Tight Lobe Separation angles

[torquefan]

great thread. how would valve angle affect timing events and therefore lsa? to put it crudely, with a 50 deg. angle vs. a 45, if you had greater high lift flow does that mean your overlap triangle would be affected and you would NEED to change the valve events and therefore a wider lobe separation?

[UDHarold]

It's late, already tomorrow, and I don't feel like a long post.
However, in 1980, I had 2 racers each set the NHRA SS/LA record the same day, Orban Thornton and Ralph Van PegPenHam, at different points meets.
They had consecutive serial number cams, both under 0020, and the grinds were 271/271 at .050, .640"/.640" gross valve lift with 1.5s, and a 102 LSA. The cams were in 4 to 6 degrees advanced.
I don't know what the valve timing was, because I never looked at it then.
I also made a GK cam on 102 LSA for Larry Torres of T&D, for his 1976 Winternationals win.
I also make cams for BBCs on 118 LSA, but I don't know their timing either.

UDHarold

[bmressgt]

MY Question is with a 454 oval port (peanut port ) what lsa do you think would be best to use, this is a super stock engine

[ItalianJohnny]

It's late, already tomorrow, and I don't feel like a long post.
However, in 1980, I had 2 racers each set the NHRA SS/LA record the same day, Orban Thornton and Ralph Van PegPenHam, at different points meets.
They had consecutive serial number cams, both under 0020, and the grinds were 271/271 at .050, .640"/.640" gross valve lift with 1.5s, and a 102 LSA. The cams were in 4 to 6 degrees advanced.
I don't know what the valve timing was, because I never looked at it then.
I also made a GK cam on 102 LSA for Larry Torres of T&D, for his 1976 Winternationals win.
I also make cams for BBCs on 118 LSA, but I don't know their timing either.

UDHarold

I know Ralph... from my hometown Boise ID, this must have been in his old Vega

[MadBill]

In general, due to their poor low lift flow, 'under-valved' engines (and a PP 454 would certainly qualify!) need more overlap and thus tighter LCAs to allow a good exhaust system to kick-start the intake flow. I know nothing about SS racing, so can offer no more...

[swatson454]

I'm hoping I can find AMC 258 cam cores that will let me play around with several different lobes on a 105 LSA. I'm lookin' at 24.59 ci per inch of valve diameter

[levisnteeshirt]

i'm building a 395 ci , street /strip motor , heavy emphasis on strip ,,,, 220 pro action heads, 10.8 comp , victor or holley strip dom ,3.875 stroke 5.850 rods , 4.030 forged SRP pistons -14cc dish , 1 3/4 headers , 750 dp carb , i have one Crower Cam , 256/260 solid roller on a 105 ,, another Crane 256/266 -106 ,, one old Lunati 252/260 - 108 ,,, i was wondering how the Crower would do being so tight ??

[cjperformance]

Relative is the word! So its sometimes easier to look at a specific combo/application rather than use general overviews where one combo will react differently to another given the same changes.
To simply say 104lsa WILL do this or 116las WILL do that is very difficult unless you talk specifically about one particular combo.

Look at your application, how does it perform for the particular cam you use in it, just assuming that the cam is fairly good for your usage. What width of rpm band do you use, where does the tq peak need to be, do you need or how much over peak hp rpm do you need/use, does the tq come in quick enough for the given hp or does it come in too hard? Asses the dynamics of how the engine performs for its given app then play with valve events to get it right and you will then find the lsa it wants to do this.

Change the intake manifold or exhaust system etc etc and you'll need to change valve timing/events to re-optimise the combo and bingo, you then find a new las that the combo likes.

In standard catalogue stuff where you're dealing with eg, factory basic engines the las can be counted on to react a certain way as many of the combos are pretty coles to one another, but build something custom and you need to look at valve events to make it work, then just write down the lsa for posterity.

If the cam you have in your combo does indeed work well for you, then the lsa is a byproduct of the correct valve events for your application.

The lsa is in many cases a handy way to differentiate one similar cam to another just because it is far easier to say, 250/260@.050" on 106 ccompared to 250/260@.050" on 111 than it is to reel off the entire list of valve event figures!

[pdq67]

1st, Happy new year Harold and all.

I played around with D2k a while back with a 283 just for the fun of it.

It was a 10 to 1 engine with -601 heads on it along with a 600 Holley on a 300-36 and cheap, 4-tube, Long headers.

Cam was a little bitty solid lifter jobber like this ...

250/210, 104/108, .425" net lash.

Deal about the whole sim. exercise was to make a torque engine.

Well the torque curve is basically flat off 2,000 rpm up to 4,000, then noses down at 4500 rpm I had never seen a T-curve like this what I consider off idle to some speed!

I don't know if an actual engine combination like this will do this or not, but it sure is food for thought regarding scaling the timing of the FLAT T-curve up and over say on a 454 BB Chevy engine.

pdq67

[Darracq]

I know some guys that run comp street rolles, on a 107 in there heavy big block cars and they run mid 10s with oval port heads.