whats the deal with 2V vs 4V ?
10-15-2007, 10:41 AM
#71
5th Gear Member
Join Date: Mar 2007
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Posts: 2,441
RE: whats the deal with 2V vs 4V ?
ORIGINAL: Dsmfighter
I was using the 100% volumetric efficiency figure as an example, similar to that found in a high dollar race engine. You mean to tell me that v-8 F1 engines, which use maybe 2.5l andmakes around 700bhp isn't close to 100% volumetric efficiency? I used the term "generally" for a reason when I spoke about the saying 'bigger is better', but it seems to be working for the guys who run thier nitromethane top fuel cars..
ORIGINAL: 2002GTAUTOVERT
itsabout impossible to get a motor to reach 100% VE even with forced induction. And you have to remember, its not just N20 or F/I that helps, its the entire design of the motor. If the heads dont flow well and its turbulant.. those valves will only be open for so long.. so unless you plan on timing them to stay open for 4 seconds, i doubt you will reach even 90%. A Supercharger on a 4 valve will skyrocket the VE due to the PSI forcing air through 2 intake valves (DOHC)instead of one (SOHC). Its not a matter of displacement guys, its a matter of VE as this gentlemen stated. Bigger ISNT necessarily better. The more valves, the better head design and the better flow equals better efficiency. Its not one of the 3 but all of those factors.
Look at fords new cyclone 3.5 V6 (rumored to produce over 350HP in the future). how about that 3.5ish liter engine in the altima putting out 263hp. they are simply more efficient due to design.
ORIGINAL: Dsmfighter
Who freaking cares weather a car is a 2v or a 4v...What your looking for is Volumetric Effcientcy(sp). Your average car has a V.E. of approximately 60-75%. Meaning it only fills its cylinders 60-75% of thier FULL CAPABILITY. Generally the saying "bigger is better" is true. If you have a 4.6l which has a V.E. of 100%, it's using a total of 4.6 liters of air/fuel, or a 7.0l engine which has a V.E. of65.5%, its only using a total 4.6ish liters of air/fuel. The reason why the4.6 sohcheads suck?Thier design for one, and the amountcfm hasA LOT to deal with the potential powerthey can accomplish. The average PI head flows a max of 160cfm on the intake and 138cfm, vs the 4v c head which flows a max of about 233cfm & 169cfm respectively.
You can make a TON of power on either head. My opioning... put a blower or N20on either and be done with them. Thats how you improve you V.E.
Who freaking cares weather a car is a 2v or a 4v...What your looking for is Volumetric Effcientcy(sp). Your average car has a V.E. of approximately 60-75%. Meaning it only fills its cylinders 60-75% of thier FULL CAPABILITY. Generally the saying "bigger is better" is true. If you have a 4.6l which has a V.E. of 100%, it's using a total of 4.6 liters of air/fuel, or a 7.0l engine which has a V.E. of65.5%, its only using a total 4.6ish liters of air/fuel. The reason why the4.6 sohcheads suck?Thier design for one, and the amountcfm hasA LOT to deal with the potential powerthey can accomplish. The average PI head flows a max of 160cfm on the intake and 138cfm, vs the 4v c head which flows a max of about 233cfm & 169cfm respectively.
You can make a TON of power on either head. My opioning... put a blower or N20on either and be done with them. Thats how you improve you V.E.
Look at fords new cyclone 3.5 V6 (rumored to produce over 350HP in the future). how about that 3.5ish liter engine in the altima putting out 263hp. they are simply more efficient due to design.
as for superchargers boosting VE past 100%.. the size of the supercharger (2.1, 2.3, etc.) also counts as displacement as it is being filled (not sure of the VE on one) with air. So in theory if you have a 2.1 KB as i do, youre cramming 2.1L more worth of air through your heads at a certain PSI. Problem is for the duration your intake valve is open, i dont see 2.1 L worth of air making it into your motor. So even your F/I isnt at 100% and probably hurts your VE. Again, this is just numbers so dont start a flame war because i say F/I hurts a number, cause it benefits the numbers that matter to us.
10-15-2007, 08:09 PM
#72
1st Gear Member
Join Date: Apr 2007
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Posts: 51
RE: whats the deal with 2V vs 4V ?
Good point about the nitro.
But as for VE above 100% with FI, it is very easy, in terms of engine only. All you have to do is look at a tuning table for any stock turbo/supercharged car... VE vs RPM, VE goes way above 100%... For NA tuning table it is limited at 100%, and at peak powerband most WELL designed engines are around 90%.
But as for VE above 100% with FI, it is very easy, in terms of engine only. All you have to do is look at a tuning table for any stock turbo/supercharged car... VE vs RPM, VE goes way above 100%... For NA tuning table it is limited at 100%, and at peak powerband most WELL designed engines are around 90%.
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