88 350 tpi formula

iTrader: (9)

does any one have any math calculations to figure out around how much boost I will make with my S/C 400? I have a powerdyne with 9lb pulley on it it was from a 302 mustang with the crank pulley at very close too 6 1/2 " and the head unit pulley is just under 3" (2.89"?) is there any way to figure this out?


also It look like I will have to pick up a stock 88 crank pulley which is closer to 7 1/2" to run it

83 Crossfire TA

iTrader: (2)

Assuming that it actually makes 9psi on a stockish 5.0 and your 400 has a similar power band, you should be able to expect about 7psi (it's just a question of how much air the engine can breath).

Damon

Not really. Cubes are only part of the problem. Cam, heads, intake, exhaust all play a part. Once you've got a "Frankenstein" going you really need to invest in a good boost gague and see what it's REALLY making and then pulley appropriately.

Bigger cubes, bigger cam and higher flowing heads all drop your actual observed boost, but by exactly how much can vary wildly depending on your exact combo of parts.

A modest cam change on my roots-blown 383 required a 10% change in pulley ratio to get back to the same boost level. 10% is a lot.

Kenwood

iTrader: (1)

Exactly...there is no really accurate MATH formula you can use due to all of the variances given above and then some.....

83 Crossfire TA

iTrader: (2)

Actually, you can come reasonably close with enough info or just some fairly accurate guesses. Torque will always be proportionate to VE * displacement. HP is proportionate to VE * displacement * ½ * rpm and one can be calculated from the other using hp=(torque*5252)/rpm. Mass airflow will always be proportionate to HP (this is considering standard temp and pressure). If you add boost or non standard ambient conditions to the equation then you have to calculate a density ratio for the air, and then torque and HP are pretty much what they would be otherwise * the density ratio. If you build 2 engines with similar power bands and similarly matched parts VE will be similar and you can come pretty close to predicting any of this, including airflow and HP. The only difficult part is attempting to predict VE, but most parts combinations have been tested enough times that with a little research you could make a pretty good guess.

Anyway, all of this goes both ways… if you've got a blower that's moving a known amount of air and an engine that is moving another known amount of air you can go backwards and figure out what the density ratio will be, convert that to a pressure ratio and you have boost…. Or if you have the blower on a known engine making X boost then you can figure out how much the blower is moving...

Will this be dead on? No, but only because your numbers won't be dead on. With reasonable guesses for the numbers you can easily get within 2-5% which in this case works out to the difference between 7 and 7.14 PSI… do you have a boost gauge that can measure that accurately?

MrDude_1

5" off road tire pressure gauge...

Kenwood

iTrader: (1)

I understand that part of it BUT again you not understaning what he is asking....

He gave EXTREMELY LIMITED information...Not to mention a totally different engine combo with NO SPECS and a BOOST level based on a manufacturer claim on a different motor entirely...

Am I to assume he will use/ HAVE....Same heads, same cam, same exhaust, same intake, same compression ratio but instead its a 400????Some how I doubt the 302 mustang had all the same values...

So what Im saying is there is NO FORMULA that is generalized like

Boost on a 400SBC with a 302 ford blower that should?? run 9psi =

Boost level of mustang setup / .82 = 7.38PSI LOL

Giving the base saying a "9psi pully"is suspect.... I had some "8psi" pulies on my paxton that put out 12psi BONE STOCK MOTOR....and 18psi pullies on my vortech that put out 14.. Those values are Generalized...even the manufacturer will tell you that...Look at Vortech base kits... 6-8 psi most are rated within 2 to 3 psi on a totally stock application..

Im not trying to fight here but the formulas you speak of GO WAAAYYYYYYYYY beyond what he had asked/given..

88 350 tpi formula

iTrader: (9)

sorry for all the confustion I kinda know what I am asking is not very specific. I just wanted a Idea which may be pretty hard to say. I guess my only concern was too much boost I really don't want to go more than 9psi and since I would be using a bigger crank pulley, I guess if I make too much I can always trade my friend his 6lb pulley for my 9lb and go from there

83 Crossfire TA

iTrader: (2)

If you stuck a stock 302 intake… setup on a 400 (it could be done, of course it would be a ford stroker…), you'd have runner crossections that are much too small for the harmonic tuning of the manifold and matching headers. You'd probably end up with a lower VE with a peak at a lower rpm, and boost would be greater then expected from the ci increase. A stock TPI on a 350 is a roughly similar match as a stock ford 5.0 setup, and on a 400 you'd have a similar combination with minor upgrades to the TPI. All are LTR intakes, all are severely limited in their breathing by their heads…

I will agree that there is not enough info to give a real answer, but he asked what it would take to get an answer and I gave that. I have no idea of the specifics of what he's built. Give me more info and I could come closer to a real answer… hell, if this is a vortec or other blower that has a published compressor map (I'm not going to go look for powerdyne maps right now) and you can give accurate pulley sizes, or even what the stock pulley sizes that it was supposed to use were then a pretty good estimate could be made of the HP that will be produced by the setup…

MrDude… If I'm ever in SC I'm going to find you and smack you upside the head…