D83ZXT Posted October 29, 2002 Share Posted October 29, 2002 Two cam suppliers that are recommending this split type of cam design for turbo motors. ISKY's 1).490 intake .480 exhaust w/center lobe @114 (242) (232) up to 7000 RPM's Elgin's 2).532 intake .507 exhaust w/center lobe @112 (sorry my notes aren't here for the .050 break down) up to 6000 RPM's What's your opinion/experience on these split cams? Donna Quote Link to comment Share on other sites More sharing options...
DavyZ Posted October 30, 2002 Share Posted October 30, 2002 *bump* Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted October 30, 2002 Share Posted October 30, 2002 didnt some hybrid z member design a turbo cam?i dont remember the thread but i kind of remember a gripe about jwt copying it and claiming it was thiers.cam depends on driving style or uses of car.but a little more cam could help prevent detonation by reducing cylinder pressure at low to mid rpm.i have a magazine with an article about a 1200 hp twin turbo 350 chevy in a corvette .supposed to be a daily driver.engine was set up with a cam shaft made to let engine rev to 7000 and turbos sized to not make boost to early-lots of exhaust flow at high rpms.this was done to keep cylinder temps lower .but you might end up with an engine thats flat till 4000 rpm. Quote Link to comment Share on other sites More sharing options...
Guest Tom Scala Posted October 30, 2002 Share Posted October 30, 2002 Almost all off the shelf and custom blower/supercharger cams sold by B&M & others for popular V8 applications are split pattern with more duration & lift on the intake to allow more of the compressed intake charge to be packed into the cylinder. Those engines have a wedge style chamber with 2 valves per cylinder just like a L6 and contrary to what alot of people think will respond similarly to most mods. They also have the wider 112-114 degree lobe spread that cuts down on overlap and extends and broadens the power curve & rpm range compared to a tighter 108-110 LSA. Not to mention a wide LSA will have a smoother idle with higher idle vacuum if duration is held constant. I don't know why so many people use cams that are the opposite of that (narrow lobe spread,single pattern) in the L6 turbo motors. Those type cams work great in a hipo n/a motor. To me those specs you've got seem very good for a high winding turbo motor. Quote Link to comment Share on other sites More sharing options...
Mike C Posted October 30, 2002 Share Posted October 30, 2002 It is true that most forced induction cams are split duration. But they have extended EXHAUST duration. The intake is fortified with the mechanical pressure device but the exhaust needs the added duration in order to get all of the gases out of the cylinder. Overlap definitely needs to be minimized to keep the fresh intake charge from going right out the exhaust. Before I opened my yap, I did a search at Cranecams.com and EVERY blower cam I could find had more exhaust duration and the Crane cams for Datsun turbo motors also had more exhaust duration. I don't know why they are recommending cams with more intake duration than exhaust. VERY unusual... Quote Link to comment Share on other sites More sharing options...
D83ZXT Posted October 30, 2002 Author Share Posted October 30, 2002 Nathan, The duration specs on the Elgin is 274 intake 256 exhaust. Above post was both lift and duration on the ISKY. It's being recommended by several cam supplier's plus builders to go larger on intakes. (With info of 3.0 stroked, headwork, 860CFM turbo, with TWM's individual throttle bodies,and TEC.) Richard Isky, Reed, and Elign's like the higher durations on intake over exhaust. Maybe TimO will step in to explain it. I gotta run, I need to CHEER them Z'rs that are going to Sears Point tonight Donna Quote Link to comment Share on other sites More sharing options...
D83ZXT Posted October 30, 2002 Author Share Posted October 30, 2002 I am finding this to be quiet interesting. Keep it coming I too had an the durations larger exhaust over intake on the old cam. Now, finding the good old switch-a-roo for turbo motors. lol Z-ya Donna Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted October 31, 2002 Share Posted October 31, 2002 Originally posted by D83ZXT:Two cam suppliers that are recommending this split type of cam design for turbo motors. ISKY's 1).490 intake .480 exhaust w/center lobe @114 (242) (232) up to 7000 RPM's Elgin's 2).532 intake .507 exhaust w/center lobe @112 (sorry my notes aren't here for the .050 break down) up to 6000 RPM's What's your opinion/experience on these split cams? Donna Mike C, that is a good question about the exhaust duration being shorter than the intake. My Schneider turbo cam has more duration on the exhaust than the intake as well (270/280). Donna, you are quoting durations here, not lift!?!? (just checking) Quote Link to comment Share on other sites More sharing options...
Guest Tom Scala Posted October 31, 2002 Share Posted October 31, 2002 The Crane cams for the L6 Datsun are not recomended for turbo motors because they have more exhaust duration. I haven't seen their supercharger cams with longer exhaust lobe but every other forced induction cam spec I've seen has the extra intake duration. For the L6 the Schneider turbo cams sold by Motorsport have the split patterns with the intake being longer in duration & higher in lift than the exhaust. With wide LSA's, keeping the exhaust open longer will cause it to close later and also increase overlap which reduces cylinder pressure somewhat. That is what you don't want with a turbo motor,at least in theory. Then again ask 10 people for cam specs and you usually get 10 different answers. I guess someone is just going to have to take one for the team and buy a bunch of different cams and spend some time on the dyno to find out for sure. Whos Visa card is up for it? Quote Link to comment Share on other sites More sharing options...
