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Miles
Sitting Bull

Canada
140 Posts

Posted - 29 Oct 2017 :  12:15:10 PM  Show Profile  Reply with Quote
I notice there are a lot of engines with a volume of around 463 cid. and a static compression ratio of around 10-11:1. I've also noticed a lot of them run a camshaft with a duration in the vicinity of 236-245. I wonder what cranking cylinder pressures these engines have and how they manage to avoid detonation? I can see those CRs with a larger camshaft.
My cold cranking pressure is 210 psi, and yes I get detonation, with a 10.49 static compression ratio.

As a side thought, how streetable is a 242/249ish camshaft in a 463 with 10-11:1 CR?

Steve C.
Crazy Horse

1675 Posts

Posted - 29 Oct 2017 :  1:08:12 PM  Show Profile  Reply with Quote
The amount of duration at .050" is not the deciding factor.

This will be of interest.....

Often stated: A lot of overlap kills low speed cylinder pressure.

This is largely untrue,and unfortunately it gets repeated waaayyy too often.

Especially when it comes up in a discussion relating to DCR theory and such.

Yes,overlap does affect the low speed intake tract vacuum (carb signal) sure enough,but that does'nt also directly affect the low speed cylinder pressure,the low speed cylinder pressure is mosty a strict derivative of the cams intake closing event timing,and not it's overlap.

See,it's easy enough to come up with a cam that has a whole bunch of overlap,yet that cam can (and will) often crank out overall higher cylinder pressures in a given combo.

I say this as I've seen plenty of "large" overlap cams crank out well over 200 psi cranking compression.

Now if what you said were indeed 100% true,that would'nt ever be possible.

So before this turns into some huge debate,just go ahead and go look at any of the DCR calculators out there and just see for yourself how many ask for information about what the combos overlap numbers are.

And understand that a late IC event does'nt necessarily always = more overlap.

Sure a later IC event can (at times) mean a cam may have more overlap,but it wont always mean such.

Lots of things affect both those areas of a cam.

But only the seat/advertised IC event timing should be used to determine the DCR.

Source: screamingchief
http://forums.maxperformanceinc.com/forums/showthread.php?t=679904&highlight=cranking+pressure

Old related post, but again more relevant information presented by screamingchief:

http://forums.maxperformanceinc.com/forums/showthread.php?t=629498&highlight=cranking+pressure

.


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Steve C.
Crazy Horse

1675 Posts

Posted - 29 Oct 2017 :  1:19:41 PM  Show Profile  Reply with Quote
"As a side thought, how streetable is a 242/249ish camshaft in a 463 with 10-11:1 CR?"

Much will depend on the camshaft profile involved. Example, for the most part a solid roller cam with the same .050 duration as a hydraulic flat tappet cam will be 'more streetable'.
At least that's my opinion based on my previous experience. But I'm not meaning a detonation situation. That said, also comparing the two with the same .050 duration is not apples-to-apples.

Or are you meaning 'streetable' regarding the potential for detonation?



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Edited by - Steve C. on 29 Oct 2017 1:29:16 PM
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Miles
Sitting Bull

Canada
140 Posts

Posted - 29 Oct 2017 :  1:37:45 PM  Show Profile  Reply with Quote
Well I wasn't thinking about overlap at all just the intake closing point.
After reading the article about the tests on the spintron machine I can see where the two types of lifter differ in respect to duration at the valve.
I've run my specs in those ccp calculators and get a way lower number than mine actually is.
Reading Cliffs answer in the octane topic you posted , he gets 170 psi with the same heads and cam I have and mine is 210. and he runs 87/89 with no detonation and I get detonation with the best gas I can buy. Which is crap compared to the leaded stuff I used to pay 25 cents a gallon for.
I have to change my lifters and camshaft anyway so thought I would try to deal with the high pressure with a later Intake closing point. Would still like a camshaft that I can drive on the street with.

I'll have to read the rest of what screaming chief says tomorrow. He does have some good insight.
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Steve C.
Crazy Horse

1675 Posts

Posted - 29 Oct 2017 :  2:00:50 PM  Show Profile  Reply with Quote
When you see specific compression numbers touted consideration should be given to the chamber design involved. Typicaly a 'heart shaped' combustion chamber will tolerate a higher compression.

"The design of the combustion chamber influences the performance of the engine and its anti-knock properties. The layout and shape of the combustion chamber has a bearing on the thermal efficiency and performance as well."

.
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Steve C.
Crazy Horse

1675 Posts

Posted - 29 Oct 2017 :  2:07:46 PM  Show Profile  Reply with Quote
Also if you are using a Dynamic Compression Ratio Calculator for interest make sure your input is based on seat timing and not events at the .050 duration.

.
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Steve C.
Crazy Horse

1675 Posts

Posted - 29 Oct 2017 :  2:20:44 PM  Show Profile  Reply with Quote
"Big cams with more duration and overlap allow octane-limited engines to run higher compression without detonating in the low- to mid-range"

http://www.hotrod.com/articles/ccrp-9812-secrets-of-camshaft-power/

Same thing with overlap calculators, use seat duration and not .050 duration.


