[slowbird]

Just thought this could be an interesting discussion.
Which cam would you choose for street/strip (idle quality and vacuum not a concern)

First one is 236-245 112ls
Second is 244-248 108ls

Both in same engine so compression is the same both installed straight up.
From what i can tell both will have roughly the same cranking compression and roughly same dynamic compression. But the bigger cam will have almost twice the over lap. Which one is a better street cam and which one would be better on the track (assume car is a typical street/strip weighing 3800lbs with 3.55 gears)

[Steve C.]

One source for cam design suggests this in their summary:

The most important cam design parameters are the four timing events or equivalently the advance, intake and exhaust duration and lobe separation angle. Once the four timing parameters are established, the cam should be designed for maximum lift . A quick opening and closing cam will provide better low end performance than one that is slower opening.

With that mind for each provide the seat duration numbers and the lobe lift involved with the intended rocker arm ratio. And if using sold lobes the valve lash involved. Some will be interested in the duration at 0.200" tappet lift as well.

To determine the DCR you need seat to seat or advertised numbers.


.

[tom s]

Do you mind doing a hydroboost?Tom

[AG]

The first cam in a 455 is a proven combination that is capable of 11.3 in the 1/4 with the right converter and makes a great street combo. Not sure how much more you would get at the track with the second cam, a tenth or two?

[pastry_chef]

Are these both hydraulic?
Rocker ratio already decided?

Valve lifts?

Can you supply --
bore
stroke
valve sizes
I/E flow at .500, .600
good exhaust, headers?
dual plane or single plane intake, any port work?

Presuming auto trans, torque converter stall will be a factor.

[Tom Vaught]

Originally Posted by slowbird

Just thought this could be an interesting discussion.
Which cam would you choose for street/strip (idle quality and vacuum not a concern)

First one is 236-245 112ls
Second is 244-248 108ls

Both in same engine so compression is the same both installed straight up.
From what i can tell both will have roughly the same cranking compression and roughly same dynamic compression. But the bigger cam will have almost twice the over lap. Which one is a better street cam and which one would be better on the track (assume car is a typical street/strip weighing 3800lbs with 3.55 gears)

I ran a 255/265 at .050 solid flat tappet on a 106 cl with .560/.575 lift advanced 4 degrees on a 400 cid engine with 11-1 compression ratio for about 10 years. 4 speed and 4.33 gear.

Cam evened out and was happy at 3000 rpm on the freeway along with the trucks and buses back in the reduced speed limit days (gas shortage).

Had a nice sound on the streets, acceptable idle was about 8" of vacuum so the normal 6.5 Power Valves could be used on the Holley 850 carb. I raised the jetting a bit on the main circuits but the idle and part throttle were clean even with the overlap as I spent time on those circuits. Not quite at Stoich on the bottom end. Good JR headers, good ported cast iron heads, 1.65 Harland Sharp roller rockers to get the posted lift.

With that combination it ran 11.55 at 117 on small slicks at about the same weight you have posted. Nice street car.

When I went on long trips I swapped the rear axle (posted this before) and worked my way thru the gears slowly to get to 80 mph on the 401 highway in Canada. Only disadvantage was it sucked gas when running the 4:33 gear but was great driving around town.

Tom V.

[fastekibeast]

Second one would be my choice LSA 108.

Because, I trust D. Vizard infamous 128
formula.
Janne

[Formulajones]

I just built a 455 with a 239/243 @ .050 hydraulic roller on a 112 LSA.

Maybe just a pinch bigger than your first choice. Perfectly fine on the street. It idled with 13" of vacuum (that's at 5,000 ft.), works the power brakes and A/C perfectly fine. Engine is 9.98:1 compression and made 507/571 on the dyno with the exhaust manifolds in place, stock intake and carb. Peaked at 5700 rpm.

Just a nice slight lope at idle, nothing radical and it drives around really nice, gobs of torque everywhere, in fact it never dipped below 500 ft lbs. on the dyno.

[slowbird]

Originally Posted by Steve C.

One source for cam design suggests this in their summary:

The most important cam design parameters are the four timing events or equivalently the advance, intake and exhaust duration and lobe separation angle. Once the four timing parameters are established, the cam should be designed for maximum lift . A quick opening and closing cam will provide better low end performance than one that is slower opening.

With that mind for each provide the seat duration numbers and the lobe lift involved with the intended rocker arm ratio. And if using sold lobes the valve lash involved. Some will be interested in the duration at 0.200" tappet lift as well.

To determine the DCR you need seat to seat or advertised numbers.


.

Just a hypothetical question so we'll say both lobes are from the same family of lobes (hyd roller) and both have some lobe lift. So with that in mind we'll say the smaller cam adv of 288-298 .200 is 158-167 .400 lobe lift. Second cam is 296-300 165-169 .400 lift both 1.65 rocker.
Engine is 4.185 bore 4.210stroke, head 2.11x1.77 310cfm intake 220 ex 1 3/4 headers single plane intake.

