Pro Stock John

iTrader: (34)

I've read Jose's faq a few times and I don't quite have a handle on a few underlying issues... So let me throw the questions out there I'd like to see what answers are offered...

-Stock stroke vs say 4.000 stroke... When is having too much stroke an issue. Let's assume a goal of 9:1 compression or lower.
-If stroke can be an issue, what is the minimum rod length that is ideal for a race application. So we can go 6.098 or 6.125, but what is the downside of say a 5.7 rod?
-What is the rule of thumb as to when piston velocity is too high to be safe, ie. the engine will have poor reliability
-BBC vs 402ci LS1 vs 346ci LS1... Goal is 800rwhp, and you run either a 76mm, T4 flange... Will all three combos make the same power, and what are the differences... heat, peak rpm, peak torque, but which combo is the least efficient and why?
-You build a 9:1 540 BBC, and build a pump gas monster... say 800rwhp. Which turbo do you pick and why. How much will going from a 76mm turbo to say a 88mm turbo affect the peak rpm of this combo? I don't really understand the compressor maps that I have seen, what is it that I am looking for on those? What efficiency percentage is the one to shoot for?

I had another question, but I can't recall the exact issue, maybe if I see Kurt on IM I can figure out what the convo was about... something about efficiency vs flange size vs heat....

JZ 97 SS 1500

iTrader: (2)

John give me a call tomm or PM your number. I will explain those questions to you. Good luck finding others to answer, that is part of the reason why I studied and test these things. Got tired of getting a bunch of BS from the "turbo gurus"...lol

BlackCamaroSS02

iTrader: (8)

I would like to know as well...planning on a turbo build very soon. Was going to go with a 408 + T-72 setup but from what i am hearing its better to go smaller motor. Send me a PM as well...my car is going to be a more of a street car then drag

SScam68

iTrader: (20)

Your not going to get off that easy. Spill the beans!

I've thought about working this kind stuff out on paper, but I think we both know thats only going to take you so far.

Frank

JZ 97 SS 1500

iTrader: (2)

Yeah, my friend...408 and T72 are a big no no...hehe. EGT's and backpressure would go through the roof...hehe.

JZ 97 SS 1500

iTrader: (2)

Paper will only take you so far. We are working on a full turbocharger test facility, but getting the bugs out of these things takes a while. And getting accurate streaming data from 20-25 sensors at once is a PITA.

Pro Stock John

iTrader: (34)

BAckpressure and egt's were my last question, ding ding ding.

Why not post your answers here Jose, since others are interested?

Pro Stock John

iTrader: (34)

I mean it seems to me that most of the turbo combos I read about except for like 2-3 max effort cars peak at like 6200 or less, so it seems like piston velocity (stroke) would not be a big deal since you're not spinning the engine to 7500.

slow trap

iTrader: (22)

longer strokes put more of a side load on your pistons and tend to rock them in the bore.longer rods speed the piston up in it's travel fom top to bottom and vice versa,aparently which helps since most race sbcs run 6.125-6.250 rods.i've seen tests comparing 5.7 roded motors verses identical 6 inch rod motors and piston speed definitely sped up but in those tests hp increase was mediocre but i can't remember exact numbers.i have 0 knowledge of the compressor maps of turbos.maybe someone will enlighten us because i would like to know as well.

JZ 97 SS 1500

iTrader: (2)

Its alot to type....lol

Anyhow, quick answer on the engine and some other key points. Stroke vs bore, they play a little role in the equation, but more on the side of engine wear then performance. The more side loading you create on the piston, the worse wear will be. As for peformance, just check out the latest mustang mag, the myths of stroke vs bore are put to rest in the article....very good reading.

As for rods, they play a role in the above question. Too long a stroke and rod, means the piston pin is higher, means less skirt, means rings are higher...yadda..yadda. Something you don't want in a FI car. Any extreme in anything is always bad

BBC, vs 402, VS 346 with a T76. Well first the BBC I imagine you mean big cubes. Well the BBC and 402 first will spool a T76 very quick, but the pressure ratio of the turbo will quickly move past the peak effciency at higher consumption rate. Remember the efficiency of a turbo blade is dependent on the compression of the air between the engine and compressor outlet. Insufficient compression means loss of efficiency of the blade. Example take a 1000hp turbo which has a legitimate compressor map. What the map will show is 1000hp is made at X pressure ratio.

Now stick this turbo on a small cube motor and X pressure ratio could be met, while a larger motor will not reach that pressure ratio so the efficiency and total output of the turbo drops. When I mean drop, that is either by insufficient blade speed (which is a value on the map) or by super heating ( or choke line) which is the blade speed and air has gone beyond what the compressor wheel can produce.

As for a conversion or straight equation of heat, vs flange size vs efficiency...their is none. Just to many variables. Like I said, this can get VERY long.

