I think I know the answer, but....

[zeiss150]

I've read Corky's book and I've read for days and days and days but I'm wondering why you cant just get 15lbs of boost out of the stock t3. I know that the smaller turbo creates more heat and more heat is a bit of a detonation problem. So is it better to use a t3/t4 that will make 15lbs of boost with less heat. But if Heat is the only problem then shouldn't the IC take care of that? OR is there only so much that a good IC can do? so the big question is... isn't 15lbs of boost from a t3 the same a 15 pounds of boost from a t4 (if cooling the charge to the same temp is achieved?) So tell me Im dumb and why!

 

Any of you turbo guys live in southern California?

[thehelix112]

I'm on my way to Laguna Beach tomorrow actually (from Melbourne, Aus).

 

Have a look at a turbocharger flow map: http://www.turbofast.com.au/FlowT3.html

 

The lines with 6 digit numbers are turbocharger RPM lines, notice that for higher pressure ratio and flow the turbine has to spin faster. That is why they produce more heat when asked to compress air more, and more air.

 

A larger compressor spins slower to move the same amount of air typically adding less heat for a high pressure/flow combinations.

 

So yes, you're right.

 

Also, a turbo will make more power if the exhaust side is larger.

 

Dave

[pjo046]

The intercooler won't cool the charge from the T3 to the same temp as from the T4. It will remove the same amount of heat from both, but with the T3 charge temp being higher initially, it will still be higher after it has passed through the intercooler.

[Guest 280ZForce]

Any of you turbo guys live in southern California?

yo Zeiss150...me and violacleff are in Corona. maybe we can help out. i'm ditchin my t4 maybe u can use. where in So Cal u @? violacleff and I r looking for some good help on gettin his stroker in my Z and workin on gettin his rb25 in his Z...any takers on some help? we can provide lunch and stuff gladly. we're tryin to beat the clock to MSA. thehelix112 has already told me when he gets here and we r ready 2 start he wants to help! so let us know ur whereabouts and what not

[zeiss150]

Hey Zforce, I live in Covina, its off the 210 and 57. I would love to give you guys a hand. I don't have a lot of time but I'll do what I can. Let me know some details.

 

Matt-

 

 

So just to be clear 15lbs of boost is 15lbs of boost whether from a t3 or t4. The only differance is in the heat of the charge. so if thats the case .... then really all you have to worry about is detonation? right?

[Dallas J]

Boost pressure is actually just a measure of resistance to flow. Ask someone with a mustang what happens to the Supercharger boost levels when they change to an aluminum head. Hint, it drops because their's less resistance.

 

So really when youre talking about boost on one engine, its doesnt nessessarily mean the same amount of airflow as on another engine. In the dsm world we dont really talk about boost pressure, we use airflow in either lbs/min or grams/rev. This gives us a more accurate estimation of what the engine/turbo combination are doing.

 

So why did I go through that? Well say an engine is at 20psi and running 36 lbs/min of air. That was good enough for my car to run 12.7. Then you add cams to make the car more efficient at a higher rpm, and the airflow rises to 40lb/min. Now I can run in the 12.4 range. The turbo is able to push more air into the engine, but it still runs at the same boost. What did that do to may intake temp? Well it depends on what the compressor map says. Youll get a shift to the right on the map because the airflow increases, but where was I before. If I was to the left of the peak efficiency island then my temp will go down, if I was already at the peak effiency then I might move out of that range, and heat will increase.

 

If you just increase the boost, then you increase the heat regardless. But the rate at which the heat increases depends on where you at on the island. If youre running an L28et at 15psi I would guess you have around 30lbs/min. Look where that is on the map that thehelix112 posted. 30lb/min is way out there in a very low effiency place, so when you up the boost heat is increast alot. Higher temps actually decrease your airflow, so increase in pressure is negated by the increase in heat, and now you are at the same airflow, higher boost, but more prone to knock.

 

A larger turbo may not even be at its peak island, so when you turn up the boost and it hits the peak island then your airflow will increase also. That is what you want.

 

Ok, Im done babbling. I hope I didnt confuse you more.

 

-Dallas J

[big-phil]

I'm hitting 15lbs on my stock t3 with crap intercooler and no ping.

[Clifton]

. isn't 15lbs of boost from a t3 the same a 15 pounds of boost from a t4 (if cooling the charge to the same temp is achieved?) So tell me Im dumb and why!

