Thinking of going to smaller cam for torque & MPG
Hello, I haven't been here for quite some time.
Here is what I have:
1972 Monte Carlo
4.56 posi, TH400 with GV OD (3.56 in OD) 3000 RPM convertor
355 with forged flat tops .025" in hole with .015 steel shim head gasket, 4 valve reliefs
stock rods & crank, balanced
Edelbrock ProFlo 3500 EFI
1-5/8" headers & 2.5" dual exhaust, H-pipe
Summit aluminum heads (rebranded Brodix IK180) 2.02/1.60 64cc 180cc
flow is suppose to be 244/175 cfm @ 28" H2O
Good PAC beehive valve springs & Smith pushrods
Lunati 50156 retro roller cam & lifters 232/242* @ .050" .510/.525 lift (stock rockers),
rated to 6500 RPM + Comp full roller rockers 1.6, lift = .544/.560
SCR = 10.25, DCR @ sea level 8.66, at Denver 5280' about 7.6
I live in Colorado & drive from 5280' to 8500' altitude
It SUCKS gas!
I'm thinking of putting in about 20* smaller cam for street torque & MPG
I have my eye on Howards Cams 113215-08
217/225* @ .050" .495/.500 lift (stock rockers) 108* LSA
With my 10.25 CR, this cam would have a very high DCR of 8.95 at sea level, but about 7.9 @ 5280
Not sure about that dcr it seems high. But have absolutely no experience with that kind of altitude. But usally a dcr of 9:1 is pretty much the limit for street use and sometimes alot less will knock with pump gas. Can you run 87 now?
That cam is not crazy big does it lope really bad. Cause it seems like a gear change is in order either way i would try and change the gears and see if it is drivable or just aweful with 4.11 i bet it would still be very happy on the street and track. I bet you could squeak away with 3.73s and be ok. Either way you got to do both but the gears is where the fuel milage will come from. I would rather deal with a tall gear then tear down a strong engine.
you are losing a tonne of HP at that altitude. Maybe look into turbo normalising.. That cam can be changed out too.
The Howards cam that I'm looking at would gain low & mid-range torque and MPG.
.3 higher DCR & 12* less overlap. I plan to use my 1.6 rockers for .528/.534 lift
I will loose some HP above 5400 RPM.
The Edelbrock 3500 has only a small control panel that stays attached. It lets me control timing & mixture as cells every 1000 RPM & 3 vacuum ranges. No PC port.
Has storage for 3 data sets, I use 1 for power settings, & 1 for lean mixture.
Unit shows about 4" of vacuum with key on & motor off, due to altitude.
I have an O2 sensor in each side. Passenger is used by 3500 & it displays red/green LED real-time. Drivers side has a seperate gauge that I monitor. They generally agree with each other.
Dizzy is special for & controlled by 3500
As I have low vacuum, I put on a hydroboost brake unit rebuilt from Astro van.
I spent lots of TLC setting up the 12 bolt gears & it's dead quiet. I would hate to tear it down. Next rear tires will be taller so as to turn less RPM on highway.
In OD my gear ratio is 3.56 I usually leave it in Auto mode & it acts like a 4 speed auto.
sounds well thought out. I guess you have no choice when you live at altitude.
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