JZ 97 SS 1500

iTrader: (2)

BTW, before you ever pick a turbo for a build, you need to answer these questions. What Max hp, daily hp, cubic inches, and how much lag do I want. The rest of the combo is their to make the turbo system work.

Jose

Pro Stock John

iTrader: (34)

Take for example an 88mm T4 flanged turbo, perhaps something like what you have on your SS....

88MM + 346ci LS1 = ?
88mm + 402ci LS1 = ?
88mm + 540ci BBC = ?

The "?" I would be after here is..
-Compare efficiency
-Which will run the hottest
-Which will be the quickest?

I'm guessing the 346ci will be the hottest... But the 540 BBC would be the quickest?

How about torque, will it get so rediculous with the 540 example that it cannot be hooked up at the track?

Pro Stock John

iTrader: (34)

Sean made a good comment in IM about how Pro5.0 cars only run about 380ci or 390ci cubes...

JZ 97 SS 1500

iTrader: (2)

Okay first and most important thing to remember the turbo dictates the HP, not the cubic inches. An 88 mm turbo will only flow XX amount of air. So whether its a 1.0L or a 10.0L the 88 flows XX. Now efficiency is where the output will vary.

JZ 97 SS 1500

iTrader: (2)

I will answer the rest tomm.....I need sleep... 1am here...lol.

I will also make some consumption charts for comparison sake for the 88 and the 3 engines above.

Jose

racer7088

You are right on all except you can gear up the bigger engines to avoid as much wheel torque and tighten the converter. The bigger engine will be faster.

qqwqeqwrqwqtq

I think this is a good starting point. Rather than pick a turbo and talk about what combinations it would work well with, list your goals and build a combination around that. In the meantime, I will allow Jose to bang his head against a wall

racer7088

Mostly but not all true.

a 1 liter even turning 20,000 rpm iis still nothing to a 10 liter going 5000 rpm.

We'll say the 1 liter @ 7,500 rpm is trying to move about 132 cfm and the 10 liter @ 7,500 rpm is trying to move 1320 cfm. This means the boost will go much higher on the smaller engine than the larger with the same turbo and the higher the inlet side is on the turbo the less air will enter the turbo. The pressure drop across the turbo has a lot to do with how much mass flow goes through it.

Turbos are NOT positive displacement blowers. The truth is that even on positive displacement blowers the boost will also go up as the engine size goes down with the same blower at the same speed but again you will lose power on these due to the much higher blower belt tension on the smaller engine with the much higher boost but yet similar airlfow.

Bigger engines almost always go faster with the same turbos and you will notice very strict limits on turbo engine size even smaller than any other power adder. They do NOT do this to speed them up but to SLOW them down. Other wise they could just spec the turbo size and allow bigger engines but you will not see that as it's been done before and the bigger engines go faster every time.

Obviously you have to leave a little more piston top sometimes for the dish but quite a few of the better running outlaw engines have very short pistons and HUGE stroke. I know that there's a few 6 second 10.5 outlaw small blocks with a 4.250 crank in them right now.

y2khawk

iTrader: (5)

sorta but not quite. More often than not, you'll get more compressor flow at a higher pressure ratio. Either limited by choking the compressor, or being so far off the map that you end up in an efficiency range so unusable you will net limited gains.

in the simplest terms, you are limiting the possible mass flow into the air pump (ie engine) with the compressor size. That max limit will vary depending on where you operate on the map of the turbo, ie ideal mass flow for said air pump given a pressure ratio you intend to operate.

reguardless of how much flow you can actualy get from a given turbo, you're ultimately limited but how much heat you've added to the air. You will have to spark and fuel for that heat. Higher pressure ratios = more heat obviously, but extremely low efficiency at a low PR can give you more actually heating than a more efficient compressor at a higher PR.

There are MANY ways to look at it, and that's just on the "cold air" side of things. Turbine size and efficiency one the hot side can choke your air pump as well.

We could spend days on what effects various things will have on what's needed for MBT and LBT spark, how extreme your fueling will need to be just to keep the exhaust valves intack, how bad your knock limit will change for the given PR and adiabatic heating from the compressor, etc, etc.

too early for me, not enough coffee yet

racer7088

Show me some data aquistion where you lose air and fuel by going to a larger engine. I've seen it the other way 100 times.

There are no classes where they let you run really large engines with turbos against say blowers or NOS. If running the bigger engines at the same turbo size resulted in LOWER power and performance they wouldn't have these limits because the bigger engines with the same turbos wouldn't have a performance advantage. We all know that's not the way it is. The turbos are limited to the SMALLEST engine sizes of all power adders.

I agree that the turbo is the largest influence on total mass flow but you will make more power with the same turbo and a larger engine. You might change the rpm band the engine peaks at but you can regear and converter for that. If you are doing something like trying to make power at some given rpm then the turbo size and style vs the cubic inches is probably important but the idea in most programs is to make the more power you can and then you set up the car to utilize that.