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Old 06-25-2003, 10:22 PM
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Single vs Dual pattern cams

This is going in a 327 SB chevy. I notice CompCams has a lot of single pattern cams?? Are they any good in a SBC?? It's going in a '69 Chevy C10. Which is better in a chevy?? NOT a daily driver, just cruise and occational race. I would like around 3,500-7,500 powerband...

327: 0.030 over, 9.7:1 @64cc, 492 double hump heads, ported. 2.02/ 1.60 valves. Victor JR intake w/ 750 mechanical Holley. 5" x14 K&N. Flowtech headers 2 1/2 half way with flowmaster 40's and I just got a TCI 3500 stall. My heads are 3 angle w/ stainless valves, 550 lift springs, crane roller rockers.. I'm set up for a pretty big cam but I don't want to go to big, I just want everything to be set perfect. Any help appreciated, Thanks

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Old 06-25-2003, 11:27 PM
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cams

there are a hundred varibles that deturmin propper cam in fact the cam may be the the most important and most misunderstood part of the engine....... traditionaly the sbc has a few exhaust issues and benifits from a longer duration and higher lift on the exhaust side with camel back heads witch flow numbers lowwer then most chevy guys think you will want the duel pattern cam..... but with only 9.7 to 1 compression you will have to be very careful in choseing youre because the rpms you want the powerband to run in is a high exspections from a low compression motor youre going to find that as duration increases so dose the engine dependantcy on higher compression to fill the cylenders..... if youre compression is to low to fill the cylenders youre efficentcy will decrease and the cam will hurt you..... NEVER EVER push a cast crank up around 7000 rpms its a bomb waiting to blow........... youre cubic inches will also deturmin youre cam size..also if you wish to run the engine over 7200 rpms ever youve just surpassed the hydralic non rollar cams lifters limits and are forced to run a rollar or a mechanical cam.... dont make the cam selection on youre own and dont listin to a self proclaimed professional you WILL be disapointed...... contact comp cams at www.compcams.com they even have a 1800 number but i cant find it look on line..... you may want to talk to them about custom grinding you a cam often they can be talked into doing it at no extra charge.... there are alot of things theyll ask know youre car and be perpared to answer alot of questions,, good luck and keep on hotrodding those sbc thats what they were made for.......
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Old 06-26-2003, 08:50 AM
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I've often wonderd what the craze is about he split pattern cams. Of all the people I know tried to use one there was no difference in power untill about 14 to 1 compression and 7200 was reached. Maybe someone could enlighten me as well. I use a split cam but haven't felt that it was benificial to me in anyway unless the engine force fed.
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Old 06-26-2003, 12:00 PM
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Well for SBCs anyway the exhuast ports are really weak in the flow dept.So the longer exhuast dur kinda offsets that.Also with closed exhuast and catyltic tree hugger satisfiers your exhuast gets restrictive and needs more lift and dur to offset that.They say that if your exhuast port is less than 70% off the intake port cfm(most sbc heads) you need a dual pattern.
If you have say a 1.72/1.50 283 or 305 head with a really small intake port,its prolly more than 70% and a single pattern cam might be best.
As for SBCs,as long as the cam is within the right size range it will work,but the duel pattern would work a little better.
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Old 06-26-2003, 06:41 PM
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The main point of the split cams was the finding of running 1.6 ratio rockers on the exhaust side improved flow with alot of the newer style heads (older too...) The Vortec head benifits from this really well... Kinda of the effect of a larger exhaust valve...
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Old 06-26-2003, 07:48 PM
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(This is to be a friendly debate)


Yes, I would agree that chevies have restricted exhaust ports and lift and duration will help to overcome this malidey but the difference is never apparant untill way out of the RPM range of what most street engines see. And by the time that that they are modified by whatever means to reach the proper RPM to see this tuning the heads will have surely been modified to counteract. Agree? The ports don't even become a restriction untill 4500 or so in even really small ones designed for the purpose. If you are building a motor with exhaust restriction anywhere from the head to the tail pipes than using a split pattern cam is a crutch for a improper system. I think you are better using a single pattern cam and building it right the first time than to find way's to fix what's hasn't been done right. Of course this asumming no power adders which there will always be an exhaust restriction due to the abnormally high Air/fuel being forced into the engine.
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Old 06-26-2003, 08:14 PM
E.T. divided by $ spent= Speed
 
