[L79racer]

I would like to know how much overlap plays a role in boost and power. I know it does but how much? My cam has 14 degrees. 246/262 on 120. Is that killing a significant amount? Is it enough to warrant a cam change? I see BTRs stage 4 is only 5.5 overlap. I see some cams even go negative overlap.
Thanks in advance.

Vinny

I will add that I have Up graded to a Kong 2650. 3.0 upper, 9.55 lower making 15.5 to 16 psi.

 

[Rubber Duck]

I would like to know how much overlap plays a role in boost and power. I know it does but how much? My cam has 14 degrees. 246/262 on 120. Is that killing a significant amount? Is it enough to warrant a cam change? I see BTRs stage 4 is only 5.5 overlap. I see some cams even go negative overlap.
Thanks in advance.

Vinny

I will add that I have Up graded to a Kong 2650. 3.0 upper, 9.55 lower making 15.5 to 16 psi.

I am assuming the engine is still a 376 cid LSA.
But are the cylinder heads ported, or aftermarket.
What do the heads flow if ported, or aftermarket, at 0.400" of lift to 0.600" of lift?
What is your target HP?
At what engine rpm are you targeting for max / peak HP?
What is your static compression ratio?
What size is the TB on the Kong 2650?
What fuel are you using?

Cheers

 

[L79racer]

You responded to my other thread, Attention Rubber Duck. I will give you all the info here. 430 Cid, 11:1 comp. Aftermarket Genx 255 heads, flow from 400 to 700 is 294 to 381, E-85 and 102mm TB, Shifting 7200

 

[Rubber Duck]

You responded to my other thread, Attention Rubber Duck. I will give you all the info here. 430 Cid, 11:1 comp. Aftermarket Genx 255 heads, flow from 400 to 700 is 294 to 381, E-85 and 102mm TB, Shifting 7200

I remember your name.
Are you the one that leaves on a Trans Brake?

 

[L79racer]

Yes, I run the car in pro dial and also slow it down to run 10.0 index.I use the trans brake to cut better lights.
Converter flashes 5800

 

[Rubber Duck]

Yes, I run the car in pro dial and also slow it down to run 10.0 index.I use the trans brake to cut better lights.
Converter flashes 5800

Engine rpm range then is: 5800 to 7200.
Trans Brake & not Foot Brake means low end torque is not necessary.

With these engine platforms, running an LSA Engine within that
engine rpm range, means one is looking for HP, as one is well
past the peak torque engine rpm.

This then means one is not going to install a short duration
camshaft, which holds pressure in the cylinder at the lower
engine rpm's by closing the intake valve quickly, in order to
help retain cylinder pressure, which in turn helps to generate
more torque.

Instead to generate HP at higher engine rpm, one requires
a camshaft which will help generate mass flow at the higher
engine rpm even though the time interval to fill the cylinder
decreases as engine rpm is increased.

This means more duration will be required!

Also, the smaller the cylinder head, the larger the camshaft must be.

As you might recall I stated to you during our last round of
correspondence that the heads you are using are too small for an
engine of your size, which is also equipped with a blower.

Larger duration camshafts still need the ICL & ECL to be correctly placed.

The above means the LSA number will be generated by the
relationship between the ICL & ECL. At some point, as lobe duration
is increased, and the proper LSA is maintained, your overlap period
will increase.

And yes, higher overlap camshafts will reduce Volumetric
Efficiency, as a percentage of the mass charge is simply blown
out the exhaust side.

If you respond with another question, I might not be able to get back to you until tomorrow.

Cheers

 

[L79racer]

Thanks! So I went on wallace racing's calculator. Cam specs 240/240-120 has an overlap of 0* Anything over that, the overlap will increase I see. Anything under and you go negative overlap. So the bigger the motor the bigger the cam, it will require spinning the blower faster to get to the same boost level. Time to pulley down.

 

[07GTS]

keep in mind the .006 cam specs also as even tho its minimal it still plays a roll in the overlap event, my old cam had 5 deg overlap at .050 but it had 57 deg at .006 and i could adjust the injection timing to wait until after the EVC and noticed a ~13% saving in fuel showing its still affecting it with fuel otherwise going straight out the exhaust at idle and also cruise

 

[Lt1z]

Thanks! So I went on wallace racing's calculator. Cam specs 240/240-120 has an overlap of 0* Anything over that, the overlap will increase I see. Anything under and you go negative overlap. So the bigger the motor the bigger the cam, it will require spinning the blower faster to get to the same boost level. Time to pulley down.

