Thread: Cam Help Please

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DennyW, we have just about flogged this question to the dead horse level, but you are right in the sense that the area under the curve of the valve opening is probably larger since the valves ramp slightly sooner leaving the time for the flow to be slightly longer with the 1.6 rockers. I calculate that the exhaust valve lift is 0.420 x (1.6/1.5) = 0.448 and I do have eyebrow pistons and so far turning the engine manually does not reveal any binding or clicking so laziness could lead me to keep the 1.6 rockers on there as long as there is no piston-valve contact. The missing piece of information I do not have is how much was milled off the heads when the pockets were reduced from 76 cc to 73 cc. I personally titrated one head and it checked out to 73 cc. So assuming the stock head can handle 0.500 valve lift and I have eyebrow pistons and the block was not decked leaving some stock deck space above the TDC level of the piston there is apparently enough clearance now but I do not know how much. Did you give the plot above on how the valve opening occurs? It would be interesting to see how much the area changes with the higher ramp rate, although as Tech1 said, the cam lobe opening and closing points will still be the same. Some cam advertisements make a big deal about the area under the valve curve so is there any easy way to plot the two curves for comparison? The bottom line for me is that I would leave the 1.6 rockers on as long as the clearance is OK. Sorry to keep beating this topic to boredom. Thanks for your interest.

Tech1, if you have a chance what does the dynosim software say about this assuming:

0.030" overbore SBC 350
Blue Racer cam with 1.6 rockers, roller tips (see spec site above for the cam)
GM 882 heads with a three angle valve job and polished exhaust ports
Edelbrock 600 cfm carb
Edelbrock Performer RPM intake (I know this is too big for the cam but I got conned into it and it is on there now)
eyebrow flat top pistons with 73 cc pockets (about 9.2 CR), stock block deck
stock GM HEI distributor
shorty tube headers (1 5/8" tubes)
2 1/4" H pipe exhaust with turbo mufflers

Will it make 250 HP?

Don Shillady
Retired Scientist/teen rodder

Don, I think you're underestimating this little motor. I Dyno'd it with my best estimation of intake and exhaust opening and closing events because they were not published anywhere. I put them in the sim at IO19/IC57/EO62/EC20. If you have the cam card and can give me the actual timing events, I will re-sim the combination, but I think these figures are VERY realistic for a 112 LSA, 194/204 camshaft. This looks like a very nice little street motor that will idle smoothly and provide good vacuum for accessories such as power brakes. The torque peak at 3000 is indicative of the very short cam and should be a pleasure to drive on the street. Leave the 1.6 rockers right where they are. This dynosim reflects using them.

Your concern about the heads being shaved is unfounded in my opinion. As a rule of thumb, each 0.007" taken off the head surface = 1cc, so if you took 3 cc's out, that would be around 0.021". If we use the exhaust 1.6 lift of 0.448" and add 0.021" to it, that still adds up to an effective valve lift of 0.469" with the heads stock and uncut. V/P is a non-player. Run it.

I used the head flow figures shown here for the GM882 heads:
http://www.purplesagetradingpost.com...fo/heads1.html

RPM HP TQ
1000 49 256
1500 91 319
2000 139 365
2500 186 391
3000 228 400
3500 264 396
4000 294 386
4500 315 368
5000 325 338
5500 308 294
6000 264 231

This motor exhibits a nice, flat torque curve, making in excess of 350 ft/lbs from 1800 to 4800 rpm's. It makes in excess of 375 ft/lbs from 2200 to 4300. This is a very nice combination for a mild street motor. Good job Don.

By the way, you used the correct intake manifold. Using the standard Performer would have cost you 25 hp.

