[TransAm 474]

Good Morning to all... I have a question about what Intake Centerline to install the 2802. The cam card says to install it at 109°. This is a new build, everything is new, including the billet Cloyes timing set. My question is, should we install it a little advanced, say maybe 107° or 108° to allow for a little stretch of the new chain, or should we just install it at the stated 109° and let it end up wherever it does after chain strech? I wasn't sure which is preferred. Here is the combination of parts we are using

1970 YZ 400 .030" over
Zero Decked
Stock N crank
Eagle 4340 H-Beams
Icon forged dish piston 14cc
Stock #12 heads, Ferrea Stainless valves, cc'd at 70cc
Felpro 1016 .039" head gasket
Quench .039"
9.8-1 compression
Summit 2802 camshaft
224/234@.050 .466/.488 lift, 114° Lobe Seperation
Stock 1.5 rockers
Stock Cast Iron intake
Stock 7040270 RA III Qjet Recalibrated with Kit and Parts from Cliff
Stock 1112009 RA III points distributor recurved by Cliff
RA III Exhaust manifolds, dual 2.5" exhaust
TH400/Transgo 1-2 kit
Hughes GM25-BPO Converter
3.55 rear gears
1970 Trans am
Daily driven Street only, NO strip.
91 octane Pump Gas
1000ft Elevation (S.W. Missouri)

[Formulajones]

I move cams forward to try and achieve a certain intake/exhaust relationship at TDC. Hard to get that with a camshaft that has 114 LSA so you'll have to compromise.

last 2802 I installed I put at a 107 ICL. For your combo and being a 400 if it fell around 107-108 I'd run with it. If it falls at 109-110 I'd move it.

[Jay S]

Which cloyes set do you have? Billet sprockets and regular roller chain or the $$$ billet sprockets and chain? I would not be concerned about the billet sprocket/ billet chain stretching. Some of the others stretch pretty fast, i was into one last year that lost 4-5 degrees in 10 k miles. Might have been a roller master, but the $90 cloyes would probably be kinda similar. IMO, if it is driven much it is worth the $ for the better unit. I would not advance the cam, thinking it will wear into the ideal install position. If it is going to be driven much and the cam timing getting retarded do to wear is a concern, use the better chain. If that is what you have, install it were you want it and don’t worry about it.

FWIW.. From what I have read my thoughts on cam timing are not much different than what Jones posted. He uses lift at tdc, I use opening and closing events for overlap.

I always add 2 degrees on to the installed position for your effective cam position. I.E. if you want to the cam to run at 110, install it at 108. So the 109 position is running 111. At 111 the 2802 cam, which is a pretty old symmetrical profile has the intake events on the overlap 1 degree ahead of the intake events in the overlap/scavenging cycle. At 109.5, or dynamically out at the valve you assume 111.5, the events are dead even. On that cam you should not have any issues yet.

Different cam profiles respond differently on the overlap. Some cams have lazier profiles on the exhaust and you can run them retard more, at least they appear retarded looking at the seat timings, the events using .050 numbers might look totally different. The 2800 series is pretty straight forward though. Same symmetrical designs on both lobes.

Installed range for me on that cam is 107-110. The 109 installed is probably ideal for your combo imho. Personally I would shoot for 109, and if it happened to come out 108 or 110, I personally would not change it.

[TransAm 474]

Originally Posted by Jay S

Which cloyes set do you have? Billet sprockets and regular roller chain or the $$$ billet sprockets and chain? I would not be concerned about the billet sprocket/ billet chain stretching. Some of the others stretch pretty fast, i was into one last year that lost 4-5 degrees in 10 k miles. Might have been a roller master, but the $90 cloyes would probably be kinda similar. IMO, if it is driven much it is worth the $ for the better unit. I would not advance the cam, thinking it will wear into the ideal install position. If it is going to be driven much and the cam timing getting retarded do to wear is a concern, uses the better chain. If that is what you have, install it were you want it and don’t worry about it.

