ezss

I guess this post is for personal interest sakes and curiosity, since it looks like I am going to be swapping out my heads (which will make my second set of ported heads after the first set was reworked once, and Im on my 4th aftermarket cam, 3rd set of headers, 2nd shifter, 3rd rear end configuaration, 2nd air box lid, 3rd set of injectors, has to be about my 45th set of tires...well anyhow, im off on a tangent..)

so anyhow...some things to think about--
How much effect does valve size actually have on power -- I have heard different theories, ranging from the bigger the better to it does not matter, they do not make power.

How much parasitic loss on the valvetrain do double springs cause? Mated to a cam with big lift, how would you be able to tell when you have reached the point where the parasitic loss overcomes the gains from the additional lift?

How can you measure runner velocity vs. flow rate?

If I put 5.3 litre heads on a stock displacement LS1 to bump up CR, will 5.7 litre lS1 heads on a larger displacement engine also bump CR? How much impact does CR actually have anyhow? Ive heard estimates of ~10rwhp per full point, this doesnt seem right to me.

feel free to give a shot at any one or more of the above...

MEAN LT1

iTrader: (2)

Personally I think head porting is a voodoo,black magic type of thing. Its more than just opening up ports and promoting a certain type of flow. If that was the case I guess everybody would be good head porters.

JS

iTrader: (4)

Personally I'd leave the car alone.
450RWH/450RWT is fine for your setup.

Most guys making more power than u are running 12:1 CR.

Just change the cam and retune via Brian H./JD's.
I bet with the right cam and a retune(Brian/JD's)and it'll hit 465RWH/460RWT no problem EZ...

Good luck bro...

ezss

Well, without going into all the details, I think I would like to try a set of really good heads and see what kind of power I can make. I really think if JPR h/c A4 cars can make 450+ rwhp, that I should easily be able to make 480+ with my setup.

Regardless of that, Im curious about all the other factors, wanted to see what people thought.

FASST

Ideally, you'd like the highest velocity possible througout the lift range with the highest volumetric flow numbers as well. The flow part being the easier of the two to maximize...just make the runner big enough to avoid port stall. The trap allot of people fall into is that they look at just peak flow numbers, usually at a lift that there cam is never going to use. Almost all reputable LS1 head porters have good flow numbers at .600"-.620" lift, yet very few cams run to those lifts. To get high lift flow numbers, you usually have to sacrifice low lift velocity. That's one of the reasons why there are cars that have great peak flow numbers and just so-so dyno/track times.

For example: Say the head porter totally hogs out the runners and the valves. That will make good volumetric flow numbers, but your cross-sectioned port velocity will be low. This will hurt A/F mixing, swirl, etc.

Just like a dyno curve, the best heads have the most area under the curve (velocity vs. lift) over the useable lift range of the cam.

Lift doesn't tell you everything when matching a cam. Duration also plays a big role. Say you have a head with great velocity, and a little bit lower flow. You can increase your intake duration, and pick up more total air intake. On the other hand, if you have crap for velocity but great flow, increasing your duration will not necessarily help (to a point).

In a perfect high tech world, we would be able to see an infinitely variable lift/duration across the rpm range to maximize runner flow at all rpms. Until they perfect electomagnetically controlled valve actuation, we'll just have to settle for defining what our useable rpm range is.

Bear

iTrader: (1)

I know what makes for some good head. That is where she doesnt use her teeth, she tongues your *****, and then swallows and gets the *** out.!!!!

JPR

What Bear said...

JP


Seriously, FASST nailed it right down to a tee, basically, knowing whats involved to produce awesome power is all in the flow numbers and runner sizing, conversley, it's not just peak flow numbers either, matching a package correctly and hacking away at an intake runner for peak flow numbers are 2 different things, but thats what seperates the two.

JP

ezss

Thats a spin I had not heard before on why high dyno cars do not always run well, but Im not sure I agree with it 100%. Ive seen high dyno cars just kill lower dyno cars all across the power band -- just produce more power not at peak but throughout. This is what happened with my old h/c setup, 400rwhp but got crushed under the power band by as much as 60rwhp by other h/c cars.

