IROC-Turbo

Weird question but im curios and looking at turboing a tpi(maybe).My question is;Is 8psi from a cheap $100 turbo the same as 8psi from a $1000 turbo??All info appreciated be it difference or simularity.

JoBy

A less efficient turbo will require more exhaust power (more back presure) to make 8 psi, and it will heat the air more.

Dan W

Maybe....

The amount of heat the compressor adds to the air charge will be different between the two... if one of them has a hotter air charge at 8 psi then it will make less power.

As said above, the exhaust portion of the turbo is a restriction. This is a compromise situation where generally speeking the more restrictive choice will provide boost faster but the less restrictive choice will make more power once it comes onto boost.

89JYturbo

I Ditto the above answers. There is so much more to turbocharging than boost pressure.

And I'll add that if it's an SSAutoChrome turbo from eBay, it may only make 8psi for a few moments before it grenades. They sell cheap, foreign made replicas of Garrett turbos. Poor machining and assembly took out two of their turbos on my TTIROC in less than 200 miles. I'm selling one of the ones that actually didn't blow up on eBay now. Check it out: http://cgi.ebay.com/ebaymotors/ws/eB...RK%3AMESE%3AIT

FatherFrank

Wow, with that kind of honesty, you'll never sell that thing.

And I really respect that.

IROC-Turbo

The turbo i'll be using is one from a 80 TTA(start the bashing now).Dont remem if its a airflow research or a garret.I'll be pulling it from its drawthru setup that is installed and running and making adapters for the inlet/outlet becase they are 3 and 6 bolt flanges and installing it directly on the pass-side exhaust manifold.Not sure on intercooling it or not yet.The turbo is quiet!!All you hear is a slight gear type whine when it starts spooling while cruising but not all the time.When its full spooled i dont hear anything and my exhaust is pretty quiet.The turbo is supposed to max at 10 psi and was pushing 8 for me in drawthru mode through a either 2 1/4 or 2 1/2 downpipe into a 2 3/4 intermetiate thru a raven wave muffler with duel 2 1/2 outs.I hear exhaust restriction will lower psi output is why i listed exhaust specs.I'll prolly set it to run at 6psi to save engine trouble.

My biggest fault with turboing atm is while cruising my boost/pressure guage is at 0 so the carb was full rich.Does maf tpi use vacuum like a carb to set fuel??If it does i'll back off the adj wastegate to push 1-2 psi till i can get the stuff to burn a chip.Plus do you put the maf senser pre or post turbo??All im wanting to do is get rid off the 4800 rpm dropoff of the tpi.Dont want to spin it over 5500 though.Will this turbo do it(with a cam)??With minimul ecm adjustments??I cant even start to list how many times power has saved my car and my life by dodgeing rearenders,side swippers of all types,and even idiots with guns.All i want is power when i need it with good drivabilty--not a track monster.Thanks

IROC-Turbo

Forgot to add--do they even make BOV's that small(6 psi and down)??Ty

CrazyHawaiian

To me boost is boost but you guys are definately right that power output is a completely different subject (can be different at the same boost levels depending on the application). But I have to answer the question as boost is boost because if you had a small turbo boosting 8psi and then you switched it to a huge turbo boosting 8psi, the motor will be seeing 8psi the entire time (even though the power levels and powerband characteristics are very different).

I think the only limits of BOV's are on the high end, but you'll usually be using a wastegate to control the boost. Those are usually adjustable by either a spring or electronically, I imagine all the way down to 1psi (but who would want to do that?!)

89JYturbo

Actually, it is basically impossible to lower the boost on a turbocharged engine to below the WG's basic spring setting (short of bleeding off intake air). If your WG is calibrated with a 6psi spring, that is as low as you can go (unless you modify or swap out the spring).

Raising the boost, OTOH, is a snap. Many ways to do that, from simple air bleeds all the way up to fancy EBC's.

