LSA Question

[Gunner1]

I’m new to mopar big blocks. Back in the day I built quite a few SBC 400s. Typical 30 over flat tops, 64cc iron world products heads. With my home port jobs they would hit from 280 to 300 depending on how extensive the customer wanted to pay for. After trying a lot of cams over the years I settled on a solid flat tapped cam from Elgin. E1090 or E1091. Low lift cam .500 high lift .557 if I remember right those are with 1.5 rockers. It was a 105 LSA on a 99 ICL. I found that it worked really well in my target of 3000 to 6500 rpm. What I’m wondering is why so many of the street cams for 440s seem to have wide spaced lobes? I’ve been retired for 15 years but I still love to do the engine stuff. |
My own 440 has a 108/104 Isky. 242@050 and 500 lift. It’s a mild street grind for a big inch street motor.

 

[lewtot184]

It's been years since I looked into Chevy stuff but if I remember correctly those small Chevy tight LSA cams were more directed for short track engines. Who'd short track a 440 mopar? Usually the tighter LSA mopar cams are longer duration stuff and i think that's done to keep from closing the intake valve too late.

 

[Gunner1]

You’re right on target. I found that an 11 to 1, tight quench .027, 3.75 stroke motor with a wide [ for a sbc 4.185 bore]calmed down the tendency to ping on CA’s 91 summer blend. Since most circle trackers at the time running 400s were single gear for the whole track the rev range worked out to 3 to6.5k. Same as my street motors. I know cam tech has improved greatly but I still am running a 10.5 to 1. 3.75 stroke 280 flow head motor that peaks before 5800 and most likely torque peaks at 3k. The bore is bigger so flame front time is different but not a huge deal at street rpm’s. My quench is .056 piston to head. Seemed to me that the tight LSA beefed up the mid range a bunch.

 

[lewtot184]

For a given lobe profile a tighter LSA should compress the power band making for a peakier torque curve. I always thought those old short track cams would be good street cams. Not sure if modern gas skews that idea up, or not.

 

[Gunner1]

Don’t know. It’s been 10 years since built one. But one is still running 287/295 adv 256/264 @050. I’m just thinking that if I build this block with a Scat lightweight stroker kit then I might have a cam ground to bump up the mid range. I think this will be my last motor and car so I might as well have fun.

 

[Geoff 2]

This is why you use the 128 rule to determine the correct LSA. It works for parallel valve heads with 9 -10.5:1 CR.

As far as 'tight LSAs' go, one person who was light years ahead of the pack was Sig Erson, decades ago, with this....

 

[Gunner1]

I agree with this. Street cars need mid range. My numbers are 3 to 6.5k. Pump gas. 3000 converter. My 440 has 270 to 280 Cfm at .500 to .600 lift. Not a lot for a big block. So a fat mid range would be fun if you could hook it up.

 

[Curiousyellow71]

Food for thought,
David Vizards 128 rule is for 10.5 compression then uses other factors to widen it. There is a lot of information there and lots of interesting stuff. But, be careful, a pump gas engine isn't going to be a winner on a dyno if its detonating.
I think we have V8 cam LSA's from 103 to 115. A wider LSA cam can run higher compression on pump gas, the intake closes later and has less dynamic compression. On most our builds if we run a wide LSA cam we typically like to run higher compression then we would with a narrow LSA cam on pump gas.
Cams are compromises... Compression is not a compromise; as compression goes up engine efficiency goes up.
If the gas octane isn't a factor you can run a narrower LSA and not worry about detonation and the cam can make more usable power in the power band.
Pretty much all cam companies will make it the owners problem to put in the necessary octane gas with the minimum compression they recommend for their cam.
Also with a wider LSA you can run more duration and have the same overlap. Stroker engines can sometimes fit the build better as a wider LSA moves the power higher, plus more duration is needed to feed the larger dispacements. More duration then feeds air and fuel to the bigger engine and more lift makes power if the heads will support it. There is also a relationship between crankshaft stoke and LSA. But, this is a relationship to the power band...not horsepower.

 

[33 IMP]

I have an old cam dynamics roller ground on a 104 sep angle that I wanted to use in a 11-1 406. Unfortunately, with 5.7 rods in it, the rods hit the cam lobes. I ended up using a reground solid roller, with a reduced base circle.
I'm betting the 104 would have made more power and torque.

 

[33 IMP]

I think my old .590 purple shaft was ground on a 106. I've got a .557 solid in it now, but I don't remember what the lobe sep angle is. 108?

