ct26 part 2

[brian89gp]

Just a couple more observations.

The cam timing on the DOHC is set for a powerband of around 3.5-4k to 6.5k. Since I had the misfortune of picking a small turbo I got to experience boost at 1k if I wanted. The verdict: the engine still doesn't "kick" in till 4k, below that it is a tad torquier then NA but for the most part all it does is make a lot of noise. Once 4k hits it pulls like a mofo.

Now for Getrag vs auto. The stock stall is high enough on the 4t60e that the engine RPM's are rarely under 2k, for the most part simple driving around keeps you in the 2.5-3.5k range. On my 5spd I see 1.5k to 2k way too often, and most city driving is in the 2 - 2.5k range. (both examples assuming you don't beat on it)

Whats this mean? You can get away with a smaller turbo on an automatic car, the stall speed and torque converter keep the engine RPM's high enough that it skips the lack of power under 4k (the engine starts pulling a little sooner with the turbo, around 3.3k). With the 5spd it is pretty much utter hell trying to drive it. The turbo is spooled in normal driving and it feels like you are lugging the engine a good amount of time. It also feels a bit resistant to rev like it did NA.

In conclusion, if you have an automatic and looking for 6psi then go for an small turbo. If you have a 5spd and/or looking at more then 6psi then I suggest picking a turbo that will start spooling around 3k and be fully spun up at 4k.

And yes TimG, I should have listened to you way back when.

[SappySE107]

How much difference would tuning make though, with the auto or your 5 speed setup. I know you never got it 100% before, and im sure its not 100% now either, so aside from the turbo being wrong for the application, do you think tuning it better would make the 5 speed and smaller turbo more bearable?

[MyGt]

Bump*

[MyGt]

brian89gp
brian89gp
I have a question, since I have a turbo from a '87 single turbo Nissan 300z, with a .63 exhaust turbine in it (T3), but a very small compressor.

I was thinking to upgrade the compressor side to a TO4B and this will making it into a T3/T4, but according to you, the limiting factor in turbo-charging this engines is the size of the exhaust turbine, since it likes to breath a lot, and I was wondering if this is Ok, to do the upgrade on the T3 .63 exhaust or I should rather go with a full T4?

BTW how big it?s your turbo CT-26 exhaust? Maybe if I know the size of your turbine I can guesstimate mine.

How about a Stage II T3/T4 were the exhaust wheel gets trimmed to give a better exhaust flow?

How about a stageII T3/T4 were the exhoast wheel gets trimmed to give a better exhoast flow?

Thanks!

[brian89gp]

First, what are your goals?

http://www.jblmk3.com/id134.htm

The inducer/exducer measurements are not the all telling truth but their size will give a good comarison factor (things such as clipping, number of fins, and fin rake play a role)

Not really the limiting factor, but a factor in the equation. Everything is so closely tied together that it gets quite confusing. Thing about factory turbo's is that they are designed for low lag at the expense of up high power. The CT26 could be made to work quite well but I find the powerband fairly annoying. I got a BOV and 25-35% throttle shifting at 3k it is constantly releasing and it has started to piss me off.

The compressor must be able to pump enough air for the engine or else no boost will build, and the exhaust must flow enough otherwise it will plug up the engine (feels exactly like a horribly plugged cat), boost will sky rocket, and you will be wondering why the car feels so slow.

What are the specs on the 300z motor? Size, displacement, rev limiter, HP/TQ at what rpm and boost, etc. Usually those values are a real good decider for a junkyard turbo. You might consider finding a 300z board and finding out the amout of power they can put out before upgrading.

Also remember, the cam timing and specs sets the powerband at 3.5k-7k no matter if it is NA or boosted. A turbo Quad4 owner has said the same thing as me, "power before 4k even with boost is non-existant, but once it hits 4k it pulls so much damn harder then NA", and the Quad4 motor is comparible for cam specs and powerband.

For the exhaust, the decimal value denotes housing AR not the size of the wheel itself. If you are going to stay with a T3 turbine side I would stay towards the largest possible, I believe the larger T3 turbines overlap the smaller T4 turbines some...

TimG's turbo which he is quite happy with is a T04E "60", P trim .68 AR I believe. The one I plan to use is a T04B 60-1 HiFi, P trim .69 AR.

Also add up the prices of all the upgrading on the 300z turbo, I got my 60-1 for $450 and I know of a place that can make you any T04E turbo for around $350 as long as it is an on-center housing (older, less efficient housing, but much cheaper).

[Canada]

I'm going to be using a TO4B as well........I might opt for the 62-1 over the 60-1......its only 10% larger.

[Gemmer]

wait...a smaller turbo gives you boost starting at a lower RPM...

its the auto keeps around 2.5k rpms and up and the 5spd hits a low 1.5...and you say you can get away with a smaller on the auto?


see where Im goin with this?

