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Need good cam for supercharger app.
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af2
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Joined: 01 Sep 2003
Posts: 5558
Location: grassvalley, ca
71227.76 points


1933 Willys Coupe

PostPosted: Fri Jan 18, 2008 11:20 pm    Post subject: Reply with quote

Boy I messed that post up!! Read the whole thing and you might see me put my foot in my mouth!
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squeeezer
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Joined: 02 Mar 2007
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Location: new richmond WI
191524.76 points


1991 Chevrolet Camaro

PostPosted: Sat Jan 19, 2008 7:40 am    Post subject: Reply with quote

clay wrote:
I sort of agree with 96capriceMGR on this one. That's why I like the "E" cam. It has a little tighter seperation that a normal "blower" cam but still not a lot of duration. Now I'm about to ramble on about cam theory that I have sort of put together from lots of reading - take it for what it's worth. Following Vizards cam philosophy, as the cubic inch goes up, the lobe seperation needs to get tighter for the same head flow to take advantage of the "fifth" cycle - exhaust scavenging aiding in pulling in the intake charge. Overall duration still needs to be in line with the application or the increased overlap will not be beneficial - for example too much duration / overlap with not enough static compression ratio. The better the heads get, the wider the seperation can get. If he is making 348 at the wheels N/A I would think he has a pretty good setup. For this displacement in carbureted form, I would think 106 - 108 would be good, but this may cause problems with idle quality in a computer controlled situation. 112* seems to be a good compromise and easily available in this situation. Another rule of thumb with centrifugals is to mostly treat it like a N/A setup to increase bottom and midrange since the centrifugal is doing nothing down there. This problem is much worse on a manual transmission setup due to more rpm drop on shifts than a properly stalled automatic. Once everything gets going and up more in the rpm range, there isn't enough time for the intake charge to get blown out of the exhaust which is one reason for the wider seperation. The other is to advance the exhaust event and start blowdown sooner to evacuate the extra exhaust volume. This is more beneficial in a nitrous setup where cylinder pressure rises to a higher level faster and it is beneficial to start exhausting sooner since most of the cylinder pressure has fallen off. Supercharged setups don't build quite as much peak cylinder pressure or as fast, but they maintain higher pressures over a longer period of time. This is a reason to delay the exhaust event slightly to make use of the pressure that is still there. Also why nitrous is harder on parts at the same power level - the more sudden pressure spikes are just harder on parts. I'll stop rambling now and I'm sure this will start a mess, keep in mind this is my opions and ideas to date and am always open to learning more. Clay








im sure most can agree.....if the most important cam timming event is in fact intake closing(for filling any engine n/a, supercharged roots or centrifugal turbo's etc)
and now you want a smooth idle moving the lsa is the only thing that makes sense......not to mention loosing boost /or cylinder pressure through to much overlap

i don't understand if a centrifigal's powerband is more spread out within the rpm range what is wrong with a cam that follows suit with the longer lsa assuming there is still plenty of torque for your 60 foot

for example the second cam i mentioned in this post (the smaller) are we saying that may be a good cam if it were ground on a 112lsa vs 114......or a smaller cam all together

i better learn this stuff someday.....i can see forced induction in my future

what is the current cam??????????........third inquiry
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squeeezer
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Joined: 02 Mar 2007
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Location: new richmond WI
191524.76 points


1991 Chevrolet Camaro

PostPosted: Sat Jan 19, 2008 7:44 am    Post subject: Reply with quote

ummmmmmm....yeah i just looked at that second cam i mentioned they got the cam card messed up

intake closing at 42 deg Laughing Laughing Laughing
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96capriceMGR
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Joined: 23 Aug 2003
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Location: New London Wisconsin
20327.88 points


1996 Chevrolet Caprice

PostPosted: Sat Jan 19, 2008 9:20 am    Post subject: Reply with quote

af2 wrote:
96capriceMGR wrote:
I know NOTHING about the Ford motors. What I do know is 112-114 are the most common off the shelf LSA numbers for the computer controlled small block Chevys. Reasoning, and I use the term loosly, being the computer needs the wide LSA.

I also know my cam is tighter than that and I know of guys running as tight as 106 in an LT1 without any tuning hassles Shocked .
Conventional wisdom like this needs to be reexamined.

I know that there are a lot of cars with "better" setups than mine that can't touch me at the track. By better I mean ported aftermarket heads, more displacement, more duration, wider LSA, MUCH more lift etc.