[tom s]

I have never had a issue with power brakes on a 236-242 on a 112 but the 245-252 on a 110 was only good for one panic stop without let it build vac back up.That was in 455 stick shift cars.FWIW,Tom

[pastry_chef]

Originally Posted by slowbird

smaller cam adv of 288-298 .200 is 158-167 .400 lobe lift. Second cam is 296-300 165-169 .400 lift both 1.65 rocker.
Engine is 4.185 bore 4.210stroke, head 2.11x1.77 310cfm intake 220 ex 1 3/4 headers single plane intake.

If limited to your two cams I'd use the larger cam and pair with a good converter ~ 4000 ish stall.

[Jay S]

There really isn’t close to enough info to make a judgement call either way. Knowing what I have seen of some on other “slow bird” engines I would tend to say the 108 cam. But the engine needs to have head flow/port volume and induction to spread the HP out higher to really utilize the overlap. Or it will just idle poor and run about the same. That extra overlap is also going to want some more converter.

For more limited head flow and induction and with longer stroke engine, less converter, probably should be looking at the 236/245 112LSA cam.

[Stan Weiss]

Originally Posted by slowbird

Just a hypothetical question so we'll say both lobes are from the same family of lobes (hyd roller) and both have some lobe lift. So with that in mind we'll say the smaller cam adv of 288-298 .200 is 158-167 .400 lobe lift. Second cam is 296-300 165-169 .400 lift both 1.65 rocker.
Engine is 4.185 bore 4.210stroke, head 2.11x1.77 310cfm intake 220 ex 1 3/4 headers single plane intake.

Brian,
What is the CR?

Stan

[slowbird]

Originally Posted by Stan Weiss

Brian,
What is the CR?

Stan

10.5:1

[PAUL K]

242/248 on a 110 would be the best

[Formulajones]

Originally Posted by PAUL K

242/248 on a 110 would be the best

I run that in a 454 BBC here, with AFR heads and 10.2:1 comp. Been a great engine with plenty of power. Only idles with about 7 inches of vacuum up here at 5,000 feet though so it doesn't like power brakes too much. Like Tom mentions, good for one panic stop and then has to replenish.

[PAUL K]

I had no problems with the brakes.... 11.3 @ 119 weighing 3900 and change. Used a tight 11" truck pulling converter and 3.42 gears. 462 cid, 9.3 compression, ported 7F6 heads. Thing scooted on the bottle also. I think it was the third custom hydraulic roller cam Comp ground for a Pontiac.

[Formulajones]

Originally Posted by PAUL K

I had no problems with the brakes.... 11.3 @ 119 weighing 3900 and change. Used a tight 11" truck pulling converter and 3.42 gears. 462 cid, 9.3 compression, ported 7F6 heads. Thing scooted on the bottle also. I think it was the third custom hydraulic roller cam Comp ground for a Pontiac.

I don't have issues with the brakes when I'm at sea level where it makes 10-11 inches of vacuum, but up here on the mountain a mile up, they aren't too happy, lol. I went 11.38 at 118 best at 4,108 lbs, using a tight 10" Continental converter and 4.10 gears. Great camshaft. Mine was custom ground through Comp with input from AFR. Valve lift is .612/.638 with 1.7 rockers.

[Cliff R]

Not really enough information provided to recommend either one. The missing players are CID, static compression ratio, how big the lobes are, and .006" duration would also help.

I did a 455 once with a 246/254 @ .050" cam on a 108LSA. The advertised duration was around 311/320 nearly as i can remember, so pretty "hefty" cam. That was back in the days when I had the time to test these things. The 455 it went into was topped with well prepared #48 heads so the compression was pretty high. Idled with a heavy "lope" some reversion to about 1800rpm's, and STRONG power in the mid-range. "Explosive" would be a better word to describe the power. It literally felt like you hit the engine with a 150 shot of nitrous from 3500-5500rpm's.
On the street the car was an absolute "animal". When the engine hit that RPM range it was IMPOSSIBLE to hook it up and quite a challenge to keep the car between the ditches.

At the track it was somewhat of a disappointment. With good traction it just left a little "soft" and even with the strong mid-range and top end charge just didn't run nearly as well as expected. Clearly we needed more gear and a "looser" converter to take full advantage of that engine combo.

The car was raced like that for several years, then we swapped it out for one of Dave's "Road Paver" cams with a supplied set of ported #62 heads. On the street I thought we "cut the balls" off the engine. Don't get me wrong, it pulled really hard, but the power curve was smooth and "flat". It just pulled hard from the instant you went to full throttle till you decided to move the shifter. No "rush" of power anyplace and somewhat "boring" if you were evaluating it by the seat of your pants.

At the track however the car left harder and ran quite a bit quicker. We picked up nearly a full second in ET and a solid 6mph on top end. That was an early lesson is listening to the "butt meter" to evaluate engine and vehicle performance.......FWIW......

[pastry_chef]

Originally Posted by Cliff R

Not really enough information provided to recommend either one. The missing players are CID, static compression ratio, how big the lobes are, and .006" duration would also help.

All given above.