Venom Twin Turbo SRT: 713 rwhp & 757 rw tq

[Jerome Sparich]

With only 6.2PSI of boost

The Gen 3 motor is totally stock with 140 miles on it and boost was set at 6.2 psi. The first dyno pull made 735 rw hp and 775 rw tq. But this run was inadvertently deleted from the dyno. The second pull made 713 rw hp and 757 rw tq.


Dyno sheet here.

 

[treynor]

What other mods did the vehicle have? I'm having slight difficulty with these results, considering a stock SRT makes about 440 RWHP, and you're running 140% of atmospheric pressure. I would have expected low/mid 600s RWHP at that boost level.

 

[Jerome Sparich]

Ben, I will get more details and get back to you.
For now the car has stock internals, but it will be pushed to the limits seeing how it will become a 522 Stroker with all the upgrades anyway.

 

[fluffy]

All that matters are the ETs. When does that thing go to the track?

 

[Paolo Castellano]

What other mods did the vehicle have? I'm having slight difficulty with these results, considering a stock SRT makes about 440 RWHP, and you're running 140% of atmospheric pressure. I would have expected low/mid 600s RWHP at that boost level.

Ben, I do not understand either, but boost is a relative measurement. If there are huge turbos on there that almost double the amount of CFM, then the power would certainly be there and the boost number would be relatively lower. From looking at the dyno graph, the power curve would not support the large turbo hypothesis as the torque peaks at around 4500 RPM.

 

[Miles B]

Mmmmm... even assuming 100% intercooling, 1.4 times the number of air molecules is still only 1.4 times...

Surely you aren't disputing John?!

 

[John Myrick]

Mmmmm... Doesn't seem out of line to me.

I suspect that the pressure ratio analysis took less than a few seconds of thought. Here's my thoughts after a few more seconds...

A Roe blower will make about 600 rwhp on less than 6 psi of non-intercooled boost.

I would guess that the addition of an intercooler would result in a higher mass flow rate of air at the same manifold pressure. That may put you in the low to mid 600 rwhp range. Belt driven blowers are a substantial parasitic drag on the motor. They require a substantial amount of power to turn the blower and hence all the problems with the belt and spinning the crank pulley. For a turbocharged system, that parasitic drag that was required to spin the belt driven compressor will show up as increased rear wheel power.

Anyway, add all the above with the benefit of a little additional boost pressure over that of a Roe system, and 700 rwhp does not seem unreasonable.

I think this is a little more complicated problem than assuming that the horsepower will be directly proportional to the ratio of the intake manifold absolute pressures.

I think it's great that you guys are challenging these numbers, but you need to take everything into account before you can come to a reasonable conclusion.

It's my opinion that we will all just have to wait until there are more turbocharged or supercharged SRT-10's available for comparison.

 

[Torquemonster]

It's the Texan air!

Everything is bigger in Texas.

 

[treynor]

> Everything is bigger in Texas

Mmmm, perhaps as a result all the weight has caused TX to sink several hundred feet below sea level? THAT would certainly explain the results...

 

[Miles B]

John Myrick,

if you read mine carefully, you will note I am considering the pressure ratio and intercooling to give a "perfect" increase in density ratio. In reality, this wouldn't happen. You are not going to lose THAT much power to a Roe charger either. I would expect in the 30-40hp region TOPS, but probably not even that high at only 6psi.

 

[fluffy]

Miles, it doesn't work like that. Just because a turbo is operating at 40% more pressure than atmospheric says nothing about the density change of air in the cylinders. A massive turbo will flow a much higher volume of air than a smaller one at a given pressure. Without knowing the size of the turbos it's simply not possible to determine how much additional air is being crammed into the cylinders using only the pressure.

 

[treynor]

It is, however, possible to put an upper bound on the air mass. Obviously air is governed by PV=nRT equation regardless of induction method; we can thus state that a turbo engine running 6 PSI of boost will make at most (14.7+6)/14.7 times as much power as the same engine running 0 PSI of boost, assuming nothing funny is being done to supercool the intercooler.
The reasons smaller turbos make less power that large turbos at the same boost pressure are twofold: (1) increased backpressure on the exhaust side; (2) increased intake air temps.

