Hot Rod Forum banner
1 - 17 of 17 Posts

·
Registered
Joined
·
68 Posts
Discussion Starter · #1 ·
Ho boy here we go……….

I read all over the net about lsa.
There seems to be a consensus around the power band with tight and wider lsa.
1-Flattened and broader power band for the wider lsa and higher but narrower power band for a tight lsa.
2-More vacuum and good idle with wide lsa and less vacuum and ruff idle with narrow lsa.
3- supercharge and nitrous oxide works better with wide lsa.
4- wide lsa have less overlap and narrow have more overlap.

Now seems to be confusion around lsa in relation with compression ratios and cubic inch.

Some says that a tight lsa tricks the engines to build higher compression in the mid to high rpm range.

Some says that a wide lsa works better with big cubic inch motors and some says it is for computer cars or cars equipped with power brake and such.

Anyway, it is very confusing and would like someone to point me out in the right direction for my next solid flat tappet cam, I am looking for something in the 265/275 @ .050 and .630/.640 lift.

Is there a rule of thump to select the right lsa on engines that have somewhat large cubic inch (496ci) with 10:1 to 11:1 compression ratio and 3-speed transmission?

I do not mind the idle quality and I have a good stall converter, the car is around 3620 pounds with me also have 28 inch tires with a 3.73 gear.

Does it matter at all, if you have 2 or 3 speed transmission to select the lsa for the power band?

I know that it is very touchy subject and may vary with combination but there must be a rule of thump…

Thank you in advance.
Luc.
 

·
WV hillbilly
Joined
·
781 Posts
If you have a 3600 LB car, go with a 108, If you run Nitrous and have a heavy car run a 110, High compression? go wider, lower compression go tighter, the street ginds with 110 and wider is mainly for idle quality, the lobes arent very aggressive..


in your case, 10- 11:1, 496 , 3620, 3.73 rear gear I would run a cam around 250/255 duration @.050 <--- ( on the intake side) on a 106 N/a with a 3000 stall, and a decent intake (Victor JR) and at least 2" headers, and 3 " exhaust, it should pull hard to 6000, and make a ton of torque and Hp in the process..

I think your looking at too much cam...you dont need that much to make awsome power...

2wld4u
 

·
Registered
Joined
·
68 Posts
Discussion Starter · #6 ·
If you have two cams with same specs with the only difference having one ground on 110 and the other ground on 108 which one would have the highest cylinder pressure at mid and high rpm???? :confused:

As for the cranking compression it is obvius that the 110 would have a lil more.
 

·
Registered
Joined
·
722 Posts
You would really be confused if I explained. LSA and LC's are a by product of Valve Events, the correct phasing of the valves to get air in and air out of the engine. It's just alot more complicated.

I don't know what your goal is but I assume you are worried about dynamic compression and running pump gas. If this is the case, something in the 112 range with an intake centerline of 108 would bleed enough off to run on 93 octane.

Chris
 

·
Registered
Joined
·
68 Posts
Discussion Starter · #8 ·
My goal here is to make the most cylinder pressure possible at mid to high rpms because I have arround 10.0 compression ratio.
So I want to have the max duration with lsa that would compromise.
 

·
Registered
Joined
·
722 Posts
Iron or aluminum head. What type of gas in this old girl? What is max rpm for engine? I love compression and cylinder pressure, but let me warn you, they don't love low octane gas.

Chris
 

·
Registered
Joined
·
722 Posts
Those heads are "small" for the CID and desired rpm you want. The "correct" camshaft as is would be huge. This can be changed if you want to port the heads, but I will assume not.

So I lowered the max rpm. . .it will still pull beyond, but to make peak power at 6500 you need more head.

Based on a peak of around 5500rpm, cam would be in the 250 duration range with an 8 degree split favoring exhaust, and mid 600 range in lift. lobe sep needs to be a 108.

That would be my input.

Chris
 

·
Registered
Joined
·
68 Posts
Discussion Starter · #12 ·
Thank's Chris,:thumbup:

I will go with the 108lsa.

Now what do you mean by (8 degree split favoring exhaust)?

What do you think abouth those cam from Crane

1- Opens Closes Max Lift Duration
Intake 25 BTDC 55 ABDC 105 260 ° .628 lift
Exhaust 65 BBDC 23 ATDC 111 268 ° .648 lift

2- Opens Closes Max Lift Duration
Intake 23 BTDC 53 ABDC 105 256 ° .618 lift
Exhaust 63 BBDC 21 ATDC 111 264 ° .638 lift

Thanks for your input.
Luc
 

·
Registered
Joined
·
722 Posts
Sorry, if you have duration of 250 on intake, you will need about 258 on the exhaust based on E-brocks published flow numbers. Duration split is based partly on the flow % between exhaust and intake. Higher the percentage, the tigher the split.

Chris
 
1 - 17 of 17 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top