cam selection

[tayto]

Cliff we talked last Sunday on the phone about selecting a roller cam for my 350. To refresh your memory it's a 350 bored .030" over with flattop pistons. squish will be in the in the .035-.038

[Cliff Ruggles]

What are the rest of the engine specs?

Static compression ratio?

What brand?

What cylinder heads?

Type of vehicle?

Auto or stick shift?

Converter stall speed?

Rear gear ratio?

Intended use of the vehicle, etc?

[tayto]

What are the rest of the engine specs?

Static compression ratio?
I think with flattops bored .030 over, .035 squish and 64cc heads its in the 10.2-10.3 range

What brand?
SBC 350 roller block

What cylinder heads?
191 TBI heads, 64cc

Type of vehicle?
1986 GMC 1500

Auto or stick shift?
Auto

Converter stall speed?
1800

Rear gear ratio?
Has 3.08s but I will be going to 4.11s

Intended use of the vehicle, etc?
Hauling/towing, want a nice driver

My answers are in BOLD. I need cam to have a fuel pump lobe, I do not want to retrofit an electric pump. There is a cam grinder locally that can grind to my specs. but i wil have a reduced base circle and have to run longer push rods.

We talked about the 350 TPI cam, 202/207 @ .050  .404/.4 114.5 LSA. These apparently have a fuel pump lobe on them even though they were used in a fuel injection application. You had mention when we talked about something in the 210 duration and no less than 112 LSA.

[Cliff Ruggles]

Will your cam grinder to a HR grind or are you talking flat tappet?

[tayto]

Hydraulic roller

[Cliff Ruggles]

I'd have him grind one based on the 350 TPI profile with about 6-10 additional degrees of seat timing.  This will reduce octane requirements at the higher compression ratio and still idle smooth, and have pretty much the same street manners as the 202/207 TPI cam would in a 350 build around 9 to 1 or so compression.

Another option is to just use the 202/207 grind an put high ratio rockers on it.  This will add some effective duration and probably less cost than have a custom cam ground for it.......Cliff

[tayto]

I will already be running 1.6 fill roller rockers, unfortunately they are the self aligning type and I am limited to higher ratios...

[tayto]

 I found the correct TPI roller cam with fuel pump lobe on eBay for $100. The local cam grinder only chargers $175 to regrind cams, maybe less depending if there is less grinding involved. With the TBI what should I shoot for for lift? The TPI cam with 1.6 rockers is .430/.442 should I shoot closer to .500 if I get a custom grind?

[tayto]

I found a set of 1.7 Scorpion aluminium full roller rockers, would this be a better choice rather than regrinding the cam? Or maybe regrind and use both?

[Cliff Ruggles]

1.7 ratio rockers on the 202/207 TBI cam would be a home-run, IMHO......Cliff

[tayto]

Thanks for the help cliff. Will let you know how engine turns out in the next few months. get block back from getting decked and crankshaft balanced next week then can start assembly.

FYI, apparently the 90-92 "773" TPI cam is the same duration and LSA but has about .010" more net lift VS the the 87-89 "643" TPI cam that I purchased. I have a feeling the later cam does not have a fuel pump lobe but have not seen one to verify.

[tayto]

Cliff, finally got short block assembled, will be degreeing cam in the next few weeks. Do I want to install it "straight up"? due to it being a factory cam, I have no cam card. are the duration @ .050" enough for me to degree correctly?

[Cliff Ruggles]

Yes, I always install them "dot to dot" and in most cases don't have to move them, but I do use factory timing sets, not aftermarket as they tend to be more accurate....

[tayto]

I am using the "heavy duty" GM timing set that came on the roller motors.

[tayto]

Cliff, I have measured my deck to piston height on my short block. I took a measurement on the left, then right of each piston added the values and divided by 2 to get an average. It varies cylinder to cylinder from .0125" to .0165" in the hole. Probably what I get for using cheap summit brand pistons or budget Eagle rods. Originally I was going to run the .028" GM head gaskets you had suggested but this would put my quench between .0405" and .0445". After talking to you I have found some Cometic .023" headgaskets on summit that would put my quench between .0355" and  .0395". I talked to the machinist that decked my block and he thinks I am being too picky and should just run the the GM head gaskets and "call it a day". Usually when I succumb to this pressure I end up with something I am not happy about...

What do you think?

BTW, my compression is basically bang on 10:1 with the .023" headgaskets.