Cam swap question

Got my engine stumble issue straightened out ....fuel pump, go figure.... anyway, here's a little backstory my car is 1970 GS with the 350 4V 315hp, 410tq engine. All stock, compression test results are 150-165psi across all 8. No leaks, no smoke, and runs good now....I want to do a cam swap, as well as TAperformance intake, and enjoy the car for a bit from there. I haven't picked out a cam yet, but I don't want to run a stall converter, so I plan on keeping it small. Now, I've done overhead cams before, but never a traditional cam. So heres my question, if I do the cam and intake together, do not pull the heads, and go with the TA 284 cam or similar (small enough to not change springs) I install the new cam, lifters, pushrods, and time the engine. Correct? I know theres a lot to come off and go back on, and I've watched a bunch of vids on guys doing it, I'm not afraid of it, I've done tons of precision machine work being a millwright and electrician by trade I have all the calipers, dial indicators, etc.. one can ever need, I guess my real question is if I don't change the springs to I need to do anything to the heads?

Thanks

Vince

 

If you crack that beautiful engine open I'll have to shed some tears...

I wish I could save you some head/heartache right now and tell you that if it isn't broke, don't fix it, but...

Best thing you could do for that engine is put a small "X" pipe in the exhaust. Either 2" mandrel bent or 2 1/4" press bent, with downpipes from manifolds leading to "X" pipe being 2" or 2 1/8" MANDREL bent. From the "X" pipe back can be press bent.

If you insist on opening it up, get the Federal Mogul CS647 camshaft, new (stock) valve springs, the matching stock timing chain/gear set, and Crower camsaver lifters, making sure your oil pressure is good. Freshen up the rings, hone the cylinders, grooved cam bearings, new bearings on mains and rods, better main and rod BOLTS, polish up the exhaust runners on the heads and exhaust manifolds as far in as you can go on the inlet sides, then polish the exit port best you can, as smooth as you can. Intake runners on heads and intake manifold, just smooth over casting flaws, taking out as little material as possible.

Shave the heads a little to bump DCR a little more for premium and set the ignition timing according to Larry's recommendations. (EDIT: 150-160 lbs. compression is good, may not need to shave heads much, other than truing them up).

THIS will give you more power than adding a camshaft, and you will have a 200,000+ mile engine before anything major needs doing to it, providing you keep the oil changed with good oil (Mobile 1 fully synthetic 5w30 high mileage oil, which has plenty of ZDDP in it for the stock cam).

The stock intake will be just as good as the TA dual plane on a stock engine, though it will add a little more if you open the exhaust up as mentioned earlier.

*fingers crossed*


Gary

 

well to be honest, I am on the fence about the cam, the intake is a definite, as well as headers and 2 1/2 mandrel bent exhaust with H-pipe in it, I know x's are a little better, but I don't like the x-pipe sound. the reason the cam is still a question mark is because it doesn't use any oil, leak anything, and runs very well now that I am not starving the carb at high rpm. like you said, if it ain't broke....

 

Gary has some really good points. But the cs647 is actually smaller in duration then the rated duration on the 70 GS cam. Compression is about 9.7 as is if it has original steel headgaskets. If you pull heads and use aftermarket head gaskets you will actually drop compression to about 9.45 as there is .023 thickness difference. So if your engine is original leave the heads on unless you are getting porting or big valves installed. 284 cam needs a 2500 on more convertor 3000 for strip use. The 284 also likes Alittle more compression but it will still work at 9.7well. The 212 is ok with stock convertor but torque come up around 2000 so a 2000-2200 would net best gain. Ta stage 1 -350 cam brings torque up fast but might not add much more than that to thay engine,i would say they are very similar to the original cam. I suggest the crower level 3 cam. Strong torque and your compression is about what you need for it.the othe cams really need porting and big valves to make similar power as the crowemanifoldswill do it with stock intake and exhaust manifolds.Add a electronic conversion to the original distributer and recurve kit. TA has 350 downpipes from manifolds them get a H or X system from flow master(the have just pipe kit if you don't want their mufflers) magnaflo(I use this one) or pypes kit. Get springs as they are old and will float above 5000. Can be installed with heads on engine. Use stuff rope or use air pressure to hold valves up. Unless you go with the sp3 intake you don't gain much unless you port intake. You will need to jet carb up some ,bigger accelerator pump and hi flow needle and seat along with secondary rods and hangers. You will need at least a 3.08 rear or 3.23 minimum to get that performance that engine will put out. I would consider the convertor even on the stock cam.

 

Any cam mild enough to.tbe point of not needing a converter is pointless imo, as is using stock springs that are certainly weaker now than they were. Youve got a solid shortblock with good compression put a decent cam.in and new stiffer springs and a 2500 stall . Anything less and your gonna be asking yourself why did I do all that work for so little improvement jmo

 

Also, if that engine has not been apart yet, look forward to snapping several of the bolts of in the timing cover/ water pump... They do NOT take kindly to being disturbed from their long time set. GALVANIC CORROSION... If you ARE going to do it anyhow, be sure to get a new timing chain and sprocket set as well. The factory nylon upper sprocket should be well worn, and running on borrowed time.