Fastkingcab

here are some compressor maps. a 2.0 pressure ratio is about 14.7psi you can see the the maps the air flow from one turbo to the next can vary by quite a bit.

on average in a single turbo setup the lbs of air per min. X10 = the aprox. WHP

Fastkingcab

LOL I'm not sure how to post multiple pics


The firts Pic was a straight 50trim T3

The secone is a To4B H-trim


The To4b flows twice as much air at any given boost.

CrazyHawaiian

I was implying a spring change, but to be honest I dont know the different types of springs out there, so I'm not even sure if they have springs for such low boost levels. Wouldnt make any sense anyway hehehe.

IROC-Turbo

Wastegate that i have on it is adjustable.I can back off the psi by bleeding off exhaust gasses.I was wondering about the BOV because i can floor it and let off and it kills the engine and its hell to get it started for min so i may be getting that compressor turn around or dead lock.I just dont want to over boost the engine on decell.So 6 psi then set BOV on 6.5 or 7 be good??Bleeding it off with the adj wastegate--would that mean it would spool slower and boost would start at a higher rpm??

ColdGTA

You can make the wastegate adjustable by threading the rod in the diaphram. Some of the the TTA (80-81) had a threaded rod so that the boost can be adjusted. Go with atleast a 2 1/2" down pipe. The turbo will thank you. Though that turbo design is old school it's good enough if you are just playing around and if the price is right. Most people usually try to upgrade to a t-4/t-3 option. That turbo is capable of making 19 psi,BUT it's not the most efficient at that level. Still though nothing wrong with using what you got. I did.

JoBy

The BOV should open as soon as you get engine vacuum. It should not have anything to do with the boost level.

You adjust boost with the wastegate only.

ColdGTA

He is correct.

83 Crossfire TA

iTrader: (2)

With factory style wastegates, you can lower boost a little by cutting and threading the rod and then adding a threaded sleeve to make it adjustable, but not much before you end up leaving the wastegate open all the time. If you want to go lower you can put a spring between the canister and a washer over threaded rod before the sleeve, with a nut that allows you to tighten the washer down. The spring will counter the spring in the housing and will lower boost. I’ve used a mountain bike front fork spring for that before…

Raven90IROC

If it helps i bought a wastegate that came with a 6psi spring. That was too high for me so I swaped it out with a 3.something spring and adjust it up from there using a boost controler.

IROC-Turbo

ColdGTA has the turbo on his 81 pacecar that i'll be using.Maybe he can enlighten us on turbo type,spring,brand,and compressor trims so we can get a better understanding.Btw this turbo has a turbo-mounted wastegate with a flap in the outlet flange and a rod with the end that attaches to the WG flap is threaded and the other end goes into some type of vacuum canister that has 2 vacuum line hookups--1 hooks up to the turbo where its mounts on the intake(boosted side),and the other one hooks to carb flange(non boosted side).

What i understand so far is:

Wastegate is where you set the boost by releasing/letting bypass hot exhaust gas.I'll be setting mine at 6psi.

BOV releases intake air when decellerating to keep the compressor from overboosting the engine,causing compressor lock and keeping the compressor from wanting to spin in reverse??Set it to where it pops immediately after throttle is released??

My main concern is will this type of turbo at 6psi help the tpi breath past 4800??How much of a gain on a stock 5.7 maf tpi can i look for with this turbo.How bad if any will it affect the low end grunt of the 5.7??Where do i mount the MAF??Does TPI rely on vacuum to set fuel like a carb does??

This is really starting to confuse me now!!Thanks

Fastkingcab

A standard Garret T3 interanal wastegate actuator has a 5.5psi spring in it. If your turbo is internaly gated it's most likley a T3 exhaust housing, so you can just get the garret peice and use a Manual bleed valve type boost controler to get up to 6psi.



