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Cam Specs from Comp Cams |
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AWhite70 
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Joined: March-05-2004 Location: United States Status: Offline Points: 242 |
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 Topic: Cam Specs from Comp CamsPosted: March-17-2004 at 10:53am |
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Comp Cams just gave me the following recommendations for a cam:
Cam Blank: 35-000-5RR Grind # FW 5442/5444 H112 +2 Duration: 218/226 @ .050" (I/E) Lift: .308"/.320" (I/E) Lobe Separation: 112 This is based on a 351 buildup with GT40 heads and an Edelbrock Performer RPM intake. I haven't run the calculations yet but it looks like it should yield about a 9:1 compression ratio. Any comments on those cam specs? Comp says they should give good bottom end and midrange for pulling skiers, and should pull up to 5000rpm. Any comments or suggestions would be appreciated. |
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tryan
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Joined: November-12-2003 Location: United States Status: Offline Points: 345 |
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Posted: March-17-2004 at 11:45am |
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look at the head chart link. you might save some cash and rework your heads.
 that sounds pretty close to 79's cam.
did your block clean up with 30 over? research the ring composition on a stock setup, but guessing either your power valve might have been dribbling fuel, or someone used havoline. i still like to use non-detergent oil. IMHO. |
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79nautique
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Joined: January-27-2004 Location: United States Status: Offline Points: 7872 |
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Posted: March-17-2004 at 12:04pm |
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Maybe I'm missing something. How do you calculate compression from cam spec's and how does a cam vary compression? It's my understanding that compression is directly related to stroke, piston diameter and cylinder volume. Changing the amount of air volume appove the piston on TDC is the only way to increase or decrease compression. i.e. domed pistons, decking the block or heads.
My duration is the same put I have a different lift on mine. the gross lift is .476/.481 |
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AWhite70
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Posted: March-17-2004 at 12:04pm |
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Tryan, am I missing something? What head chart link?
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AWhite70
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Posted: March-17-2004 at 12:10pm |
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The CR was a guess based on the bore, pistons and heads that I'm using. It had nothing to do with the cam. I just stated it with the cam I'm using to give some background info for the setup I'll be running.
I'll get a more accurate calculation of CR when I get the block back from the machine shop and start assembling. More importantly I should have asked have those of you with similar setups still been able to run cheap gas (87-89), or have you had to use premium (91+)? |
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tryan
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Posted: March-17-2004 at 1:28pm |
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head flow chart
ii run premium in everything just for the hell of it. if you buy lake fuel, i would drop the cr just for the sake of the starter and the possibility of the dreaded detonation. the 'book' says not to take more than 10 thousands off the heads and ford small blocks are weak at the top of the deck. try not to deck it to much, if you don't have to. a 69 or 70 block is THE block to have with the higher deck. more room to play i guess. it only takes 100 horses to get my skinny butt up on a ski, but i can stop a 100 hp boat on a hard cut. (250 or so is plenty enough to rip somebodies arms out with a bad driver.) i'm ready for the perpetual ear infection, a big bruise all the way up my left shin, sunburn on the top of my bald head and some excruciating back pain. 'cmon summer. it's time to ski. 
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SS 201
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Joined: October-20-2003 Location: United States Status: Offline Points: 232 |
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Posted: March-17-2004 at 3:22pm |
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They are right a good cam, Gt 40 heads will yield app 9.1 comp. 64 CC
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79nautique
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Posted: March-17-2004 at 3:32pm |
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If you haven't got the intake yet I would go with the AIR GAP version. I'm running the straight performer don't really need to run it to 6500rpm, 5000-5500rpm is all I will ever turn and I would rather have the off idle to 5500 range verses a 1500-6500rpm that the RPM versions are. You really wouldn't notice the difference but if they had the air gap when I bought mine the cooling advantage of the air gap would be worth it.
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79nautique
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Posted: March-17-2004 at 4:10pm |
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CAMS HAVE NOTHING TO DO WITH CR.
 deep breaths deep breaths
on a 351W with a stock bore and stroke and heads with a 64cc combustion chamber, will yield about a 9:1 compression ratio with flat top pistons with a stock, mild, hi-lift or any cam you choose. Any way, I have basicly the same cam and induction system, a little higher compression (piston's are oversized) I do not buy gas at the marina and do use high octane gas don't have to but choose to. As long you don't have a bing using 87 then your fine, me 3-5 bucks more to fill it up with premium and gain the advantages of a cleaner, better running engine. Just don't fill it up with the cheap stuff. start out with a quarter tank then you can add higher octane gas if you have a bing. Gas stations only buy high (94) and low (87) octane gas from the supplier, anything in between is a blend of them. |
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danman
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Joined: February-04-2004 Location: United States Status: Offline Points: 56 |
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Posted: March-17-2004 at 11:12pm |
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camshaft has NOTHING to do with compression
the stock compression ratio for our 351W's is 9.17:1..... one point to keep in mind - If you start adding horse power to these engines, you cannot run marina (on the water) gas any more, you are going to have to fill up with premium and premium only... unless you want to burn a valve or a piston 
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ReidP
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Posted: March-18-2004 at 11:34pm |
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Guys,
I know this was yesterdays news, but I'm somewhat confident that most everyone on this site knows that cams don't affect the C.R. Let's please try and always stay constructive, and while of course it's OK to disagree, the response is better posed as a question and not a demeaning retort. Several postings back, Bill simply agreed with AWhite70's initial statement about CompCams recommended spec, and then secondly, a different issue, about the GT-40's C.R., and we're trying to imply something opposite. Keep breathing deep BC, we'll get passed it. Thanks. |
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tryan
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Posted: March-19-2004 at 6:56pm |
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my compression ratio was about 15 to 1 after wrestling the lower unit on my brothers formula this morning. an hour to mount it because its under a molded platform and another hour to adjust all the linkages, free up the trim rams (20:1), adjust the trim stops, calibrate the trim gauge and fire it up. inboards are great, i/o's suck.
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