bortous

In a LS 408 stroker engine,
How would a 242/250 113 LSA +4 camshaft perform compared to a 242/257 113 LSA +3?
What are the advantages and disadvantages of each?
My guess is cam one might have better power lower down.

Spec one was specified to me by a known guru.
However I didn't really think it was suitable with a small split and the overlap too biased to the intake side.
What do you guys think?

Tuskyz28

First choice would be better naturally aspirated.

Second cam would be a badass nitrous cam.

bortous

What brought you to this conclusion?
Reasons please.

Double06

The 257 exhaust duration or 15 degree split is more for the LS7 head. Not sure what heads you have. I think also depends on what you are doing with the car. It may be a little large for a street car with a stick (the old cam surge at low rpm in traffic).

bortous

Actually the LS7 is very close in it's split requirements compared to the LS3 with the LS7 requiring a little more split. The intake to exhaust ratio is almost identical with the LS7.
Camshafts that work for the ls3 heads also work for the ls7 heads (of course with the same size engine). Most camshafts have a 12-17 degree split for these heads.
However, the vehicle it's going into is an auto with a stall converter.
No way I would use such a camshaft with a stick.

I posted that up up to see if anyone could tell me the performance differences etc. between those two camshafts.
Hopefully someone chimes in that could give a detailed explanation.

AndyTA

I'm curious myself. The former is a 20 overlap cam vs the 23 overlap cam.
I understand that overlap isn't everything - but, wouldn't higher overlap provide bigger hp numbers on an N/A setup anyway?

a) What makes the higher overlap cam better for nitrous in this situation?
b) What makes the lower overlap cam better for N/A in this situation?

bortous

They are good questions too.

Smokey B

Higher overlap is used also for Higher RPM na builds. More overlap makes better top-end hp vs less....

bortous

I know overlap does that.
Darth or Jake could answer the original question I'm this thread.
I'm not knowledgeable enough to know the specifics.

DavidBoren

I'm not an expert, by any means, but I don't think it's about the overlap. Overlap just happens to be what it is after the valve events are chosen. And it's not like the 3* difference between the two is going to be all that noticeable, anyways.

The difference between the cams you mentioned is when the exhaust valve closing event happens. This is going to change how the cylinder/chamber builds pressure, as well as the ability to evacuate the exhaust.

Tuskyz28

The exhaust duration is why i said that about the second cam. Nitrous motors LOVES lots of exhaust duration.....

bortous

So do LS3 and LS7 heads :-)

Darth_V8r

iTrader: (4)

It's a subtle distinction, but here is the difference...

If I have a motor with a cathedral head and swap nothing but heads to LS3 style heads. Like KCS said in the other thread about this, you don't need to add exhaust duration. You need to reduce intake duration,because the flow is so much higher. So you have similar or better performance with overall LESS cam. So if I started with a 232/240 cam on a cathedral, I'd likely end up at 228/240 or similar on a rectangle. Or, let's start with a cam like BTR LS3 cam at 229/244. On a cathedral head, that's going to be more like 236/244. intake changes, exhaust doesn't

Now, if I have a heads cam engine and then add nitrous, I'm adding exhaust duration, not cutting intake duration. The end result may be similar (wider split), but the underlying reasons are different. Now, take the hypothetical 228/240 above and add spray, I'm now at 228/246.

So far, this doesn't look too different, right? But you also need to look at WHERE you add the duration. On a nitrous cam, I'm going to add duration on the opening side of the exhaust (have it open earlier). On a rectangle head, I'm going to take duration away from the open side of the intake (have it open later).

So, let's get back to the hypothetical cams, but include LSA...

232/240-112+3 would become 228/240-113+2. Add more duration for nitrous per above, and it's 228/246-114.5+3.5
Or take the 232/240 cam and turn it into a nitrous cam, that's 232/246- 113.5+4.5

So you see, the splits end up similar, but the specs have subtle differences.

Hope that all made sense...

G Atsma

I get DECREASING intake duration, rather than INCREASING exhaust duration. Because exhaust ports on LS engines are generally about the same size, but rectangular ports are HUGE compared to cathedral. So you adjust to what changed. Intake port changed, decrease duration. Exhaust did not, leave it alone. I know this repeats what was said above, but just trying to clarify for myself. (Crap, starting to sound like KingTalon…)

Darth_V8r

iTrader: (4)

I like the first cam better, honestly. The second cam will need more compression or it will feel sluggish compared to the first.

Second cam has a later IVC and earlier EVO. without compression both will impact midrange RPM performance and throttle response (that gut-pounding feel when you tip in the throttle) Neither are big impact, but combined it will be noticeable.

The main advantage to the larger cam is power past peak. The two cams will likely peak within 5 HP of each other. first cam will fall off a bit faster, so the delta between the two cams will grow as you rev out past peak. For the second cam to really work, you will want about 12.3:1 compression. First cam will work better if you're in the 11.5-12 range.

bortous

I like that explanation Darth.

Can you explain in the same detail the answer to my thread question with those 2 camshaft specifications and the advantages and disadvantages of each in a 408 stroker engine of course with the ls3 heads.
I like the way you explain things.
To the point and clear.

bortous

That's what I was looking for.
I thought that too that cam 1 would fall off faster as it is very intake biased and the EVO is 3 degrees later.
Lucky my compression is at 12:8.1 so I'm well within spec for either one but looks like the larger one suits my compression better.

bortous

So Darth, what about a 244/256 112 LSA +4 cam with this combo?
This is the cam motion stroker king cam.
How would it compare to those other 2 and which one do you think would perform the best?

Tuskyz28

By you having ported LS3 heads.... you may not need that much of a split. After a good CNC job the intake/exhaust relationship should increase on the heads and the change up how the cam gets specced out.

bortous

No that doesn't make a difference.
When they are ported it pumps up both flow numbers and doesn't really change the intake to exhaust flow ratio difference.
You would only do a different cam spec if you were focused more on top end as that where the CNC gains are to take advantage of