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  #91 (permalink)  
Old 07-24-2010, 10:13 PM
zildjian4life218's Avatar
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So I think I might go with some bigger turbos...........

Can someone with turbo knowledge or any knowledge that can help check my math. I bought a book titled "Street Turbocharging" by HP Books. In here is a step by step calculations for plotting turbo compressor maps.

Okay first off you figure out the specs of the engine
305ci
assuming 80% VE
8.5:1 CR
12psi
Redline 5000
IC Eff 60%

Figure out the Pressure Ratio of the compressor
(12+14.7)/14.7 = 1.816

Then the Pressure Ratio of the System assuming a 1 psi drop through the Intercooler
(12-1+14.7)/14.7 = 1.748

Now we figure out the temperature rise after the compressor assuming ideal
Toutideal = [(Tin+460)*PR^0.283]-460
[(85+460)*1.1839]-460]
185*F

Now we find the actual temperature assuming the efficiency of the turbocharger which is 72%.
Toutactual=[(185-85)/.072]+85 = 223.8*F

Now we find the temp of the air coming out of the Intercooler.
TempIC=224-[.60*(224-85)]
140.6*F

The Density Ratio is then figured out by
DR = 1.75*[(85+460)/(140.6+460)] = 1.5869

Then you figure out the VFR which is the volumetric flow rate at redline of the NA engine.
VFR=305*5000*.80/3456= 353cfm

Last step is to find the Mass flow rate which is
MFR=(2.703*14.7*353*1.5869)/85+460 = 41 lb/min

Sorry its so long I want to make sure I have this somewhat right. Thanks! These turbos flow 15 lb/min at a PR of 1.82 so idk if they will quite cut it. I think I will be spinning them way too much and burn them up.

I attached a compressor map for the turbo I am using. The red dot shows where I would be sitting.
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Last edited by zildjian4life218; 07-24-2010 at 10:52 PM.
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  #92 (permalink)  
Old 07-25-2010, 09:42 PM
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Very, very goo grasshoppa....now I show you calcula5tor to do math for you :

http://www.turbofast.com.au/javacalc.html

Now that you understand the math you can plug things in to the above listed calculators and actually understand what you are seeing.

There are some points to consider. First, you are only calculating peak RPM. How much are you going to operate at full power? Second if you run those numbers again for the same boost numbers at 3500RPM and I think you will find that it is about perfect. How much time will you spend around this range? Third, the map does continue and if you continue the lines you can see it will be right at the edge, but will in fact still feed the engine sufficiently.

My point in all of this is if it is a street car, it will work very nicely and spool instantly which will make for a very fun ride.

I also dont disagree that they are a little bit small, but not much.....in the end it comes down to what you are wanting to do.
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  #93 (permalink)  
Old 07-28-2010, 08:32 PM
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Quote:
Originally Posted by TurboS10
Very, very goo grasshoppa....now I show you calcula5tor to do math for you :

http://www.turbofast.com.au/javacalc.html

Now that you understand the math you can plug things in to the above listed calculators and actually understand what you are seeing.

There are some points to consider. First, you are only calculating peak RPM. How much are you going to operate at full power? Second if you run those numbers again for the same boost numbers at 3500RPM and I think you will find that it is about perfect. How much time will you spend around this range? Third, the map does continue and if you continue the lines you can see it will be right at the edge, but will in fact still feed the engine sufficiently.

My point in all of this is if it is a street car, it will work very nicely and spool instantly which will make for a very fun ride.

I also dont disagree that they are a little bit small, but not much.....in the end it comes down to what you are wanting to do.
Thanks for the link. I made an excel chart with the same idea as the above link just not written in java script. where on one side you put in the constants and it outputs on the right. Oh well at least i now know what the formulas do. Thanks for all your help everyone. I am waiting to get sometime so i can go down and bore my block. The forged pistons my machinist gave me are .030 or .040 over so gotta punch out the block.
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  #94 (permalink)  
Old 08-19-2010, 09:08 AM
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Any idea what I should gap the rings too. I got some enginetech El cheapo rings. Just putting some dished stock pistons back in it. I'm having a hard time believing this is gonna make over 400hp with the t25 turbos. Later ill build a 305 with the forged pistons I got and bigger turbos. I put the top ring in and its sitting at about .020. Thanks for all the help and support.
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  #95 (permalink)  
Old 08-19-2010, 09:19 PM
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Anyone any ideas on the ring gap? Stock bore 305. Gonna be running 12-15lbs
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  #96 (permalink)  
Old 08-30-2010, 08:10 AM
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Well I went to keith blacks website and used their calc for ring gap. I put the top ring at about .028" and the second ring at .030". The calc said .026" and .028" but i would rather things be on the loose side as opposed to the tight side.
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Old 08-30-2010, 08:16 AM
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be sure to get the incoming charge as cool as possible. heat soak is a problem with smaller turbos, but isn't a big deal if you cool down the charge.
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  #98 (permalink)  
Old 08-30-2010, 09:31 AM
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Quote:
Originally Posted by turbolover
be sure to get the incoming charge as cool as possible. heat soak is a problem with smaller turbos, but isn't a big deal if you cool down the charge.
I will definitely be running an intercooler and possiblly a Meth injection setup
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  #99 (permalink)  
Old 09-05-2010, 01:06 PM
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The short block is all together. I will be ordering the cam soon hopefully and then I can degree the cam, put the timing cover on, and the oil pan.


For those of you who are observant you probably noticed that piston 1 appears to be in backwards due to the dot on the piston facing the back. It was for the even side but the only piston I had left. I had a pile of pistons from two different 305s. One came apart so most of it was junk. My machinist said the orientation on the pistons doesn't matter for that style heads just the rod orientation does which is correct.
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