My custom intake for L28.

[1 fast z]

Here is a picture of my intake in progress that I am making for my NA 280.

 

 

 

It is just a test fit on a parts car of mine.

[john kosmatka]

Cool. Is that efi, looks like it but cant tell.

[Guest Magnum Rockwilder]

Looks cool. I assume you did all the math necessary to figure out the velocity and capacity of the airflow before you fabbed it?

[1 fast z]

No, I am not good enough in math to figure that out, it may not be optimum, but should sure help my motor.

[kalium99]

Where did you get the throttle bodies from ?

[Guest Domspun]

I think your runners are too long, but it depends on what kind of power band you're looking for? Long runners will help low-end torque, shorter will hepl high-end HPs.

[Drax240z]

I think your runners are too long, but it depends on what kind of power band you're looking for? Long runners will help low-end torque, shorter will hepl high-end HPs.

 

Not necessarily true. The runner diameter also plays a large role. A large diameter long runner won't necessarily boost low end torque more than a small diameter short runner.

 

Stick to keeping it relatively close to the stock plenum/runner dimentions and you'll be in the right ballpark when it's all said and done.

[Guest Domspun]

Not necessarily true. The runner diameter also plays a large role. A large diameter long runner won't necessarily boost low end torque more than a small diameter short runner.

 

Stick to keeping it relatively close to the stock plenum/runner dimentions and you'll be in the right ballpark when it's all said and done.

Also true, but I didn't want to get too technical! One of my friends brought a whole book about manifolds, pretty complicated!! it's especially complited if you want to be precise about the powerband, fuel consumption and emissions, but it's pretty easy to make a race-only(high RPM) ITB(individual throttle body) intake, just put the shortest, largest runner you can and should be close to optimal!

[Drax240z]

Well I disagree again. The shortest, largest runner you can fit will not give you anything close to optimal.

 

Rather than go through this all again, I'll list some reference links:

 

http://forums.hybridz.org/showthread.php?t=94252&highlight=intake+manifold+design

http://forums.hybridz.org/showthread.php?t=78952&highlight=intake+manifold+design

 

There is tons of info here on intake manifold design.

[Guest Domspun]

Well I disagree again. The shortest' date=' largest runner you can fit will not give you anything close to optimal.

 

Rather than go through this all again, I'll list some reference links:

 

http://forums.hybridz.org/showthread.php?t=94252&highlight=intake+manifold+design

http://forums.hybridz.org/showthread.php?t=78952&highlight=intake+manifold+design

 

There is tons of info here on intake manifold design.

you didn't read me well, I said "optimal" for a high-rpm itb Na race engine and for tuning you only need to change the horns lenght.

Why would I read the links you posted when i can read this:

http://www.normas.com/SAE/pages/R-274.html

don't need any more references!

[johnc]

Well, on the L6, your efforts are better spent improving the exhaust side. Once you get the exhaust side working (in particular the exhaust ports on 3 & 4) then efforts on the intake side will bear fruit. The exhaust ports on the L6 head are the limiting factor in getting good flow on the intake side.

 

Below is a shot of the ports on the best flowing L6 cylinder head Sunbelt ever built (as of early 2003):

 

 

There is a lot of welding and shaping done on the exhaust ports on 3 & 4.

[1 fast z]

Well on my own flow bench I have got 141 cfm at 25" of water on the exhaust, and on the intakes I have 204 CFM at 25" of water, and these numbers are at .500" of lift. THe head was the first thing I did. What are the numbers on that head you have pictures?

[johnc]

I was never told the exact numbers but Jim did say that all 6 exhaust ports flowed exactly the same and the exhuast port flow numbers were within 5% of the intake port flow numbers.

[RB26powered74zcar]

I know of a members N42 head that was flowed @ 218 and 135, and I belive that was with the TB's and exh manifolds attached.

 

Lets see if he wants to chime in with all the details...

[BRAAP]

Disclaimer:

For those of you that are educated in the realm of engine tuning, I do realize that it can be argued that Flow Benches can be compared when using set values, and to a certain extent I will agree that carries just a little water, but the intent of this post is to educate the uneducated car buff to NOT use Flow numbers to judge how good a cylinder head is but use the HP produced, i.e. a DYNO, as the ruler to compare just how powerful an engine is or is not

I’ll try and be nice here, sorry if I step on any toes, but I take issue with people trying to compare quoted Flow Bench numbers. This is a subject that most, if not ALL, true engine builders and tuners HATE when our car buff customers go home and start quoting and bragging about Flow Bench numbers! That is like comparing “initial ign advance” figures! These figures are not to be used to determine if the engine will make GOBS of power or not. Flow benches have their place in engine building and tuning, but the numbers they produce are not for comparison. Flow bench numbers will give only a very limited general idea as to air flow for making HP through the head and only should be used as tool to “help” make improvements on ONE head, not compare to someone else’s flow numbers from a different flow bench!

Now for those that are curious as to WHY I feel this way about using flow bench numbers for comparisons. Since a flow bench cannot duplicate the dynamics that are happening within the intake and exhaust tracts while the engine is actually running, i.e. sound pressure waves, pressure surges, exhaust heat, fuel enriched intake charge, valve overlap extraction, etc, flow bench numbers are nothing that should be used for comparing one head to another or bragging how good one thinks their head is! The best way to use flow bench numbers is using the SAME flow bench to compare ONE cylinder head for improvement after modifications have been performed, making note of any changes in air flow whether improvements were made or lost, NOTHING MORE!!! Flow benches are essentially not standardized so a person can not compare 2 different flow numbers from 2 different heads from 2 different flow benches, not too mention those flow numbers are purely static numbers! (Again, for those of you that are educated in the realm of engine tuning, I do realize that it can be argued that Flow Benches can be compared when using set values, and to a certain extent I will agree that carries just a little water, but the intent of this post is to educate the uneducated car buff to NOT use Flow numbers to judge how good a cylinder head is but use the HP produced, i.e. a DYNO, as the ruler to compare just how powerful an engine is or is not). Flow benches do not represent what is actually going on within the intake tract OR the exhaust tract as mention previously, i.e. Dynamic air movement, pulses, waves, heat, etc!!!!. In real life, the valves are opening and closing causing the air to stop and move, stop and move, over and over and being as air has weight and is compressible, this constant surging will cause the pressures to rise and fall FAR above and below ambient. Depending on RPM, runner length, runner cross section, port shape, number of bends in the port and radius of those bends, valve shrouding, air density, cam timing in relation to the piston movement, (this has a HUGE effect on how the air gets moving within the intake and exhaust tracts, hence lopey idles, hard hitting powerbands, etc), there could be higher than ambient pressures at a particular RPM, i.e. a natural supercharging effect, that is why intake and exhaust runner lengths are TUNED! I have seen where some Nascar engine builders have achieved over 110% volumetric efficiency on a naturally aspirated 2 valve engine Tuning the intake AND exhaust tracts to a specific RPM with specific runner cross section and runner lengths. This tuning is using the Helmholtz principle. Your basic garden variety flow benches do NOT and can NOT duplicate this. The only real measure of how good a port can make HP, is to run the engine on a Dyno, (and this is what we are REALLY after right, HP! Not just some arbitrary static flow number through a head port)! An example would be if one head that on one flow bench indicates it will outflow all the others tested, when all are attached to equivalent short blocks, the high flowing head could easily make LESS power on the dyno, but then again change the configuration a little with a different cam, intake tract, piston some shape, etc, the results would get even more confusing.

Ok, I think I’m finished now. Thanks for allowing me to vent..

 

May the Torque be with you all…