bowtienut

iTrader: (1)

Lets think about this .........Overlap helps fill the cylinders using the exhaust pulse negative pressure. You DONT want overlap allowing the falling piston to pull exhaust gas into the cylinder. You want that big stroke to create the negative pressure in the intake ports and manifold, which will respond better to a later IVC event, which means a wider LSA.

LT1STROKER

iTrader: (3)

Don't know if this is a question for me or not, but see the cam that I had for this motor when I started this build was speced by cam motion, and it was speced at 240/250 @0.050 and 269.8/280 adv and .609/.604, designed to run as solid roller with .010 lash i/e. It was cut on a 110+4. I sent my intake to Lloyd Elliot to be ported and in our discussion, he asked what I planned to do with the car seeing that I wanted monoblade porting for the mono I am running. I told him the setup, and asked him ?'s regaurding my cam I had. CamMotion said this cam would keep motor punchy in the middle where I was to using it mostly and still pull well. When talking to LE he said that there was a better choice of cam that would allow me to better benefit from my motor setup, and he proceeded to ask me to send all the specs and he sent back his recomended specs based on the parts I am using. The body of the email reads like this; this is quoted

" The current cam will make peak HP at 6100 RPM on your engine. It just doesn't have much duration and the 106 ICL will have the intake valve closing pretty early. this makes some low end TQ but will kill top end power on an engine this size. it is a good 6500-6800 RPM cam for a 355 or "maybe" a 383. It is really small for a 396/410/414, etc. The bigger stroke just wants more duration and definitely a later IVC (wider LSA with higher ICL).

Here are how the HP #'s compare at 6000, 6500 and 7000 RPM with both cams . . .

240/250 - 596-584-563 (peak at 598 HP @ 6100 RPM)
247/255 - 630-627-610 (peak at 632 HP @ 6250 RPM)

TOO MANY variables to know the EXACT RWHP or even Fly Wheel HP #'s but with all things being equal (heads, intake, TB, headers, exhaust, etc, etc) you can still expect to see the difference in HP mentioned above from a cam swap (34, 41 and 47 HP at 6000, 6500 and 7000 RPM).

A 247/255 (280/288 adv duration) .668/.668 112 LSA cam will work much better.

You will see an extra 30-35 HP from 6000-6500 RPM and over 40 HP from 6500-7000 RPM over the current cam with about 25 HP at 5500 RPM, 15 HP at 5000 RPM and around 4500 RPM. Below 4000 RPM, the Cam Motion cam will make a lil more power and be 20-25 RWTQ better in the 2500-3000 RPM range where the cam is seeing its biggest improvements over the 247/255 cam that I spec'd fpr you.

These RWHP/RWTQ comparisons are based on the lobes that you currently have and ignoring the fact that the ramp speed is VERY aggressive and will be hard on parts. If we slow the cam down to a comparable ramp speed, the Cam Motion stacks up even worse"

I called and got further info after I got the email, but now maybe you see why I was going the direction I was going with my cam, I was basing it off of the info I got from Lloyd Elliot, reguarding a 112 LSA, and later ivc point etc. I dont remember him saying things about on most motors running such short LSA having so much carbon, and sut in intakes because the intake is being filled with exhaust gasses, and it contaminating so to speak the intake charge (that is not quoted, I am just going off of memory on that stuff, because I asked him why not use a tighter LSA and that was what he told me, to some degree, and how it makes for slightly more difficult tuning, and etc...) He also told me in talking that this would keep me under the 7000 RPM shift point, and keep power from falling off after peak, ie going through traps. FWIW, his specs actually did not even give up much down low on simulator, compared to the smaller tighter Cam Motion Grind, I think at most was 22lb ft somewhere in the early 2000 area, but it did show to pull harder up top and make more power.
This is where the cam stuff is like a black box sometimes, Toby says tighter LSA Faster ICL, and so did T&L, but LE has been tried and true with LT1 cars uses a totally different method to accomplish what looks to be the same goal, with what theoretically should be a smoother running engine ie the wider LSA.
This situation is what brought this thread to life, for me. The motors I based my build on went one way, LE sent me another, and here I am in the middle.
What say you guys now!
Luckily I was able to sell my cammotions cam, the lifters together, but at one point it was looking like I should have kept it listening to all the input. Selling it did give me the opportunity to throw around running these SR lobes with HR lifters, this may be a perk of it all .

Wicked94Z

iTrader: (26)

My *thought* is that you're getting no help from the 7"ish intake runner length in "charging" the cylinder with a late IVO. More overlap will help cylinder filling letting you close the intake valve earlier, building more average hp and tq in the midrange. A wider lsa to extend the powerband a few hundred RPM isn't the answer when you're dealing with a 7k rpm limited engine, it will only hurt average power numbers.

Wicked94Z

iTrader: (26)

you need to look at the .200 numbers as well... that tells you what the lobe really looks like, and determines (along with the closing ramp) what kind of spring pressures you need to run.

LT1STROKER

iTrader: (3)

THANKS TO ALL WHO HELPED IN COMING TO SOME SORT OF CONCLUSION WITH CAMSHAFTS; I HAVE DECIDED TO GO WITH LLOYD ELLIOT AND HIS LT1 KNOWLEDE, SINCE HE DID SOME WORK FOR ME ALREADY AND HAS EXPLAINED HIS REASONING FOR HIS DECISION. WE HAVE SELECTED A 247/255 AS HE SUGGESTED, WITH MID 660's lift on both intake and exhaust, and we kept the wider LSA. I am very confident in the choice and feel good about it.
I hope to get this thing put together by the next month end.
Thanks guys

BOLO

iTrader: (40)

I definitely think you made the right choice going with Lloyd Elliott. I'm more than happy running his custom killer combo. Congrats and good luck.

bowtienut

iTrader: (1)

Good choice going with Lloyd's recommendation.
Solid roller as he originally recommended?

Wicked94Z

iTrader: (26)

you should make some killer power with that combo man, good luck