Brock-Lee Posted February 2, 2009 Share Posted February 2, 2009 Okay i am putting a cam into my turbo a15 project. I am getting a rally cam modified to be more turbo friendly. I am getting ready to start putting the engine together and was wondering if i need a adjusable cam gear. I can make one easy enough but was wondering if it was required. I know for a twin cam engine it make sense so you can adjust the exhausat cam timing in relation to the intake. But for a single cam (ohv) motor like mine then is adjusting the cam timing going to create any benefit? any help or links towards help would be heaps appreciated. yuh. Dave Quote Link to comment Share on other sites More sharing options...
Unclejake Posted February 2, 2009 Share Posted February 2, 2009 If it was me I guess I would set the new cam up and measure the timing with a dial gauge on an inlet and exhaust valve and then compare the split to what the cam grinder has suggested (it should be on the spec sheet). That way you will know if the factory dowel (or whatever locating mechanisim you have) is close to optimum. Adjustable cam timing gear usually adds rotating weight and cost so if you don't need it you may as well avoid it and spend the money on beer. Quote Link to comment Share on other sites More sharing options...
Brock-Lee Posted February 2, 2009 Author Share Posted February 2, 2009 Cheers UJ, That is the answer I was looking for. also cost is irrelevant. I would make my own adjustable cam gear if it was needed. so the only thing it would cost is time. Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted February 2, 2009 Share Posted February 2, 2009 Shit Dave, you dont need an adjustable cam gear on an Aseries datto. Just take the dowel outta the cam, turn the sprocket around 180'. Get the cam set up right, and drill a new dowel hole in the end of the cam and bang, your away. Quote Link to comment Share on other sites More sharing options...
Brock-Lee Posted February 2, 2009 Author Share Posted February 2, 2009 lol yeah i know bart. I was gonna do that but i thought adjustable be cool for fine tuning/wank factor Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted February 2, 2009 Share Posted February 2, 2009 The timing cover is a cunt to get off with the sump on/even harder to get the front seal back in. What I did on an old motor, was make a removable hatch on the front of my timing cover. I drilled a series of holes (all on the same pcd) in the cam sprocket. Set the cam up "striaght up" and drilled the first hole. Then rotated the crank 1 degree, and drilled the next hole in to the cam, and so on. Then opened up the holes in the cam gear to the tapping size for an 8mm thread. I got an 8mm capscrew, and turned the end down to the same size as the dowel holes in the end of the cam. So to advance/retard the cam All I had to do was remove the hatch, remove the capscrew, back off the cam bolt, and rotote the crank untill the next hole lined up. Whack the capscrew back in, tighten the cam bolt, and bobs your uncle! I still have jig to drill the cam sprocket if you wanna borrow it. I also left the jig bolted to the cam sprocket when drilling into the end of the cam to ensure that the drill bit was parralle to the camshaft. Quote Link to comment Share on other sites More sharing options...
forced Posted February 2, 2009 Share Posted February 2, 2009 To me , you'd have been better off with the proper rally cam. A turbo cam just favours bottom end torque while loosing the top end. You'll be wanting to change it later. Spinning the camgear 180 deg is a bit hit and miss. It's better to just make the hole in the camgear bigger, then braze one side and file it to get it back to the right size. Steve Quote Link to comment Share on other sites More sharing options...
slipsittin Posted February 2, 2009 Share Posted February 2, 2009 To me , you'd have been better off with the proper rally cam. A turbo cam just favours bottom end torque while loosing the top end. You'll be wanting to change it later.Spinning the camgear 180 deg is a bit hit and miss. It's better to just make the hole in the camgear bigger, then braze one side and file it to get it back to the right size. Steve Rally style cams are not turbo friendly as Brock-Lee said from my experience due to the overlap and valve lift being to big when force feeding the air you need less of both. Also I would spin the gear and drill a series of holes and tap them or machine an eccentric dowel like we used to fit to all the older engines when we were to cheap to buy or make adjustable wheels. We used to have all the engines we built marked the same way with number punches to easily change it. eg: A was advanced, B was retarded, C was centre lined etc. The window idea is a bloody good one also. It would be better if you could make the cover 2 piece. A guy used to do that for the crossflows and Toyotas we built. Corey Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted February 2, 2009 Share Posted February 2, 2009 Rallly cam+forced induction=fail! Hot atmo cams rely on valve overlap to purge the spent charge from the chamber, and utilise the the exhuast gas's velocity to draw fresh charge into the cylinder. Forced cams have a wider lobe separation angle, with a smaller overlap area and often with more duration on the exhaust cycle. Since you're forcing it in, the zhost cycle needs held to get rid of the spent charge. Nitrous cams will open the ex valve sooner before BDC, to begin the zhosrt cycle sooner. With turbo cams it's about maintaining some kind of pressure differential, but I was drunk (drunker than I am now) when I read it. So I didn't quite get my head around it. Blowers like 110-112' of lobe seperation. Some nitrous cams have an even wider angle. But the wider the angle the sooner the ex valve opens and the more potential power is lost. But if you're squirting 400hp of nitrous into a motor, thats the tradeoff. Cams are a bit (read a LOT) of a science. Quote Link to comment Share on other sites More sharing options...
