Seriously considering a PTK turbo setup and was hoping for comments/guidance. I'll make it as short as I can :

motor : 396 LT1 forged motor, 210 AFR head /w 70cc heads for ~9.7:1 CR
fuel : 60lb/hr injectors, Racetronix intake pump setup (255 liter/hr)
valvetrain : 1.6 non-SA rockers and a smallish cam (218/218 114 or less)
full details of CURRENT setup : http://161.58.59.82/specs.html (N/A setup)

turbo setup : PTK Gen 2 /w a-a intercooler and a PT-70 GT-Q .96 A/R head

Goals : *stock-like* drivability, ~530-600rwhp on 93 pump

I do not drag/road race ever and will probably not want more power on the street, so I asked for the turbo to be sized appropriately. I was told by Dalton @ PTK to run the listed turbo at about 7-8 lbs. He also stated I should be able to do it at 10:1 CR if I wanted. I have an email out to Jose @ forcedinductions . com, but have not heard back yet.

If you need any additional info about my current or planned setup, please let me know.

-Alex

 

I, personally, wouldn't go that route. 530 - 600 rwhp is a modest goal from a PTK turbo. With your engine, that power level would be very easy with an intercooled Vortech T-trim for less money and hassle. As much as I like the PTK kit, it's not required for that amount of power.

You're also handicapping it with that turbo. The T-76 will spool up very quickly on a 396 and produce alot more power.

When the kit will go to 1000 rwhp, why stop at 550?

Mike

 

Hey Mike, I was hoping to hear from you as I've read many of your posts. I've thought of the SC vs turbo argument, especially based on my power goals. It is true that I could get a vortech/ATI kit, but I can't easily control power as I could with a wastegate on a turbo. Also, I'm afraid to put any real strain on the crankshaft as it is only held in with 2 bolt mains (ARP). As for cost, it seems a good SC kit cost $4000 or so - I can get the PTK kit for about $5,700. There is also the uniqueness factor...

Turbo sizing - I thought the T76 would work well too after going over the compressor map. My calculations showed that a T70 would not flow enough at the boosts levels I wanted to run. Then again, those old graphs on the internet are not the same spec as the turbo that was recommended to me. To be honest, I don't know what A/R and turbine trim that map is (or the T76). I'm not certain I can get my hands on such a graph. I was told the turbo is good up to 850hp and should spool quickly.

I would like to hear your thoughts on the T70 vs the T76 (the modern day ones) though!!!

-Alex

P.S. - Forgot to address the "why stop at 550?" question. The truth is I don't think I'm ready to have that much street power and I've read that anything over that is really just too much anyway. Plus the fact that I'm not certain if the 2 bolt mains will hold.

 

The difference in crankshaft stress will be minimal. If it's going to break with a supercharger, it would break with a turbo also. If your safety factor is .7, then it will still fail at .8, but take just a little longer to get there.

As for the 2-bolt mains, I have fretting on my block and steel 4-bolt main caps, indicating that my caps are moving at only 680 rwhp. I'd be concerned at 600 rwhp on a 2-bolt block.

As far as T70 versus T76, the MPT70 has gotten popular lately because it's the cheapest turbo that will support a decent power level. However, it has a very small exhaust side, especially on a large 396 cid engine. The exhaust backpressure will be high. Keep in mind that the 850 hp is the limit of the compressor and does not indicate how much power it will actually make on an engine. At 396 cid, the exhaust/intake pressure ratio will be way outta' whack becaust the little compressor will not be able to make much boost without alot of exhaust flow and pressure.

Then again, at 550 rwhp it may not be a problem. The T76 sure leaves alot of room to grow, though. . .

Mike

 

Not exactly what I wanted to hear. Is this "fretting" something that you are really concerned about? Do you think it may have occured from heavy drag racing vs street driving?

I see that Jose lists the PTK kit with a MPT70 @.96 A/R (about $800 cheaper than the Precision T76 GT-S). I'm trying to understand what I will win or lose when choosing between the T70 and T76. Is the lowered exhaust back pressure of the T76 (based on the 396 volume) that much of a gain over the T70? You make it sound like a complete win to go with the T76. Or if I do truely stay near the 600rwhp, would it be better to stick with the T70? BTW, what A/R are we talking about with the T76?

I appreciate all your comments!

-Alex

 

The fretting, in and of itself, won't hurt anything. However, it does indicate the mains are moving around. This could eventually lead to crankshaft or block failure. I'm sure the fretting occurred at 20 psi boost, whether it was track or street.

You have nothing to lose if you go with the T76. It will spool a little slower, but you'll never notice the difference. The 76 will make more power because it has a higher flow capability, will be more efficient (lower boost temp) in the range you run it in, and have less exhaust pressure.

