AT,I'll pdf your engine build info to you monday,, will be a better copy

Is good to have the cam decision done,, now working through the process of optimizing the cam timing.

I know IVC is considered the most important cam-valve attribute, with IVO running second.

found a neat article that speaks to the relationship of piston speed and cylinder fill,,, would be good to have those intake valves really open when the cylinder is ready to really pull.
the article walks one around and through the methodology to figure out when in the crank cycle that is, at the end of the article there is a chart showing the V max for the slants 1.62 rod ratio..

http://www.epi-eng.com/piston_engine_te ... basics.htm

DT - incredible thread. What are you an engineer or something?

_________________
66 Lil' Red Piggie Valiant (Mater Crusher) - Thanks Zilla!!!!! 72 Demon (Number 1 Son's)

A.K.A.

BILL, (wjajr)

I noticed that you were asking about LSA (lobe separation angle) optimum of 106.5 deg, and you "have yours in at 99 deg".

LSA is the angle between the intake and exhaust lobe centerlines, BUT the centerline that you use to degree the cam is the relation between the intake peak (centerline) angle and the crankshaft - a totally different and independent number.

99 deg intake centerline is correct for your cam and most performance 225 cams.

Lou

_________________
Home of Slant6-powered fun machines since 1988

I've actually had fair success in short cam "torquer builds" by leaving the valves the stock size and cleaning up the ports, with little bowl work...this allows a higher velocity through the narrow port which seems to be better matched for the BBD/Super Six/Holley 2300 setups.

-D.Idiot

This is my idea for my next street motor/low RPM build.

Aside from things like - no kickdown, a throttle cable that loves to break, and the Holley not staying in tune, I am really happy with my unit!! LOL

I know with a little bit of tuning and a few new parts, I should be able to get under 17 easily with this brick.

I was shooting for 15's in the 1/4 and with my build I should be able to do that with out a lot of problems.

_________________
"I may be slow, but at least I'm not very fast!"
'69 A108 - 225, 727, 3.55, MSD6AL, a.k.a.-the brick

DT,
Excellent thread you are carrying the torch on here. This is right up my alley as I, like Josh, plan to do EFI with knock sensor and need a good hydraulic street grind. I have a 225 '69 Dart with an 833od and (anticipated) 3.55 rear. What, if much of anything, happens in the sim as you bump up LSA towards 108 or 109 on the 1527 profile? Thanks!

Nate

Nate
used my existing engine set up and ran two additional iterations

the cam 14 is the Oregon 1527 with 106 LSA, 102 intake and 106 exhaust centerlines
the cam 14a is the 1527 with 110 LSA, 102 intake and 118 exhaust centerlines
the cam 14B is the 1527 with 110 LSA and 110 intake and 110 exhaust centerlines

moving from a 106 LSA to the 110 did reduce the overlap from 43 to 35,
so perhaps a bit more duration could work for you with the wider LSA

for torque, 14 and 14a are really close and 14b lags a bit,up to 3000 rpm, them 14a really drops and 14b takes off, with 14 in between
for hp they are all really close to about 3500 rpm, then 14b has a bit more and 14a drops with 14 in between

http://www.flickr.com/photos/13718356@N02/5409129634/

http://www.flickr.com/photos/13718356@N02/5409124374/

here are the valve events
14a
IVO 23
IVC 47
EVO 68
EVC 12

14b
IVO 15
IVC 55
EVO 60
EVC 20

DT,
Yeah I think it could take some more duration. I suppose less overlap would mean a quieter valve train to use with a knock sensor, yes? (Maybe I need to spec out the GM 3.8L cams from mid-80s to see what they used as that's where my batch fire setup comes from, but it's a different engine altogether) I was wondering about that 105/106 LSA as it seemed to lean towards a more racy cam, but is that what the slant needs: more overlap to allow exhaust scavenging the intake charge because we are working with small bores? Going back a bit on the sims, is that 1527 grind advanced 4 degrees (#14) basically a Comp Cams xe250h grind installed straight up? Thanks

Just to be clear, overlap won't affect valve train noise. Valve train noise is about clearances and acceleration.

As you mention a 225 needs a narrow lobe centerline (106-107° with a stock intake valve) because of the relatively poor intake flow to cylinder volume. A 170 on the other hand wants a 112° lobe centerline.

The proper way to spec a cam is to first determine the overlap. Then find the optimum lobe centerline. With those numbers you'll derive your duration. Then, since we know the slant has relatively more exhaust flow than intake flow we can shorten the exhaust duration a few degrees and increase the intake duration the same amount to keep the overlap the same.

For example, the 170 I'm building has a cam with 282/275° advertised duration, 248/243° @ .050" lifter rise and is ground on 112° lobe separation. This is 54.5° overlap at advertised duration and 21.5° at .050" lift. If the simulation is accurate power peak is 7500 RPM and only 4hp down at 8500 RPM. I have over 200 ft/lbs at 3500 RPM peaking at over 250 ft lbs at 5800 and still just over 200 ft/lbs at 8500.

_________________
Joshua

Well I guess I mean a noisier engine in general. Not due to valve train but the overlap because isn't it the low pressure reflected wave scavenging the intake that can find its way up the intake tract and then reflect again at the intake manifold plenum into a high pressure wave which is essentially sound? Although that's more a highly tuned motor with tuned headers I'm hypothesizing so... I just don't want to introduce noise due to cam design as I try to eliminate it with hydraulic lifters and the computer starts pulling timing out anyhow.

8500 RPM? Goodnight! What are you building, Josh? A slant version of those INDY 500 Navarro-built AMC turbo sixes from the late '60s?...Regardless sounds like fun and I can't wait to hear it!

Nate

The 170 is to push my '66 Barracuda for a record attempt at Bonneville. I'll probably keep it to 8000 RPM, but you never know what might happen on the last run if I've already set a F/CPRO record I can be proud of.

_________________
Joshua

About the 'no kickdown' Check out the new cable kickdown from http://www.bouchillonperformance.com

For the throttle cable and pedal check out http://www.lokar.com you'll want to talk with them about a extra long cable.

Oh and get a different carb

spoke with Oregon cam again today, wanted to confirm how much the LSA could be adjusted on a regrind,, answer was some,, but less is better,
the more the LSA is moved the more needs to be ground off the cam,, per the person on the phone, the hardened area on cast cams can run as much as 1/4 inch deep,,but not as much on others,,

I am wanting to go with a narrow LSA anyway and the stock cam is a 105 so I worked up an analysis of retaining the 105 and moving around the cam advance,, cams 14D, 14C and 14G move the installed advance,, see cams 14F, 14E and 14G for the same moves with the profiles reversed

good news is any choice will get me about a 10% increase in torque and HP in my target zone of 1500 to 3000 rpm,, and if the rpm's are run up to 4000,, will be at least a 70% gain.
Note: In the analysis I was seeing more HP and torque than I really need for this vehicle, moved the carb down from a 350 cfm to a 230,, mileage will be important.

here is the cam analysis
http://www.flickr.com/photos/13718356@N02/5414518870/

and here is the HP and torque spread sheet
http://www.flickr.com/photos/13718356@N02/5414925774/

with the settings I am using,, reduced carb CFM,,low RPM the advantage of a RDP cam is not apparent, it may be a high RPM
and much large CFM and duration is needed to pull that factor in to play,
or the selections are all so close, they are operating within the resolution of the program