I know duration is of key importance in specing out a cam, but the duration has no affect as far as I can tell on pushing springs to the limits, this would be more of a factor of lift. So duration aside, when would lift (or other criteria) start maxxing out the valvetrain, and how would you know?

JS

iTrader: (4)

U guys might wanna take his heads off and re-flow and check runner volume then make an edjucated guess as to what cam will work with his heads.

If his heads are in fact hogged out monsters I would think a cam with small duration and more lift may help but thats a guess.

Either way he isnt doing as bad as he thinks.His power is there and its in a usable rpm,not to mention EZ has gobbs of TQ at his disposal

But I woudnt waste the time or money EZ....

I like his engine personally.
450 RWH at 6000---->Easy on the bottom end
I'd shift it at 6300 if it were in my car.
Not to mention he has TQ out the wazoo

Just for S&G's,Lets take his motor and put it in MY CAR car and I'll show u guys some 10 SEC passes outta that baby

CHRISPY

I think your motor is doing fine. I wouldnt waste anymore money on it.

Dont get caught in the dyno bullshit. you MIGHT get 5-10RWHP with an aggressive high comp head swap. MIGHT

Maybe another 8-12 with a REALLY radical cam. Is that worth all that money? I dont think so...

Chris

JS

iTrader: (4)

I agree with Chris and thats what I was trying to say in my previous post.Even with more cam and abetter head your only looking at 10 to 15RWH max.Is it really worth it,IMO NO....

I have alot of knowledge in this area EZ
Just leave it alone and have fun EZ.....

ezss

Well I hope you arent paying that much for that kinda head!

Anyhow, I know there is a balance between port velocity and peak flow numbers, Im just trying to get a grip on how one could actually measure that and know you have the right combination, other than trial and error how would it be done?

ezss

Bah, if people are making 440-450 peak power with h/c, and there are several over 500rwhp 388 ci engines, I think I should be making more power. I dont think its 8-10hp, I believe im leaving a lot more than that on the table. Of course this obsession with trying to find the perfect combination is starting to serious set me back $$$ wise. Joe's giving me a killer deal on these heads, right joe?!?! This is starting to get nuts, I really cant afford to be doing this anymore.

I also think im leaking oil badly through the valve seals or somehow related to the heads (since this problem I believe really started once the heads were on), and I dont want to rework the existing heads anymore. if I thought the oil issue could be resolved by doing the ls6 oil management, catch can, etc...upgrade which im doing anyways, then I could live with the power.

JS

iTrader: (4)

Well I hope u get the 40+ RW your looking for with a H/C change otherwise your gonna be dissapointed.

Good luck but I dont think your gonna see more than 20 MAX.

JPR

I agree with alot of things mentioned here, but to understand the WHOLE picture, when EZ originally bought his heads, they actually lost 3rwh or -0- over the stockers, I re-worked the toilet bowls for a bit more flow, because new heads were out of his budget at that time, My point is.. replaced stock heads for ported 2.08 nonsence on stock cubes and lost 3rwh or -0- gain, touched up the nonsence for about 20 more cfm peak flow without that great of low lift numbers and yeilded 450/450 on a 388 and a 232 dur cam. swaped out the 232 for a 242.. result +6 rwh -6rwt so the way I figure, a new set of heads with correct flow should gain him at the very least 20rwh and retain the 242 cam right now. It's my guess just going by the "as bolted on" power figures from stock cubes when a good set will net 40 rwh in that same situation.


JP

JS

iTrader: (4)

Its worth a shot.....
Get to work

99 Black Bird T/A

iTrader: (4)

What makes for a great set of heads?

Port work is very important...but I think the valve job will make or break even the best set of heads.

ne14a6t9

this is simple and old school- flow verses port volume. I know from buliding some of my old small blocks that port volume plays huge on how and were you get your power. i would think it is the same with the new small block ls1
blackbird I would agree about the valve job, but I also think a good or bad valve job will show in the flow