I'm referring to the .96 A/R ratio. You can go smaller, but backpressure will increase even more.

Most people say the 76 isn't even big enough for the 396. Exhaust pressure will still be 2.5x boost. Switch to a T91 large-frame and you're all of a sudden seeing backpressure 1x boost and an additional 200 hp at the same boost level.

Mike

 

So the advantages are many for the T76, I just have (slightly?) more turbo lag. Is there any way to predict how much additional lag there will be? I want to keep the RPMs under 6K, so I have a shorter RPM band to play with...is this still within the range of the T76? Is the turbo you are recommending the one you are running (56 comp trim, 85 turbine trim, .96 A/R)?

I guess this also begs the question - can I choose something in between? Like a PT-72 or PT-74. Or am I over analyzing this? I'd hate to pick the wrong turbo seeing as they cost a bundle of money.

Now I see why you say "Vortech T-trim".

-Alex

 

I doubt you'll even notice the difference. Just to give you an example of the turbo lag to expect, I'll share a logged run. I was cruising in Drive at 3500 rpm and stabbed the throttle. It took me .6 sec to go from 27% to 100% throttle. By the time I hit full throttle, boost was at 7 psi. It took another .6 seconds for it to hit max boost of 20 psi. Of course, at lower rpm, lag will be more - my 60' time slowed down a bunch when converting from a T-trim to a T-76. It's definitely not direct-coupled like a supercharger.

Lots of people run the T-76 on 4.6 and 5.4 liter Fords. The 5.4 won't go much past 5200, so draw your own conclusions. . . And yes, the 76GTS is the same turbo I'm running.

Skip to the 76 and you won't regret it. Like I said, amongst the turbo v-8 community, the 76 is too small for anything over 350 cid.

Mike

 

Thanks for the backup Mike. Mike has been correct with everything so far. The 76GTS is by far your best option. A 70 would be way undersized and backpressure would shoot through the roof.

Jose

 

Mike and jose thanks for posting... I usually look for both of you guys posts... very entertaining and informative!!!

I like the YSi... Sat in a mustang with one... Can't wait to finish mine.

 

Thanks Mike and Jose, your input has been wonderful!

Are there any other concerns I should have? Do you maybe know what the BSFC is for a turbo LT1? It seems this number has a lot to do with calculating what injectors to use. I was told by Dalton that 60s should be adequate. Also, is it better to go high or low impedance?

-Alex

 

If you want to go with low impedence and use the stock PCM, I have an accelleronics box that I bought and don't plan on using... it's used, but in excellent conditions and comes with the original instructions. Selling because I went with a FAST system instead. I'll let it go for $225 shipped.

 

60's should be ok for 600rwhp, but if you ever decide to go bigger then you'll have to ditch the injectors. I would get 72's at the minimum.

As far as turbos are concerned, yeah T76 should make a ton more power and be more EFFICIENT. What does this mean, the turbo will have less backpresure, it will push cooler air (the more ineffecient the more heat in the charge), and you'll make much more power at a give boost level. Example:

600rwhp @14psi with T70
600rwhp @10psi with T76

This is just an example to show what I as saying.

I would ****** that box off roadie for that price if I were you. I paid $275 shipped for mine.

 

His price looks good, but I'm still not certain if I should so low Z since they make injectors that work with the stock drivers. Do low Z drivers have better drivability characteristics?

Also, I am understanding the T76 > T70 argument....I guess the only reason I still feel reserved is because what if I never want to go above 600rwhp? Does all the "potential" of the T76 disappear while just leaving me with a turbo that will have more lag?

I know Mike mentioned that I "wouldn't even know the difference", but I'm being honest with myself here. I street drive the car and love to have lots of power from 2K RPM on up. My fear is the T76 (even though more efficient) may have too much lag at these very low RPM. Is this a valid fear? Or will neither turbo produce boost between 2K-3K RPM? Remember, 396 /w a small blower cam (like 218/218 14).

-Alex

 

low impedence injectors allow you to run big injectors with near stock quality idle.

The 600rwhp was an example, let show it again:

T70 - 500rwhp @ 10psi
T76 - 500rwhp @ 6psi............see what I am gettin at

The T76 pushes more air at any boost level, more air = more power.

With the T76 upgrade you are up to ~6500 for the PTK kit.....definitely the best kit on the market hands down.....but now that $4k T trim looks even better. You want such a small amount of power...its up to you

As fas as lag, you probably wont it full boost till 2800-3krpm, but try hooking that power on the street (550-600rwhp), a tiny bit of lag can be a good thing.