Supercharged SBC

Big_G

Big_G

Active Member
Combo: 383, Vic. J.r heads and EFI intake. ProCharger D1SC with 16-18 lbs. boost with large front-mount intercooler. 8.3:1 scr, cam currently is 230/236/114* solid roller, about .540 lift. A/F ratio is about 11.2 to 11.8 at boost. Timing is 30* at boost. Manual trans. Problem...I believe this combo. can make 2 hp/ci. at the flywheel. I have seen the dip in the dyno run at about 5,500 before...is it the intake manifold? Trying to find my missing 50 or so hp. Comp cams is suggesting a 244/248/114* with .615/.609.
dyno0423.jpg
 
is the cam installed in the 4 degree advanced , ie the (DOT-TO-DOT) location, if it is you may find retarding it to 4 degrees retarded will help the power curve, noticeably, and while the 240 plus duration cam, suggested will without doubt boost power I think there's a good deal more in the current combo, so Id install the current cam 4 degrees retarded, (that's 4 degrees retarded from split overlap,or a total of 8 degrees not just 4 degrees from current)as a first step, I found that helped on my 383 with a similar 119661 crane cam, and you can use an adjustable strobe light to check the valve train for problems, and ID try to get the fuel air ratio up to about 12.4:1
 
Thanks, Grumpy. I had installed it 4* advanced per Comp. Cam's cam card using a degree wheel. I have a Cloyes hex-a-just timing gear and a 2 piece cover to make timing changes easier. How would you install the bigger cam I have coming from Comp?....here's a look at the specs...

in exh
valve adj .018 .020
gross lift .615 .609
duration @ .020 274 280

valve timing open close
intake 12 52
exhaust 62 6
specs for cam installed on 110 deg centerline
duration @ .050 244 248
lobe lift .410 .406
lobe separation 114 deg.
 
Id start installing that cam with an install at strait up not 4 degrees advanced, but before swapping cam Id retard the current cam as a test the results might surprise you. the change should move the whole torque curve about 350 rpm higher in the power curve
keep in mind many cams are built with that 4 degree advance because the cam company's know from experience that the average customers knows damn little about the details of engine function or volumetric efficiency or port flow characteristics, they found from customer feed back ,that over the years that adding a bit (4 degrees of advance) helps compensate slightly for customers that select cams with a bit too much duration, for the application, or have too low of a compression ratio for the cams effective duration,advancing the cam gives you back some low rpm torque,but it also tend to reduce high rpm power potential, Ive NEVER understood the (CHARMS) of a lopey idle, that idle is the result of low rpm port reversion and poor fuel/air distribution, and while its come to be associated with race cams its basically a P.I.T.A. for low rpm engine tuning and low rpm operation, with a supercharger producing over 15 lbs of boost you should not need to add significant duration, BTW are you running open exhaust or full mufflers?, your exhaust system back pressure from a restrictive exhaust system could easily cause the power to drop off if its restrictive to flow in the upper rpms, ID be running a MINIMUM of a 3" full length with an (X) and that would be slightly restrictive
 
Good discussion here. IMO, it's always going to end up being a compromise. This vehicle is mostly on the street. With the low scr and associated low rpm torque, I am trying to not give up too much down low in the chase for top end numbers. Dean @ Comp. cams is crediting me on the new cam, but I need to ship him the current cam. I am already spending too much $$$$ at the dyno as it is..although your ideas on retarding the cam carry great merit.
On the exhaust. It is 3 inch mandrel with an X-pipe ending with 3 in. Hooker Max-flow mufflers. No back-pressure to speak of there.
Another reason to go with a larger cam is to add lift. The Edelbrock Vic Jr. heads work great at .600+ lifts. Current cam is giving some away at the lower lift.
 
The new cam should easily allow you an extra 50-70 more hp,and move the whole torque curve up about 550-650 rpm, but before you go and get the next dyno results after installing that new cam Id suggest you install two cut outs behind the header collectors, they don,t cost a great deal, and they are not hard to install, and side bye side testing with them open then closed will tell you a good deal about the exhaust back pressures effect on your cars power curve, you won,t be the first guy that found the supposedly free flow exhaust was restricting power potential
S_4341.jpg

keep in mind that at those boost levels ,the roughly 3.2 sq inches of surface on the back of the intake valve resisting the port flow,slowing intake valve springs being closed, they have a good deal of resistance too closing, adding 600 rpm plus of inertia loads to the lifters plus the boost might get you into valve control issues, that boost effectively compensates for about 50 lbs of reduced effective intake valve spring pressure
 
I had those cut-outs before I was running the blower and made 2 back-to-back pulls and uncapping yielded only about 2 hp...almost not worth the effort. The Max-flow mufflers reportedly flow 521 cfm each, the same as a 3 inch diameter length of open pipe.
 
Ive seen it work both ways, sometimes there's little or no benefit, sometimes you make significant gains, only testing will really tell, its great that you took the effort, to test,so many guys assume they know answers without testing., its the guys that test and take a few notes , along the way,that get the experience to build the better engine combos
 
grumpyvette said:
The new cam should easily allow you an extra 50-70 more hp,and move the whole torque curve up about 550-650 rpm, but before you go and get the next dyno results after installing that new cam Id suggest you install two cut outs behind the header collectors, they don,t cost a great deal, and they are not hard to install, and side bye side testing with them open then closed will tell you a good deal about the exhaust back pressures effect on your cars power curve, you won,t be the first guy that found the supposedly free flow exhaust was restricting power potential
S_4341.jpg

keep in mind that at those boost levels ,the roughly 3.2 sq inches of surface on the back of the intake valve resisting the port flow,slowing intake valve springs being closed, they have a good deal of resistance too closing, adding 600 rpm plus of inertia loads to the lifters plus the boost might get you into valve control issues, that boost effectively compensates for about 50 lbs of reduced effective intake valve spring pressure
Click to expand...

You dead nailed it, Grumpy. My post in the Supercharger.etc. sub-group has the dyno graph showing exactly 70 rwhp gain, with wheel-spin at the top end of the power curve.. I am pleased. I can now say that I can smoke the tires from a 60mph roll, and my engine needs no more work...ha ha. Thanks.
 
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