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Old 11-15-2013, 01:13 AM
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cam choice for mild sbc

Hi guys, so I have a 68 camaro and im slowly changing out all the wrong parts installed on the car/motor, im stuck on camshaft choice and have been reading for hours and hours, and cant seem to be able to decide.

the setup is...
4bolt 350 ( block originally from a 70s c30 i think)
flat top pistons with large valve reliefs
76cc 3998993 heads
1.5 ratio roller rockers
600cfm holley vac secondary carb
msd 6AL
crane fireball coil
hooker headers
flowmaster H exhaust think its 2.5"
weiand speed warrior intake manifold (used to be called stealth i think?)
turbo 350
2.73 diff ratio
stock stall converter

ive sorta rougly figured out the compression ratio and I think its around 8.7:1, a bit difficult without measuring deck height and relief cc's, headgasket etc

the cam im thinking of running is the summit k1103 (.443/.465 lift, 214/224 @ .050, 112 LSA) , but ive also been considering the 268H (.458/.458 lift, 218/218 @ .050, 110 LSA)

but im worried that with the small diff ratio, and stock stall, it might not be suitable and maybe I should just go with an "RV" cam, like the k1102

car is sort of a daily driver, but I work from home so it only goes to the shops or out for social events, doesnt ever see the strip.

MPG is fairly important to me but I have a racing background so I'm really quite disappointed at how much of a slug this motor is.. i'm willing to change the diff ratio, but would prefer not to until I put a 12bolt in, on a bit of a budget... so might not be for a while

so please fellow hotrodders, advise me in your infinite wisdom what cam you would choose?

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Old 11-15-2013, 04:13 AM
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Without getting into a debate about flat tappet cams vs roller cams out of the 3 you listed I would suspect the best fit would be the K1102.
With likely very low compression, a relatively heavy under geared, stock converter car its going to offer you good all around performence for a daily driver.
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Old 11-15-2013, 05:21 AM
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1. You don't need a 12 bolt. Just upgrade the OEM 10 bolt. Ditch the stock (OEM , Dana type) diff and get a Eatons posi or the Auburn posi for the 1968 10 bolt rear end . Get some quality 3.73's or 4.10's for it.
The OEM 10 bolt is plenty strong once the diff is replaced with a Eatons or the Auburn.
And the install/gear set up is done correctly.

Both-all the cams you are looking at work very well with good high perf heads and 10:1cr. Get a 750cfm carb.
Get a real deal 10" 3000+ stall converter.

1970 was a long time ago and the 350 has probabily already been rebuilt and may have the wrong crappy 1.54" CH pistons in it.
You will have the measure the deck height to get it right.
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Old 11-15-2013, 06:46 AM
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A 1968 Camaro deserves a decent engine. Sell me the car,,,,
consider a head change if the heads are not unleaded fuel ready.If you want this car as a daily driver and you want good fuel economy,then build a blue printed 300 hp 350 and use a couple bolt on performance/economy parts,it will go well.
If the diff is original,it probably has 3.08 gears
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Old 11-15-2013, 11:41 AM
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Pass on the Auburn unit. They are throw away units!
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Old 11-15-2013, 12:08 PM
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The 76cc smog heads in stock form have a poor exhaust flow compared to the intake flow, so a split pattern cam seems to work best most of the time. The 2 split pattern cams you're considering, the K1102 and the K1103, according to the listed specs, both have pretty "lazy" ramps with a lot of advertised duration compared to the @ .050" duration. They both show advertised durations 74* larger than their .050 durations. Slightly bigger on the .050 specs than the Summit K1103, Howards cam #112571-12 (.455/.465, 269*/279*, 215*/225*/, 112* LSA 108* ICL) only has 54* degrees more advertised duration than .050 duration, it's a more modern, shorter ramped cam without getting into the very short aggressive ramps like the Comp Extreme Energy and Lunati VooDoo grinds. Even tho it's a slightly "bigger" cam than the K1103, by the advertised specs it closes the intake valve 4.5* sooner than the smaller K1102 for a better dynamic compression ratio for better "low end", theoretically it's better than the K1102 on the bottom, but still better than the K1103 on the top! It costs a little more than the Summit branded cams, but if that price difference doesn't deter you that's the one I would be seriously considering puttin' in there. $165.97 at Summit Racing
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Old 11-15-2013, 12:17 PM
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Quote:
Originally Posted by BigEd36 View Post
The 76cc smog heads in stock form have a poor exhaust flow compared to the intake flow, so a split pattern cam seems to work best most of the time. The 2 split pattern cams you're considering, the K1102 and the K1103, according to the listed specs, both have pretty "lazy" ramps with a lot of advertised duration compared to the @ .050" duration. They both show advertised durations 74* larger than their .050 durations. Slightly bigger on the .050 specs than the Summit K1103, Howards cam #112571-12 (.455/.465, 269*/279*, 215*/225*/, 112* LSA 108* ICL) only has 54* degrees more advertised duration than .050 duration, it's a more modern, shorter ramped cam without getting into the very short aggressive ramps like the Comp Extreme Energy and Lunati VooDoo grinds. Even tho it's a slightly "bigger" cam than the K1103, by the advertised specs it closes the intake valve 4.5* sooner than the smaller K1102 for a better dynamic compression ratio for better "low end", theoretically it's better than the K1102 on the bottom, but still better than the K1103 on the top! It costs a little more than the Summit branded cams, but if that price difference doesn't deter you that's the one I would be seriously considering puttin' in there. $165.97 at Summit Racing
X 2
on this cam, much better choice for your combo.
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Old 11-15-2013, 12:49 PM
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I suspect that the pistons are 12cc crown displacement and if that's the case, the static compression ratio of the motor is 8.5:1 and no amount of aftermarket cam will wake the motor up. It needs a STOCK cam to close the intake valve early enough to make decent cylinder pressure. Everything is wrong with this combination from a performance standpoint. Find an L31 long block with heads or short block if you have some decent heads on the shelf and start over.
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Old 11-15-2013, 01:08 PM
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Quote:
Originally Posted by Daedalus View Post
Hi guys, so I have a 68 camaro and im slowly changing out all the wrong parts installed on the car/motor, im stuck on camshaft choice and have been reading for hours and hours, and cant seem to be able to decide.

