: 427 bbc advance or retard cam timing?
Apr 6th, 10, 06:11 PM
Looking for some experienced info here. 69' Camaro (approx 3200 lbs.) street car,/shows and it has a 427 bbc.the engine has great low end response but seems limited to top rpm range.I'm looking to balance the engines over all abilities for the road.I wondered if I retard the cam timing 4*,would this give me better over all performance.The engine is in the car and I have not degreed the cam.It currently is installed straight up.It only likes to idle @ 1000 rpms.Timing is 22*initial,all in @ 3000rpms @ 38*(Mech)
The set-up I have is:
69 427-.30 over
heads 3919840 (rec port closed chamber 107cc)
Comp Cams #11-450-8 Hyd.roller (290 grind)
lca 110,ic 106
duration@.50 lift 232--232
valve lift .578--.578 lobe lift .34--.34
TRW forged pistons (machine shop says combo is 10.5-1)
Tremec 5 speed
Cloyes "True"double roller chain
Msd 8360 (w/ advance can),6al box
Apr 6th, 10, 06:39 PM
Base on the specs you provided, that cam is already ground 4 deg advanced. 110 lsa - 106icl is ground with 4 deg advance.
Retarding the cam will increase top end, but a very limited amount... maybe 200rpm tops.
Personally if you want more top end, pick another cam.
That is a rather small cam if you want top end.
The 110 lsa also tends to bring down the power band more into the mid range.
What are you trying to spin it to?
Right now you have heads that do not work well until 4000rpm & a cam that quits by 6000.
Apr 6th, 10, 06:50 PM
My biggest concern is piston to valve clearence.(Don't want to start ripping pieces apart),but hoping to move the power band more to top end.
Also by advancing the cam timing,will my ignition timing change and need reajusted? :confused:
Apr 6th, 10, 11:57 PM
As Stated over at Team Chevelle that cam will not rev beyond 6200rpm. Although a Roller Cam the lift is rather low and the lifters rather heavy requiring spring pressures that will not get you beyond.
You have to Degree the Cam 1st to know where it is installed. Retarding the cam can move the torque into the upper RPM Scale for the Cam but you also loose DCR. At that present 7.9:1 DCR straight up, loosing any more will not benefit the Top end. You are slightly over Camed and suggest change out the cam for something like the XM278H-12 with 925 Springs which would put you at an 8.2:1 DCR. With the lighter Hydraulic FT Lifters you can pull to approx 6400 with hydraulic lifters and your Tremec will love that 112 LSA. The alternative, which the 427 thrives on and providing the Crank is Forged, is Solid Lifters, SFT or SR. 6800 rpm with a cheap SFT solution or 7000+ rpm with a very expensive SR System. If your Crank is Cast and the Static Compression is indeed 10.5:1, I highly recommend that XM278H-12 with a manual Tranny Ride but seems to me you would be happy with a SFT CAM like the XS282S, even if the Crank where Cast, in that engine ;o)
In my opinion, HR may be good for BIG Displacement 500ci BBC's but SFT and SR are best for Hi-Winding Small Displacement BBC's like the 396,427 and 454 with Forged Cranks.
Compare the following cams:
290HR-10 2500-6200, Adv 290/290, 232/232 @ .050", .578/.578 Lift, 110 LSA
XM288H-12 2500-6500, Adv 288/304, 244/254 @ .050", .570/.575 Lift, 112 LSA
XM278H-12 2000-6200, Adv 278/292, 234/244 @ .050", .564/.566 Lift, 112 LSA
NOTE: The Advertized Duration of the 290HR-10 on the intake is some 12 degrees longer then the XM278H-12, considering the LSA angles the Intake opens approx 5 Degrees sooner then for the XM278H-12 but the Duration @.050" of the XM278H-12 is 2 Degrees longer then the 290HR-10. You will have over 2 more points in the DCR with a longer duration @ .050" plus considerably more exhaust scavenging and lift really isn't that much less. The 925 Springs work great with this cam. You are unnecessarily sacrificing Dynamic Compression and adding weight to the Valve Train with heavy HR Lifters that can't spin as high as the lighter HFT lifter.
I've run the XM278H-12 in a 10.25:1 454\Muncie21\3.31 and believe me it's a bear of a torquer that pulls strong to 6200+rpm. I can't see why it would not work in a 10.5:1 427 with a Cast Crank.
With a Forged Crank reaching for 7000rpm consider the following Cams:
SFT: XS282S 2400-6800, Adv 282/290, 244/252 @ .050", .590/.598 Lift, 110° LSA
XE282S Same thing or Lunati equivalent Profile.
SR: 502A1LUN 2000-6500, Adv 278/290, 244/255 @ .050", .630/.630 Lift, 112 LSA
I will be replacing my 288AR-10 in a 10.25:1 460ci with this one shortly.
Every one of these cams have shorter Advertised Intake Duration which boost the DCR and have longer Durations at .050" then that 290HR-10. I've put this argument forward before in explanation why I believe an HR is not a suitable Performance choice for a Small Displacement Hi-Winding 10 to 11:1 Static Compression 396 to 454 MKIV Street Engine.
Apr 7th, 10, 01:56 PM
PS: Should have given my agreement with Lonnie on this one when he said:
Personally if you want more top end, pick another cam.
Hey! Cam Shuffling is Fair Game ;o)
Apr 8th, 10, 07:52 PM
Lots of good cam info above.....
Yes the DCR with a big cam & low compression is not great, but it will still run decent. I would take this over a mismatched setup.
I believe even the low compression LS6 had a cam somewhere around 242 degrees.
You either need to make a good running mid range HP motor, by changing the heads to match your cam & bottom end, or build it for top end HP.
Unfortunately I cannot vouch for your bottom end & how it will live, but a 2 bolt cast crank motor should hold up at 6500 if in good condition.
Personally I do not like hyraulic rollers in rectangle port or big valve oval port big blocks due to spring pressure/valve float concerns.
I have a 427 in my 4x4 truck with a 224/230 hydraulic flat tappet cam & it runs 13's with 3.73 gears & 35" tall mud tires weighing 5300lb. It is 9:1 comp & oval port heads & is done about 5900rpm.
Conversely, my little 396 in my Camaro with 11:1 & 256/260 solid roller went 10's with 4.10's & 4 speed.
Also take into account drivability. Your car may not run as good as you want, but I'm sure it is a pleasant cruiser as is. My Camaro is miserabe to drive under 3000rpm, but is still pulling like a rocket at 7200rpm.