Hi everyone, I recently bought a '71 c3 and have been trying to figure out whats up with my engine as it seems to not be running to its full potential.
It sounds mean but I can't even burn the tires... in a corvette... so something is very very wrong.

Previous owner had no idea what parts were on it other than it looked rebuilt at some point.

So far according to the stamps, it seems like its a 350 block out of a '69 c20/c30 truck, so guessing it was a spare that was built up somehow. does that sound right?

It sounds like it has a cam in it, idle is pretty lumpy and I only seem to be pulling 6-8in of vacuum at 700rpm idle which is pretty bad... when driving around and off the gas it pulls a healthy 16in give or take a few... so thinking the carb needs tuning here as there is a newer looking Holley unit on there and Holley valvecovers. It starts and runs pretty reliably, doesn't get too hot etc... just lacking on power.

So I dug a little deeper and once /I wiped the grime off the cylinder heads I found they have been changed for aluminum ones. also the intake is a performer rpm intake on it.

The thing is the stamp says 60109 on it... and when I look those up it says that its for a Jeep/AMC edelbrock performer rpm???

Did they change part numbers.. or how did I end up with AMC heads on my sbc 350 motor. I am also wondering what all has been done to this motor as it sounds pretty beastly with the sidepipes, I guess there isn't a way to tell if it has a stroker kit without taking the thing apart is there? or checking what kind of cam is in it?

any help on the heads would be appreciated. it seems to have typical bolt ons from that era.. anyone know what kind of power ballpark wise I should expect out of this thing once its running right again. Its also got ceramic headers on it, but the piping from headers to sidepipes looks a little restrictive.

Also as a sidenote, there is a sticker on the windshield that says "Brunos Corvettes" on it as car was in california at some point.
I read that he had a pretty awesome shop that did repairs and restorations... hoping that doesn't mean this was crashed at some point.
Did that shop do engine builds also?? I saw they closed in the 90's so probably no way to get in touch with Bruno or the shop to find out.

I will be taking it to the local Vette shop here in Denver to get it looked over and tuned up, I am hoping its just off due to the altitude changes, the prevoius owner was at an even higher elevation but I am positive that person had no idea what they were doing based on other stuff I have found, I wouldn't be surprised if they just brought it over from cali and never re-tuned it. I threw a new HEI unit on there and it helped a hair but not enough. Just wanted to get some thoughts and suggestions from here cause you guys really know your Vettes, Thanks!

 

Hi AV,
While the WT suffix indicates the 69 block you describe, the shape of the pad isn't what I'd expect to see on a block of that era. I'd expect it to be a later engine.
???
Regards,
Alan

 

Thanks for that info, it seems I have a good mystery on my hands here.
I'm going to snap some shots of the whole motor and post them up here later today when I get a chance.

Also when I was reading the code, I noticed there seems to be an extra number in there.

V is for Flint, then there is the 05 / 16 which I think are the date codes...
Then the 5WT. I only saw codes for WT being the '69 small block.. but what is that extra 5 doing hanging out there... lol. First chevy so I am a little confused on the whole thing.

 

Hi AV,
Have you checked the block's casting number that's located on the rear flange near the bell housing? That might help identify when the engine you now have started it's life.
Regards,
Alan

 

Can you get some better shots of the engine?

Do the heads look like these?



Maybe you have an AMC engine.

 

AMC engine would be really interesting for sure, that thought did cross my mind.
Your link isn't working for some reason can't see it.

 

Set your timing correctly......try to achieve 36 total at 3000 RPM.
Check for intake leaks around carb base and intake gaskets......
The heads are most likely 60909......
Start there.....

Jebby

 

Ddawson the heads don't look like those. I changed the intake gaskets when I first got them and I used the standard 5.7l gaskets that fit perfect.

In fact the heads look like the 60909 pattern that Jebby mentioned so that is probably what it is, maybe it was an error or something odd going on with the stamping, no telling how old these are. I will pop open the valvecover and try and find some more numbers, and get the number off the back of the block also.

I set the base timing but haven't verified the total timing, will give that a try... sidepipes are so loud I have to be careful about where I do it, not to mention I finally got the tacho working... put in a digital one from a '76 which was no easy task... everytime I fix something on the inside I break 2 new things or find new things that are broken =/

 

The squarish type stamp pad from Flint appeared in late 1977. Don't know if the stamping is correct but the pad shape is similar to my 78.

 

I would venture to say that the cam installed on that engine is one with a lot of duration. It may have performed ok in California but up at altitude the same cam tuns into a gutless pig at lower RPMs.
For altitude builds you need lots of CR, DCR and a shorter duration cam to compensate for the loss of air density and therefore loss of cylinder pressure.
I'm guessing it's an auto. If so then a higher stall torque converter can help as this gets the engine higher up in the RPM range where it's making more torque before the converter achieves full stall.
With a big cam your engine is going to want lots of initial timing. Think 19* to 22* range. Then you have to limit the vacuum and mechanical timing to achieve the desired total timing 36* ish maybe, and the cruise timing of maybe 52* or so.
Due to the relatively thin air you will also need to lean out your carb.