Is that speed desity? or MAF. I feel he is in a MAP situation. I have been wrong before!!!!
With a MAF I would run any cam that allows!
A LOT of over engineering going into cars these days and rarely working.

I am NOT that experianced, I just align myself with those who have great info to offer and listen closely. I am also pretty good at reading 10 pages of garbage and pulling the one paragraph of useful information out of it. That skill does not get to work here because the average poster here is great compared to every other board I have been on, but on other boards it is the only way to learn anything.


The LT1 was sold both ways and the MAF equipped cars pcm will support speed density. Speed density is a little more work to tune but will handle whatever we throw at it, some of the guys with race cars making in the 500rwhp vicinity through automatics go speed density to remove the MAF restriction. The only limitations the 94-7 LT1 pcms had was they lose control about 7-7200rpm, and they have a single BAR MAP other than that they will do pretty much anything asked of them. This is probably the cheapest and easiest OEM system to reprogram though, the 94-5 the tuning software is even available as shareware with a suggested donation of like $30 and cables to connect start at like $35.

The early speed density stuff like the TBI trucks of the late 80s early 90s are VERY difficult to get to work with much cam and I think this is part of where these myths come from, but I think it was a limitation of that computer and likely it's processor speed.

I do need to remember more often how lucky I am to have choosen a car with a computer so easy to crack, I should remember that not all cars are so easy. The LT1 pcm works so well I was talking to someone with their hands in a 480+rwhp NA 355 LT1(M6) and when they tried a FAST system they were able to rev it higher but saw no additional power over the stock pcm.

I know I type too much but I guess what I really want to say is question conventional wisdom, a lot of times ideas get stuck there LONG after they no longer apply.

In this discussion even if you want a wide LSA for a blower you need to understand everything off the shelf is already spread wide.

One of the Impala guys got carried away with what "should be done" and let a computer program spec a cam something wacky like 222/234 116 for nitrous, NA the car slowed several tenths from his old 214/224/112 cam and didn't make up for it entirely on the bottle, these days he is heading towards the other extreme. He has since opened his eyes to the fact that even the 112 cam was spread quite a bit from optimal NA and thinks if he had sprayed it with like a 300shot the funky cam may have finally worked.
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clay
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Joined: 24 Nov 2002
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Location: South Carolina
318129.23 points


1972 Chevrolet Nova

PostPosted: Sat Jan 19, 2008 9:48 am    Post subject: Reply with quote

Definately was originally a MAF setup. I believe the Mustangs have been MAF since 88. California might have happened a year earlier, can't remember the exact details, but that is irrelavant here. That cam on 116* sounds crazy wide for the duration. I would personally only go that wide with a nitrous setup but using duration in the 250 - 260 range at 0.050" It actually sounded like a decent turbo cam though. I do like the slightly added duration on the exhaust on the Comp cams, might be beneficial. Centrifugals are sort of peaky in their output. Roots and even turbo's have a better boost curve. The general rule of thumb on centrifugals is when rpm doubles, boost output squares. You can see this makes for a rapidly climbing curve. This is the main reason I like them much more in front of an automatic with the right converter, the engine can stay up in the rpm range and keep boost coming. Clay
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wagon train
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Posts: 258
Location: Orange City, FL
7307.16 points


1983 Mercury Capri

PostPosted: Sat Jan 19, 2008 10:13 am    Post subject: Reply with quote

In a real street nmra class car we used a cobra cam retarded 4*, it ran 9.80's at 3250lbs.
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MufflerBearings69
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Joined: 22 Jul 2007
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25364.28 points


1968 Ford Galaxy

PostPosted: Sat Jan 19, 2008 10:58 am    Post subject: Reply with quote

96capriceMGR wrote:
I am NOT that experianced, I just align myself with those who have great info to offer and listen closely. I am also pretty good at reading 10 pages of garbage and pulling the one paragraph of useful information out of it. That skill does not get to work here because the average poster here is great compared to every other board I have been on, but on other boards it is the only way to learn anything.


Sometimes I don't think I have a lot to contribute around here for how much I have learned, and the local guys who have been guiding me along through my first build humor me and explain to me the errors in the information I was finding other places... But maybe someday I will be onthe level... So I hope!! Very Happy
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clay
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Joined: 24 Nov 2002
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Location: South Carolina
318129.23 points


1972 Chevrolet Nova

PostPosted: Sat Jan 19, 2008 3:32 pm    Post subject: Reply with quote

Quote:
In a real street nmra class car we used a cobra cam retarded 4*, it ran 9.80's at 3250lbs.

I love what can be done with stuff like that. Amazing. Clay
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