 

 

Let's say you need 40 lbs/min. No T3 compressor will supply that. In that case it's not just a heat issue but you are overspeeding it. You can run a turbo into a lower eff range but it will quickly go off the map if you try getting a little more out of it. Then there is the case of getting the air out. T3 turbine wheels are small and more restrictive. That's why even T3/4's don't make big power on L28's. You can run 20 psi on a stock T3, some do but they are way down on power comparred to boost.

[zeiss150]

So whats the most you can run on a stock T3 without "waisting boost" due to low efficency. 10lbs , 12lbs or is it just the stock 7?

[Clifton]

An 2.8l motor at 6500 rpms at 12 psi will need 36.5 lbs/hr. 15psi would be 41lbs/hr. This is a stock T3 map. 12 psi is 1.8pr. 1 lb/hr is about 10 hp.

[zeiss150]

wow... if only I knew how to read those graphs....

CRAPPY PUBLIC EDUCATION!

[big-phil]

An 2.8l motor at 6500 rpms at 12 psi will need 36.5 lbs/hr. 15psi would be 41lbs/hr. This is a stock T3 map. 12 psi is 1.8pr. 1 lb/hr is about 10 hp.

So should I turn mine down to 12psi to be safe

[Clifton]

If you are running a 1.8 PR (12 psi), draw a straight line across the map, then draw one verticaly up from 36 lbs. Were they intersect is were you'll be at 6500 rpms at 12 psi. You want to stay in the map. The higher the % the better (less heat).

[pjo046]

How is boost pressure in psi converted to the PR rating on the turbo graphs?

(Perhaps I am just stupid when I'm not seeing this connection right away? )

[Clifton]

14.7 + boost / 14.7 = PR

[Pyro]

Flow required is engine volume and rpm dependant. Turn up the boost and shift at 5000 (not 6500). The stock turbo cam is pretty much done at 5000 rpms anyways. Plus the T3 comes on very low in the rpm range so no need to shift at high rpms.

 

at 15 psi, 2.8 liter and 5000 rpm, you will only need 32 lbs/hr.

 

The T3 is a good match for the stock cammed 2.8 liter Z engine up to 15 psi of boost. When bigger cams are added and higher shift points are used, the T3 will start running into a wall when used on a 2.8 liter.

[zeiss150]

so its better to build a slightly higher CR engine so you don't have to use as much boost to get hight HP. As long as you can controll detonation then a higher CR build is better .... right?

 

With an L28 with a CR of 8.6:1 with a stock P90 head and stock T3(and good IC) could 10 or 12lbs of boost get the engine in the 300 + RWHP range (also stand alone engine managment). or is that pushing the T3 and engine to far?

[Dallas J]

so its better to build a slightly higher CR engine so you don't have to use as much boost to get hight HP. As long as you can controll detonation then a higher CR build is better .... right?

 

With an L28 with a CR of 8.6:1 with a stock P90 head and stock T3(and good IC) could 10 or 12lbs of boost get the engine in the 300 + RWHP range (also stand alone engine managment). or is that pushing the T3 and engine to far?

 

Its easier to build higher power on pump gas with a lower compression ratio, higher boost, on a bigger turbo. But upping the CR does have advantages like off boost power. Makes daily driving it much better.

 

-Dallas J

[Clifton]

The T3 is a good match for the stock cammed 2.8 liter Z engine up to 15 psi of boost. When bigger cams are added and higher shift points are used' date=' the T3 will start running into a wall when used on a 2.8 liter.[/quote']

 

 

A T3 at 15 psi is not a good match for a 2.8 with stock cam. I managed 368 rwhp at 15 psi with a stock n/a cam with a full T4. Same boost with a T3 or T3/4 would be 100 hp less.

[zeiss150]

Ok Clifton, so the stock t3 is good for about 270rwhp. which would translate to 15psi on a stock T3 with a P90 head on stock short block(7.4:1 CR)? does that change with better mods... i.e. 420cc injectors, 60mm TB, 3in down tube and exaust, megasquirt, flat top pistons CR 8.6:1. Do those mods get you any more power out of the T3 or are you just hitting a wall with the old T3?

 

By the way, Thanks for all your help, I hope this isn't boring for you.

 

P.S. what kind of HP does that sweeeeeeeet Z in your signature put down.

 

Thanks again!