 

I agree. Jegs has a 2000-2200 stall convertor for 100 bucks free shipping and just a performance tune on carb/distributer will change the feel a lot. Springs are a definate should change even with the stock cam just by age. You can see a performance gain just with springs since they are old and underrated from the factory.

 

Thanks guys, I just had her out again this morning, and I swear every time I drive her she seems to run better and better, the exhaust needs to be done, system is rotted, and one manifold is cracked, got the headers from Doug's ordered already. Then 2.5" flowmaster kit with H-pipe back from that. Still get a hint of hesitation when I step on it, but I'll find it. Going to do timing set when I do the water pump next weekend, I'm sure the original timing set is tired as Steve mentioned. Wouldn't be surprised if the hesitation goes away once the timing is redone. Already did Plugs/wires/cap/rotor/coil, didn't see any major advantage to getting rid of the points for a 1-2x a week car. Yes the SP3 intake is the one I am looking at, makes more sense as I know at some point I am going to do a full teardown and rebuild on the motor.

 

Sounds like it runs pretty good ,exhaust ,dial in carb,distributor and run it till u decide to pull motor and do it up right!

 

Yep, that's where I'm leaning to

 

The SP3 intake is not going to run correctly on your stock engine. You will be kicking yourself. That's a manifold for use in the 3000 and up RPM range and you don't even want to change out 45 year old valve springs?

 

Isn't there a simple way to check the valve springs to see if they are up to spec? I recall being told awhile back that the OEM springs were better than the replacements available.

 

There is a tool but you need to pull them to check as far as I know. But with the heat cycles of an engine and their age chances are slim of them being up to the needs.

 

The CS647 has the 'advertised' durations @.006, while the OEM in those days rated them @.002, so they will appear larger with that different measurement rating. Even so, I believe those '70-'72 cams were a bit larger than the '68-'69 cams; and the CS647 sits in-between those sizes. It's like Federal Mogul took the cam sizes of all years and averaged them out into a single cam for all Buick 350's. So it's actually larger than the '68-'69 OEM cams, while slightly smaller than the '70-'72 cams. The differences are pretty insignificant, with the main difference being the tweaking Federal Mogul did to make the current 'stock' cam better than the older ones were. (my opinion)

According to the dyno program I use (I know it's not 100% spot on, but does give a good general idea), the CS647's torque peaks at around 2800-3000 RPM, depending on what else is done to the engine, and horsepower peaks at 4600-4800 RPM, again depending. Typically, a 2800/4600 RPM torque/hp peak is normal. Both torque and horsepower powerbands are incredibly wide, with peaks less noticeable because they're so wide, so it will feel super strong between 2500-5000 RPM taken as a whole.

The cam will pull well past 5000 RPM, trailing off from peak (4600-4800) to around 5300 RPM, then it starts to trail off pretty fast until around 5700 RPM where it is pretty much spent. The powerband is incredibly wide, with the tradeoff being that it doesn't make max power like other, more intense lobe profiles. What you get for that power loss (and it's not as much as people think) other than the wide powerband is camshaft longevity and durability.

Also, the compression is very good, particularly for that old of an engine. With 150-165 lbs per cylinder, it sits at around 7.75:1 dynamic compression already. It's actually sitting in its ideal zone right now, so messing with it is ill-advised, especially when you consider the intake valve closing points on whatever cam he may put in could bump DCR too high or too low without tearing the entire engine down to properly match it (unless, obviously, he replaces it with the Federal Mogul cam or one with a similar IVC point of 71*).

In short, it's fine the way it is. Do some external mods but leave the engine intact.

(GS350's came with a 3.23 axle from the factory as standard, at least they did in '68)

Gary

 

P.S.- The Crower level 3 cam is an excellent choice for extra power over the stock cam, but comparing the two side by side with equal dynamic compressions, it really only gives about 5-10 ft. lbs. and 10-15 hp over the stock cam. While this would be felt, 10 hp on an already strong 300+ hp high comp engine is pretty small when the tradeoff is about 25% the life of the stock cam... o No:

However, for a car that's driven occasionally, what the heck right? Problem is with his engine though is a 66* IVC point (what the Crower level 3 cam has) would bump his DCR too high unless he used a composite gasket instead of the steel one.

The Crower level 3 has a similar powerband, but is slightly narrower than the stock one, with torque coming on a little later. Horsepower still peaks around the same though, give or take ~100 RPM, but peaks are more noticeable. It's a fairly mild cam longevity wise, but can't compare to the low lift, asymmetrical lobe design of the Federal Mogul cam. Don't let its size fool ya. It is engineered to fit the Buick 350 head flow pattern, even with moderate porting, which peaks between .300 and .400 lift. You have to really port those heads to get them to flow up to and beyond .500 lift.