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Freindly debate

Yea but when I explain things useing percentage #s and terms like cfm,I sound smart. j/k
As far as the cam being used as crutch for restrictive exhuast.Your right but,some people are forced to use single exhuast and cats for smog purposes.They need an offsetter.Yea they make 3 1/2 single setups but for more money than the tresury can hold.Allot of the MonteSS guys are running shorty headers into the Y a Cat then single 2 1/2 or 3".
I know on my car I have a XE262 218/224dur. .462/.469 cam.I have stock unported 993 1.94s. The cfm flow(per online)was something like 151/61.So that coupled with duel 2 1/4(only system with a resonable price)I figured A duel pattern would offset my restrictions.I didn'twant a large tube free flowing mufflered exhuast because I drive the car ALLOT and wanted it quiet,despite the fact that I rag it on weekends so I wanted a middle ground.
If the same setup had say open 1 3/4 primary headers I would consier a single pattern with them heads.
In a way running a duel pattern to make up for restrictions is just matching to the setup.You could build around the cam or buy a cam to work with your existing setup.
That be my pinion.
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Old 06-26-2003, 08:54 PM
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I like copying stuff from books so I really sound smart, although I gain nothing but typing skills!

It's still possible to build a free flowing exhaust system that's not overly loud. Cat's can be made or bought that flow really well. and 3" single pipe will out flow almost all but what most street engines can deliver and around here that's about 150 to 200 for the typical crimped bend's and smog stuff. This coupled with a flowing muffler will get you as close to a free flowing pipe as one could realy hope for. In no doubt of my mind split pattern cams due indeed have there purpose. Hell, even I run one. 308 and 318 respectivley. But the point is that you will never see the difference in power untill you are on th ragged edge of destruction for a typical street engine. I'm really debating to my self that most hotrooder's from my experiance love to play follow the leader. That is they do whatever the leader does in order to go fast. But the leader has tricks up his sleeve such as a split cam, and a lot of RPM. that's where the advantage is. For the guy who can't turn the RPM then he never see's the advantage. So as my puny brain thinks, split pattern cams are used too often and for the wrong purpose. (This not copied) Eric
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Old 06-26-2003, 09:11 PM
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(Dueling banjo's playing in background)
Moreless I read the logic behind duel pattern cams and it seemed good to my thinking.So I allways more less"rule of thumb"ed it that with stock chevy heads with less than 70% use a duel.I haven't read any dyno comparisons but I still feel that the duel pattern would add a little down low,maybe only a few HP/TQ but some.It prolly don't make a whole hell of allot of differance till up high,but my theory is it keeps a more balanced flow between intake and exhuast.
And see I got to use the % again,see.
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Old 06-26-2003, 09:38 PM
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Porting cylinder heads don't cost me a dime so untill I get restricted on what i can use then I will consider them a crutch. Can three legs run faster than two? Works for horses.
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Old 06-26-2003, 10:16 PM
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Well I called Crane, Isky and Comp and so far Comp has the best support and were very helpful. They asked me if I wanted Solid, solid roller, hydraulic and hydraulic roller. I told them either soild or hydraulic because you get up in the $$ with roller, they said soild would perform better but be more to maintain. I told them that I would live with solid because it's only a crusier, they reccomended there Xtreme Energy Mechaincal 274S.
It's 501-510, 230-236.. 110 deg seperation. How often do you have to adjust solids?? are they really that bad?? And for Hydraulic they reccomeneded the 292H
The 292 is 501-501 and 244-244 duration and 110deg of seperation. This is choosing between four things: single pattern, hydraulic, mehcanical, dual pattern?? Thanks guys
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Old 06-26-2003, 10:36 PM
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hey gearhead,
go with the 274s you will be much happier with the solid and as far as matinence, once you set the valves it will be 6months to a year before youl need to do it again
solids make more power than hyd's and are well worth the minimal adjustments
besides youl have those valve covers of for one reason or another before then anyways

also with roller rockers and polylocks solids are a breeze to set

ps.. I would run the lash at .18 intake and .020 exaust it will make the valvetrain a little quieter and be alittle softer on components
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Old 06-27-2003, 01:28 AM
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I took my heads to get done today and I'm having a 3 angle valve job and having them mill 0.025 off the surface for a little more compression. Now I should be in the 10:1 #'s.... I'm still looking at hydrauic cams, I don't know why but I have had good experience with them and I will accpet the performance loss.
Here's a list of the Hydraulic cams that I have narrowed it down to.

Comp 292H: 501-501. 244-244. 110deg
Comp Xtreme Energy 284H: 507-510. 240-246. 110deg

- 292H is called Street/Strip and calls for 9.5:1, 3,000 stall, headers, gears. The powerband is: 2500-6500 It says "very rough idle"

- 284H is also Street/Strip and calls for headers, gears and 2800+ stall "rough idle" Powerband: 2300-6500

Well I think it's between those two, tell me what you think. I want a fast rough idle kinda like this link.. What cam would give me that?? Thanks I want myn to sound like this
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