You won't see many running a cam with no split on these type of engines. You will end up with more overlap the more aggressive the combo and the larger the engine size but it will still be what would be considered "mild" compared to an NA cam for that same size engine

 

[Rubber Duck]

Thanks! So I went on wallace racing's calculator. Cam specs 240/240-120 has an overlap of 0* Anything over that, the overlap will increase I see. Anything under and you go negative overlap. So the bigger the motor the bigger the cam, it will require spinning the blower faster to get to the same boost level. Time to pulley down.

As Matt pointed out, a cam with no splits won't work with this
engine platform as you must compensate for the insufficient exhaust ports of these heads.

A 12* to 15* split in duration is very typical for these heads.

I am not sure what you are looking for, as when your engine rpm is at
5800 rpm at launch, this cam is giving you an ~98% efficiency
regarding potential VE%.

At 7200 rpm, this cam has the potential of delivering ~125%
efficiency regarding VE%. Now take that 125% and multiply it by the density ratio of the blower and everything is good.

What is not good is those cylinder heads, which not only are far to
small for your application, but also are most likely (99% sure) not
flowing what you think they are above 0.600" lift as the depression
generated by the piston moving down is far greater than the 28"
of water depression generated by the flow bench. And if using just
28" of depression is showing issues with those heads, that serves to
tell one that depressions of 40" to 60" will only tend to increase
those problems.

So if we continued to multiply induction variables, as I did within the
paragraph above, at or around 0.600" of lift you would not be
multiplying whole numbers. Instead you would be multiplying by
decimal points, as the mass flow will not be sufficient to continue to
fill the cylinders,when the valve lift is at, or around 0.500".

----------------------------------------------------------------------

Finally; your running a 10.0 Index.
Am I wrong when I state; I think I remember you posting the car ran a 9.2?

Sorry my posts might sound like I am only focusing on the negatives,
but to move forward one must understand what is holding one back..

----------------------------------------------------------------------

Also, for anyone reading this who might have a stock bore and
stroke 376 cid engine, please do not attempt to use this camshaft.

This camshaft, regarding duration values is fine for this 4" stroke
engine operating within the rpm ranges stated above.

Cheers

 

[L79racer]

Thanks for your input. Yes I remember you telling me the heads are too small in the previous post. Ill have to work with what it gives me for now. Lets see what I can get out of it the way it is.

 

[Rubber Duck]

Thanks for your input. Yes I remember you telling me the heads are too small in the previous post. Ill have to work with what it gives me for now. Lets see what I can get out of it the way it is.

What elapsed time and mile per hour has the car run?
Did the car run a 9.2 second ET, or I am I remembering wrong?

Also, what does the car weigh with you in it?

 

[L79racer]

it has been 9.42 with the lsa blower with timing out of it to get it to leave. I just put the 2650 on it and I am working things out with it. We took ti to the track once so far. It spun bad I let off got back in it and it ran a 9.60 at 147.5mph.

it has been 9.42 with the lsa blower with timing out of it to get it to leave. I just put the 2650 on it and I am working things out with it. We took ti to the track once so far. It spun bad I let off got back in it and it ran a 9.60 at 147.5mph.

Trying to figure out how to post a video.

Engine rpm range then is: 5800 to 7200.
Trans Brake & not Foot Brake means low end torque is not necessary.

With these engine platforms, running an LSA Engine within that
engine rpm range, means one is looking for HP, as one is well
past the peak torque engine rpm.

This then means one is not going to install a short duration
camshaft, which holds pressure in the cylinder at the lower
engine rpm's by closing the intake valve quickly, in order to
help retain cylinder pressure, which in turn helps to generate
more torque.

Instead to generate HP at higher engine rpm, one requires
a camshaft which will help generate mass flow at the higher
engine rpm even though the time interval to fill the cylinder
decreases as engine rpm is increased.

This means more duration will be required!

Also, the smaller the cylinder head, the larger the camshaft must be.

As you might recall I stated to you during our last round of
correspondence that the heads you are using are too small for an
engine of your size, which is also equipped with a blower.

Larger duration camshafts still need the ICL & ECL to be correctly placed.

The above means the LSA number will be generated by the
relationship between the ICL & ECL. At some point, as lobe duration
is increased, and the proper LSA is maintained, your overlap period
will increase.

And yes, higher overlap camshafts will reduce Volumetric
Efficiency, as a percentage of the mass charge is simply blown
out the exhaust side.

If you respond with another question, I might not be able to get back to you until tomorrow.

Cheers

it has been 9.42 with the lsa blower with timing out of it to get it to leave. I just put the 2650 on it and I am working things out with it. We took ti to the track once so far. It spun bad I let off got back in it and it ran a 9.60 at 147.5mph.

 

[Rubber Duck]

it has been 9.42 with the lsa blower with timing out of it to get it to leave. I just put the 2650 on it and I am working things out with it. We took ti to the track once so far. It spun bad I let off got back in it and it ran a 9.60 at 147.5mph.