 

[fluffy]

Except that automobile engines don't operate at atmospheric pressure internally, they operate at some lower pressure (depending on engine design, intake, heads, etc.). When the intake valve closes the cylinder has an air charge, but is still at a lower pressure than atmospheric which is why ported/polished heads, intake mods etc. increase power... they allow the cylinder to reach a pressure closer to atmospheric due to higher airflow. We can only calculate an upper bound for forced induction power gains if we know the stock operating pressure of the Gen III engine's cylinders.

 

[Miles B]

Treynor is right, you are wrong.

PV=nRT helps tell us the density of the air in the manifold. There is no MAGIC associated with bigger turbos flowing more. You are thinking of bigger turbos being more efficient at compressing the air. That is, less heat is added when the air is compressed. The amount of air flow is governed by the manifold and head design. It will flow the same volume of air at the same manifold pressure, no matter what device compressed it. 6psi from a tiny turbo will put the same volume of air in an engine as 6psi from a huge turbo. Now chances are the tiny turbo will produce hotter air meaning the MASS is less.

If you read my response properly, and know the actual physics behind this, you should understand Ben's response.

PV=nRT

I am giving the intercooler the benefit of the doubt and saying T is the same at 6psi as at atmo. R is a constant. V is fixed. P is 1.4 times atmo at 6psi. Therefore n (number of moles of air) is AT BEST (ie 100% intercooler efficiency), 1.4 times that at atmo. So the best the engine could do at 6psi is approx 1.4 times at atmo. Well sized turbos operating at or above 80% efficiency, with very good intercoolers, will come *close* to this, but not achieve it. There are a few cases where you can use some tricks to very very slightly exceed this, but they are mostly related to exploiting deficiencies in the engine at atmo which change its volumetric efficiency at boost.

It *IS* possible to put an upper bound on the mass of air entering the cylinders, based solely on the density ratio. It does not matter what is producing this compressed air. If you don't understand this, you don't understand the means by which an engine aspirates compressed air, and the workings of the device producing it.

Your second post is wrong too. You are just explaining volumetric efficiency of the engine, which you are planning on changing from, say 85% for atmo, to 100% for FI. It doesn't work like that, either.

 

[Jerome Sparich]

Seeing gains of 45+ rw hp per pound of boost due to the fact that the car has stock 9.6 compression. At some point it will get lowered to 8.5-9.0. But for now the specific output is pretty strong. The boost will be worked up to 8 psi next then 10 maybe 12 psi and see what kind of power yields on a stock motor.

Most people have a power to boost ratio reference point that is derived from SC. The fact that the turbos do not rely on crankshaft power helps make more power. The ball bearing turbos that are used in the Venom twin turbo systems usually make 5 psi as low as 2000 rpm. Thus this car made over 500 rw tq at just over 2500 rpm.

This car will most likely get dyno tested again this coming week. When it does, we will get somebody like SmokinV10 to come and watch the boost meter so that everyone knows that this car is in fact set at 6 psi right now. The car will eventually get a boost controller but for now just has mechanical springs that actuate the wastegates.

 

[fluffy]

Raising the volumetric efficiency of the engine is precisely what forced induction does. You cannot just say P=1.4 based on pressures and no other information and be done with it, because that 1.4 ratio is an assumption based on nothing. P is an unknown, it is not 1.4.

Your 1.4 number comes from two assumptions, both incorrect. 20.9/14.7 is ~1.4, but 20.7 is not the upper bound on cylinder pressure because many engines can, and do, exhibit >100% volumetric efficiency. 14.7 is not the starting point because the VE of the Viper's V10 is probably closer to 85%, but I don't know for sure. Both numbers are simple assumptions that have no rational basis.

 

[treynor]

Jerome - to be clear, I'm not saying the car doesn't make the power specified at 6.2 PSI of boost. I'm simply saying there must be more to this story, because the numbers don't yet jive. Did the car get a baseline dyno pull on the same dyno with all the bolt-ons it is now running, but no turbos?

Fluffy - perhaps you can explain in simple English how pushing air into an engine at 14.7 PSI absolute(atmospheric pressure) compared to pushing it in at 20.9 PSI absolute (the boost level stated) will produce superlinear results? We all agree that the pressure ratio in the intake manifold is ~1.4; how that becomes a pressure ratio of ~1.6 in the cylinder is the mystery?