Wow! Thanks Tech1! The original goal for the engine was to make 300 HP somehow but I thought the cam might be too small. As for the Performer RPM intake I have to give credit to John York of York Sports Cars (mostly turnkey Cobras) for talking me into the Performer RPM but I later thought it would be too big. Yes, the whole design including our discussions of three years ago emphasized street-ability and high vacuum for the power brakes but apparently the higher flowing intake allows higher HP within the range of the stock HEI distributor. A torque peak at 3000 RPM should be plenty with the 700R4 OD. My workaday Pontiac Sunfire has esentially the same gearing and even on the InterStates it seldom runs over 3000 RPM in OD and I have to push it to get to 4500 rpm in the first two gears, so the SBC 350 should have enough torque to push the Model A aerodynamic brick on the Interstates between 2500-3000 RPM. As I recall you also recommended the 700 R4! Actually DennyW has also sent me analysis indicating that I should keep the 1.6 rockers on and as long as the lifters don't pump up too much I should have adequate clearance. I should mention that I just have stock SBC lifters.
Here are the numbers from the cam card that came with what was for a long time a "mystery cam" until I finally found it on the Blue Racer site:

Cam Timing @ 0.005" lift Advertised Duration
IO/22 BTDC IC/58 ABDC 260
XO/71 BBDC XC/19 ATDC 270

Cam Timing @ 0.050" Max Lift Duration
IO/10- BTDC IC/24 ABDC 107 ATBC 194
XO/39 BBDC XC/15- ATDC 117 BTDC 204

I am not sure what numbers you need for the simlation so I am giving both the 0.005" and the 0.050" numbers. I am not sure about the "-" on the IO and XC numbers as to whether that is actually a negative degree number?

Do these numbers change the simulation much? I note for discussion that both DennyW and Tech1 reached the same conclustion to leave the 1.6 rockers on there and that is easy to do since they are already on there!

Thanks Again!

Don Shillady
Retired Scientist/teen rodder

Yep, those are negative figures @ 0.050" lift. Normally, the intake valve opens before top dead center and the exhaust valve closes after top dead center. But when you measure a short cam @ 0.050", the intake opens after top dead center and the exhaust closes before top dead center, resulting in a negative overlap condition @ 0.050". In this case, overlap @ 0.050" is -25.

Re-running the cam with different open/close figures changes the results a little.

RPM HP TQ
1000 49 259
1500 93 327
2000 134 352
2500 172 361
3000 224 392
3500 271 406
4000 307 403
4500 336 392
5000 340 370
5500 332 317
6000 290 254

Denny's simulation favors torque while mine favors hp. If you average the two, you get 325/420 and I think that's how I would talk about the motor to anyone who asks. Agree with Denny about the Quadrajet. Finest carburetor ever built. The guys who call 'em names like Quadrajunk are the guys who never took the time to understand 'em and dial 'em in. Best mileage and best power all in one package.

Tech1 and DennyW, Thanks a WHOLE LOT! I never dreamed my setup would exceed 300 HP or 400 ft. lb. of torque and even if the simulations are a bit high it seems to be in range. I appreciate that Performer-RPM a lot more now! Hey, I have a Quadrajet on the shelf in my garage with about 100K miles on it but the rebuild is really expensive. Maybe I will get it rebuilt when I can afford it. I bought the repair kit for the Quadrajet but I will have to be in an optimistic mood to do that overhaul myself. If both of you are so high on the Q-jet I will take another look at the overhaul procedure. I do like the small primaries and the secondaries are enormous! In fact the secondaries are so large that I wonder if the Performer-RPM holes need to be carved out a little bit? I like DennyW's graph but I surely hope my HEI distributor signs off before the valves float with Z28 springs; in fact I am hoping the distributor will be my governor! The crossover at 5252 is plenty for me so I do not see any purpose to extend the graph beyond 5500 rpm! What amazing results predicted for a mild 350! Now all I have to do is get the wiring on there and hopefully start it up this Spring? This is great news for me!

Don Shillady
Retired Scientist/teen rodder

DennyW, I wonder if you could send me an e-mail with the numbers from that simulated dyno graph?