FWIW.. From what I have read my thoughts on cam timing are not much different than what Jones posted....I always add 2 degrees on to the installed position for your effective cam position. I.E. if you want to the cam to run at 110, install it at 108. So the 109 position is running 111. At 111 the 2802 cam, which is a pretty old symmetrical profile has the intake events on the overlap 1 degree ahead of the intake events in the overlap/scavenging cycle. At 109.5, or dynamically out at the valve you assume 111.5, the events are dead even. On that cam you should not have any issues yet.

Different cam profiles respond differently on the overlap. Some cams have lazier profiles on the exhaust and you can run them retard more, at least they appear retarded looking at the seat timings, the events using .050 numbers might look totally different. The 2800 series is pretty straight forward though. Same symmetrical designs on both lobes.

Installed range for me on that cam is 107-110. The 109 installed is probably ideal. Personally I would shoot for 109, and if it happened to come out 108 or 110, I personally would not change it.

Jay, the Cloyes chain set we are using is the 9-3512X9

[Jay S]

That is not the billet chain.. it is std HD rolller chain with billet gears.. That timing set I would shoot for 108 installed. They do stretch.

[Stan Weiss]

The ICL on the cam card is just a best guess for the average engine. Some engines may want it early and some may want it later. The only way to know where your engine wants it is to move the ICL around on the dyno.

Stan

[TransAm 474]

Originally Posted by Jay S

That is not the billet chain.. it is std HD rolller chain with billet gears.. That timing set I would shoot for 108 installed. They do stretch.

Thank You Jay and everyone else who has commented, I appreciate it

[TransAm 474]

Just as an update for future readers.... We ended up degreeing the camshaft by watching the Intake and Exhaust Lobe relation at TDC, like Pastry, Paul Carter, Formulajones, Harold Brookshire and others like to do. Most want the camshaft placed in the engine so that the Intake Lobe Lift is between .025" and .045" higher than the Exhaust lobe lift at TDC. We degreed the camshaft so that the Intake lobe lift was .0275" more than the Exhaust at TDC, the Intake Centerline came in at 106.125° using this method, but we liked the relation between the Intake/Exhaust lobes at TDC when installed there, so we left it at that. We did check it at the 109° Centerline per cam card, but the Intake was only .0185" higher than the Exhaust at TDC, too little according to most people, so we advanced it. Hope it runs well!

[Formulajones]

Originally Posted by TransAm 474

Just as an update for future readers.... We ended up degreeing the camshaft by watching the Intake and Exhaust Lobe relation at TDC, like Pastry, Paul Carter, Formulajones, Harold Brookshire and others like to do. Most want the camshaft placed in the engine so that the Intake Lobe Lift is between .025" and .045" higher than the Exhaust lobe lift at TDC. We degreed the camshaft so that the Intake lobe lift was .0275" more than the Exhaust at TDC, the Intake Centerline came in at 106.125° using this method, but we liked the relation between the Intake/Exhaust lobes at TDC when installed there, so we left it at that. We did check it at the 109° Centerline per cam card, but the Intake was only .0185" higher than the Exhaust at TDC, too little according to most people, so we advanced it. Hope it runs well!

Yep, that'll work and that's about as good as you can get it since that cam is on a 114 LSA. The wider the LSA the harder it is to accomplish that goal. Tighter LSA cams don't have to be moved forward as much to accomplish that.

[Stan Weiss]

Originally Posted by TransAm 474

Just as an update for future readers.... We ended up degreeing the camshaft by watching the Intake and Exhaust Lobe relation at TDC, like Pastry, Paul Carter, Formulajones, Harold Brookshire and others like to do. Most want the camshaft placed in the engine so that the Intake Lobe Lift is between .025" and .045" higher than the Exhaust lobe lift at TDC. We degreed the camshaft so that the Intake lobe lift was .0275" more than the Exhaust at TDC, the Intake Centerline came in at 106.125° using this method, but we liked the relation between the Intake/Exhaust lobes at TDC when installed there, so we left it at that. We did check it at the 109° Centerline per cam card, but the Intake was only .0185" higher than the Exhaust at TDC, too little according to most people, so we advanced it. Hope it runs well!