the setup is...
4bolt 350 ( block originally from a 70s c30 i think)
flat top pistons with large valve reliefs
76cc 3998993 heads
1.5 ratio roller rockers
600cfm holley vac secondary carb
msd 6AL
crane fireball coil
hooker headers
flowmaster H exhaust think its 2.5"
weiand speed warrior intake manifold (used to be called stealth i think?)
turbo 350
2.73 diff ratio
stock stall converter

ive sorta rougly figured out the compression ratio and I think its around 8.7:1, a bit difficult without measuring deck height and relief cc's, headgasket etc

the cam im thinking of running is the summit k1103 (.443/.465 lift, 214/224 @ .050, 112 LSA) , but ive also been considering the 268H (.458/.458 lift, 218/218 @ .050, 110 LSA)

but im worried that with the small diff ratio, and stock stall, it might not be suitable and maybe I should just go with an "RV" cam, like the k1102

car is sort of a daily driver, but I work from home so it only goes to the shops or out for social events, doesnt ever see the strip.

MPG is fairly important to me but I have a racing background so I'm really quite disappointed at how much of a slug this motor is.. i'm willing to change the diff ratio, but would prefer not to until I put a 12bolt in, on a bit of a budget... so might not be for a while

so please fellow hotrodders, advise me in your infinite wisdom what cam you would choose?
Not that I'm opposed to going into this engine but the changes to get both power and mileage would require cam and head togehter. Right now it doesn't have the compression to carry any more cam, and certainly doesn't have the gearing either in the rear end nor the transmission. A slightly larger cam like the k1102 will do nothing for you and may show less acceleration with more fuel consumption than you have now. The gear ratios are way out of whack for the engine. These go back to the days when the manufacturers convinced the EPA that mileage ratings should be based on cruise as given the hardware they used this was the simple, low cost solution for the OEM's. In the real world this is a disaster neither delivering the performance nor mileage anywhere close to what was "promised".

Except for the heads you've got a pretty good start with this engine, flat top pistons are good but tend to drive the compression too high with a small chamber head. The head you have is OK volume wise for the cam you have but is a crappy burning chamber. Something like the Dart Iron Eagle with a standard face that would accept your intake would be a great improvement, you can get these with a 64, 72 or 76 cc chamber to tailor your compression ratio (DCR) to the cam you choose. These bring better ports with a modern fast burn chamber which even the larger chambers pattern after. DCR is the Dynamic Compression Ratio, this is what's really doing the work. It is found by taking the your Static Compression Ratio (SCR) and adjusting it downward for the piston stroke used up at the time in crankshaft degrees for the point of intake valve closure. The longer the cam duration the later the intake closes and the lower the DCR. Since more cam moves the torque peak further up the RPM band, the engine's existing compression ratio will not support the needed DCR and the gearing turns the engine too slowly to gain the advantages of more cam timing. The net will be less installed performance everywhere except the very top end. Plus this will come at an increase in fuel consumption everywhere. The heads, the cam and the pistons and the dimensions between the piston at TDC and the head need to work together and they need to work with the gearing. What you have now and what you are proposing is a mish-mash that will be a lot less performance than you expect for the money than you spent.

A better choice in gearing would be an up to date 4 speed automatic as the 700R4 with a deep low and over-drive high combined with a lock up converter. Mix this with a 3.08 or 3.27 rear axle ratio and you will have robust acceleration from a stand-still with a high mileage cruise with OD 4th and converter lock up. I'm not really sold on positraction for every application although I have and have had many vehicles with it, I find that unless you are doing balls out acceleration going straight ahead on a dry surface they otherwise really don't do much for you. You really don't need a 12 bolt unless you're planning on power well in excess of 400 horses at that with laughing gass and expect to do a lot of drag racing. A 350 doesn't need a 12 bolt any more than it needs a TH400 because it just cannot make the bottom end torque of a big block that busts smaller rear axles and transmissions so going with killer sized parts is unnecessary and costs money better spent in different ways.

