Advantages to bigger turbo on pump gas?

[RealFastV6]

Originally posted by strikeeagle
I didn't mean as compared to a stock turbo running way off its design point. I meant that a stock turbo running at its design point will produce a cooler charge that a larger turbo running well off its design point. Evidence the compressor curves. Lower efficiency = more heat.

Of course. Nobody is saying bolt a T88 with a Stage 3 turbine so you can spool it on a stock motor. The stock turbo isn't in its in its peak efficiency at 18-19psi. This was a hypothetical question that started this thread, simply... will a slightly larger turbo add any benfit on pump gas.

Answer, yes.

So far as surge goes, for a centrifugal compressor stage, surge is the condition where there is insufficient flow for the particular head (boost, if you like). If the compressor associated with a large turbo can't deliver sufficient flow into the motor for the boost you're running, trust me, it will surge.

Right.

However, most of the standard GN turbos that bolt up (TE44, T66/P, T70/P/Q, T62,P,S3) are speced out to run 25-29psi. Going a size up on the turbine wheel without going a size up on the compressor will free up some flow and some power. Again, surge shouldn't be a concern since you'll see 21psi MAX on pump gas anyhow. If you speced out a turbo to be in its peak efficiency at around 21#, and then tried to run 27psi with it, THEN it'll surge like you said.

Also, I think we're confusing the relationship of turbine and compressor. It is the expansion of hot exhaust gases across the turbine which provides the power to drive the compressor, not the other way around.

Of course. Where did I say otherwise? But just because the turbine spins the compressor doesn't mean the turbine can't be choking the motor and in-turn the compressor also.

[/B]A bigger turbine wheel and cover are wonderful from a pressure drop point of view, but not if you need a 4000 stall to get the motor to make enough air to drive it to design speed. [/B]

Again, nobodys talking about bolting a T88 onto a stock motor here. The question was simply this... will a slightly larger turbo add any benfit on pump gas...

The answer is yes.


Back under my dash...

 

[UNGN]

Originally posted by RealFastV6


The stock turbo isn't in its in its peak efficiency at 18-19psi.

With a stock long block, it is Very close to its peak efficiency at 18 psi. A car with ported heads would be a different story as the mass flow for this would be above the stock turbos peak range.

Below 18 psi with a stock long block on a stock car (stock converter, stock gears), it is very hard to beat the stock turbo. With a Cam and/or ported heads a larger turbo will likely be faster.

 

[ijames]

Originally posted by cool 84
You're reducing backpressure and getting a cooler intake charge but at the same time you're increasing cylinder pressures which negates the cooler intake and less backpressure as far as boost level is concerned.

Umm, then why was I able to run 3-4 psi more boost just by changing from a TE34 to a PTE54 turbo (see my previous post for combo's and times)? Until you go so big that you actually make the efficiency go down at the boost level you want to run, bigger is better for hp (lag is a different story). Some of it is reduced compressor heating and some of it is lower backpressure reducing the pumping losses. Wasn't it Red A. who said that boost is the exhaust that can't get out of a motor, not the air you are stuffing in?

 

[OneLethal87GN]

When I went from the stocker to my TE-60, the car felt stronger at 12 psi than my stocker did at 16-17. Nothing else was changed.

 

[Wht87T]

I'm only getting 16-17psi on 93 octane, with a TE61 P-Trim, Cotton FMIC, and a Vigilate "0" pump. How are guys with similiar combos running 20-21psi on pump gas?????? That totally contradicts everything that I know about these cars. Will someone let in on the secret???

 

[scottyb]

It looks as if the original poster's car is somewhat similar to mine, so I'll throw this for both of us: At this stage, would a better intercooler be a better first choice compared to a bigger turbo? I'm thinking stock mount and running pump gas.

Thanks,
Scott

 

[strikeeagle]

I dunno. Seems to me if everybody got 20+ PSI on 93 octane there would be no aftermarket at all. But, I've given up arguing about it.

So far as a bigger turbo providing more bang than a stock turbo on a stock motor operated at stock boost, that's the equivalent of denying the compressor curves, so now we're reinventing thermodynamics...

Somebody had better phone up Garrett and Turbonetics and tip them off regarding this discovery...

 

[RealFastV6]

Originally posted by strikeeagle
I dunno. Seems to me if everybody got 20+ PSI on 93 octane there would be no aftermarket at all. But, I've given up arguing about it.

So far as a bigger turbo providing more bang than a stock turbo on a stock motor operated at stock boost, that's the equivalent of denying the compressor curves, so now we're reinventing thermodynamics...

Somebody had better phone up Garrett and Turbonetics and tip them off regarding this discovery...

Wow, your car came stock with 19psi?

Ahh, well I guess the rest of us will upgrade our turbos then.

 

[strikeeagle]

I think you missed the point. What I said is that if we were all capable of doing 20+ PSI on pump gas I don't think there'd be such a long line at the parts counter...

 

[azgn]

small gains in efficiency aside (at the lower boost levels being discussed), upgrading the turbo and running pump gas would be a bad investment.......a much better investment would be an octane enhancing device (alky)......THEN upgrade the turbo and you got something!

