Hey in looking at a t70 with a .68 ar exhaust. How will this perform on a 383 with stock ported heads and a cc305

 

Go a bigger exhaust like a .96 or larger, the .68 will have quite a bit of backpressure and not perform well the higher the rpm goes.

 

My bad it is a .96 ar exhaust. My goal is 600rwhp. Engine a 9:1 cr cc305 with a 114 lsa. Stock ported heads and intake. I was thinking of going rear mount with it mainly because of room. I will be happy to hit 600rwhp but more the better. I built the motor to easily take 20psi

 

Any info I can get about turbos will help. I already bought a mpt70 with the .96 ar exhaust.

 

Look at some compressor maps.

Find out the engine CFM at the highest RPM you will run.
Then decide on your boost level, find the PR.
Then plot some points on the compressor map.

 

auto or m6? .96 on a rear mount will have some decent lag, the stroker will help but depending on what you do with exhaust it could be pretty laggy. dont run long tubes, they make exhaust pressure worse and it will have a hell of a time spooling.

keep the exhaust piping small for the rear mount (if thats the route you choose) 2.5 is more than enough and should help keep velocity high and temps high to create a good spool time.

whats the turbine wheel size?

 

@xrambbc the car is a m6 with 4:10 gears. I already know the gears will suck for a turbo. I want to go 3:55-3:73. I have shorty headers right and a 3 inch pipe over the axle. I will have to look up the turbine wheel... im super new to turbos. I only ever done blowers.

 

@f0x.. I dont plan on spinning any higher then 6500. Iwould like to stay arou d 6300. How can I find out cfm?

 

I am going to copy and paste this article from a book I have (Basic Turbocharging Concepts)

"Selecting a turbo size to match your engine is not at all difficult. You need to find a few things about your engine, decide how much boost you want to use, and then plot the information against a turbocharger's compressor map. There is a little bit of math involved, but it’s easy.

First you need to know the CFM of your engine when running naturally aspirated. You can find this by using the following formula:



volume of air (cfm) = engine rpm x engine cid
3456

So, an example engine with 350 cubic inches of displacement would look like this:



volume of air (cfm) = 6000 x 350 = 2100000 = 607.639
3456 3456


The engine in this example needs about 600cfm of air at 6000 RPM naturally aspirated. Now we know our NA cfm requirements, but in order to read a compressor map we'll need to figure out the airflow in pounds per minute (lb/min) required by our engine under boost. For our example, let's use a boost pressure of 10psi.

At this point it is important to talk about the difference between absolute pressure (psia) and gauge pressure. The boost level that you read on your boost gauge is really called psig or pounds per square inch gauge. The absolute pressure is 14.7 + psig. The 14.7 comes from the pressure of air at sea level. So 10psig = 24.7psia.

We can find our engine's requirements by plugging our numbers into the ideal gas law. The ideal gas law relates volume, pressure, temperature and mass of air. It is:

PV = nRT
Where P = absolute pressure, V = volume cfm, n relates to mass, R is a constant and T is the air temperature in Rankine.




Let's simplify the ideal gas law to find our engine's required airflow in lb/min with 10psi boost. We will need to know the temperature of the compressed air coming out of the turbo. Let's assume an intercooled intake air temperature of about 130F. Turbo cars that do not have an intercooler can see intake air temperatures around 250F. To get the temperature in Rankine, simply add 460 to the air temperature in F.



n(lb/min) = (14.7 + psig) x V cfm x 29
10.73 x T deg R


n(lb/min) =(14.7 + 10) x 600 x 29 = 24.7 x 600 x 29 = 429780 = 67.888 lb/min
10.73 x (130 + 460)R 10.73 x 590R 6330.7
We find that ideally, our engine will require 67.9 lb/min of air under 10psi boost at 6000RPM. I say ideally because that assumes our engine has a volumetric efficiency of 100%. We'll assume that our engines have a volumetric efficiency of about 85%. Now we can correct our airflow.

67.9 x .85 = 57.7 lb/min

By the way, as a rule of thumb, horsepower can be found by the following:

Hp = airflow lb/min x 10 = 57.7 x 10 = 577

Now that we know our required airflow in lb/min, we need to find something called a pressure ratio. This is the ratio between the inlet and outlet pressure of the turbo's compressor. Inlet pressure is usually 14.7psi. (standard barometric pressure at sea level) The outlet pressure is 14.7psi + boost pressure. Take the ratio of the two and you get:


Pressure Ratio = 14.7 + boost
14.7


We decided to run our project at 10psig. That gives us:


Pressure Ratio = 14.7 + 10 = 24.7 = 1.68
14.7 14.7

We now have all the of the information that we need to read a compressor map."

 

Drats I should have looked it over before posting it, the formulas are missing the slash. If you see a number stacked it is slashed. Let me see if there is a link to this info.

 

OK found a web site with the infor better stated than my suck-job above.

http://www.gnttype.org/techarea/turbo/turboflow.html

They say things a little differently in a few spots, but the concepts are the same.

 

Ok great. I will read this tonight. Thanks alot

 

Another site to check out for info on rear mount setups would be http://junkyardturbos.com/Rear-Mount-Turbo.php

This will provide you with plenty of info on what to look for when designing a rear mount turbo setup

 

@myltwon. Great info thanks

 

Hi I race in a street legal street race it is a 1/8 mile I'm running a 12 to 1 383 with a gen one it does real well. But lost one race last year to a mustang that was bad fast. I cant run my nitrous in this event but can run a boosted motor was thanking of running one 88 turbo with twenty pounds of boost and vp116 fuel. Need help with parts list for turbo set up on a budget, especially the exhaust manifold cant seem to find a reasonable one, also need to know what boost controller is needed running msd 6 digital ignition. with a built in retard was thanking msd boost controller might work to back timing of under boost. The engine put out around 600 hp on motor with a cheater plate system. I'm running all forged parts with iron eagle platinum heads.

 

^^^^^wrong section, you need sbc/bbc section, and to start your own thread