TimZ Posted October 31, 2002 Share Posted October 31, 2002 Originally posted by Mike C:It is true that most forced induction cams are split duration. But they have extended EXHAUST duration. The intake is fortified with the mechanical pressure device but the exhaust needs the added duration in order to get all of the gases out of the cylinder. Overlap definitely needs to be minimized to keep the fresh intake charge from going right out the exhaust. Before I opened my yap, I did a search at Cranecams.com and EVERY blower cam I could find had more exhaust duration and the Crane cams for Datsun turbo motors also had more exhaust duration. I don't know why they are recommending cams with more intake duration than exhaust. VERY unusual... This is true for supercharged engines (which I would guess that Crane is more used to supplying cams for), but in most streetable turbocharged applications, the exhaust manifold pressure is higher than the intake manifold pressure. Reversion is the problem with long overlap periods and turbos, not blow-through. Quote Link to comment Share on other sites More sharing options...
Mike C Posted November 1, 2002 Share Posted November 1, 2002 Agreed, but that explains overlap and not extending intake duration. What is the/your theory there? Quote Link to comment Share on other sites More sharing options...
TimZ Posted November 1, 2002 Share Posted November 1, 2002 Originally posted by Mike C:Agreed, but that explains overlap and not extending intake duration. What is the/your theory there? I'm not convinced that it's really effective, but I would imagine the reason for increasing the intake duration is the same as always - to move the torque peak higher in the rpm range. It's just a balancing act to keep the exhaust reversion to a minimum, and try to move the torque peak to a higher rpm. Quote Link to comment Share on other sites More sharing options...
TimO Posted November 3, 2002 Share Posted November 3, 2002 I'm deciding which new cam to buy and in the process I asked John of Elgin Cams the question regarding turbo cams having more aggressive duration and lift on the intake side. His answer was essentially the same as Timz...the biggest issue it to maintain flow volocity, to maintain a little more pressure on the exhaust side, that the torque curve is adjusted (flattened, moved up or down the rpm range, peak) by duration and degree of L/C. Overlap kills a turbo engine unless you want a peaky high rpm motor that can't be driven on the street. Quote Link to comment Share on other sites More sharing options...
D83ZXT Posted November 3, 2002 Author Share Posted November 3, 2002 Mine's been ordered. So I guess we shall see Hey TimO... Would you like for me to order your's? I have this special Credit Card... Giggle giggle.. Gotcha Donna Quote Link to comment Share on other sites More sharing options...
TimO Posted November 3, 2002 Share Posted November 3, 2002 Donna (LS)......you've got mail! Still on the left! TimO Quote Link to comment Share on other sites More sharing options...
TimZ Posted November 3, 2002 Share Posted November 3, 2002 Originally posted by D83ZXT:Mine's been ordered. So I guess we shall see ...So which one did you decide on? Might as well put one on that card for me, while you're at it. Quote Link to comment Share on other sites More sharing options...
DAW Posted November 3, 2002 Share Posted November 3, 2002 I'm naive here but could the cam designers be looking for optimizing low-end off-boost performance to minimize turbo-lag, knowing that the intake profile has to remain constant but compressed intake charge will increase with r.p.m and can increase intake filling at a relatively low duration on boost? Looks like there may be two approaches, one for maximum boosted h.p. and one for maximum driveability off boost with more modest max h.p. gains. Could this be the case? (and don't beat me up because I'm just theorizing) DAW Quote Link to comment Share on other sites More sharing options...
TimO Posted November 4, 2002 Share Posted November 4, 2002 TimZ I ordered my cam on Friday from Elgin. Specs: Lift at the lobe .355 in take,.338 exhaust -with a rocker arm ratio of 1.47 that's .521 and .496 respectively. Duration (net) intake 240, exhaust 236 Lobe centers @ 114. I decided to go with the L/C of 114 rather than 112 for a flatter torque curve, and 236 duration on the exhaust rather than 226 because I want to take advantage of my higher red line (than Donna's). Should get it in a few weeks... I'll call ya. TimO Quote Link to comment Share on other sites More sharing options...
D83ZXT Posted November 4, 2002 Author Share Posted November 4, 2002 SURE TimZ... I'll place yours on the Card too! TimO, My numbers might be changing Since we have to wait until they get the Cold Forged in. I have a few question's to bring up after being at Sears Point. And Yes.. You'll Always be on the Left, you're alot lighter then I!!! Darn 240's!!! Why do you think I need more HP lol Donna PS.. what's this LS? ROFL Quote Link to comment Share on other sites More sharing options...
D83ZXT Posted November 4, 2002 Author Share Posted November 4, 2002 Hey Nathan... I was looking at my old Schneider cam specs. Now this was a mild cam for a kinda stock L6 Turbo, it was .460 valve lift intake 270/260 exhaust duration. .050= camlift of 230/220. I never got to run this, but it does show the intake was larger then exhaust. Donna Quote Link to comment Share on other sites More sharing options...
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