Let's talk LSA

[blykins]

In regard to the tunnel port and Cleveland needing more overlap to help scavenge , what is usable in this situation assuming maybe a 6500 power peak?  (106-108cl?).  A lot of “it depends” is in this, I’m sure.  Crane used to always recommend a 114 center on any that I inquired on.   And how narrow can the lobe centers get to where an engine tends to get like a two stroke dirt bike with a abrupt point to where the power hit comes on?  Do breathing limited engines , such as a factory headed small block benefit from narrow lobe centers also?

In your case, I'd try a 108 lsa, with 234 deg @ .050. Installed 106 intake but, try 108 or split over lap (straight up) too. I'd also try 104 or, 4 deg advanced, if you have the time and resources. That said, if your still close to 350 CI. If your in the 400 CI range, you might be better served with 236 @ .050

You can’t make LSA suggestions without looking at advertised durations.

[70tp]

My tunnelport is 9:1. 458”  roughly 4000 stall converter.  4:10 gear.   Single four barrel.     Has a f244 crane in it now.  I think it’s 244@.050.  Solid flat tappet.   Going by memory here.   I think about .580 lift.      I thought it was on a 114 spread.     I tried to get closer lobe center but the crane rep didn’t think it was wise.     I always thought some power was left in the table.     Motor ran ok but always seemed like it needed something

[70tp]

Crane f 248.   248@.050. .587 lift. 112 center

[blykins]

You’re leaving a ton on the table just  by using a single pattern cam alone. 

[70tp]

A “ton” of power as in 20 or like 50?      I have been seriously thinking of doing a big 460 ish engine (385 series) swap, but it starting to seem like this combo may need more attention before a full on engine swap. 

[blykins]

30-40 at least. 

Without knowing the rest of your specs, my gut says the wide lobe center with the single pattern was a big shot in the foot.

[frnkeore]

"Again, LSA is relative and overlap is application specific."

Yes, that is my point. Duration dictates most of the rpm band. What I'm looking for are trends and limits, to lsa, in the last 2,000 rpm of the HP/torque area. Dyno testing, using the same duration and varying the lsa would show what happens in that regard. Of course, it would be engine specific and depend to some extent to intake and exhaust but could show a direction to focus on.

In other words, less separation of the of the max torque and the max HP torque. Torque is what moves the car and it falls off as the max HP is reached.

HP is how fast you can generate torque.

[frnkeore]

And again, I put this in Non-FE, because I wanted more than FE specific input (or output, if you like ).

Cup engines use valves that are longer than FE valves. They even use valve seems that are as small as 6mm (.236). A scary size to me!!

To me, unless your budget is very limited AND your staying 6000 rpm, or less. There is no reason to use 3/8 valve stems. I do note that some builders on this forum, use 11/16 11/32 valve stems.

[blykins]

I use 7mm and 11/32” in most of my stuff, but even an 11/32” FE valve can be heavier than a BBC valve.  3/8” stem valves are horribly heavy and there are still a lot of guys running them.

I agree with Blair that the modern spring/retainer packages overcome a lot of issues, but IMO, a light valve with the correct cam lobe is a necessity on a lot of applications, mainly hydraulic rollers.

[70tp]

I had a Cleveland once that had power that came on like a two stroke.   That was a fun motor.  I always thought that it was the combination that made the exhaust pull on the intake system and made it run. “Came up on the pipe”. Change one thing in the combo and it was a dud.  If this tunnel port would run like that Cleveland , it would be What I hoped it would be.   Maybe time for a cam swap in the near future to see?     Thanks guys for the cam lesson today

[My427stang]

Saying any certain number is too big or too small for anything generally is dangerous in my book. Cam design did change quite a bit (an understatement) and what we did in the 70s isn't what we all do now.   Heck 10 years ago a 230 @ .050 cam wasn't making 500 hp with a pocket port in a small bore street wedge, but they can now, with non-adjustable rockers and zero maintenance.