 

[fluffy]

I'm going to change tack here, since I don't know if the pressure drop across the cylinder heads is linear with respect to the pressure difference or not. However, we do know that the turbo (tries to) maintain a pressure of 20.9# in the intake manifold, so then the question I have to ask is this: was the pressure in the intake manifold really 14.7# before turbocharging? If there are restrictions leading to the manifold I would suspect that it was not. Was it enough of a difference to drop the intake pressure to 13# for a 1.6 ratio? I have no idea. I'm just trying to explain the dyno results. When an empirical test shows an apparent superlinear increase in power that contradicts what we know about basic physics there is either something being overlooked, the laws are wrong or the evidence is false. Since I cannot question the laws, and the benefit of the doubt must go to the evidence until it is proven one way or another (certainly several more dyno runs, along with base runs and atmospheric conditions for the runs), the only alternative is that the 1.4 number is wrong somehow.

 

[fluffy]

Something else... it would also be interesting to see before/after A/F ratio graphs. How much power is left on the floor in the stock SRT due to conservative tuning? How much work did JH put into tweaking it? There are too many variables.

 

[Miles B]

Right.. so you are proposing the best the SRT can get is -1.7psi, or a whopping 47 inches of water of vacuum at WOT?

Don't mistake a stock VE multiplied by the PR as a new VE, and then try and multiply it by the PR again. We are talking *volume*, not mass. To get a volumetric efficiency greater than 100%, you need to effectively get the pressure inside the cylinder *higher* than that inside the manifold as the valve shuts. This is difficult to achieve.

For this sort of gain at 6psi, I would have expected head work, a cam, rockers.. something like that.

 

[fluffy]

Right.. so you are proposing the best the SRT can get is -1.7psi, or a whopping 47 inches of water of vacuum at WOT?

No, I'm proposing that intake pressure is probably something less than atmospheric. Whether it's 13psi or not i don't know. It would be something to measure.

Don't mistake a stock VE multiplied by the PR as a new VE, and then try and multiply it by the PR again. We are talking *volume*, not mass.

That was a mistake I made earlier, but I don't think it really matters. It's the PR that I'm disputing, and not on the basis of VE. In fact, I think VE is pretty much irrelevant, and the only relevant figure now is the pressure inside the stock intake manifold at WOT and at again at full boost.

To get a volumetric efficiency greater than 100%, you need to effectively get the pressure inside the cylinder *higher* than that inside the manifold as the valve shuts. This is difficult to achieve.

Relatively difficult, but it still happens, and quite often though mostly in DOHC VVT engines. The s2000, for example, peaks at 112% VE from just over 8000 to 8700 rpm, and even the older Prelude H22 engine achieves 102% (sae paper 2000-01-0670).

For this sort of gain at 6psi, I would have expected head work, a cam, rockers.. something like that.

As would everyone. So if it doesn't have this work, then there is either a severe restriction in the stock intake system or something else is going on.

 

[WESTCOAST JASON]

Based on my experience with my personal TT Viper the boost level would seem wrong for the HP stated. I can show 10PSI time and time again from twin turbos making 715RWHP on a stock VERY high mileage motor. Granted, this is on a Gen2 not a VGX motor. However, the difference between the 2 motors INCLUDING stock cam profiles are minimal and there is no reason to believe that a VGX would make better gains under boost than a Gen2. I would tend to believe that maybe the 6psi stated in the original post was closer to twice that. Being that the motor also has only a stated 140 miles makes it even tougher to understand. We have seen as the miles add up on the SRT's, the HP goes up. We have seen a customers SRT go from 440 RWHP to 460RWHP once it aged 4500k miles. (no mods at all)

My only other observation would be regarding the psi being 6.2, that is an exacting number. How is it achieved and maintained on multiple pulls? Why was it chosen as the boost setting? I have run numerous different boost controllers and multiple brands of wastegates on my car along with many other turbo cars I have owned in the past. Setting boost that exact is nearly impossible, especially to repeat. Usually turbo boost levels change based on the enviorment and temp. My system at 10psi is just an average that goes as low as 8 when hot and as high as 12 when cold. This is just the results when you use aftermarket parts when building a turbo kit for any car.

Just my .02

 

[Torquemonster]

There is a 50hp difference between the Gen 3 and gen 2 engines based upon the slightly extra cubes and the better heads. That figure is without boost and the differential would increase in proportion to boost providing a 70hp difference at 6.2lb - all other things being equal.

That would mean 715hp at 10lb on a Gen 2 should make 800hp on a gen 3 - quite a difference assuming both use stock heads or have equivalent prep work done to maintain flow differential.