TGP Stock Cams?

[god910]

Stock 3.1L cam, as used in the 2.8L, 3.1L Vin T and Vin V

 

So now are we saying that the V & T's have the EXACT same cam? That seems a little rediculous. Especially when I read in a previous post of yours that, "... the stock cam isn't that bad to work with."

 

Then wouldn't we have a big power maker in the cam alone? If we're running off a n/a cam, we should be able to make a lot more power w/ a better cam/suited to a turbo application.

 

On another note, (following the same cam theory)would a computer friendly aftermarket cam (For a vin T), be just as friendly to a Turbo computer? (If you want to start a new thread 4 this last paragraph, be my guest.)

[Jeff M]

Additional Nested Accumulator Springs, other little changes to the tranny, some not listed until it's taken apart for inspection

 

Any more info on that? You're referring to the additional "inner-springs"?

 

Same thing different name . Some changes to the valve body layout, more clutches in 2nd and 3rd, been while since I looked at stock, rebuilding them is all I remember when I read my notes. The extra clutches became more common in rebuilds to all 4T60s and 4T60Es later, and some versions that use different friction materials and layouts (grooves cut in different directions). Different channel plate versions, some better than others, it gets really detailed to go through it all, changes from 1989-90 and during those periods total a lot, then later updates, enough to make a library :shock: ! You just made me remember, need to add that check valve at the vacuum accumulator, going to have to add that to my post above, thanks 8) .

 

Jeff M

[Jeff M]

Stock 3.1L cam, as used in the 2.8L, 3.1L Vin T and Vin V

 

So now are we saying that the V & T's have the EXACT same cam? That seems a little rediculous. Especially when I read in a previous post of yours that, "... the stock cam isn't that bad to work with."

 

Then wouldn't we have a big power maker in the cam alone? If we're running off a n/a cam, we should be able to make a lot more power w/ a better cam/suited to a turbo application.

 

On another note, (following the same cam theory)would a computer friendly aftermarket cam (For a vin T), be just as friendly to a Turbo computer? (If you want to start a new thread 4 this last paragraph, be my guest.)

 

Yea, I know , been lots of people in the past that wondered this and why, but when I know good/smart guys running GN/T-Types with stock cams (lots of other stuff) running 10s, and now quite a few Syclone and Typhoons with stock cams running 10s, its not a killer of power, BUT you are right, it will help in making more power, but messes with the chip tuning, even a “computer friendly†one. I had a local TGP owner who did a cam upgrade, Crane H260 I believe, a quoted turbo cam that was not too radical, but his car had a hard time starting and running in all weather conditions, ran the scan tool on it and the fuel trim (BLM and INT) were topping out trying to add enough fuel to compensate, open loop was worse since there was no fuel trim compensation (since long term BLM by itself was not enough), never really got a chance to final chip tune him before he retired his car, we got it better but not what I would want for him. Back to the “stock†cam, all my GM parts books show the cam part number the same as I posted, all aftermarket companies show same as well though I would be more inclined to trust GM, but even then someone a while ago sent their TGP cam in to be checked for spec’s, it was a stock NA cam. So as you quoted me as saying, “stock cam is not bad work with†is still true, and some of that based on the 10 second cars above, nothing “wrong†with upgrading the cam for more power, just the challenges it brings. Those not wanting to take their engine out and all, can just get bigger (someday) turbos and intercoolers that will give more bang for the buck. As for another posting topic on this, if we end up getting more discussions here, but I believe I covered this once in the past that you must of gotten that quote from me on, cannot remember all the posts and emails I do, so we could take it there if needed, just need to give a link so I know where to go :oops: .

 

Jeff M

[god910]

Yeah, I usually run across a post from like 1935 that had a nice tidbit of info (I love using the search function) then can't remember where I saw it. Here's why I ask about the cam change: GMPP cam #12364059

 

"the basic Rpm Range 1500-4500 with 6500 atainable with proper valve springs. Cruise RPM for 2200-2600 and a compression ratio of 8.0-9.5 to 1

the duration at 0.50 lift (intake/Exaust) is 204*/216* while the valvelift is .454"/.427". LObe centerline is 112.