This will sound cocky, but even on the street it isn't just idle vacuum, it isn't always just HP, it's the whole personality and performance of an engine when you aren't just banging the rev limiter for 1320.  I have built, and will build, plenty of engines with tighter LSA, but when right is right, its right.

I can't even say I think 114 is wide, the nicest little street 390 I know is at 112, but the cam is an absolutely baby compared to a healthy cam at at 114, and as you move into electronics and un-natural aspiration, we'll keep adjusting all the cam design specs to make the engine do what we want.

Heck I'd go 116 LSA on a street vehicle in an absolute heartbeat if that's what it took to get the valve events correct for the combo,  especially as we go deeper in all throttle condition EFI use and better performing heads, but again, the LSA is just a machining reference, it's all the valve events, not just the standard few we talk about that drives the overall cam design.

I'd also add that most hyd rollers are lazy in my book, that is unless you don't care if they are noisy or try to bounce valves against the seats.  Always getting better, and why lobe design matters so much, but they are where they are. 

[CaptCobrajet]

Yes, that Tunnel Port needs tight centers and 10-12 more duration on the exhaust.  The single pattern and 114 is killing you, but the 9:1 compression is REALLY killing the TP!  The same ideas that pick up the Cleveland are relative to the Tunnel Port.  Big intake tract with lots of flow, somewhat shitty exhaust.......needs a fast rocker or extremely aggressive intake lobe, opening early, then tight separation and a long exhaust......fast to open, slow to close on the exhaust to yank on the big intake port.

So put the cam that works there over in a very efficient, properly sized aluminum head with a good flowing exhaust and blow all the potential power right out the tailpipe........cam has to be right for the combo!

[My427stang]

My tunnelport is 9:1. 458”  roughly 4000 stall converter.  4:10 gear.   Single four barrel.     Has a f244 crane in it now.  I think it’s 244@.050.  Solid flat tappet.   Going by memory here.   I think about .580 lift.      I thought it was on a 114 spread.     I tried to get closer lobe center but the crane rep didn’t think it was wise.     I always thought some power was left in the table.     Motor ran ok but always seemed like it needed something

Although the cam is old school, 310/310 244/244 112 on 107, as Blair said, your main issue is compression, absolutely and positively.

I am wondering if your 9:1 is a typo, it takes a good dish to get that low, even with a big TP chamber.  That's in the ballpark of 6:1 DCR for those who use it.  I would expect that the cheapest way out for you to be a little happier would be to run a shim head gasket (if you think it could seal up) and crank that cam forward to 103/104, then run as much initial and as quick of a curve as it will bear. 

It sure wouldn't be as efficient as getting above 10:1 and getting the right lobes in there, but another option would be the same cam at 11:1, get that old school cam popping like they did in the old days   With that much duration, it'll still run on pump gas.  At 86 degrees overlap, it's not as good as the asymmetric lobes would be, but with some compression it would feel like you gained 2 cylinders

As cool as that ride sounds, either pistons and cam, or even just pistons would make all the difference in the world.

[70tp]

The motor has been together forever.   The low compression was to make it happy on a decent shot of nitrous but never hooked that up.  The pistons are flat top venolia.  Heads have been cut a mile, 72cc, I think.   Going by memory, I dont remember the pistons being down the hole.  Most of it was done by the machine shop.   I kinda think I may have the piston box with all the info on it somewhere. I’ll look for it after the Christmas holidays.  Pump gas was pretty bad around here in the late 80’s when this was done.  I drove it a lot on the street and wasn’t too concerned about nice drivability.     It’s in a 70 Mach 1.     Previous motor was a 11.7:1 medium riser and keeping that from rattling on anything but race gas got old. 

[blykins]

So it's a 4.280 x 3.980 combo? 

With a 72cc head, you'd need a 33cc dish to be at 9:1.  Running a 72cc chamber with a normal 6-8cc flat top puts you in the 11.6-11.8 range.  An 82cc chamber with an 8cc piston is 10.4. 

I love that 4.2x-4.3x bore with a 3.980" stroke combination.  I have made 600 hp with that combo and unported Tunnel Port heads.  Worked heads put me at 700 hp.