 

[ijames]

Originally posted by strikeeagle
I think you missed the point. What is said if that if we were all capable of doing 20+ PSI on pump gas I don't think there'd be such a long line at the parts counter...

Except that it's the mass airflow that matters, not the boost. A bigger, more efficient turbo gives cooler air and so more mass airflow at the same boost (plus the lower backpressure meaning more mass airflow even at the same outlet temp and boost). I'll take 20 psi from my PTE54 any day over 20 psi from a stock turbo. Sure, you can go so big that spoolup is forever so your converter melts and your crank thrust gets wiped and you are over the surge line at 15 psi boost, but if you stay reasonable you will make more power with a bigger turbo than the stock one even at 15-20 psi on 93 octane. Until you get somewhere bigger than a 66 compressor wheel the efficiency of the larger wheel is at least as good as the stock turbo in the 15-20 psi, 300-450 hp range. I've done the exact experiment going from a TE34 to a PTE54 turbo, tuning both to the max with 93 octane, and the 54 was 4-5 mph faster. At even higher boost, with race gas or alcohol or whatever, it's all in favor of the bigger turbo.

 

[matt87]

geez i must be lucky to be able to run 22-23 psi on 94 octane. i guess bigger cams also keep cylinder pressure down so more boost on less octane can be achieved.

 

[NEARING]

22-23 psi on 94
must be the heads?

 

[GNSCOTT]

geez i must be lucky to be able to run 22-23 psi on 94 octane. i guess bigger cams also keep cylinder pressure down so more boost on less octane can be achieved.

Matt, i couldn't agree more. I'm wsing now iever changed my old combo. I guess i figure when i'mdone,i'll end up selling the car. My combo was..
AC 3k stall
CPT 66 bb
218 cam
bone stock longblock (except cam above) no head porting, stock tb, plenum etc.
V-2 fm
good fuel system
good exhaust system

I ran 11.2's @119 with 94 octane, 25psi, 18 degrees of timing and zero knock. I wicked it up to 26psi and got 3 degrees. i put in a race chip ad it knocked immediatly @ half throttle. Drove the car almost 200 miles each way to and from the track, and had fun.. I'm sure wth a race chip and good fuel it would have been 10 second slips for me. There is no way a 44 or 51 could match that performance at those levels.

As for the alky argument, alot of people do not want to worry about running out of alky and blowing he motor. Lasttime i looked at an alky kit (last year) they had no way of turning it on or off while driving, so if you were driving wit it hooked up, it ran continuously.

 

[azgn]

I think you better get that combo into GNTTYPE recipe section right away! We could have all saved a ton of money had we known this!

 

[86brick]

The SMC alky kit lets you know when your low on alcohol and the alky comes on at a set boost level (I have mine set to come on @ 12lbs of boost), so the alky will last if you can keep your foot out of it. Best $320 I ever spent

 

[cool 84]

Originally posted by ijames

Umm, then why was I able to run 3-4 psi more boost just by changing from a TE34 to a PTE54 turbo (see my previous post for combo's and times)? Until you go so big that you actually make the efficiency go down at the boost level you want to run, bigger is better for hp (lag is a different story). Some of it is reduced compressor heating and some of it is lower backpressure reducing the pumping losses. Wasn't it Red A. who said that boost is the exhaust that can't get out of a motor, not the air you are stuffing in?

Why was I (and my dad) able to run more boost with the stock turbo and no intercooler vs big turbo and FM? 02s were the same before and after so it's not fuel. Of course I made more power on pumpgas after the IC and turbo but I couldn't run as much boost.

 

[GN and Sho's]

Holy **** are you guys confusing! On a side note for you alky users: how exactly is it used, how much per gallon, is it tougher to tune? Feel free to email me if you feel no one wants to hear about alky again.

 

[Wht87T]

I have a CPT65, and my alky kit is on the way. I'm gonna have a blast with that combo. If you guys want any info on the SMC kit just call up Steve, he'll answer all the questions you want.

John

 

[Intercooler]

Originally posted by ijames

Umm, then why was I able to run 3-4 psi more boost just by changing from a TE34 to a PTE54 turbo (see my previous post for combo's and times)?

Plain and simple the 34 is an old design with a 14 blade compressor wheel as opposed to an 11 your 54 has and also the turbine wheel isn't as effecient. John Craig will explain all that to you just like he did to me with my Stage 3 Cheetah. Actually even a 49 will put out cooler air by design than the Super H Turbonetics. Your 54 has better wheels! I found with my turbo experiences that I could run 17-19 PSI on pump gas with the stocker and same with the 63 with zero knock. Any more and both setups would show knock. I can say the 63 at that level opens up a can of whoop ass over the stocker! Actually at 12-13 PSI the 63 would put the stocker in the weeds! The way I have viewed it with my experiences to guide me is go as big on the turbo as you can tolerate on the convertor and other components to support it! I don't really consider a 70 series turbo and 3800+ stall and 72's (I had 83's and they are too much!) as a good 100% street setup. For me 50's, 3200 stall and a TE-61 will keep me happy regardless of the type of driving I may need to do! Big turbos kick ass!