 

Someone wants that cam in their car, and has it in their current N/A 3.1 w/ no problems. Just wandering if there will be problems.

 

As far as a GN/TType or a SyTy, do the N/A versions of those motors (Buick 3.8 and Chevy 4.3) have the same cam? Or was GM smart enough to give them better exhaust parameters designed for a Turbo app. If so, that would lead me to believe our cars would see better gains (aside from the obvious extensive chip work) than those cars would.

[Jeff M]

Yeah, I usually run across a post from like 1935 that had a nice tidbit of info (I love using the search function) then can't remember where I saw it. Here's why I ask about the cam change: GMPP cam #12364059

 

"the basic Rpm Range 1500-4500 with 6500 atainable with proper valve springs. Cruise RPM for 2200-2600 and a compression ratio of 8.0-9.5 to 1

the duration at 0.50 lift (intake/Exaust) is 204*/216* while the valvelift is .454"/.427". LObe centerline is 112.

 

Someone wants that cam in their car, and has it in their current N/A 3.1 w/ no problems. Just wandering if there will be problems.

 

As far as a GN/TType or a SyTy, do the N/A versions of those motors (Buick 3.8 and Chevy 4.3) have the same cam? Or was GM smart enough to give them better exhaust parameters designed for a Turbo app. If so, that would lead me to believe our cars would see better gains (aside from the obvious extensive chip work) than those cars would.

 

Yea I think of my brain as a hard (yea hard head too ) drive, it can only hold some much, then I need to offload or print the excess . Did the NA guy check the fuel trim and what it said about closed loop, that would be something to check out, is he running that much faster with the cam without some chip tweaking, hard to say without having the car here. Though a cam "says" it works in a range does not mean its not different in that range from a stock cam, still has a chance to mess the fueling up.

 

As for the GN, SyTy etc :oops: yea stock cams, some of that for eaiser tuning and getting these out the door, some for less challanges to meet emissions, and cheaper to stock one cam for all those engines, sucks yes but cams are really the baby for NA guys since their options are limited, they only got heads and cams to find big gains from, and go all out in those areas to find hp. Special heads from like (overpriced) SLP and others being their own casting are so much different than stock that a cam becomes a nessesity since the heads are making power in one area and the stock cam is making it in another area. I got more so if you could find that post where I opened my big mouth (the PMs and emails always back up when I start posting ) we can move this over there. Wife is ragging on me (their job I guess) so need to head out, be back later to see if I know how to move these posts to the other location.

 

Jeff M

[SleeperRed90TGp]

Jeff M wrote

Those not wanting to take their engine out and all,

 

 

Not nessassary. For 22.50 you can put a hole in the fender well. 2 1/4

hole saw about 15.00 and a piece of alum from the hardware store. After

several cam changes I have found this to be one of the most worthwhile mods I have made. About an hour's worth of work.

 

Don't even have to take the tire off. But taking the tire and the plastic splash shield off sure makes it easy to get the damper pully off. I use an impact wrench on my puller. You might have to pry the heater tube out of the way but it's well worth it.

 

Just thought I would through this in for thoes contemplating changing a cam. It's easy.

 

 

Jud

[Jeff M]

Check this W-Body TGP Thread on Turbo Cams (yes being a smart ass showing this from our own board ).:

 

http://www.w-body.com/forum/viewtopic.php?t=856

 

Jeff M

[Jeff M]

Jeff M wrote

Those not wanting to take their engine out and all,

 

Not nessassary. For 22.50 you can put a hole in the fender well. 2 1/4

hole saw about 15.00 and a piece of alum from the hardware store. After

several cam changes I have found this to be one of the most worthwhile mods I have made. About an hour's worth of work.

 

Don't even have to take the tire off. But taking the tire and the plastic splash shield off sure makes it easy to get the damper pully off. I use an impact wrench on my puller. You might have to pry the heater tube out of the way but it's well worth it.

 

Just thought I would through this in for thoes contemplating changing a cam. It's easy.