Don Shillady
Retired Scientist/teen rodder

Thanks DennW,

Sadly, I am seemingly unable to recieve messages via the Forum due to my popup blocker. I have lost other messages as well as yours. If you have a chance can you put the numbers here and I can copy them to a separate file. I lost a reply from Tech1 due to the same problem.

I am very surprised at the HP these simulations predict. Your simulation seems to favor torque which is what I would expect with the small cam but I am surprised the Performer RPM intake works at higher rpm when the cam duration is so short so I would like to see the torque numbers from your simlation.

Don Shillady
Retired Scientist/teen rodder

Tech1,
I was unable to extract numbers from Denny's graphs, although you have given good estimates. While it is the lazy thing to just leave the 1.6 rockers on the engine, I wonder if you have saved my input file and can run it again with just the 1.5 roller-tip rockers? I down loaded the Comp Cam simulator but it only treats Comp cams, of course. My present Blue Racer cam looks similar to the smallest Comp 250H cam but the dyno chart for that cam is for an engine with better heads.

http://www.compcams.com/Technical/DynoSheets/

Sorry to bother you, maybe I will eventually buy DynoSim. You know when we see the news and the push for electric cars the folks on this Forum are hiding their heads in the sand. While it is still enticing to build up a powerful engine for a vehicle that may only be used occasionally, it only seems reasonable to ask what the mpg will be relative to some future rise in gas prices or even some government policy that disfavors hydrocarbon fuels. It could well be that unrealistic energy mechanisms will not be practical in my lifetime so why not build up a gas-ICE setup for the forseeable ten years??? On the other hand I wonder if my engine with the cam that is in there now can still make 300 HP with just the 1.5 roller-tip rockers and make a little better mpg? I was surprised that the Performer RPM intake makes such a difference in the top end HP so I wonder if I can still make the target 300 HP without the 1.6 rockers?

Don Shillady
Retired SCientist/teen rodder

Don Shillady

I can Run your set up on Comp Cams Dyno P.C That I have . I am Sure you have the Spec's in the 5 Pages you Posted . But if you can Re-Post what Engine ci heads and Pistons and Camshaft Specs / Intake/Carb . I can give you the #s 300 H.P on a L/C 350 is not to much to ask . If you want to Run them 1.6" Rockers you need to enlarge the Pushrod Holes even with a Low Lift Camshaft . Also the 1.6 Rockers will wear Valve Train Parts Quicker .

Tango, Thanks! I am of course a real worry wart and your points are well taken. Here is the data I gave to Tech1 (again) and I will add the specs from the cam card in edit mode so all the information is here in compact form. How are you able to use the Comp Cam simulator with a non-Comp cam? I looked at the input and it requires the curve for the port flow which is also available for my GM 882 heads. In edit mode I will go back and get the flow data. It is somewhat of a chore to input all this data but If you can tell me how to use the Comp cam simulator for a non-Comp cam I could do it myself but if you can do it for "fun" go ahead by all means! I have wondered about the pushrod holes but most folks just slough over that. Basically I just have resurfaced heads with 73 cc pockets (I cc-ed them), a three angle valve job and and polished exhaust ports. Basically I am just trying to get what I can with what is little more than a "blueprinted" rebuilt SBC 350 with an Edelbrock Performer RPM intake and 1 5/8" shorty tube headers. The Blue Racer cam looks like it is slightly "hotter" than the stock cam. This particular engine was originally the low HP SBC 350 from a 1976 Corvette, one of the most detuned engines ever offered in Corvettes but my goal was to end up with a torque motor to run the OD in my 700R4 but according to Tech1's simulation the Performer RPM intake seems to add some top end so maybe with the 1.5 rockers I can get some better mpg and still make 300 HP somewhere around 5000-5500 rpm? As far as I know the HEI distributor will sign off around 5500 rpm anyway. Thanks for you interest in my worry wart question!