To answer your turbo flow question we would need to know EXACTLY what turbo you have. because as you can see in my posts above there is a diffrence in FLOW and PSI of boost.


sort of what happens is when you run full boost WOT the turbo is spinning around 120,000rpm+ when the throttle plate closes the turbos built up inertia (SP?) keeps the turbo spooled up at 120k RPM for a second or so, that will create a full boost presasure spike 2-4 times the set boost inside the intake piping.
The engines internals will never see that boost the throttle plate blocks 99% of the surge, what happens is the surge backs up the line back to the turbo's compressor wheel where the turbo is rapidly slowed and the cusion of oil the main shaft rides on is momentairly disrupted. (bad for anything that idles @ 40K RPM)
At your 6 PSI of boost you will NEVR have a serious problem, just pick the one that makes you favorite sound. your spikes, depending on how big your intake pipes are and I/C is won't ever be much over 10-12psi and just about every turbo in the world can handle that.

The BOV is mosty helps extend the life of the turbocharger, I't won't affect the engines life in any way other than perhaps the idle air motor. and won't increase HP at all other that allowing less LAG betwene shifts on a 5-speed car. The BOV will be totaly inviable on a auto 80% of the time.


and BOV's scew with MAF sensor cars BAD, because of the air surges that are't used by the engine that ARE acounted for by the MAF. most MAF cars (ANY MAF CAR) will go INSANELY rich betwen gears. you would want that MAF sensor as close to the throttle body as possibe, and the BOV should be recurculated back to the intake pipe betwen the Turbo & air filter.

ColdGTA

Ok I'm a little confused on what you want or maybe I'm just reading it wrong. Are going to use the TTA turbo or have you been using the turbo and in what application? Also what is your goal for the set up you want? From your posts it sounds like you are already using the turbo. As for my turbo well.... she is pretty much the way Pontiac threw it out back in 81...... Almost. The only thing different with my actual turbo is the trim wheel. After consolting with John Craig at Limit Engineering he suggested a new trim wheel for me to rid the problems of my out dated T-3 stock trim wheel. The wheel allows the turbo to spool up faster while eating less boost and allows for more top boost. Otherwise the my wastegate is the stock form the factory . Ok so I jet coated the housing as well.

The turbo for the 301T is a Garret T-3. Also used in the some of the Shelby Chargers and the Mustang SVO's along with some others. See the pattern? 4cly...... From day one it was already to small for the Pontiac V-8, but since the 301T has such crappy heads and intake apparently it didn't matter,(the odds were even). Maybe if we had some insight as Fastkingcab suggested we can help understand you better or atleast help with the logic.

IROC-Turbo

Thanks for posting a pic.Ok i must not be up to par on my turbo language.I AM using turbo right now!!Your pacecar TTA system is sitting on top off my SBC 350--retrofitted and drawthru too.Im going to tear the whole system off back down to the long block.Im going to mount the turbo directly to the exhaust manifold like a normal blowthru configuration and install tuneport.I am getting 8psi out of the turbo as it is now setup to drawthru the carb so backing off the wastegate to 6psi is easy.Problem with leaving it drawthru is when cruising and the turbo starts spooling my vacuum is at 0 which means my front needle valves/metering rods are completely open(full rich) and thats why im doing away with this setup and going blowthru-tpi.

As for pipe i'll use??This sound ok??Intake side-3.5" clamp-on K&N cone filter mounted directly to the front of the turbo.Turbo to intercooler pipe(maybe-depends on if i can find one cheap enough) will be 2 1/4 or 2 1/2 as the flange on the turbo is for 2 1/4.IC to MAF will be 2 1/2 and adapted up to maf.From the MAf to the TB will be the stock grommet.
Exhaust side already listed before.Feal free to reccomend if i need to change something.

What part do you need clarification on and i'll try to explain the best i can??My turbo lingo does suck.And mounting the TTA drawthru turbo on a SBC 350 was my first time ever touching a turbo.The turbo was free thats why i would like to use it.

Edit-ColdGTA could you get a pic of the inlet and outlet on the compressor side so it shows the hole sizes and flanges if its not much trouble??Might help bring a bit of understanding.Thanks all

Fastkingcab

is the trubo placed before the carb or betwene the carb & throttlebody. I have only ever seen one 80 pace car and I belive it was draw through.