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tjs44
Cochise

USA
412 Posts

Posted - 29 Oct 2017 :  8:22:06 PM  Show Profile  Reply with Quote
Guys,this has been discussed for EVER.Here is my take after building a ton of HiPo pump gas street engines.We have for the last 70 some years put in bigger cams to make more HP.HP comes a lot from cyc pressure.And we find that big cams bleed off cyc pressure at cranking RPMs.The only deal is we DONT drive our cars at cranking RPMs.That is why we have all read and heard about the silent killer,detonation that cant be heard.I have found with iron heads and our Calif 91 pump gas that if my engines pump much more than 180-185 they are at risk.I built a 455 with TRUE 9.5 CR and with a 2801 cam the damn thing pumped 200 and we had to mix race gas to drive it.I always wanted to pull the front cover and retard it a couple degrees and see what it would do.I just did a cam change on the 455 engine that is now in my 69 bird.When first built the engine had a 228-230ish hyd roller on a 110 and it pumped 180 when built.Drove fine on our 91 gas.A few years later (last summer) I replaced the cam with the new SP II hyd roller on a 112.It was put in at 106 which is what Dave and Comp said to do.It pumped 195 on all cyc on the dyno.Not liking what I saw I asked Joe Sherman to pull the front cover and retard the cam a touch.As I remember it was now in at 109 and now pumped 180-185.I drive the car a lot,have had no issue with detonation I could hear.Also the engine ended up making more HP when we did the retard.FWIW,Tom
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Steve C.
Crazy Horse

1675 Posts

Posted - 29 Oct 2017 :  8:59:23 PM  Show Profile  Reply with Quote
Personally I'm a firm believer of not pushing the compression envelope on a street car with pump gas. This for engines leaving a shop to be used under all types of driving conditions, unknown gas quality, and not knowing how the end customer would tune and operate the combination.

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Miles
Sitting Bull

Canada
140 Posts

Posted - 30 Oct 2017 :  10:15:01 AM  Show Profile  Reply with Quote
No, don't mean streetable in regards to detonation but in respet to being able to idle and have low rpm performance. I know some guys that have put in large cams and like the top end performance but the engines are dogs at anything below 3500rpm.
SP II? Is that another version of Dave's Stump puller? If so what is the difference from the original SP?
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Steve C.
Crazy Horse

1675 Posts

Posted - 30 Oct 2017 :  10:59:00 AM  Show Profile  Reply with Quote
The first cam he called 'Stump Puller' was first ordered with grind number P8 3111B/3122B HR112+5
286/289
230/236
.3770/.3800 lobe lift
112 lobe separation

I've seen the second one, refered to as the revised Stump Puller, ordered with grind number P8 3194/3196 HR112+5
281/287
230/236
.3890/.3910 lobe lift
112 lobe separation

Both could be purchased from SD Performance or direct from Comp Cams.
The lobes are listed here:
http://www.compcams.com/Technical/Catalogs/CamLobeMasterCatalog.pdf

Nothing special, a hydraulic roller cam ordered with those specific lobe numbers as a custom cam with a 112 lobe separation.

A good cam for a truck motor combination :)

.

Edited by - Steve C. on 30 Oct 2017 11:01:17 AM
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Steve C.
Crazy Horse

1675 Posts

Posted - 30 Oct 2017 :  11:10:15 AM  Show Profile  Reply with Quote
Asked- "As a side thought, how streetable is a 242/249ish camshaft in a 463 with 10-11:1 CR?"

Here is one example of a friends car with a 242 degree solid roller cam. Very street friendly...

http://www.hotrod.com/articles/0804phr-bob-davis-64-pontiac-tempest-custom/

Myself personally, my previous street pump gas combination with a 254 degree solid roller cam....

I'll assure you it was no dog below 3500 rpm !

http://www.pontiacstreetperformance.com/psp/rebuild455sc2003.html

Later for interest I changed to a smaller 248 degree solid roller cam in that engine, so tame it was a pussy cat :)

Since you are interested in using a solid roller cam here are other street cars from this website using solid roller cams....

http://www.pontiacstreetperformance.com/psp/rebuild461RG.html

http://www.pontiacstreetperformance.com/psp/rebuild461DS.html

http://www.pontiacstreetperformance.com/psp/rebuild428TW.html

And I suspect there are others lurking here that have used solid roller cams.
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Edited by - Steve C. on 30 Oct 2017 11:51:52 AM
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Miles
Sitting Bull

Canada
140 Posts

Posted - 30 Oct 2017 :  6:24:54 PM  Show Profile  Reply with Quote
Hmm, shorter at 0.006 duration and the same 0.050 duration and more lift. I wonder why he switched?
That tempest is a nice looking car. Short block, head flow and chamber size close to about the same as my build.
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Steve C.
Crazy Horse

1675 Posts

Posted - 30 Oct 2017 :  6:40:14 PM  Show Profile  Reply with Quote
Advertised duration:
286/289
281/287

"When comparing two different cams, if both profiles rate the advertised duration at the same lift, the cam with the shorter advertised duration in comparison to the 0.050 duration has more aggressive ramp. Providing it maintains stable valve motion, the aggressive profile yields better vacuum, increased responsiveness, a broader torque range, and other driveability improvements because it effectively has the opening and closing points of a smaller cam combined with the area under the lift curve of a larger cam."

Billy Godbold at Competition Cams

Lobe lift:
.3770/.3800
.3890/.3910

"If you want to build a street motor with the most power without a sacrifice of idle and low speed qualities, then lift is the most important factor to maximize, not duration. The best street cams are those that seek to maximize valve lift while only adding a minimal amount of duration."

David Vizard
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Edited by - Steve C. on 30 Oct 2017 6:46:25 PM
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ta man
Tribal Scout

Canada
19 Posts

Posted - 21 Nov 2017 :  08:51:18 AM  Show Profile  Reply with Quote
My new engine at 100 miles..is 185 for cranking compression,10.75 to 1 KRE heads can run on 87 octane.

1980 Trans Am
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