0.030" overbore SBC 350
Blue Racer cam with 1.6 rockers, roller tips (see spec site above for the cam)
GM 882 heads with a three angle valve job and polished exhaust ports
Edelbrock 600 cfm carb
Edelbrock Performer RPM intake (I know this is too big for the cam but I got conned into it and it is on there now)
eyebrow flat top pistons with 73 cc pockets (about 9.2 CR), stock block deck
stock GM HEI distributor
shorty tube headers (1 5/8" tubes)
2 1/4" H pipe exhaust with turbo mufflers

The flow numbers for the GM 882 heads are given here:
http://www.purplesagetradingpost.com...fo/heads1.html

Specifically the numbers for the GM 882 heads from that site are:
Lift Intake/Exhaust
0.100 70 / 58
0.200 125 / 108
0.300 175 / 135
0.400 204 / 141
0.500 205 / 142
0.600 205 / 142

I think you need those numbers for the simulation.

Blue Racer cam
Cam Timing @ 0.005" lift Advertised Duration
IO/22 BTDC IC/58 ABDC 260
XO/71 BBDC XC/19 ATDC 270

Cam Timing @ 0.050" Max Lift Duration
IO/10- BTDC IC/24 ABDC 107 ATBC 194
XO/39 BBDC XC/15- ATDC 117 BTDC 204

I am not sure what numbers you need for the simlation so I am giving both the 0.005" and the 0.050" numbers. I am not sure about the "-" on the IO and XC numbers as to whether that is actually a negative degree number? In a past communication Tech1 confirmed the minus signs.


Don Shillady
Retired SCientist/teen rodder

On that Comp P.C Link they have many Camshaft as you said the one Look a Lot Like Yours . There DE Cams are a Match to some of the Blue Race Grind's . Now on your 882 Heads did you remove the EPA intake port corners ? Or just Clean up the Exhaust Ports . Any Valve Pock Porting done ? With your Camshaft Card and this Cylinder Head info I can check your Build .

What # is that Blue Racer Camshaft ? Ok here is your Crane Blue Racer Part# 975213 no Longer made . At .050 it's Dur is 194in / 204" ex and its Lift is 398"in / 420"ex with a 112 L/S . As you said just a slight step above the GM 390" / 410" Stock Grind . First you do not have to worry about valve Clearance with that Grind even with 1.6" Rockers . It's a Very Mild Camshaft but will make real good Power down Low . I will see what H.P#s I can come up with . That RPM intake is more then what is needed for this Build .

Here is what I came up with . 298.8 H.P at 4200 RPM's and 413.1 Ftlbs at 3000 RPM's . If your Looking for max H.P . That Camshaft is on the Small Side . Yes the 1.60 Rockers would Help this Build make more Power . But all and all it's not a Bad Street car Engine . Dial in that 600 Holley and HEI and you will Like it .

Thanks Tango! While the heads were polished on the exhaust side the intake ports were left untouched. The old Blue Racer numbers are CD194-11C 975213 and it is the lowest performance cam on the list at:

http://www.cranecams.com.au/pdfs/blu...et_14-5-07.pdf

This goes back to discussions I had with Tech1 on cam selection for low rpm torque and maybe mpg also. Can you tell me more about how you used the Comp Cam simulator? Also can you provide a list of rpm, torque and HP in say 500 rpm increments? Thanks again. Does this mean that I can eventually use the Comp Cam simulator for other cams as well?

Don Shillady
Retired Scientist/teen rodder

You need to work with that Comp Cam P.C Dyno . There are many Options that can be made when checking your Builds H.P and Torque #s . Some of there Camshafts Like the DE Cams are the same Grind as other Brands . Then you have other Grinds that are a Near Match to Different Brands . As for Power #s they show Max H.P and Torque #s only . What is Nice about there Dyno . They Show what They think is the #1 Camshaft Pick for your set Build . For me I buy mostly ELGIN Brand Camshafts because of the Great Price they are sold For .