Late Model Racecraft

We have received our LT1 castings from GM and have already flowed/torn down and started grinding on them. Overall we should have numbers very soon.

Our before numbers were as follows:

Was flowed on a 4.060 bore at 28" of water with a Untouched port and valve job.

lift Intake Exhaust
.200 134 120
.300 204 164
.400 258 193
.500 291 204
.600 285 208
.650 291 210


And now for some pictures





And now the fun part begins!

Roughed in Exhaust port

UGotBeaT

I still dont understand why GM made that exhaust port that way....anyhow im sure yall will have a very stout program!

arghx7

^ please see my thread on this topic https://ls1tech.com/forums/advanced-...on-system.html

You need to consider tumble & swirl motion on a DI head as well as flow.

UGotBeaT

I don't think I need to consider tumble swirl motion or cross tumble. All goes out the window once the valves are closed and it begins the compression stroke. Main factors will be chamber shape and piston profile shape. Im sure a flat faced or dished valve will have an effect as well. We'll see once results are out..I could be wrong

They angled that exhaust port mostly for packaging imo..its kind of in the way.... The valve layout is like a SBF now

nastychevelle

iTrader: (7)

More Port Development pictures

UGotBeaT

nice!

Late Model Racecraft

Updated flow numbers (still not finished)

Lift Intake/Exhaust
.200 137/116
.300 208/154
.400 270/197
.500 310/228
.600 331/245
.650 335/252
.700 340/257
.800 345/260


Still have quite a bit more development to do, this was first attempt.

96 Comp T/A

iTrader: (8)

Hmm, watching with great interest. As tall as that intake port looks in the pictures, I am really surprised it wasn't better out of the box at moving air, even though mixture motion was probably as big or bigger a focus than the airflow quantity.

nastychevelle

iTrader: (7)

Just because the port is high doesn't necisarrily mean that it will move more air. Alot has to be optimized to take advantage of that. There is absolutely zero short turn in these heads from the factory. Just a gradual slope to the valve. Combine that with a low velocity port and it doesn't surprise me it didn't move that much air out of the box.

The Alchemist

iTrader: (19)

Hmmm, the other texas shop's stock cylinder head flowed almost 30cfm more stock... guess not all flowbenches are created equal lol. Maybe their dyno is calibrated the same way.

snowman47

Maybe they were tested on different bores? Idk if it would make that much difference though...

ringram

Flow does not always equal power.
Efficiency is important. What coefficient of discharge were the heads before and now?

Late Model Racecraft

The " Discharge Coefficient " is the measure of how efficient a given area is in regards to volume flow verses area, divided by a theoretical maximum.
So in order for me to give you a answer i would need to know a Theoretical Maximum. What dictates this number? Is it left up to the person porting? So really this number your asking for could change depending on the person you ask. So to me, its irrelevant because it uses a variable that we cant account for, but i will calculate it for you sometime today if i get a chance.

The Alchemist

iTrader: (19)

I simply posted that as a joke since there's two threads in here with shop's in Texas who have their hands on a new LT1 head and both put up stock flow numbers. Just goes to show that even something that should be reliable like flow numbers is subject to 'user discretion'.

Wnts2Go10O

iTrader: (12)

however, both shops should see somewhat similar results in gains of flow and how high the lift will be when it runs out of steam. at least thats how i see it. the flow itself isnt as important as logging the change.

we're getting to a point where CFD will be more important in creating a head that flows well AND is efficient. GM gained 30+ hp from a head that flows less, a cam that is slightly smaller, and a new injection system. working with the system and GM's improvements is probably going to be important for drivability, avg power, etc. the first dyno tests on teh 4? shops' heads will be very interesting me thinks. so will timing, fueling, and g/cyl readings.

The_Bishop

iTrader: (10)

What is that area you've broken into?

arghx7

Typical start of injection on a DI engine in single injection mode is 280-320 degrees BTDC firing, right in the beginning of the intake stroke. The charge motion has a huge effect on the mixture distribution, hence the high swirl on the Gen V intake port. Injector pulsewidths max out between 5 and 7 degrees depending on fuel pressure, for a crank angle window of roughly 150-200 degrees.

On PFI, the fuel sprays on the back of a closed valve (closed valve injection) or on to an open valve, depending on the strategy employed at a given load point. Injector pulsewidths can max out at 15milliseconds and over 600 degrees. Charge motion isn't nearly as important on a PFI engine (relative to DI), which is why the LS7 style intake port can be very high flowing and still have good combustion.



Here we see:

• a single GDI injection starting at 292 degrees BTDC compression/68CAD

• the first injection used during split injection: starting at 254 BTDC/106CAD

• the second injection used during split injection: starting at 80 BTDC/280CAD , fired in the compression stroke to create a stratified mixture

• Ignition timing: here I am showing 20 BTDC/340CAD

• Port fuel injection: for closed-valve injection, this occurs in the exhaust stroke, here ending at 450 BTDC compression /630 CAD

Note that the injection timing is set by SOI (Start of Injection) for DI and EOI (End of Injection) for PFI. On the PFI, fuel pressure is basically fixed, while on DI it can vary (although full power runs typically go at max fuel pressure).

Also, basically every production DI engine has a piston bowl rather than a flat top.

FSAE_Junkie

The theoretical maximum is dictated by physics. You have a given 'physical' valve flow area (circumference of the valve * Lift). When you put the head on the flow bench, you are putting a specified pressure drop across the port. For that physical valve flow area, you could calculate the flow rate based on the pressure differential using isentropic compressible flow equations.

Your measured flow will obviously be less than this 'ideal' airflow. For all intents and purposes, the ratio between the two is your discharge coefficient as you mentioned.

This is actually an easy calculation with the right equations. However, finding the right equations that are physically valid is not trivial. Personally, I tend to use the pressure ratio variant of the 'flow function'. I'm too tired to do the calc at the moment, but if I remember tomorrow I'll post it up. I was always curious what the Cd was on a stock vs. a modified port.

J-Rod

Good luck with the testing, please keep us posted.

I am interested in seeing if the modifications to heads improve peak power, but have a negative effect on low to midrange power. I understand the swirl and tumble are supposed to be important.

My guess (and this is only a guess) is that if you can improve the flow without removing any of the wings or vanes that create tumble and swirl, or radically reshape the port you might increase both raw flow without destroying the port. My guess is there is going to have to be some iterative testing to see what works and what does not work.

Late Model Racecraft

There isnt really a vane or wing anything in the factory port to remove. Now people used to think (Some still do) swirl and tumble were important on regular port injection engines too. But as time went on people started grinding them (Wings/Vanes) out. Take the ls7 heads for example. They came with a wing, people ground them out, lost airflow but made more power. Now how important is swirl and tumble? I know DI is different from PI but the question still remains.