Reading Max Boost - Question about bhp formula

[Schmieder]

Reading Maximum Boost by Corky Bell. It is everything I expected plus some. A really great book and I should add to the often noted 'Must Read' when going turbo.

So, about the formula...Pretty easy but there is a question of variance.

3100v6 (191 cu in) with 8 psi boost intercooled.


Lower Value = 0.052 x displacement x (PSI + 14.7) = X bhp
Upper Value - 0.077 x displacement x (PSI + 14.7) = X bhp

Lower Value = 0.052 x 191 x (8 + 14.7) = 225.45 bhp
Upper Value - 0.077 x 191 x (8 + 14.7) = 333.85 bhp

That is a great variance. How can I narrow down the figures more accurately? Should I expect 50% of the variance, being 279.65 bhp?

Or since I am using an appropriate intercooler (sized to turbo) should I expect higher, like 85% = 317.59 bhp?

Better question yet, what is the definition between lower and upper values?

I know I ask a lot of questions, but I admit, I have much to learn.

Thanks guys!

[IsaacHayes]

Big or small port 3100? Exhaust work? Port work?

Midnights 3400 which I think was just ported put down 328 wheel HP on 9psi. This was with a 5spd though, 4T60-e will eat a lot of that up.

Since BHP is direct engine output, minus trans, alternator, power steering, exhaust, etc. I would go towards the higher end of the numbers. Put on the accessories, exhaust, and then filter the power through the trans and it will drop a lot.

Hard telling, but that might give you some relative numbers to work off of.

[pocket-rocket]

I believe the upper and lower values have to do with Volumetric Efficiency.

[Schmieder]

Big or small port 3100? Exhaust work? Port work?

Midnights 3400 which I think was just ported put down 328 wheel HP on 9psi. This was with a 5spd though, 4T60-e will eat a lot of that up.

Since BHP is direct engine output, minus trans, alternator, power steering, exhaust, etc. I would go towards the higher end of the numbers. Put on the accessories, exhaust, and then filter the power through the trans and it will drop a lot.

Hard telling, but that might give you some relative numbers to work off of.

lol sorry.

3100 with 3400 top swap and 65mm TB. T3T4 compressor .60/ Turbine .63

Ehh, once I read the Book 5-10 times through, I'll have all the knowledge I need.

But I always enjoy the wisdom from experienced users

[Schmieder]

I believe the upper and lower values have to do with Volumetric Efficiency.

Thanks. From what I've read so far, my VE should be around 89-98% with the intercooler, 1.54 pressure ratio. If I am correct but that seems high.

[IsaacHayes]

But VE of the motor.......

[pocket-rocket]

But VE of the motor.......

Yeah, I should have said that to make it more clear.

See the street definition of Assume...

[robertisaar]

See the street definition of Assume...

is to not do it because it makes A ass of u and me?

[pocket-rocket]

is to not do it because it makes an Ass of u and me?

You, my friend, win a cookie even though I corrected your typo

[Schmieder]

Yeah, I really try to avoid assumptions at all costs.

I think I have everything figured out so far.

I'll have the funds this friday and certain items that are shipped will arrive 10-14 days from then. If all goes well, I'll be racing down the parkway with my hair on fire...lol

Something I read about the transmission in Maximum Boost, I would like your opinions.

It was said the turbo will not be able to apply as much torque on the transmission, when it spools up past 2-3k RPM, as much torque that will be applied in NA from 1st gear standstill acceleration.

Basically the tranny will see the most torque at the beginning of acceleration in 1st gear w/o the turbo even spooled up yet. Once the turbo is spooled up it will still apply greater amounts of HP/Torque, but inertia will prevent the max torque reaching levels seen from base acceleration.

I have no reason to doubt Corky Bell but this book was written years ago and he may have been implying a manual trans but didn't specify, IIRC.

So this means my trans at 8 psi will barely see any damaging stresses as long as the fluid is kept cool and the mechanics of it are in good shape.