Drawthrough = Turbo draws Fuel / Air from the carb, compresses it and pumps into the intake manifold.

Blowthrough = Turbo draws in fresh air, Compresses it and forces it through the carb

------------------------------------------------------------------------
I'm not 100% shure how much crank HP your TPI 350 will be laying down. But for example if your 350 with TPI on top created a 250hp engine your engine will be drawing in about 25lbs of air per min. at full power. So to get a performance increase you will need a turbo that will flow atleast 26+ LBS per min. it will take around 35LBS per min. to hit 350HP at the crank.

What are your power goals? I strongly think that that T3 you have is MAXED out on a 301cu.in. engine with poor heads & an in efficent intake system.

Here is a pic of the largest T3 compressor ever made by garret which os what I assume the 301T got.

It is a super 60 T3, the super 60 T3 is maxed out At 300WHP @ 18psi on a 3.0L V6 300ZX and barley suports 160crank HP at 7psi

Fastkingcab

ABOUT FLOW MAPS:
Flow Rating X-axis (LBS Per min.)

Turbochargers are often described as having a certain flow rating. As you can see, this is an extreme simplication of the compressor's performance. The flow rating is simply the volume air flow (or mass air flow) at a pressure ratio of 2.0 and some "reasonable" efficiency at a wheel speed below the choke speed.

Pressure Ratio Y-axis (PR)

The pressure ratio, or PR, is the ratio of the air pressure at the discharge opening divided by the ambient air pressure at the inlet, P2C/P1C. A pressure ratio of 1.5 means that the air has one and a half times as much pressure leaving the turbo as when it entered. At sea level, where atmospheric air pressure is about 14.7 psi, the air leaving the turbo at a 1.5 PR would be at 22.05 psia (psi absolute) or 7.35 psig (psi gauge or boost pressure; 22.05 minus 14.7). However, in Denver, Colorado, where typical atmospheric air pressure is about 12 psi, air would leave the turbo at 18 psia (6 psig) if the PR is 1.5.

Wheel Speed

The wheel rotational speed, in revolutions per minute (rpm), at various values is shown on the flow map as a function of air flow rate and pressure ratio. When air flow is held constant (a vertical line on the flow map), faster rotation means a higher pressure ratio. When the PR is constant (a horizontal line on the flow map), faster rotation generally means more air flow. However, air flow does not appreciably increase after the outer tips of the compressor wheel are moving faster than the speed of sound. When the air flow reaches sonic speeds, the diffuser becomes choked and only very small increases in flow rate are possible even with large increases in wheel speed. Larger compressor wheels have maximum rotational speeds less than smaller wheels because of this limitation.

On the flow map below, the air flow regime to the right of the dotted line marking maximum wheel speed is called the choke area. The choke area is almost never noted on a flow map. To determine the choke area, you can drop a vertical line from about where the fastest wheel speed curve ends on the right side of the map. This vertical line is the approximate maximum air flow the compressor is capable of, regardless of efficiency or pressure ratio.

As can be seen near the lower left corner of the flow map, there is no significant air compression at wheel speeds below a certain rpm. A properly designed and matched turbine section is required to keep the compressor wheel spinning between its minimum and maximum speeds for the engine the turbocharger is used on and the desired boost levels. The turbine wheel is driven by the heat energy and velocity of the exhaust stream. Rotor speed and efficiency are higher when the pressure gradient across the turbine section is higher. How fast the rotor changes speeds is determined by the inertia of the turbine and compressor wheel assembly and the A/R ratio of the turbine housing. Either higher inertia (larger or heavier wheels) or higher A/R (the ratio of the turbine inlet at its narrowest point to the distance from this point to the shaft) will increase the time it takes the turbine and compressor wheels to "spool up", or increase in speed. Compressor output can be limited to a certain pressure level by controlling the speed of the turbine wheel with a wastegate, which diverts exhaust gas around the rotor.