I have a lobe lift file for a Summit 2802 Intake, but am not sure how accurate it is. Setting it at 106 ICL it shows 0.0667" lifter raise. How is this compare to what you got?

Thanks
Stan

[TransAm 474]

Originally Posted by Stan Weiss

I have a lobe lift file for a Summit 2802 Intake, but am not sure how accurate it is. Setting it at 106 ICL it shows 0.0667" lifter raise. How is this compare to what you got?

Thanks
Stan

Our results showed the Intake at .0655", and the Exhaust was .038", and at these measurements our Intake Centerline came in at 106.125°.

Thanks Stan

Brian

[Jay S]

Just keep in mind the summit is a symmetric cam. It likely will not like a lot of advance. Just like a Crower 60919 or a Ram air 4 spec-8 melling. Both those cams when run with the optimum compression seem to have a sweet spot they like when installed on 109 Icl. Which is probably close to 111 Icl dynamically when the engine is at speed. That is where they often like to be, and make the most hp. Each of those have a have a little less aggressive exhaust profile than on the intake, but both are similar to that summit grind. The relationship at tdc is not exactly the same, it makes a difference how the cam profile is designed.

Summit grinds have a little different ICL window than one of Harolds cams. The last 6 cams I have had ground were designed by Harold (RIP). You may be able to advance a summit or Crower, ect...question is will the engine respond? I obviously have respect for his opinions on cam design. Harolds comments were many times related to the cams that he designed, and may not be that friendly to someone else’s design. The optimum ICL for a Crower 60919 is a pretty good example of a difference in design. At tdc the 60919 likes the exhuast and intake lifts closer to the same, only slightly higher on the intake opening at tdc. Mainly because the opening rate is gentler on the exhaust profile that the intake profile, and it is a symmetrical grind.

[TransAm 474]

Well, I hope it runs good Lol, maybe by the time the new chain stretches a little after break-in, it will end up in the 107-107.5° ICL area anyway.

[Will]

Originally Posted by TransAm 474

Well, I hope it runs good Lol, maybe by the time the new chain stretches a little after break-in, it will end up in the 107-107.5° ICL area anyway.

I was just going to say, run the snot out of it and it'll retard itself.

[TransAm 474]

Originally Posted by Will

I was just going to say, run the snot out of it and it'll retard itself.

Haha.... I have a feeling it will do fine, it will only end up a couple degrees advanced over where the Cam Card wants it after break-in, so the fingers are crossed Lol

[Formulajones]

The idea with this intake/exhaust relationship is that as the piston starts it's decent, it's sucking in a cooler intake charge, rather than a hotter exhaust charge, so that when the piston comes back up on the compression stroke, it's a slightly cooler combustion process, and as a result less likely to detonate.
Heat is the enemy.

[Stan Weiss]

Had a few minutes. The Summit 2802 has 114 LSA. If install on a 114 ICL you have the green line showing the intake lift and the red line showing the exhaust lift. If I advance the cam 8 degrees so the ICL is 106 the blue line shows the intake and the cyan line shows the exhaust.

Stan

[TransAm 474]

Originally Posted by Stan Weiss

Had a few minutes. The Summit 2802 has 114 LSA. If install on a 114 ICL you have the green line showing the intake lift and the red line showing the exhaust lift. If I advance the cam 8 degrees so the ICL is 106 the blue line shows the intake and the cyan line shows the exhaust.

Stan

Thanks Stan, that is some great info, could you do a chart showing the 109°/106° comparison? Thank You

[Stan Weiss]

Originally Posted by TransAm 474

Thanks Stan, that is some great info, could you do a chart showing the 109°/106° comparison? Thank You

Sure.

Stan

[TransAm 474]

Originally Posted by Stan Weiss

Sure.

Stan

Thanks Stan, I appreciate it. That comes out real close to the actual lift that we measured at TDC, within a couple thousands on each anyway, but our I.C. was coming in at 106.125° and 109.125°, so I assume that is where the couple thousands difference is coming from. I believe when we measured at 109.125° Centerline, we had right at .060" on the Intake and .0415" on the Exhaust. At 106.125° we had .0655" on the Intake and .038" on the Exhaust.