stock 98 HY35? top, will it spool as good as just the stock turbo does with a tight auto?
From the two days of reading(slow reader ) on the subject this seems like the way to go for my needs and $$ but would like to hear from people with this on the spool up. I dont tow to much but spool up and smoke control for city driving are important. Also as $$s saved down the road I will be able to go with a set of Don Ms mach3s and HX40 on the top or a modified 35 Piers has a great set up and only needing to buy one turbo to start would sure help the $$$ situation.

 

ratsun- you have an HX35 in your truck stock. The HY has a much smaller exhaust housing, quicker spooling but rather crispy- would seem like a nice turbo as a top if you have a high flow external wastegate (Internal won't flow enough) and don't want to go crazy on hp.
Did you do something for your headgasket? Studs or O-rings would really help holding the stuff together.

HTH
AlpineRAM

 

Sorry HX is what I wanted my fingers to type (need more Coffeeee)I was hoping to set the waste at about 45 at this time as I dont think I need any more boost to cool the Jammer IIs with the comp. I was hoping to go twins now for better spool up than a bigger single, and you never know if Santa has a set of F1s in his sac At that point I can see Oring and studs.

 

Small twins (with an HX-35) will give you better spoolup than big single.
To answer your original question, have been told that the small turbo in twins always spools a little slower than the same turbo as a single. Don't believe it's a major difference.

RJ

 

Rjohnson is right.

The reasons that the the twins will NEVER spool faster than the small charger by itself are as follows:

1) The small charger must "pull" air through that resistance of the big charger's compressor. This creates a partial vacuum in the cross tube that the small charger has to fight to light.

2) The small charger's turbine section has less of a pressure differential across it because the other side of the turbine is more restrictive (another turbine section) than would be a downpipe.

The difference in spoolup can be significant depending on the twins configuration. If the large charger is fairly small, then air won't bypass it, forcing the small one to work harder.

If you have a Bigt Brother like Jim Fulmer, for instance, then air can bypass the larger charger pretty easily, which makes the small charger's job easier.

Also, dumping the external gate past the larger charge will help the small one spoolup faster but hurt the spoolup of the large charger. Let's face it-- the large charger is what you want to spool!

Don't get crazy trying to get your small charger to light really fast. They key to a good twins setup is matching the chargers to each other and to your fueling level.

Justin

 

Hohn- your comment on the wastegate puzzles me- I think that hte wastegate of the smaller charger is there to dump exhaust gas directly to the big charger when you reach the edge of the efficiency map of the small charger. (Naturally you can also wastegate the big one)- So this means that this doesn't do anything to the spoolup of the small one. The cause that I mentioned an external wastegate is that in some situations there simply is more exhaust gas than you can reasonably get through a small charger even with the wastegate wide open. A proper external wastegate makes for less restriction between the head and the big charger when you are at high power and boost levels.

At least that's what I figure about twins

AlpineRAM

 

Markus, I was referring to the LOCATION of where the small charger WG dumps. If it dumps into the large charger, there is more of a theoretical hindrance to flow than there would be if it dumped into the pipe past the large charger.

But in this case, you WANT the restriction to flow because it will spool the larger charger faster.

Edited by me.


JLH

 

I have my system down pretty good considering there is no external wastegate.

With the comp completely off just running the truck on the DD3's i see 44 psi total and the big charger is putting out 20 psi.

With the comp on kill I am seeing 58 psi + and it pegs the 60 psi boost gauge inbetween shifts... (Stock head gasket... I know I know) The pyro never sees anything above 1300 pre turbo.

Accelerating with the comp off I can get up around 1000 degrees pre turbo @ 80 MPH with the pedal on the floor and past that speed the pyro drops to just under 900. That is the exact results that I was looking for in a staged setup.

My system uses a modified HX 40/35 14 wg housing and a BHT3B with a non divided 22 cm housing. When I say modified I mean I put a bigger wastegate flapper in the housing with a bigger hole and plasma cut the divider in it to allow exhaust to be wasted through all 6 cylinders.

At 13 total psi there is 3 psi in the cold pipe. @ 20 total psi there is 8 psi. So spool up is right around the same as a stock HX. I am very pleased with the perfomance of the system.

On the dyno its just shy of 500 RWHP, but the power is very drivable, can't say how much better then a big single because I never have owned one...

Take a look in my gallery. Please dont make fun of the finish, I haven't taken it to the chromer yet. Its just too much fun to drive!!!

I took the filter pipe off to get a better picture of the system.

All the cold piping is 4" exhaust piping. The filter pipe is composed of a 5.5" angle reducer to 4" and hooked to a 14" long afe filter.

And of course it all wastes through 5" into a 6" stainless tip

 

Finish, schminish! It's ALL ABOUT THE AIRFLOW!

JustinP-- I like your system a LOT.

JustinH

 

So maybe im dense today while im reading this sounds like the same thing ive heard before but, you are saying to use a HX35/14WG on top with a HT3B/22 on the bottom correct and the reasoning for this is the 14WG will flow more exhaust to the HT3b than a HX35/12cm WG housing and get the bottom moving faster which will inturn aid the HX35. So in therory a 16cm housing would help speed the lower turbo up even faster, because it allows even more flow to get to the lower turbo while the top one is still spooling? But lag would increase because of the amount of time it would take both of them to get going. What improvement does the 58mm or 60mm Hybrid offer as a top turbo over the stock 54mm or 56mm? or will it hinder the process.




Clean system justin, good picts gives me something to model one after as soon as i find a 98 QC SB 5spd with 100-150k and under $16k. That might be soon too

 

The spoolup of the smaller housing on top is going to be better. This is because when you have turbo lag, you have smoke. Smoke is oxidized fuel, which was NOT burned. When fuel BURNS, it converts to EXHAUST GAS.

So the smaller housing will stoke the coals faster, thus you get better spoolup of the big charger.

My original comments were ignoring combustion, and talking purely airflow. You'll see this on the top end, where the small housing(s) are choking the flow and the engine won't pull anymore.

That's why with a 35/3b combo, you can totally change the nature of the setup based on housing swaps.

BIG difference between a 12cm/22cm housing pair and a 18cm/ 26cm pair. One will spool in a blink but die after about 475hp. The other will have a lot more lag, but should support at least another 100hp or more. (Just WAGging numbers here)

Justin

 

Tests on flow benches have proved that a properly modified 14cm housing that is internally wastegated out flows an extrude honed 16cm non w/g housing. But I have not seen any tests done on a 18 cm housing.

Thought that was some interesting stuff...

 

Wow Thanks guys I think that answers most of it. As I said I will have to stay with the Jammer IIs for awhile so I'm going to try the stocker on the top. If its still to toasty I will just have to save up for the next round Still taking baby steps its just that their a little quicker now

 

Ok, I have a question. I am thinking of doing what ratsun wants to do too: a mild street twins setup with minimal lag and support 450-500hp. What I want to know is if 4" exhaust will be ok. All the twins set-ups that I have seen have 5". I want to twin my 98.5 but I already have 4" exhaust.

 

You could keep your 4" and just neck down after the 5" outlet on the big charger. It would appear to be restrictive, but the truth is that it won't mean much at all until your pushing a LOT of hp (550+)

Justin