Whose Twins?????

[NoSeeUm]

B1 = s300

B2 = s400



Right?



Jim

 

[RPA]

Bd Twins

Junior,



I have run the set of BD twins on my truck for the last 2 years and have had very good luck with them the egt's stay cool when towing under 1200deg unless you try real hard that is towing about 14K. Good spool up nad street manors. But they are not high horsepower twins. I don't know what they run for drive pressure because I have never had a gauge on them. What I can tell you is they have seem 60psi plus boost numbers several times and my stock headgasket and bolts are still holding. maybe I have just been lucky. The bolts have been retorqued several time though.

 

[PC12Driver]

Going the other way, when you are trying to make Hp with the engine. Drive pressure is the relative amount of braking Hp that is exerted opposite to the output Hp of the engine itself. It is significant.

To expand that a bit; the RATIO of the drive pressure vs. boost is where the restriction comes in, not drive pressure by itself. 40 psi of drive pressure with 40 psi of boost is a wash at 1:1. The drive pressure restriction is countered with the boost charge. Once you start getting upside down in the ratio (more drive pressure than boost), then the engine starts pumping against the turbine and you get the "braking" restriction against the engine (choking). This is when your HP starts to get robbed (and not immediately - a little more drive than boost can still provide a beneficial air charge).

 

[NoSeeUm]

To expand that a bit; the RATIO of the drive pressure vs. boost is where the restriction comes in, not drive pressure by itself. 40 psi of drive pressure with 40 psi of boost is a wash at 1:1. The drive pressure restriction is countered with the boost charge. Once you start getting upside down in the ratio (more drive pressure than boost), then the engine starts pumping against the turbine and you get the "braking" restriction against the engine (choking). This is when your HP starts to get robbed (and not immediately - a little more drive than boost can still provide a beneficial air charge).

Well Hmm... .



Junior will start to hate this thread, but sorry I don't agree with that.



Because... .



Back pressure on an engine is back pressure. It does not really matter where it comes from. In the case of the turbocharged ISB once the intake valve closes, the exhaust opens and the piston begins its exhaust stroke that is the case. From that point forward the engine must force the exhausted gas out and it must consume Hp to do that. Think of it (on exhaust stroke) as a gas compressor vice an air compressor, which will require Hp to operate.



The super heated pressurized gas (the Hp) that is used to drive a turbo (turbine-compressor) has to come from some place. In this case it comes from the ISB as exhaust gas and takes the form of increased back pressure on the ISB.



Many would say that the Hp to drive a turbo is free, but I would disagree with that also.



If you are talking about turbo efficientcy, then I would aggree that a 1:1 ratio is probably optimum. Mostly, because in many cases that is simply as good of an efficientcy that the system can get to with current turbo designs. For what I understand some of the newer turbo's are beating that ratio over part of the range of operation. The ones that are beating it over the entire range, probably have surge issues.



Jim

 

[Junior]

Seems i always start a debate:-laf



Thanks for all the info.



Have to choose if 600 is max i will go. if i want higher sounds like i go with rips



trying not to lose the daily driver

 

[PC12Driver]

Back pressure on an engine is back pressure. It does not really matter where it comes from. In the case of the turbocharged ISB once the intake valve closes, the exhaust opens and the piston begins its exhaust stroke that is the case. From that point forward the engine must force the exhausted gas out and it must consume Hp to do that. Think of it (on exhaust stroke) as a gas compressor vice an air compressor, which will require Hp to operate.

That is completely accurate, but you're leaving off the other side of the equation. Apply the same thing to the intake side, and let's still assume a 1:1 ratio. When the intake valve opens, a 40 psi air charge is pushing the piston down, effectively offsetting the 40 psi of backpressure. The net reaction is zero. As hard as one piston is trying to push exhaust out of a cylinder, there is another piston that is getting pushed down just as hard with the intake charge. No different than a teeter-totter on a playground with two equal-sized kids on the ends - it is in perfect balance.



Imagine taking off the turbo charger and putting the engine in a sealed room. Then pressurize the room to 40 psi. This is the same thing as having a 1:1 ratio at 40 psi with a turbocharger. There wouldn't be any more resistance to turning the engine over because the intake and exhaust manifolds have equal pressure.



Or, keep with the multi-cylinder air pump idea. Let's say the pump is at rest and we apply 40 psi to the intake side and leave the exhaust side ambient. The cylinder(s) with open intake valves will allow the charge into the cylinder, which in turn forces the piston down. The cylinders with open exhaust valves aren't acting against any increased pressure, so they're free to move up without resistance. The pump turns forward. Turn it around and put 40 psi on the exhaust and ambient on the intake and the pump with turn backwards. Put 40 psi on both the intake and the exhaust and there will be no rotation. And if you try to turn the pump by hand with these equal pressures, it will feel the same whether there's 40psi, 100psi, or zero psi because the pressures cancel each other out.



Exhaust backpressure will not hold an engine back if there is another cylinder with an equal amount of boost pressure on the opposide side of the cycle. It's a balanced teeter-totter at that point. Throw off the balance and the pump becomes a compressor, work is being done, and energy is being dissapated (i. e. - an exhaust brake or an inefficient turbo). Then you have a restriction and the "air pump" has to work against a load, and energy is wasted.

 

[NoSeeUm]

Seems i always start a debate:-laf



Thanks for all the info.



Have to choose if 600 is max i will go. if i want higher sounds like i go with rips



trying not to lose the daily driver

LOL Yeah sorry... .



I think no matter which set you choose, as long as the set is from a good vender you will be happy with them.



Jim

 

[NoSeeUm]

Roger wilco and thanks. Good disscussion, makes allot of sense and I had it wrong.



Along those same lines, then the Hp to drive the turbo is free (ideal) maintaining a 1:1 boost exhaust pressure ratio? By that I mean if like there was a super charger running from an external power source compared to running at a 1:1 ratio turbo charged.



What about the added force needed to compress an additional 40 psi? Just an offset Hp for the price of super charging?



At any rate I can see the effects of trying to run a HX35 at 35 psi boost and 70 psi drive. Its huge.



Jim

 

[Fishin Guide]

I am also runnign a set of Rip's twins.



Dodgezilla or S400. Modified gate in a 14cm housing on top.



Dave

 

[NoSeeUm]

Getting back to the topic, I installed my M4's a few days ago and did some testing.



The DZ over s400 seems to be fully awake now and is performing quite nicely. Power is up and EGT's are down even running up to level 7 on the TST. Whats not to like about that?



I can recommend the DZ/s400 set combined with M4's.



Jim

 

[WDimig]

i absolutely love the color combo of that engine! i hope i can do the to mine someday... ... ... :-laf Oo.

 

[Junior]

My wife got me a set of mach 4's for my birthday this past saturday so know is decision timeOo.



BD or Rip can't figure it out.

 

[TwinTurboDave]

Junior you need to look into the detail. . As in pipe welding or not(cold pipes). If it is welded what type of welder? What type of steel? Also how dificult to reverse if you want to sell your truck. . And yes we do often look at prices also. . good luck on your pick





For your info, this is a stainless steel set i built for a 96 it has no welds on the cold pipes. The U is all one piece and their all bead rolled on the ends. The rubber couplers allow flexibility for different turbo swaps.

 

[NoSeeUm]

Nice looking set.



Top one is a HX35 or hybrid? Bottom one is a HT3B?



Jim

 

[AFarmer]

Where's the intake pipe??