Anybody know what the difference (if any) is between the turbo & non turbo cams? I've got a regular 84 3.8 I plan to turbo charge but I can't find teh cam specs anywhere. The repair manuals don't even specify cam lift in the overhaul sections. Reason I am asking is I was wondering if the regular 3.8 valve springs could handle a cam about equivalent to the stock GN cams.
Non Turbo Cam Specs
- Thread starter LemansWagon
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well i know some change the cam. the most important thing i have seen is the different rocker set ups. one set for intake and another for exhaust. The exhaust stays open longer to get the exhaust out. try the comp cams program to find your cam. I would attach the program but i don't know how to. It will help you with keeping the compression low and boost high.
The turbo cam tries to reduce overlap more (that's when the exhaust and intake are open at the same time) in order to allow the turbo to build more pressure. Overlap in a non-turbo engine can help the exhaust scavenging process but it's not needed on a turbo.
You don't want a used turbo cam because if you re-use a flat tappet cam, it will most likely wear out the lifters prematurely. You can get a new stock GN profile cam from PAW for 160 bucks or so. Lifters are separate.
Get a stock 87 GN cam (or 89 Turbo Trans Am, same thing) for the best performance on a budget. The Melling number is something like M77-229-1841...
Don't run the older carb turbo cam. They can be had for about 70 bucks but they don't make any power, really. You want 84-87, and it will work great with a carb...
Lift on the turbo fi cam is .3970 (or 10mm) off of the cam lobe itself. I don't have duration numbers. If you multiply that by 1.5 rockers, you get .596 lift! That means you need better valve springs and the guides must be cut down a little as well.
One of the biggest problems you are about to encounter in your $10 engine is piston/ring failure. Buick made special HD pistons for the turbo engines because of early failures in the carb turbo models. You need to at a minimum buy a set of aftermarket turbo pistons. You can find used sets on eBay, so you can still do it on the cheap. You must do it if you want the engine to survive.
Good luck!
You don't want a used turbo cam because if you re-use a flat tappet cam, it will most likely wear out the lifters prematurely. You can get a new stock GN profile cam from PAW for 160 bucks or so. Lifters are separate.
Get a stock 87 GN cam (or 89 Turbo Trans Am, same thing) for the best performance on a budget. The Melling number is something like M77-229-1841...
Don't run the older carb turbo cam. They can be had for about 70 bucks but they don't make any power, really. You want 84-87, and it will work great with a carb...
Lift on the turbo fi cam is .3970 (or 10mm) off of the cam lobe itself. I don't have duration numbers. If you multiply that by 1.5 rockers, you get .596 lift! That means you need better valve springs and the guides must be cut down a little as well.
One of the biggest problems you are about to encounter in your $10 engine is piston/ring failure. Buick made special HD pistons for the turbo engines because of early failures in the carb turbo models. You need to at a minimum buy a set of aftermarket turbo pistons. You can find used sets on eBay, so you can still do it on the cheap. You must do it if you want the engine to survive.
Good luck!
Well, I didn't find the n/a cam specs but The .392 lift you referenced is actually valve lift. Cam lift would be .392/1.55 = .253. I did find the valve spring specs in my "Guide to Buick Perf Engines" book and the turbo springs are quite a bit heavier than the n/a springs afterall. So that answers my question. I have a set of turbo heads I think I will swap those springs over since other than the springs the heads themselves are the same. It should be a direct swap because the installed heights are the same. The cam I was looking at is a comp cams that has 212 duration & .459 lift w/ a 112 lsa. It a GN upgrade cam and might be a tad big for a $10 engine to handle. They have a few smaller ones too which may be a better choice. One is 206/.425. I'll have to check out that melling cam you mentioned too. I will probably leave the stock n/a cam in initially just to see how it performs.
I also agree that the weak point will be the pistons, but for $10 who cares. I have a wide band a/f sensor that I will have plugged in during the tuning process. I think if I can keep the mixture fat the pistons will survive. The methanol injection will help keep things cool in the cylinders as well. We'll find out :lol:
I also agree that the weak point will be the pistons, but for $10 who cares. I have a wide band a/f sensor that I will have plugged in during the tuning process. I think if I can keep the mixture fat the pistons will survive. The methanol injection will help keep things cool in the cylinders as well. We'll find out :lol:
if you go to comp cams you can download the camquest6 program for free. i'd use that to pick a cam, and it will tell you what springs to use. using the right springs will also assure the right seat pressures. you do not want valve float!!! the hardest thing on the pistons is the level of boost. i'd run a decent cam so that you have the power and use a boost control to regulate it. this way when you want to have fun, just turn a knob and GO!
The 980-12 springs are what Comp reccomends for all thier 3.8 cams and they are actually just slightly lighter than the stock GN springs.
I know boost is harder on pistons but it's usually heat or detonation that actually does the piston in. If you avoid those even stock cast pistons can take quite a bit in most applications. Trouble with cast pistons is there is no room for error like with forged or hypereutectic. One mistake and boom.
I know boost is harder on pistons but it's usually heat or detonation that actually does the piston in. If you avoid those even stock cast pistons can take quite a bit in most applications. Trouble with cast pistons is there is no room for error like with forged or hypereutectic. One mistake and boom.
Hmnn you might want to inquire about what you are wanting to do over at turbobuick or turbobuicks.com. The turbo cars (GM) used a "109" block. I know racers that break blocks would either look for an older clapped out 84/85 GN/Ttype that they could pick up cheap for the block (and other stuff) or the 4.1 block. They never use the standard 3.8 block and I know their is a reason I just don't know what it is. I have an 87 intercooled GN and use a system specifically designed for methanol and it works great. I bought mine from a guy that goes by Razor on turbobuicks. He designed sells races & supports it. I used a 50/50 mix of meth & water. Very pleased so far. I run 24 pounds boost on it with pump gas.
From what I understand the block, crank, & pistons are all stronger on the turbo cars. But I have also heard (on turbo buicks actually since you mention it LOL) that the stock (81+) 3.8 cranks are plenty strong and many run them into the 10's. The block will rip the mains out under high boost levels. For now, for what I am doing I think I'll be ok. Pistons are a question but my 85 T3 turbo won't push more than about 275 hp anyway. If I upgrade to a bigger turbo later I will go through the short block at that time.
But right now I'm looking for a cheap way to get into turbo 3.8's. Always loved them.
For the methanol injection I have a spare efi pump and regulator I plan to combine with spray nozzles from mcmaster car and a hobbs switch. Speaking of which, what's a good source for an inexpensive, preferrably adjustable, hobbs switch.
But right now I'm looking for a cheap way to get into turbo 3.8's. Always loved them.
For the methanol injection I have a spare efi pump and regulator I plan to combine with spray nozzles from mcmaster car and a hobbs switch. Speaking of which, what's a good source for an inexpensive, preferrably adjustable, hobbs switch.
Methanol is harder on parts than iso alcohol and needs a few upgrades to hold up long term. Razor had a component, description & reasoning to his kit on his page linked from his profile. He will tell you that you can build your own for less and tell you what to & what not to do. Most just won't go to the trouble and buy his or another kit. Their is another poster on turbobuicks that has a site that has great info & help on meth/alcohol/water kits amoung other things but I can't think of his name at the moment.
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