Rear gears and transmisison is where I'd start, then move to the engine.

Bogie

Last edited by oldbogie; 11-15-2013 at 01:22 PM.
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Old 11-15-2013, 03:45 PM
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For the money spent,you would be miles ahead with an L31 Vortec engine.You could just about buy a new 1 & still come out ahead of replacing everything that wrong in yours & still have a more modern & reliable format to work with.It will have better heads,roller cam,9.4:1 stock CR,1 pc rear seal.

Last edited by jokerZ71; 11-15-2013 at 04:05 PM.
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Old 11-16-2013, 12:32 AM
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I take it this build is on a budget? The 993 heads are a deal breaker they will fight against the rest of your combo like stated above,you need more flow and more compression and these will fill the need:SBC Chevy Aluminum Cylinder Heads Assembled 190cc 64cc Straight Plug .650 Spring No, they are not a high dollar AFR or Trick/Flow but they will get the job done without breaking the bank if you have to take some time to save up the cash it will be worth it in the long run.
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Old 11-16-2013, 01:12 AM
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thanks for everyones advice.

id love to get new heads but yes its on a tight budget,
I'm in Australia so freight on heavy parts like heads adds a lot of money to the price, and there's basically no second hand vortec heads around.

If i bought heads id also want to do h/roller cam retrofit, and combined with freight i wouldnt be far off the cost of a 330hp vortec h/roller crate motor, which might be a better option?
or half way to the cost of an LS conversion.
so I really cant justify spending that amount of money on this motor, id rather just start fresh with a crate vortec that I know has been assembled right.

I do plan on building a better motor/ buying a crate or doing a conversion for this car in the future, and at that point ill probably put this motor into a cruiser project like a bel-air shell or a truck or something, so thats why im still trying to milk some power out of this on a budget.

i redid my calculations and its possible to get the motor to 9:1 compression if i use a 0.016 thick steel shim head gasket. what are peoples opinions on these gaskets? I assume theyre not as good as the thicker ones?

I need to pull the lifters out as one is sticking anyway, so I may as well slap a cam in it.
i'm thinking I get the .016 head gaskets, to make sure the compression is around 9:1, buy some 3.7:1 diff gears...
would that be enough to run one of these cams and pick up a noticeable amount of power?

Last edited by Daedalus; 11-16-2013 at 01:27 AM.
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Old 11-16-2013, 06:46 AM
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Aluminum heads don't cost that much to ship. I don;t believe there are not speed-industry distributors that already have aluminum heads there. Edelbrock etc etc. You are not the only one there hot rodding a SBC. The RHS stuff is cast in New Zealand .
A option is to modify and fully port a 305HO head. You got old 305's there.? 4416, 083 (TPI) 113 (aluminum)
041 186 461 all SBC castings respond very well to porting. All these are a big step up from the 993 smoggers.
more air flow when ported and more compression 58 to 64cc chambers.

Again bare aluminum heads are light weight.
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Old 11-16-2013, 01:42 PM
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Hi mate, I too live in AUS - "the land of expensive car parts" - it sucks, I know.
I don't even bother with Rocket or any of em over here, too freakin dear!
I use Summit Racing. They will ship you a set of bare aluminium heads for $186 (freight cost) to your door using i-parcel in 7-10 days.

You got a '68 Camaro, as Vinnie says, don't wimp out on it. Don't set the bar so high that it'll never get done though. I friend of mine got a 67 black on black RHD, beautiful conversion, fully optioned. Pulled it apart 20 years ago and it's still apart. It's a shame.

Whichever way you decide to go, be sure to do your homework on SCR / camshaft duration relationship.
If you got around 8.5:1 SCR at the moment, the SUM-K1101 cam comes to mind. That'd be a cheap way to keep your cylinder pressures up to where they need to be, and let you have some fun. Keep the car on the road!!!.....while you work on another 'better' engine.

Here's a rough guide....pic

Good luck!


Duke
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Old 11-17-2013, 10:42 AM
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Duke, thanks much for posting the chart. Matching up the duration to the static compression ratio is something I've been pushing for some time now and it's good to see some verification from someone else of what I've been saying. I agree that the K-1101 would work just fine in this motor, even though I have no info on the grind to calculate the dynamic compression ratio (need at least intake centerline).

A Crane 114102 would be another good choice. Closing the intake at 16 degrees after bottom dead center makes a dynamic compression ratio of 8.12:1 and would work well on a daily driver using cheapo pump gas and 8.5:1 static compression ratio. Chevrolet Motor Division actually purchases this cam kit with lifters from Crane and re-boxes it under GM part number 12353914 which includes the cam and 16 lifters.
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