Trying to figure out how to post a video.

Thanks for the info and video..
You've got yourself a hand full there.

Controlling Rise or Squat is important for 60' times.

Look at the gap between the fender when the car is staged.
Then pause the video just as the car leaves.

The back end of the car is rising and is therefor storing energy.

Then look what happens to the back end of the car when the
energy, which has been stored in the chassis unloads, just as
the front wheels are coming down.

-----------------------------------------------------------

A question; if your running a 10.0 index class, and the car
has the power to run mid nine seconds, can you not use
a delay box to kill the bottom end power?

Cheers

 

[L79racer]

Yes, we pull timing off the line and ramp it back in to get it to leave. I also have a mechanical throttle stop to slow it down. That was one and only qualifying run for pro dial. We had all timing in off the line hoping the track could hold the power. It couldnt. It planted the tire and lifted the front end but then unloaded and spun. Going to tighten front shocks to slow rhe front end sown from topping oit to fast. Time to play with suspension.we feel if it hook and didnt spin it qould have trapped 150 mph and a very low 9.0

 

[Rubber Duck]

Yes, we pull timing off the line and ramp it back in to get it to leave. I also have a mechanical throttle stop to slow it down. That was one and only qualifying run for pro dial. We had all timing in off the line hoping the track could hold the power. It couldnt. It planted the tire and lifted the front end but then unloaded and spun. Going to tighten front shocks to slow rhe front end sown from topping oit to fast. Time to play with suspension.we feel if it hook and didnt spin it qould have trapped 150 mph and a very low 9.0

Are you still running the stock independent rear suspension
or have you converted over to a live axle?

 

[L79racer]

Solid axle with 4 link suspension.

 

[Rubber Duck]

Solid axle with 4 link suspension.

You should be able to work out the issues using the
4-Link then as well as other suspension tuning tools.

One brief comment; your engine is producing about as much peak
torque, as is a well developed 500 cid engine.

---------------------------------------------------------

-a couple of thoughts for you-
I would suggest you 'Not' attempt to build and set a 4-Link,
as one would proceed to do with an NHRA Super Stocker.

They are tire limited and need to get the front end rotated
up high and quickly in order to set the rear tires.

If your tire sticks within about 1 - 2 turns of the tire, and without
the front end rotating around, then drive the chassis into the
ground (slight rear squat) and limit the front end travel.

Your 60-ft times will improve over the Super Stocker method.

At or around a 9.0 second ET, and at or around 150 MPH.
you should see 60-ft times right about 1.20 second.

You have a nice car there.
Good Luck and Enjoy Racing it. . ..

Bruce

 

[L79racer]

Thanks Bruce for your insight. yes I have been trying to get it up on the rear tires fast thinking as you described since I run a small tire on a 7" rim. I have now like you suggested am leaning and trying to keep the front end down like a modern radial car for quicker ETs. Its a hard balance. Anymore insight is always appreciated.

Vinny

 

[Rubber Duck]

Thanks Bruce for your insight. yes I have been trying to get it up on the rear tires fast thinking as you described since I run a small tire on a 7" rim. I have now like you suggested am leaning and trying to keep the front end down like a modern radial car for quicker ETs. Its a hard balance. Anymore insight is always appreciated.

Vinny

Okay, so I am going to assume your car is 'Tire Limited', particularly
since your engine generates so much torque.

So attempting to have the car work like a modern radial car
would be a good way to approach setting up your car.

Below is a very good article I found referencing 4-Link setups.

Which one of those pictures represents the way your 4-Link
is setup now?

Tuning 4 Link Rear Suspensions for the Drag Strip

Tuning 4 link rear suspensions. Don't have any idea how to do it? Don't worry! We show you how to set it up for the strip...

www.how-to-build-hotrods.com

The link above will bring you to the entire article.

-----------------------------------------------------------------------

Below is how many of the cars I was involved with had
their 4-Links set. However, this is just one of a few
variables one must also apply to make this work.

The picture below, while not complete by any means,
tends to show the 4-Link setup so that the 'Instant Center'
is set to 'Drive' the car, as well as the tire into the ground.

It will 'Purposefully' generate some 'Squat'.

The squat needs to be dealt with via shocks and springs
so that the car will not unload the tires.

Also, how close, or how far one attaches the rear of
the bars to the axle housing adjusts the amount of
torque applied to the bars.

The length of the bars also is important.
Those two variables must work together 'Purposefully'.

-----------------------------------------------------------------------

This picture begins to show one how to drive the tire into the ground
with high torque engines. However, it won't always work with
a tire limited car.