Jud

 

Slick, I like the idea , don't get me wrong but you have to replace the cam bearings though, why? I have a few used cam bearings that show the cam bearings wear pretty badly (NOT TGP specific!!, so no TGP Bitchen), even on an engine with only 50k miles. Also in your side install approach, you need a Cam Install Tool/Rod if you want to avoid taking out a cam bearing surface by dragging or bumping the cam (lobes mainly) into/across the bearing surface and gouging it while you are installing the new cam (or removing a cam)! NOT to make out you are wrong with this tip, just to mention to you and others some things to watch out for!

 

Also, having the cam bearings so worn out relieves/leaks a good deal of the oil volume from the rest of the engine, including the lifter oil feed galley, which I think some may find is more a contributor to lifter failings for the few who have had it.

 

Jeff M

[Jeff M]

Ok, wrapped up a big project for a good TGP customer, still hacking hard at a lot of emails and other projects, but before the thoughts on this topic got too old, am going to take the time to type up info I found in my piles regarding turbo cams (and air flow combos). These words below are quoted and not my words, not able to speak this well about such a topic, but able to understand it when someone explains it so well and in one page, so hope it explains it well for others. I quote from Grape Ape Racing and give full credit to them here for this information:

 

 

PRESSURE DIFFERENTIAL

Unlike a supercharger that is driven directly form the crankshaft, a turbo is driven by exhaust gas velocity. Turbochargers are an exhaust restriction (which raises the exhaust gas pressure), but since they use energy that would otherwise be wasted, they are much more efficient than a belt driven supercharger. Normally when the exhaust valve opens, there is still useable pressure in the cylinder that needs to be dumped so it will not resist the piston trying to go back up the bore. That pressure makes high exhaust gas velocity. With a turbocharged engine, this is the energy that is used to spin the turbine.

With a well matched turbo / engine combo, boost pressure should be higher than exhaust gas pressure at the low side of the power band (near peak torque). As the engine nears peak hp, the pressure differential will get nearer 1:1. At some point the pressures in the intake and exhaust will be equal then crossover making the exhaust a higher pressure than the intake. At peak hp there will usually be more exhaust gas pressure than boost pressure. The ultimate goal is to have as little exhaust backpressure possible for the desired boost.

If the turbocharger is matched well to the engine combination, the camshaft selection will not need to be much different than that of a supercharged engine. The problem is that most factory turbo engines have turbo's that are sized too small and will usually have more back pressure than boost pressure over much of the useable power band. Car manufactures do this in an attempt to reduce turbo lag. When a turbocharger is too small, it will be a bigger restriction in the exhaust, causing more back pressure. A big mistake of turbo owners is to crank the boost up as high as they can thinking they are going faster, but in reality, chances are that they are just killing the efficiency of the turbo and most gains are lost. If you want to run higher boost levels and back pressure is a problem, cam timing can be altered to give respectable power increases for much cheaper than a new turbocharger. Before you go increasing boost and changing cams, remember that the oxygen content into the engine will increase power, not boost pressure. A good flowing head with a good intercooler can make a lot of power without high boost. You may not need more boost to get the power you want.

 

 

VALVE OVERLAP

If your one of many factory turbo car owners with a turbo sized too small, there will be higher exhaust pressure than intake, you should see that if both valves are open at the same time, the flow would reverse. Any valve overlap is a no no if you're looking for higher boost with a restrictive turbine housing. The exhaust valve will usually close very close to TDC, but there is will still be more pressure on the cylinder than in the intake. You must allow the piston to travel down the bore until the pressure is equalized. If the cylinder pressure is lower than the intake manifold pressure, no reverse flow will take place. This means that the intake valve needs to open 20-35° ATDC, depending on the amount of boost you're using. Most street turbo's will work well when the valve opens close to 20° ATDC, only when boost gets near 30 psi will you need to delay it as much as 35° ATDC. In low boost applications (under 15 psi or so), opening the valve closer to TDC and maybe keeping the exhaust valve open a little after TDC is a compromise for better throttle response before the boost comes on. As you increase boost, you will need to delay the opening of the intake valve to avoid reversion. You want the intake valve to open as soon as possible, in an ideal situation, the intake valve should open when the pressure in the cylinder is equal to boost pressure. This can cause a little confusion with cam overlap. If the exhaust valve closes before the intake opens, the overlap will be considered negative. If the exhaust valve closed at TDC and the intake opened at 20° ATDC there would be -20° of overlap. In this type situation, pumping losses are quite large, although the turbo will still use less power than a crank driven supercharger.