This is why the asymmetric lobe pattern fits it so well. It doesn't need the extra lift when it can leave its peak lifts between .300 and .400 for longer periods of time when compared to a symmetric lobe, which has to overshoot the goal by increasing lift. Unfortunately, this causes extra wear and tear on the camshaft, along with higher spring pressures required to stabilize the valvetrain.


Gary

 

Gary, I appreciate your knowledge and advice, I have in fact decided to leave the cam alone, and go with the exhaust, and possibly an intake swap. I like the power the car has, just want a little more pop and hang on to your seat pull. It is the stock 3.23 open rear FYI. Now I know not to expect the stomp out of her like I had in my 70' tempest, that car had a monster 455 bored, stroked, blueprinted and balanced and was an 11-second car. What can I do to get more of that "HOLY ****" feeling outta her? I've thought about head work, and a gear swap, truthfully the car will rarely see anything over 50-55 mph as I don't intend to race her, just cruise nights, Ice cream runs, and beating up on the kids with there weed-wacker mufflers when the mood strikes me. Like I said, I have the Dougs headers, and a full 2.5" mandrel bent flowmaster going on her, and I was thinking about an intake swap, I also have tossed around the idea of a set of 4.10 gears.

 

I think the Crower will give Alittle more then Gary's simulation program but not much as the long duration cam in the 70 engine is decent. Going to a custom grind cam is where the real power is as most cams available use old technology. Otherwise most cams available just kinda trade lower end for upper end. An dual plane intake won't gain much on your engine. And cam doesn't really need the single plane intake. So if your going with the sp3 intake get a bigger cam to take advantage of the extra rpm range. If your going with 4.10 gears the 413 would be more what you need. My personal combo is the 310 cam with 2800 convertor and 3.73 gears on my SP 1970 engine. Can't say how right the combo is as I put gears and trans in then car went to paint/interior shops. Haven't tryed it yet but feel it should be good.

 

It's pointless to argue with naysayers, though there are some points I'd like to reiterate. The main reason the difference is so small is because the DCRs were the same, which means the stock cam has a higher static compression ratio to match for the comparison. Pulling out a mismatched factory cam on an assembly line, nonblueprinted engine and then putting in another cam that has a better DCR will most certainly feel like a larger power increase. But that is apples to oranges. I compare apples to apples.

To be fair, the dyno program isn't going to be 100% spot-on, but then a real world dyno wouldn't be either, unless you could dyno two engines side by side, and then they would be two different monsters, with other factors coming into play on why one might perform better than the other (the stock cam may very well outperform the aftermarket one in this case), otherwise, you have two separate cams in the same engine for comparison, and the DCR will be mismatched unless one took the time to redo the compression ratio and not just a direct cam swap.

Then there's atmospheric differences that occur from day to day, which can affect the outcome in the real world. So in this regard, the program actually gives a better basis for comparison, since it uses the same conditions for each combination.

The extra lift the aftermarket cam gives is a bandaid for its symmetric design, so the only real advantage it would have would be extra duration, which is why the powerband is slightly different between the two cams, but this is offset by the fact that the asymmetric lobe design takes better advantage of airflow dynamics @varying RPMs through partial open valve blowby.

Yes the Crower level 3 cam gives more power, as does other aftermarket cams of its size or larger. But the difference isn't as large as you think, especially in a mostly stock environment and with heads that won't flow past .400 lift. As long as you don't mind the cam only lasting about 1/4 as long (or much less in some cases) as the stock cam, it's all good I guess.


Gary

 

Relax Gary. Just my opinion that the Crower may be better in a nonblueprinted 70 SP engine as its kinda designed for that. And addressing his intake/4.10 gear thoughts. You know as much as anyone that with 4.10 gears he needs more upper end and the stock cam isn't there. Add the SP3 intake and he needs more mid to upper.
For the stock cam with distributed recurve and carb recalibrated, a 25-2700 convertor and 3.73 gears might be better.
Yes I mentioned that most cams just trade off lower for upper . and most cams need big valves to work right

 

Most aftermarket cams will be better in a nonblueprinted engine than the factory cam, as long as you define 'better' as squeezing a little more power out of it. Durability and longevity wise, there is no comparison.

Yes, for all-out racing intentions, you need more cam for best results, though opening up exhaust and intake on the stock cam, as well as bumping compression will also increase its upper RPM power, as with any camshaft. Just moreso with an asymmetric lobe design.

I advocate the Federal Mogul cam for every day street users who want their investment to last a long time. If longevity is not a concern, then this won't matter.

The engine in question here, however, seems to already have ideal compression and adding a Crower level 3 cam will bump DCR too high unless he wants to burn race fuel in it everywhere he goes.


Gary