On the flow map, the compressor efficiency decreases rapidly toward the choke area and the surge limit. The best efficiency is usually found near the middle of the map area and is often referred to as the "peak efficiency island".

ColdGTA

Hey weren't you over a TransAm Country for a while? Somebody over there put a TTA turbo on a IROC with a sbc. I go by 81Nascar over there. Ok I get what you are talking about. As of now you have a carbed ,draw-thru SBC. You want to run TPI.
I'm not sure if you can use the TTA turbo for a blow-thru operation unless you change the trim wheels in the compressor as it is designed to mix it's air with gas at a certain pitch. Not just blow air. Don't quote me on it but I sware that I read that somewhere a while back. I will have to check it out. You do have an advantage as the head and intake manifold design are much more efficient than the 301T so the potential is there. I know 6psi on my car ain't squat. Gotta get up to 8 9 10 before she wakes up. Stock there supposed to be at 9psi but every car I have heard of in stock form or seen would only run 4-5psi. Hints why they were such dogs. Also they were heavy cars. Mine is over 3800. That's another story.

I know you got it for free, but as your engine get's more efficient that turbo gets less useful(to small). Another step to consider is snagging a unit off of some of the later diesel pickups in the bone yard. Those units are bigger and can be had cheap. But if you want to run what you have then go for it, but understand that it will have it's limits. Anyway the exhaust outlet is 3". I would have used 3" for the down pipe, but it was just physically to big to fit between the frame and engine. Remember velocity is great for the intake part of the turbo, but bigger is generally better for the exhaust portion. Turbo's don't like much back pressure. Anyway here is a pic that might help. It was taken a couple of years ago so the exhaust along with the rest of the car is together making it tuff to get the pic you really wanted.

IROC-Turbo

So the T3 wont feed it??Wonder what i could get outa 2 turbos(one with around 500 miles on it and the other with 80k),3 carbs(one recent rebuilt-other 2 are spares),and the origional 301t intake?And when you say the diesel turbos are cheap--how cheap we talking?

Fastkingcab

A decent no name remaned T4 (400-500WHP) will be $400-800

A Turbonetics turbo will run $850 for a straight T4

a singe T70 (700-850WHP)or 62-1(600-750) will run around $800 off brand and A Turbonetics will be about $975

IROC-Turbo

What is WHP??You're going to have to dumb this down a bit for me!!

327???

horsepower at the wheels

Wheel HorsePower

Fastkingcab

yes WHP= horsepower @ the wheels.

what are your goals?

Daily driver? (to determin a acceptable amout of LAG)

How much WHP? (To select the proper trim turbine & compressor)

Don't forget the next three while you dream up your WHP goal.

Pump gas Y/N?

How Much intercooler do you have?

How much Fuel do you have (what size injectors/ pump?)

Answer the above questions, and I'l' find you a decent;y priced NEW turbo.

ColdGTA

Depends on your local wrecking yard for how cheap. I always look out in the paper for the guys parting out with stuff. I wouldn't pay more than $150 for a unknown turbo and maybe not even that. Just depends on how you feel. If you are going with a chevy motor there is no need for the Pontiac intake.

Syn

i'd run a t4,with atleast 3"downpipe. What size charge pipes are you gonna be running? if your running low boost a bov is not that important.Whats up with wanting to run low boost? i ran a t3 with 8psi 2 1/4 downpipe and it could of still benifited more from 2 1/2 but i ran that with just fuel upgrades on my saturn. I imagine a v8 could withstand more

rx7speed

I agree with that and I don't even know as much about boost as most of you guys

kinda like what will be faster 22psi or 14 psi
depends on if that 22 psi has half the mass of the air at 14psi. sometimes turbos spool fast enough that they just don't work very well anymore and heat the air up and do all kinds of not soo good things so you might actually be a little slower. least that is what I have seen with some of the guys here. same mods except for the turbo. one puts out more boost but has lower power



another thing to think about.
6 psi vs 8 psi
6psi might be the winner once again. the amount of boost can be thought of as a restriction. if you open up your heads get a little more flow going through the them you boost pressure will actually go down but your going to be putting out more power

rx7speed

also out of curiosity if he is going to run a drawthrough system what would the point of the turbo be then?

there shouldn't be any massive blockage in front of the turbo being the throttle blades are going to be behind the turbo.