If you have a well matched turbo for the engine and application, it is a different deal altogether. A well matched turbine housing on the turbo will usually work well with cams with a lobe separation in the 112-114° area. If there is more pressure in the intake than in the exhaust, a camshaft suited for superchargers or nitrous will usually works well. When the exhaust backpressure is lower than the intake, reversion is not a problem, actually just the opposite is a problem. More pressure in the intake can blow fresh intake charge right out the exhaust valve. This can be a serious problem with a turbo motor since the charge will burn in the exhaust raising temperatures of the exhaust valves and turbo. This is also a problem with superchargers, which is why supercharger cam profiles usually work well with turbo's. In this type situation, the power required to turn the turbine is nearly 100% recovered energy that would have normally been dumped out the tailpipe, basically free power. Many will argue that nothing is free and you need pressure to spin the turbine and this must make pumping losses. They are wrong because a turbo is not getting anything for free at all, it is just making the engine more efficient. It is true that there are pumping losses, but on the other hand there are pumping gains as well. If the exhaust back pressure is lower than the intake, the intake pressure makes more force on the intake stroke to help push the piston down. At the same time another piston is on it's exhaust stroke. So the intake pressure is more than canceling out the exhaust pressure. Not free, just more efficient.

 

 

VALVE LIFT

By delaying the opening of the intake, the duration of the cam will be much shorter. A short duration intake works well with a turbo, but the problem is that sufficient lift is hard to get from such a short duration. This is where high ratio rockers can really pay off. A cam for a turbo engine can delay the intake opening by over 40° compared to a cam for a normally aspirated engine. This makes for much less valve lift when the piston is at peak velocity (somewhere near 75° ATDC), any help to get the valve open faster will make large improvements.

 

 

ROLLER CAMSHAFTS

Turbo motors place a large flow demand at low valve lifts, and roller cams cannot accelerate the valve opening as fast as a flat tappet. They do catch up and pass a flat tappet after about 20° or so, but up until that point the favor goes toward the flat tappet cam. The area where rollers really help in turbo motors (and supercharged) is cutting frictional losses. Any forced induction engine will need more spring force on the intakes. If you run a lot of boost, you'll need quite a bit more spring force to control the valves. As spring forces get higher, the life of the cam gets reduced. A roller tappet can withstand more than twice the spring pressure as a flat tappet with no problems. On the exhaust side, it's not the springs that put the loads on the cam lobes. The problem there is that there is still so much cylinder pressure trying to hold that valve closed. This puts tremendous pressure on the exhaust lobes. So when high boost levels are used, consider a roller cam. I would definitely consider a roller cam on engines making more than 20 lbs. of boost.

 

END from Grape Ape Racing.

 

 

So, these are the ideals to shoot for, and the background understanding for those, not that anything less is all bad, just that there will always be some give and take with any turbo engine setup out there until there has been a lot of background testing info and a few re-tries tested once again (and again, and again) to get to an optimum turbo to engine/heads/cam combos. I strongly suggest that anyone reading this type of info for the first time to read it a couple of times before you make a conclusion or base your actions on those conclusions, you will miss things the first time around, takes a bit to digest the first time, smooth sailing for some, maybe old info for others. To extrapolate from David Vizard a wrap up to all this, who also talks the same info above; once you overcome the shortcoming of a less than perfect turbo to engine/cam/head combo the closer you will have the cam events back to a normally aspirated cam :!:. I would like to give respect (though I am not worthy to really offer it :oops: ) for David Vizard, and suggest anyone wanting to really learn from the best regarding air flow (a general term for air from the air filter/box all the way to the tail pipe, and all the good stuff in between!!) that you find and get as many publications as you can from him, might be a little hard since he has published over 3,500 articles, 29 books (5 Best Sellers), but its worth it, and/or his seminars. This man holds numerous patents, a university lecturer (when not on the road giving great seminars!), 169 track records on everything from F1 across the board to drag racing and dirt cars, all from just 8 engines, the guys just kills !

 

Jeff M