A ? about flow numbers

Posted By: dbran451

A ? about flow numbers - 01/27/10 10:07 PM

As it's cold outside and I'm thinking again and that's dangerous, was wondering how much ET a person would pick up by increasing the cfm's by say 50 if everyting else remains the same???

Posted By: dodgeboy11

Re: A ? about flow numbers - 01/27/10 10:12 PM

It's not set in stone, WAY too many variables, but you can just about guarantee 1.75 hp per cfm in a street application and closer to if not more than 2 hp per cfm on something more racy. Like I said, there are way too many variables for this to be set in stone, but it can give you a guestimate.
360 we had built at the shop, heads peak flowed 246 cfm (edelbrock RPM magnums) on our bench. I picked them up to 289 peak cfm. Engine made 442 hp before and after the port work and shaving .020 off the heads it made 508.

Posted By: BradH

Re: A ? about flow numbers - 01/27/10 10:21 PM

Quote:

... but you can just about guarantee 1.75 hp per cfm in a street application and closer to if not more than 2 hp per cfm on something more racy.

Like you said, there are really way too many variables to take into account. I've seen about 2 HP / cfm on something that was already starved for air, but also seen it drop down to about 1 HP / cfm for an application that was already closer to optimized.

Posted By: moper

Re: A ? about flow numbers - 01/28/10 12:01 AM

assuming the engine package already works (meaning it's all matched) and assuming the cfm is as a result of better port design than strictly larger volume, then a jump that large would require a new cam, prob convertor too. You're talking over 15% better on a port that flows 300. A larger percentage on worse flowing port... I would consider the " 2hp/cfm to be a very general guide for possibility of output, not a given.

Posted By: Bob_Coomer

Re: A ? about flow numbers - 01/28/10 12:18 AM

Well A moderate 493 inch RB engine with 11:1 compression had a set of 440-1 heads that flow in the 320-330 range. I had the heads CNC ported and on the same bench now flowed 380 cfm or so. I added a good size Solid roller cam (near .800 lift) to take advantage of the large flow numbers. The car picked up .5+ seconds and right at 10 mph in the 8th mile.
Of coarse the power gain/et gain was NOT all due to the flow alone, the cam switch helped some too. At least 25HP, maybe more.
So... were are talking a high 10 second ride that run low 10's high 9's in the 1/4 mile.
In the same situation of the engine was in a dragster running low 8's. The same changes might have only shown a tenth or two tops.
So just to many variables to account for.

Posted By: TheBlackCar

Re: A ? about flow numbers - 01/28/10 01:54 AM

Quote:

As it's cold outside and I'm thinking again and that's dangerous, was wondering how much ET a person would pick up by increasing the cfm's by say 50 if everyting else remains the same???

Your 10.004 will now be a 10.002.

It's rough gettin that three digit pass, huh, Dave? Save the money that your thinkin about putting in those heads and bring me the motor and I'll help you kick that door open...without the 50cfm.
If not, then expect the 50 cfm to not help too much on ET but a little on mph, which is already down a little.(ie other issues) Too much emphasis on flow #'s around here, remember, torque is ET and HP will show on MPH.
Either way, Good Luck

Posted By: clovis

Re: A ? about flow numbers - 01/28/10 04:37 AM

Its interesting to go over to the Wallace Calculators and just play with all the formulas for head flow and HP. Most of the time you will not get the same answer twice, when using the different formulas. By the formulas it doesn't seem to take a tremendous amount of flow (260-70) to get a car fairly deep into the 10's, weight pending.

Posted By: Sport440

Re: A ? about flow numbers - 01/28/10 05:55 AM

Quote:

As it's cold outside and I'm thinking again and that's dangerous, was wondering how much ET a person would pick up by increasing the cfm's by say 50 if everyting else remains the same???

If its 50 CFM more then the engine needs or can consume with its current combo. Then the extra 50 cfm will net you 0. HP.

It could even hurt performance by reducing the port flow velocity.

mikie

Posted By: Thumperdart

Re: A ? about flow numbers - 01/28/10 06:12 AM

What`s your combo now just out of curiosity. I went from well ported 906`s and a solid cam to home ported rpm`s and a solid roller w/the same 12.11 comp. and picked up a half second and 5+ mph.

Posted By: dbran451

Re: A ? about flow numbers - 01/28/10 06:03 PM

Your 10.004 will now be a 10.002.

Save the money that your thinkin about putting in those heads and bring me the motor and I'll help you kick that door open...without the 50cfm.
If not, then expect the 50 cfm to not help too much on ET but a little on mph, which is already down a little.(ie other issues) Too much emphasis on flow #'s around here, remember, torque is ET and HP will show on MPH.
Either way, Good Luck

Jeff thanks for the offer to kick the door in but I like opening my own doors,just curious what MPH do you think I should be at as the car is pretty consistent 10.0car @132-133 mph

Posted By: Sport440

Re: A ? about flow numbers - 01/29/10 02:01 AM

Quote:

Your 10.004 will now be a 10.002.
Save the money that your thinkin about putting in those heads and bring me the motor and I'll help you kick that door open...without the 50cfm.
If not, then expect the 50 cfm to not help too much on ET but a little on mph, which is already down a little.(ie other issues) Too much emphasis on flow #'s around here, remember, torque is ET and HP will show on MPH.
Either way, Good Luck

Jeff thanks for the offer to kick the door in but I like opening my own doors,just curious what MPH do you think I should be at as the car is pretty consistent 10.0car @132-133 mph

Not Jeff, But Your right there IMO with MPH.

My Lickity Split Chassis Efficiency charts says a 10.00 car should have incrementals something like this.

1.37 60ft. 6.33 1/8 mile 10.00 @ 134.5 MPH

So your close IMO. Probably a little soft on the launch. Whats your flow numbers now.

A 50 CFM increase on a already Performance head is huge IMO mike I say shave it .010 and you will have your 9.975346852 ET