IROC-Turbo

Sorry guys for not answering in a while.Guy offered me a couple cars for the turbo sys.Not sure if it will go through or not though.He is yeah man 1 day and hold off a day or 2 the next.I dont really car if it goes through or not.I have more into the turbo sys than the 2 cars are worth to me but they have a couple parts ive been wanting plus id hate to give up something i done myself.So its a tossup right now.

ColdGTA if you run across that info about the compressor wheel only made to mix the charge(air/fuel) and not just force air that will plan where i go from here.

All i want from the car and engine is a reliable daily driver with power when i need it.Decent heads around here is something you dont find at all.All you can find is swirl port junk and 882's and 624's.The only 305 heads ive seen are swirl ports and 450's.Junk yards are getting scarce here.They are here but you could about buy the part new for what they charge and then you have to remove it yourself.

As for power would around 250hp and around 350tq at the wheel be outa the question on a tpi 350??I have another identical turbo to run twins but id hate to get into modding another manifold and then the driver side downpipe will be a prob.I have taken my spare turbo and sat it directly on the manifold and seen if it would clear the hood and it seem like thats the way im gonna go if the turbo will feed it.

ColdGTA

Hey I wouldn't get to **** about the heads. That's the beauty of forced induction. It makes up for inefficencies like that. Yes a set of good heads would net more power, but that really is a concern if you are trying to net every once of power. The power you are talking about is easy as cake. Spend more time on the cam and exhaust system since you are budget challenged. I will see if I can find out about the draw-thru application.

rx7speed

from what I have seen there is quite a bit to be gained off of heads even in a boosted car. just cause it's pressurized doesn't mean it doesn't get affected by restriction.

Syn

a ported head with less boost usually flows the same as a stock head with more boost

rx7speed

saw something sometime ago where they took a car with stock heads ran the dyno and saw the boost numbers.
ported out the heads the boost dropped and power went up a very noticable amount.

Fastkingcab

Yes but..........

If a given turbo flows 35lbs of air per Min. (enough for 350WHP) at around 14.7PSI and your wastegate is set @ 14.7PSI that motor will ONLY ever see 35lbs / min

It dosen't matter if your heads can flow 40lbs/min or 60lbs/min

I'm not saying ported heads won't help on a street car. They would help everywhere except max HP/TQ. If you are trying to squeze that last 1% out of it, port away. on a street car, there are many other areas to worry about and spend time & money on.

Fastkingcab

Thats why I was bringing up the compressor maps in my earlyer posts.

If turbo A can pump out 60lbs of air per Min. at 15PSI and turbo B pumps out 60lbs per Min at 7.5PSI and 120lbs per min. at 15PSI. Then Turbo B would make the exact same WHP as turbo A at half the boost. And would also make twice as much HP at 15PSI

ColdGTA

That's true to a point but when you are on a budget and not asking for a ton of power then it's really of no concern. Boosted cars aren't nearly as sensitive as NA cars at any given rpm. When you create your own atmospshere there is less to worry about. I agree with Fastking. There are better things to spend the money on. Look at stock Buick GN heads. They really are not that good yet most of those guys run pretty damn good times with them. Lots of cars out ther that are pretty fast with stock type heads connected to thier turbo's and superchargers.

rx7speed

I'll be honest I don't know everything about turbos. actually know very little


but I do have a question
if you take a set of stock heads and it's running lets say 30lbs/min at 10 psi right?
and lets just say on those same stock heads you drop the boost down to 8 psi and now the turbo only flows 25lbs/min
(again these numbers are being pulled out my bum just for reference sake)
if I ported the stock heads out quite a bit and the turbo now runs at 8psi it's still only going to flow 25lbs/min?

doesn't seem right to me
as I said I don't understand turbo motors all that well so please forgive me. I'm just going by what little I think I might know (which I have been proven wrong on) and what I see.
but it seems those maps you show are not just a straight line.
another words if your running a 1.6 pressure ratio what flow rating are you at? wouldn't that depend upon other things like cam, heads intake exhuast and such?

