DOHC turbo sizing

[skalor]

Looks like a good setup!! Although, if you don't already have a filter on the BOV then I would go buy one. K&N makes a nice one that clamps on that I use as I also have a 1st DSM BOV on my TGP. Anyways, I pretty sure the BOV is open under all vacuum conditions which would mean that it's open at idle.

[brian89gp]

Actually the how the BOV works is 2 fold. First for it to open there must be vacuum from the manifold, but without boost in the pipes to push the thing open it will stay closed. At least that is the way mine works.

[RedZMonte]

Also yoru downpipe is too small. It needs to be AT LEAST 3 inches. 2.5 is too small and will restrict flow in that 3.4

The To4b 60-1 Hi-fi would be a good choice. Pending on how much boost you want to run in the end should determine how big of a turbine a/r you want. If you want lots of boost and big top end power go larger(.80 up) If you want low boost settings under 10 psi go with a .63 or thereabouts exh a/r.

are you kidding? 2.5" is about all your going to get in there with the ammount of space you have to work with. trust me... 2.5" barly fit on tims car. 3" will not fit, let alone any larger. if you want to get really tricky you can build a custom mandrel bent downpipe. a 2.5" mandrel bent pipe will flow better then a 3" press bent pipe.

a Hi-Fi would not be a good choice.. again you are still T3 based. and you will be restricting yourself. the trim and houseing size is also a factor in spool up time. if you are buying a new trubo then just get a t4 based trubo. flat out. don't wast your time and money.

RedZ

[RedZMonte]

Ran across a good Supra site for once, figured out what I want. I also called that cheap turbo place, $600 for a 60-1 with the 4" inlet, they don't carry the HiFi version.

T04B 60-1 HiFi, on center P-trim turbine with either .58 or .70 A/R housing. Wucha think?

T04B's are less efficent the the T04e's. but the P trim is what i have and i would do the .70 ar. i like the v-band housing better then the On center housing.

but if that is the turbo you wnat i can do it for i think $550 plus shipping. (i will need to double check the price but i think that is what i can do it for.

Shane

[nocutt]

'86-'87 GN turbos are .60 on the compressor and .63 on the turbine...
the turbos can accept wheels as big as 60 dashes...keep the .63 housing but upgrade the wheels...HP comes from the wheels till you start looking for big numbers...and for less than 3bills upgraded wheels and balance turbos can be had...this is as good as a new turbo to me...

A full fledge t4 is wonderful if you have a) the mula for it, b) If you have a stick (manual) and c) if you don't mind lag...full boost at 3500-4000RPM I guess isn't bad for a motor that wants to rev to 7K+...it is a toss up indeed!
However don't get into the marketing scheme..."this turbo is more efficient than this one"...My relative drives his GN everyday with a stock appearing turbo (TA-49) basically upgraded wheels in the stock housing...3800lb vehicle and runs high 11's all day...NO gimmicks, 19psi will get you there, did I mention stock cam and only 5500RPMs to use...lol!!
I am sure you get the point....lol!

[RedZMonte]

a) T04E is cheaper then a T3/T4 hybred. and after you buy a GN turbo and upgrading it you will be looking about the same price if not more. pluss your working with a completly different motor. 12v pushrod vs a 24valve dohc motor. you are going to get ALLOT of exhaust flow out of the DOHC. that is why brian's ct26 is falling on its face. turbo is too small. will be most T3 based trubo's. not sure what your point is. you are still ~1500 rpm's shy of where our motors rev out at.

b) mine and tims montes are both autos. as tim said his spools and has ~2-3psi untill 3400 rpm then full boost. he still spins his tires. and again this is at 5000+ ft altitude. take it to sea level and you will again be spooling faster. the 3.4L DOHC SUCKS ass in altitude. i know this for a fact.

if you are conserend about that minute bit of lag then run a smaller a/r. we are running .68 A/R on ours. take it down to a .58-.61 a/r and you will spool slightly faster. hell, try another trim. there are like i have said many many times multiple things that effect spool up.

But then again. you can do whatever you want with your cars. i am just telling you what i know from experience. I don't have 4 boosted vehicles in my driveway for nothing.

RedZ

[phantom505]

I have a 3400 with a .81 A/R on the exhaust side and 57mm compressor. It's a T3/T4. When you are talking sizing, total engine displacement is the most critical value. How effecient the engine uses the power is different question entirely. Max HP is about 450 crank.

[nocutt]

I have a 3400 with a .81 A/R on the exhaust side and 57mm compressor. It's a T3/T4. When you are talking sizing, total engine displacement is the most critical value. How effecient the engine uses the power is different question entirely. Max HP is about 450 crank.

Engine displacement...is actually not critical, a part of a sum to generate lb/min (CFM)...you however hit the nail on the head...how efficient it uses it or how efficient the engine is...another matter all together...

Shane,
you are probably right...however I spec turbos and know t3/t4 hybrids are dime-a-dozen, because they came stock on some cars...a full t4 will cost you anywhere from $550 to hole-in-pocket...lol!! The middle man always hikes the price up, for us victims...
Anywayz...not to sway away...my point is the minimum I will ever run on a 3.4TDC will be a GN turbo...a full T4 will benefit, however even a hybrid t3/t4 is already laggy on this motors...with sticks!! The more reason I recommend a .63 A/R housing...a bigger turbine wheel will make a whole lot of difference...This is strictly for street app...if you are into draggin, different arena!!