I know Im prolly missing something, but the math seemes backwards

[Dave]

... I think what he's sayin' as to why you wouldn't want smaller on an auto, is because you won't see those lower RPM's anyhow, so it'd be a waste. I know this from years of turbocharger expirence learned in the garage.

if you're never gonna see 1500rpm's, why have a turbo that will produce boost at 1500 rpm's, as the smaller exhaust wheel/housing needed for that low rpm boost will end up restricting the exhaust in the higher rpm's, deminishing the effect of having a turbocharger at all, so using a larger unit set up so you won't see boost untill say 3k rpm's will end up pulling harder in the higher rpm's, even if it's not producing the same higher boost numbers, because remember, you want CFM, not PSI in your system, the boost pressure is kinda worthless anymore, you want to know how much airflow you've got. here's a great example.

car 1 has small turbocharger which makes boost at 1k rpm's - and will hit 22lbs boost at 3000 rpm's, and hold to redline (7k) pushing (random number) 500 cfm

car 2 has large turbocharger which makes boost at 3k rpm's and full boost 14lbs at 4k rpm's to redline flowing 750cfm (mind you, the cfm numbers are random numbers)

car 2 even with a lower boost number will pull harder because more air is moving thru the engine.

an other benefit of a larger turbo which will produce more airflow then pressure is that it will not superheat the air as quickly as a smaller turbocharger will.

superheated air is bad for a few reasons, mainly is will increase your chances for dangerous knock in the engine, and secondly, it will often give you a "false" boost reading, because the air will be expanding so rapaidly it will show a higher boost level then the charger is typically able to make, and this is where you get the myth of "boost drop across the intercooler" that so many people worry about.

quick explanation of boost drop.

boost drop is when a gauage will show a higher boost on the "hot" or turbocharger side of the intercooler then it will on the "cool" or engine side of the intercooler, people think they are loosing boost, when in fact the air is cooling so efficently that it will become more dense and provide a better quality air for combustion, PSI will be lost, but CFM will not be lost, too many people thing this drop is bad, when in fact is just shows you've got one hell of a good intercooler.

okay, I babbeled, sorry.
--Dave.

[brian89gp]

... I think what he's sayin' as to why you wouldn't want smaller on an auto, is because you won't see those lower RPM's anyhow, so it'd be a waste. I know this from years of turbocharger expirence learned in the garage.

I was meaning the opposite. All things the same and especially on a pushrod motor a small turbo would be excellent, but on the 3.4 no matter how much boost you shove at it below 3.5k it still won't make incredible numbers. Sure it is a bit faster then NA down low, but to get that very slight increase of low end you sacrafice the high end because the turbo will run out of breath

Why I was saying that about the auto is 1. RPM's are bad for the tranny 2. no matter what speed you are going the engine will almost always be above 2.5-3k. From a stop with a stock converter it will jump up to just above 2k. Hit the gas and you got instant boost, but take it easy and it won't spool. While there isn't much power at 2.5-3.5k there is enough to justify a smaller turbo and a smaller turbo will produce power at lower RPM's so that means you don't have to rev it out to 7k to make power, which means that the transmission will last longer.

The 5spd is different, normal 25% throttle and 3k shifts and I was hitting boost. 1.5-2.5k where a 5spd spends much more time then an auto it just refuses to make much power NA or boosted. And trust me, gas milage will suffer from hitting boost during daily driving. I think I was getting around 8mpg city driving it as easy as I could.

Now if this were a track or strip car it would be just fine, but for daily driving it just does not work well, not with the powerband of the motor. WOT doesn't really count because only 1-2 seconds is spent below 4k, then the gearing will keep it above that till the rev limiter kicks in. I am talking purely from a streetability standpoint. Ideally I would look for a turbo that spools at or just slightly below 3k, you don't sacrafice your top end and you don't have boost below 3k where it won't make much power regardless

[MyGt]

Great Point, so at this point, where are we standing at?

In my case with the Fiero '97 3.4 DOCH, and the stock 5 speed 282(I think that is the one on the Fiero?)

What its the best TURBO to use?

T3/T4 .63 turbine & TO4B Compresor wheel with the 50 trim ???????

[brian89gp]

Depends on what your goals are.

[MyGt]

Lets say, full spull (Big intercooler-10 PSI) at 3,000 rpms and strong until 6,700 rpms?

Can we say 350 HP?

[MyGt]

Bump!

[MyGt]

Bump!

[brian89gp]

If you go with a large trim on the T3 hot side it *should be alright. The 50 trim is a T04E wheel and it should work, though 350hp will be at the top of its range.

Its all a real guesswork, so don't take my word as the bible.