And then theres torque management in the PCM. If I reduce the amount of slippage allowed by the PCM to manage torque, won't that do the transmission good? It would be less heat from slippage but then there is more direct pressure on the parts. And direct pressure can also create heat. But what is less? So, would it be a good idea to reduce torque management as much as possible while still retaining a bit of streetablility?

I know, I know, long post......

[robertisaar]

what corky was refering to is that the tranny SHOULDN'T see any more stress than it normally would with a similar engine, just minus the blower. if you had boost while standing still, then you'll have a situation where there will be more torque being transfered and will really have to consider trans durability...

oh and you're not going to overnight them from japan?

EDIT: this is why you constantly see L67 cars with blown trannies... roots blowers can make pressure the instant you put your foot down...

[Schmieder]

But VE of the motor.......

But isn't VE of the motor over 100% when boost is introduced?

So if I have a pressure ratio of 1.54 then my VE, in theory and a perfect environment, should be 154%. But if my VE is 75% naturally aspirated, then a 1.54 pressure ratio should put me at 115.5 VE. But we need RPM to accurately formulate the Engines VE.

Beyond the formulas ability to answer accurately. Because a variable that considered RPM would need to be present in the equation.

0.052 x CID x (PSI + Atmospheric Pressure) = X bhp
0.077 x CID x (PSI + Atmospheric Pressure) = X bhp

Judging from the variables involved being displacement, boost pressures added to sea level atmospheric pressure and ..............................

OOOHHHHH, I just read the formula is derived from statistical records of dyno runs with turbo chargers. The 0.052 to 0.077 is the broadest range of power recorded in relation to the turbo psi and CID.

It is just a general formula to show the extremes of power possible in a specific turbo application. Kind of like the bell curve of population genetic extremities.

[robertisaar]

But isn't VE of the motor over 100% when boost is introduced?

not necessarily. if you have a real boatanchor POS that achieves, let's say 50% VE, and you feed it via turbo, it could take up to 14psi to become 100% volumetric efficient... it's all about moving air.

[Schmieder]

what corky was refering to is that the tranny SHOULDN'T see any more stress than it normally would with a similar engine, just minus the blower. if you had boost while standing still, then you'll have a situation where there will be more torque being transfered and will really have to consider trans durability...

So the durability of the transmission is primarily concerning heat due to acceleration curve and clutch slip. Trans cooler and gauge will cover that.

oh and you're not going to overnight them from japan?

nope, when ordering from several different companies for various items, the shipping costs can get insanely high.

And yeah, the turbo is a knock off for now. Figured I be better off destroying a cheap turbo first if anything goes wrong. Once I perfect my approach and have a bit of experience under my sleeve, I will move onto a better car with higher quality items. Such as electronic boost controllers, dual BOV, precision wastegates and a ball bearing garrett with water jackets.

But for now, a cheap turbo will be fine as long as the oil feed has a restricter and the return is flowing very well. I considered buying a used T3 T04E but decided to pass for now. My quality turbo will be new when the day comes. And that sucker is going to sit on forged pistons pushing 20 psi. Until then, I can only dream. I'll have to get by with 8 psi....

I know many will flame the idea of a knock off turbo but from what I read so far, they can last a year or more if taken care of right. In some instances I've heard of good results when a knock off is rebuilt. And since the China turbo is rated up to 30 psi and I'm pushing 8psi, it's not really stressing it out yet. I read the primary failures are from higher boost levels. And I'm willing to bet the number one reason for those failures is the operator failing to use an oil restrictor or allowing the drain to flow free enough. That and not cleaning the manifold after the weld and letting weld chunks slam into the turbine blades chipping them, throwing the balance off and then burning them up right quick.

[robertisaar]

I know many will flame the idea of a knock off turbo but from what I read so far, they can last a year or more if taken care of right. In some instances I've heard of good results when a knock off is rebuilt.

i have one... and am planning on using it when the funds come around to stick a 3900/F40 in the monte... i'll give the 3100/4t60-e one hell of a time until it's too tired to continue or goes sky high...