I know there would be limits to flor being either you might hit stall speed or surge speed which I know is no good, but I don't see how 14.7 psi is always going to be 35lbs/min of air unless again you are making that turbo out.

rx7speed

ok lets take turbo a running 7.5lbs of boost
put it on a little geo metro. now take that same turbo put it on a 305.
are they going to flow the same amount of air at the same pressure?
kinda what I'm getting at

same things with the heads if you take a stock head motor with 10psi of boost port the heads and it now makes 8psi of boost why is it making a lot more power?

and if you set the wastegate back up to 10 psi it should make even more yet. again unless you are pushing the turbo too hard



but yeah I know exactly what you mean with two different turbos flowing different amounts with different amounts of boost
two local rx7 guys around here
one running a t04b at 14psi makes 320hp
the other running what I thought he said was some sort of t60?? at 11psi making 380 horsepower.
other then tha most all of there other mods are the same

ColdGTA

Well if you used that turbo off the Geo on a 305 it may produce less power because it may be to small. I know what you are getting at though. Remember boost is only an amount of resrtiction. The more resctriction the higer the boost number can be. Ideally you want the least amount boost as possible to make the most power. As we all know boost is hot air and we want as little hot air as possible to get the job done. So if you take the heads and port them you might get some more flow. I say this because there is more to porting heads than just grabbing the die grinder and making a "big hole". It's a bit of a science and if done wrong it can actually hurt performance. Let's just say that they were done right and they were run of the mill crappy heads to begin with. The ones we all have on certain cars. Sure at a given rpm you would see some more power. How much I couldn't tell you. Could be 5hp or 20hp. At lower rpms (street driving) it still flows about the same since the blower/turbo is cramming the air in. At higher rpm the restriction becomes less. The question is, is it really worth the time and effort for the little bit more boost you get if the hp goal isn't that high to begin with? Instead of going through all of that I would just rather run a couple of PSI and have a more efficient cam along with exhaust to get the boost exhaust out. Now if you want alot of power then sure port away or go after some heads, but some of that depends on what turbo you use as well . A/R ratio is an imnportant number to look at for a street car. To big a ratio and the car is a dog on the street because you need to much rpm to spool up. Then again you don't want to be to small and be out of turbo. It really can be a catcth 22.

IROC-Turbo

ColdGTA-what is the A/R on our turbos??

3.8TransAM

Heres my simple way of looking at it.

TTA was built with this theory in mind.

There are people running 10's on pump gas using 3.8 and 4.1 Buick turbos.

How u ask?

Airflow, not the boost per say.

U make 400hp to the wheels at 15psi. great.

port the heads, u only make 405hp but at 13.5 psi

Up boost back to 15psi and now you are at 450hp at the wheels.

It is simplistic at best but boost psi is a measurement of restriction in the engine. Anything u do to lessen that restriction can get you more power at the same boost and even equal power at less boost than originally running. Taking advantage of this pays benefits on street cars where 93-94 octane is the max limit and depending on the specific fuel blends in your area might only allow you 16-18psi with 18 deg timing at WOT.

I run a PT67, ported stock heads(champion), roller cam, champion ported intake, etc and so forth. Have TB and doghouse work to do yet but $$$$$ are needed lol :-) Some things I dont argu with like throttle feel and the like from a smaller TB. Nor all the airflow at lower rpms where not needed.

Yeah I know its not laminar airflow theory, but it is sound and simplistic.

later
Jeremy

ColdGTA

.60/.82