How to determine boost level with different pully sizes

[Lextreme II]

Here is an interesting article from Peter Scott of Planet Soarer about pully size and boost for the M90 and M112. I am also in the process to update some of the information based on his findings with the Whipple 2300 and compression factors.

This is the formula for determining boost. Credit goes to Planet Soarer:

Boost (psi) = (PR x 14.7 x V / C/2 ) - 14.7 - I

PR is pulley ratio, crank pulley diameter divided by drive pulley diameter. e.g. The stock Jaguar M112 pulley is 3 inches in diameter, therefore 5.5/3= 1.83

14.7 is the pressure of the air we live in, we don't live in a vacuum, we live in 14.7 psi.

V is the volume of the Eaton blower for one rotation. The M90 is 90 cubic inches or 1475 cc. The Eaton M112 is 112 cubic inches or 1835cc. Turn it once and it pumps out 1.835 litres of air.

C is capacity of the engine in cc : 4000 cc for the 1UZ-FE. The C/2 is C divided by 2 - because for one rotation, a four stroke engine is only half way through a complete cycle. When the piston is up the top and starts going down, air and fuel go in, then it gets to the bottom and goes back up and compresses the mixture. That's one rotation. Then the spark plug ignites the mixture and it starts to go down again, it gets to the bottom and then goes back up again pushing the burnt mixture out the exhaust valve and returns to the top to start over again. That's two rotations.

I (capital "i") is an allowance for boost lost due to valve overlap. All engines have valve overlap; the intake valve opens before the exhaust valve closes - the incoming fresh air and fuel pushes out the last of the burnt exhaust gases. The 1UZ-FE has a small overlap of only 9 degrees. Nissan's RB26DETT has 14 degrees, Subaru EJ20 has 16 degrees and the turbo EJ20 has 14 degrees. The allowance is quoted as 5% boost lost for every 10 degrees of overlap. So for the 1UZ-FE at 6 psi boost, perhaps boost loss is 0.05 x 9/10 x 6psi = 0.27 psi lost - it's not much.

Here is what I came up with based on what I have seen from other FI owners. Boost Level and pulley size

 

[fugly]

Using the formula i should have about 6psi
My actual boost is about 9psi
WTF???

Has anybody else compared formula to actual boost??

 

[Lextreme II]

Fugly,

You have a M90 on a 1uzfe? I took partial formula from Peter Scott. Few factors play a roll on boost. ie compression ratio & exhaust restriction

 

[Cobber]

Lex,
You have the crank pulley at 5" it is more like 5.5". I just went out and measured mine and it has an OD of 145 mm. I'm note sure where the correct place is to measue them?

Also you need to take into account the HP requirement for driving the supercharger and deduct that amount from the rwhp.

Fugly,
What is your 112 supeercharger ratio? I think we will need to work this backwards.

This will be a good sheet when complete.

Some more real life ratios should make things fall into place.

 

[quadcam boat]

Heres some other pulley sizes from other members with 1UZFE engines.

Jordy with his M112 Jag intercooled setup 65mm pulley = 10psi
54mm pulley+ 13psi

Oz Venom standard 73mm Jag pulley on M112 = 7psi

My own M90 pulley is 62mm on the outside (rather than measuring from the bottom of the grooves) and produces about 7.5psi. It is on a stock engine with Jordy manifold and marine 'log' style exhausts.

 

[fugly]

I'm running HARROP HE112 with a 90mm pulley.(stock 1UZ)
The blower was supplied with 71mm pulley, that produced 12lb by 4500rpm (untunable to say the least).
Had a 85mm pulley made that produced 9lb at 6500rpm, good but thought i would make it safer for competing in burnout competitions, so had a 90mm pulley made hopeing to lower the boost a bit, strange thing is i've still got 9lb.
Any ideas on that one!!!!

 

[fugly]

Just had a thought, maybe HARROP 112 is more efficient than the EATON 112??

COBBER,to answer your question on my ratio, the crank pulley is 140mm(measured at outer dia of pulley ribs) & blower pulley is 90mm i can't remember exactly but i think that worked out to be 1.55 to 1.

Quadcam boat, i am more confused now that i've read your post, my setup just doesn't line up with any of those results, one common with those 3 setups is there all using modified original manifolds where i am using a richwood manifold, could this make the difference?

Pulley size is measured outer diameter of belt grooves, please correct me if this statement is incorrect.

 

[Lextreme II]

Cobber,

I measure the ribbed of the belt. The ribbed is more accurate then outside of the belt. For my measurement, it got 5.0" However, I can reconfirm it one more time.

 

[Lextreme II]

lso you need to take into account the HP requirement for driving the supercharger and deduct that amount from the rwhp.

From Peter Scott's page he stated that:

5 psi @ 12,000 supercharger speed
M90: 28 hp @ Delta F: 95 F
M112: 33 hp @ Delta 130 F


10 psi @ 12,000 supercharger speed
M90: 34 hp @ Delta 185 F
M112: 52 @ Delta 185 F


Do you know what is the whipple 140ax? I would like to add that factor to it. Remember its a ball park number, some real life numbers will vary.

 

[fugly]

Sorry, i can't help with any info on a whipple.

Going back to pulley diameters, what i was trying to ask was, is the dia measured across the peaks or valleys of the pulley grooves?
Does this make sense this time?

 

[Lextreme II]

Fuly,

I just recheck the crank pulley diameter once more. Its in fact 5.5". I measured few years ago and I took it from my memory. Its official 5.5". I will correct the database.

 

[fugly]

Thats 140mm for the people in the modern...er metric world.

 

[quadcam boat]

Fugly,
I too am suprised at both Jordies and Oz Venom's boost with the relativly small size pulleys thay have fitted.
Both have 2nd hand blowers so maybe that is the difference?
Maybe its the manifolds; Certanly Oz Venum's manifold has a small plenum area compared to a Richwood manifold and Jordies has a rather sharp angle where the inlet runners meet the heads.

 

[Gazzasore]

My Pulley is 59mm So how much Boost do yopu think mine has
on a M90 & Intercooled

 

[Anish Varsani]

Dumb question, but how do you get more boost for the same supercharger speed with intercooling or reducing engine capacity?

5 psi @ 12,000 supercharger speed
M90: 28 hp @ Delta F: 95 F
M112: 33 hp @ Delta 130 F


10 psi @ 12,000 supercharger speed
M90: 34 hp @ Delta 185 F
M112: 52 @ Delta 185 F

 

[Lextreme II]

Please refer to these graphs

M90

M112

 

[fugly]

Fugly,
I too am suprised at both Jordies and Oz Venom's boost with the relativly small size pulleys thay have fitted.
Both have 2nd hand blowers so maybe that is the difference?
Maybe its the manifolds; Certanly Oz Venum's manifold has a small plenum area compared to a Richwood manifold and Jordies has a rather sharp angle where the inlet runners meet the heads.

I've been thinking about the manifold having an effect on the boost level, my line of thought is that the more restrictive the manifold runners the higher the boost reading would be, further to that restrictive inlet ports would have the same effect on the boost reading.(air being pumped into the plenium but can't out).
quadcam, do you know if Jordies or Oz Venem's heads have been ported?
What's your thoughts on this idea?

 

[tomrapid]

Boost will be effected by ports, manifold design,exhaust and most importantly the CFM capacity of the inlet tract including throttle body, air filter and the entry to the supercharger. Pulley calculations are usually only a guide .When it comes to performance and throttle bodies- size matters.