[RedZMonte]

i understand light to light you want something that spools fast. but then again a t3 based turbo will not pull well in the higher rpms, is my point. i am completely down with fukn around on the street and i can tell you 1st hand tims car is a very streetable car, he is right next to my l67 lumina. and we all know how much fun they are stoplight to stop light. as far as t4 costs, you can get them cheaper then most t3/t4's strickly becuause it is not a hybred turbo. hybred turbo's in most cases are more expensive then a straight t3 or a straight t4. a good t3/t4 will run about the same as a 60-1 standard (T4 based) turbo if not more.

I am not saying you can't use a t3/4 to make a fun streetable car, i am just saying i think it will spool very fast and have good mid range power but it will most likely flatten your power curve in the higher rpm's becuase your not able to flow as much exhaust gasses through the exhaust housing of the trubo.

Shane

[phantom505]

Yes, the #/min of air are critical and are the limiting number, but the rate that you can use it is determined by displacement and RPM. Almost every performance calculator requires you to use 3 values when fitting a turbo: RPM, displacement, and pressure. Since it's load dependent, where the power band sits is inconsequential.

BTW, my exhuast wheel is a trimmed down wheel from a larger compressor so it flows really well and will boost earlier than a typical .81 A/R exhaust side.

Assuming 6000 RPM, 210 ci, and 10 psi; the Ray Hall program I have recommends a GT25 or T3 with a 60 trim and a HSG 1.06. This is a 32.71 #/min flow rate and provides enough power for 355 HP at the crank. This is about the max of that unit though.... The GT25 still has some top end left, but not a whole lot.

Tell me how much boost and where your redline is and I'll give you some numbers and models based on their calculator.

[nocutt]

3 things to cosider in my opinion:
* do you want low-end
*mid-range
*or top end...
Unfortunately we are talking about an engine that boast 4 cams, so more than likely the first option is out of the window, the quad motors don't really "come-on" till say 3K RPMs...
Shane,
I believe to keep things streetable, one doesn't need a 'little dog' (big size turbo) sitting in the engine bay...if you aren't racing and are strictly street, maybe occasional weekend warrior...a t3 based turbo is just fine...Taking full potential of the are under the curve is more important than a brief window...understnadably the motor likes to rev, however with a very powerful midrange all the way to the top is more fun...in my opinion a big turbo is essential when you aren't intercooling and/or you want some serious power output!!

I think there is a misconception here...a t3 based turbo can have a housing as large as .82

[phantom505]

I wouldn't use a non-intercooled turbo. It's just such a waste of power and the usefulness. Maybe that is one thing SC's do really have on turbos... they really should use IC's versus a SC benefits from an IC, but it's not as much of a requirement.

I know I have a pushrod, but I get really great top and pretty good mid. Once the transmission is in and I get better loading I'm willing to bet I'll have just sick mid-range too. The biggest problem I've noticed is my stock tranny doesn't really grab until it hits higher RPMs. Right now I hit about 260 wHP and stay there from about 4400 RPM all the way up with the load/turbo/cam profile I have on the stock pushrod. If I launched earlier I would have had the power band down around 4000 RPM no dobut; that's where it was when I tuned it with DHP. I'll test that theory when the trans goes in, but it might get skewed because I'm having the heads and cam installed too.

[timg]

Agghhh...

I have a full T04E. It's VERY large!!! I have full boost by 3500 rpm and great boost by 3000 rpm. From a street start, there's very little lag(no more than stock- stock power on mine was down by 40 hp before 3500 rpm). I'd say that I have excellent mid range and high end power. When I calculated my flowrates and PR, I used primarily 3500-6750 rpm- the powerband of a stock car and the area the car is in whenever you're doing more than 10 miles per hour. If you're really worried about lag and drivability, the place to focus is engine management and boost control- not inferior turbine sections which are intentionally sized way too small to 'minimize' lag.

Superchargers are all less efficient than a new turbo. They all need intercooling even more than a turbocharged setup does. It is an incredibly common misconception that superchargers have less need for an intercooler than turbos.

Tim

[brian89gp]

I know of 2 or 3 turbo DOHC fiero's that are using T3/T4 hybrids, all with over 300hp at the wheels. It all comes down to what you want and how you want it to perform. I'll swear by a T04B 60-1 or 62-1 compressor while Tim and Shane counter right back with a T04E "60" and nocutt with a modified GN turbo. Who's right, probably nobody. I've chatted with a SHO owner that uses a 60-1 Hi-Fi with over 400/400 @ wheels @ 14psi. Similar engines so similar results.

Anyway, phantom505, the DOHC flows quite a bit more then the 3400 could hope for. I was using 7000 and 7200 for a redline.

[phantom505]

Anyway, phantom505, the DOHC flows quite a bit more then the 3400 could hope for. I was using 7000 and 7200 for a redline.

I'm willing to be that the cross sectional area of the ports are greater in the DOHC. However, I think with better internals 7000 RPM would not be that difficult even on the pushrod. At 6100 it's still very strong. Judging by the curve and profile of the cam 6800 shouldn't be an issue. Besides that the lift hasn't been played with much yet. There's so many fans of the DOHC here I don't expect to get any respect, but a hair over 300 wHP at 12 psi for the pushrod should be more than achieveable on stock internals. I'll have a cam and heavier springs, ported heads by then too.

I would love to see a dyno that shows a representative profile of what the DOHC puts out.

BTW, T040 V1 compressor with HSG A/R of 1.14 is what you get with 210 ci, 7000 RPM and 12 psi.