Brock-Lee Posted February 2, 2009 Author Share Posted February 2, 2009 if i was gonna make it adjustable i would just turn the centre out of the stock cam gear and then machine up a new centre with adjustment slots and then drill and tap it so you bolt through the og cam gear and clamp it in place, much like an aftermarket setup. would be easy enough to do. im thinking i might just set it up to the cam grinders specs. Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted February 2, 2009 Share Posted February 2, 2009 Thats a woderfull diea on paper, (the adjustable thing) but with the engine in the car adjusting it would be much harder than it sounds. Good plan though, the cunts who grind cams have more clues than you and I put together. Quote Link to comment Share on other sites More sharing options...
Brock-Lee Posted February 2, 2009 Author Share Posted February 2, 2009 lol yea if i was gonna do the adjustable setup I would make the timing cover easily removeable. I dont think im going down that road anyways. cheers for the help guys Quote Link to comment Share on other sites More sharing options...
forced Posted February 2, 2009 Share Posted February 2, 2009 Funnily enough turbos have been around for many more years than turbo cams. In my experience any hot cam will be better than a stock one.Maybe you could explain why mivec cams work so well with turbos? Steve Quote Link to comment Share on other sites More sharing options...
Spencer Posted February 2, 2009 Share Posted February 2, 2009 ^ i kind of agree with forced here, But it all depends on the size of this 'rally' cam and the size of the turbo. Whats the advertised duration on this cam and at what lift? Quote Link to comment Share on other sites More sharing options...
sholdowa Posted February 2, 2009 Share Posted February 2, 2009 I take it this engine doesn't use a woodruff key setup then? You've got the option of offset keys then, with no weight penalty. Much simpler for engineering fuckwits like me... Quote Link to comment Share on other sites More sharing options...
forced Posted February 2, 2009 Share Posted February 2, 2009 It's more likely, if you've had a problem, that it's been caused by a mismatch with the turbo, rather than the cam being no good. The turbo mivec conversion is popular these days, it will get a lot more popular once the cam myths are thrown out. The specs I've found are (dur int, dur ex, overlap) 228, 232, 28 for the low cam and 300, 285, 88.5 for the big cam. I've also had a real killer of a cam in the V8 but it was so good the fuel pump had no chance of keeping up, that was the beginning of the end..........so I suppose I could say that a hot cam is no good with a turbo...... but it wouldn't be correct. Steve Quote Link to comment Share on other sites More sharing options...
slipsittin Posted February 2, 2009 Share Posted February 2, 2009 I've also had a real killer of a cam in the V8 but it was so good the fuel pump had no chance of keeping up, that was the beginning of the end..........so I suppose I could say that a hot cam is no good with a turbo...... but it wouldn't be correct. Steve The fuel pump couldn't keep up with the cam? Get some sleep man your rambling Corey Quote Link to comment Share on other sites More sharing options...
MACKAZ Posted February 2, 2009 Share Posted February 2, 2009 Not defending the man but yes It does happen. 3x48mm sidedrafts and stock Hemi fuel pump= no revs after 3k due to lack of fuel....... Quote Link to comment Share on other sites More sharing options...
slipsittin Posted February 2, 2009 Share Posted February 2, 2009 Yeah I know but it isn't the cams fault its the "I need more fuel to carry on or I'm just going to suck air and piss you off" in front of your mates deal We don't want to put in stuff that will cause the smart arse remarks and get the topic locked do we. Did you check out the Valiant I put up in the trademe auctions Mackaz? Corey Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted February 3, 2009 Share Posted February 3, 2009 Not defending the man but yes It does happen. 3x48mm sidedrafts and stock Hemi fuel pump= no revs after 3k due to lack of fuel....... The sixpack chargers had bigger fuel pumps. Quote Link to comment Share on other sites More sharing options...
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