 

[dvw]

As duration goes up as stated a wider lobe separation is required to keep overlap in check. But that is just a function of getting the important stuff right in the first place. The real trick is choosing the correct intake closing point, the correct exhaust opening point, and the correct duration for the application. These will determine the overlap/lca.
Doug

 

[Curiousyellow71]

I think my old .590 purple shaft was ground on a 106. I've got a .557 solid in it now, but I don't remember what the lobe sep angle is. 108?

.557 the intake is 108 exhaust 112..so LSA is the average 110. Been 20 some years since we installed one so I had to look.

 

[Gunner1]

Food for thought,
David Vizards 128 rule is for 10.5 compression then uses other factors to widen it. There is a lot of information there and lots of interesting stuff. But, be careful, a pump gas engine isn't going to be a winner on a dyno if its detonating.
I think we have V8 cam LSA's from 103 to 115. A wider LSA cam can run higher compression on pump gas, the intake closes later and has less dynamic compression. On most our builds if we run a wide LSA cam we typically like to run higher compression then we would with a narrow LSA cam on pump gas.
Cams are compromises... Compression is not a compromise; as compression goes up engine efficiency goes up.
If the gas octane isn't a factor you can run a narrower LSA and not worry about detonation and the cam can make more usable power in the power band.
Pretty much all cam companies will make it the owners problem to put in the necessary octane gas with the minimum compression they recommend for their cam.
Also with a wider LSA you can run more duration and have the same overlap. Stroker engines can sometimes fit the build better as a wider LSA moves the power higher, plus more duration is needed to feed the larger dispacements. More duration then feeds air and fuel to the bigger engine and more lift makes power if the heads will support it. There is also a relationship between crankshaft stoke and LSA. But, this is a relationship to the power band...not horsepower.

View attachment 1741780

I’ve gotta go watch his video on this.

 

[Gunner1]

So the cam I’m using as an example here has pretty aggressive ramps. Only 30 degrees of ramp so that means 15 degrees from .020 rocker clearance valve on the seat till valve hits .050. Same for closing. Tight LSA but only 84 degrees of overlap. Don’t get me wrong. I know on a motor with good head flow and induction, a wider spread would be a better choice. On a drag car same thing. I’m just spitballin an idea for a mild parts dual plane 5500 rpm, torque monster Street machine that only sees the track once in a while. I’ve gotta see who does sft 904 lobes and look at their profiles. I really want to Dyno a combo.

 

[Geoff 2]

I built a 487 Pontiac stroker engine, nearly 11:1 CR. It does NOT detonate. The 440 I built has light throttle det, also close to 11:1. Both have cams are on 106 LSA.
It is WRONG to assume tight LSA will cause detonation.
The BMC Morris Mini engines came from the factory with 107.5 LSA cams, even the mildest cam. Some were on 102.

I am always amused with those who claim that the intake closing point is THE most important valve event parameter. HP is created by air entering the cyls. No airflow when the int valve is closed!

Jon Kaase won the EMC with a 400 Ford engine that made 660 hp, wide tq curve, with a tight 98 LSA flat tappet cam.

 

[Geoff 2]

98 LSA

 

[Geoff 2]

Isky Test of 106, 108, 110 LSA cams. Notice the 106 lost 3 hp at peak rpm.....but was up nearly 24 ft/lbs in the mid range.

 

[Gunner1]

I hadn’t seen the Isky one. But John K was my customer at Scat. I was their senior engine tech. Worked with drag,nascar,road race and factories. I really learned a lot working with these teams and guys from the factories. I had lots of guys we helped on the Engine Masters challenge. John used a short rod on this 400m setup because it had a huge port and valve for the cu.in. The short rod accelerates the piston away from the head faster which make the working air mass less inclined to be lazy. He has a 2.2 intake. We have a 2.14 feeding 40 more cubes. Would he use this setup in a race car. I highly doubt it. I’ll bet Doug’s car flashes 5000 and never goes below 5k till the stripe. So they don’t need a flat torque curve down to 2500. But a setup Streeter with a 3k converter or a stick, and 3.55 gears I believe would a place to experiment. I think I’ll drag out the porting tools, start saving for the rotating assembly and look for a local Dyno to do before and afters. Till then I’m enjoying the info I’m picking up on this site.

 

[dvw]

I would suggest anyone really wanting to know about cams to read Billy Godbold's camshaft and valvetrain book. None of us here have anywhere near his knowledge.
Doug

 

[Gunner1]

Yup he’s a wizard for sure. He brought a lot of tech smarts to Comp’s lineup.