 

I got a chance to check it and it says 140 10207... which is coming up as a 80-85 350 block. That makes sense with what you guys are saying with the later style pad so I think this has to be the right number as its cast into the block and not stamped.

Yup it looks like a 80-85 block, no idea whats going on with the stamp on the front someone must have added that onto it later.

Thanks for that info, I think you are onto something there with the cam. It sounds great but down low its basically gutless as you said, up top it actually runs pretty decent and I haven't gotten the timing dialed in so there is probably some more to pick up there, but all around it could be better I feel.

It is an auto for now, I want to t56 swap it later this year but I need to get the space and parts going first. The trans feels like its modified, so I wouldn't be surprised if its got a higher stall already.

I wonder what compression it was rebuilt at, I could do a compression test to get a ballpark idea I guess if its high or low.. wont be exact but a decent indication.

I am going to take it to the vette shop to have them tune the carb (it smells rich for sure) and timing and see what they think about the cam... if I can get one appropriate for this altitude and pick up power down low then I am all in for that. I installed an AFR gauge in the dash when I redid the cluster but I haven't got the o2 installed so not positive what its at right now but my guess is rich.

I would have to think this combo was running pretty well at some point, I can't imagine someone throwing on all these parts and not having it perform well so I am gonna assume its a sea level vs mile high issue going on, thanks for the advice and any more thoughts or suggestions are appreciated.

anyone know a good cam for my altitide? mile high in Denver, CO

 

Hi AV,
What side of the engine is the dip stick on?

Interestingly there were three character broadcast codes for engines that began with a digit not a letter.
That would explain that '5' (5WT). BUT, I don't see anything LISTED for 5WT. And, the codes that are similar to it appear to be for bb engines.
Amusing.
???
Regards,
Alan

 

It's gonna be hard to nail down the CR with a compression test. First the numbers will be lower just due to the altitude. Then if the cam has a late intake closing point (long duration) that also will lower your number in a compression test.
The only way I know to check the CR is to take one of the heads off and cc the head, check to see how far in the hole the piston is at TDC plus cc the piston top or at least determine the brand and type, and measure the thickness of the existing head gasket. That will give you the CR.
With a known CR you can get a cam that will match.

That being said you could take a shot in the dark with a cam. Take out the existing cam and determine it's specs or if you are lucky it will say the cam type and brand on the end. Then from that you could reduce the duration/modify the specs to achieve higher cylinder pressures for better performance.

I'm running at 4000 feet with DA's up to 8000 feet. My 350 has a CR of 10.6:1 and I'm using a 270/270 219/219 @ .050 on a 108 LSA roller cam producing in excess of 400 HP. Flat tappet equivalent would be around 288/288.

Dyno'd at 406 with Dart SHP heads @ 10.0:1 CR, now running AFR heads with 10.6:1 yet to be dyno'd.

With the likely 3.08 ratio diff that car has it will not perform really well in any case. Mine did good I felt with the 3.08, but the rear ratio was definitely holding it back.
I change mine to a 3.55 rear diff and it makes a world of difference in performance.

 

It is on the passenger side of the engine. Yeah the 5wt is a mystery I thought a simple search would have given me some more info but nothing matched exactly. That would have been nice if it was a big block but from the casting number i'm guessing its a small block.

Yeah I probably wont be pulling heads and measuring unless I blow the headgasket or something, don't have that kind of time right now but I see what you are saying about the compression test.. too many variables to tell. hopefully they went on the high side, I think I know what the head and head volume are.. but pistons no idea what the put in it.

I think you are right with removing the cam and seeing what is in there and stepping it down some for the altitude. If I can get a combo giving me 400hp and good torque down low I would be pretty happy with that. Thanks for the numbers I will keep those in mind when I get to that part, maybe the local guys at the shop will have an idea whats going on with it. I also need to learn about this whole roller cam vs flat cam thing and what I have.

When driving it around this weekend I passed one of those speed signs and I thought I was going 30-35 and the sign lit me up at 45+... so I am thinking someone changed the rear end on this thing also... and can explain why I thought it was kinda slow mph wise for how fast it felt. I don't think its too high of a ratio cause I can't spin them from a stop, but it seems like its more than whatever stock was. probably wont be easy to figure out whats in there either. I need to get one of those speedo apps on my phone and do some calculations to get an idea now.

looks like I have to spend quite a bit more time discovering what parts were installed on this C3

 

It could be that just the trans has been changed and the driven gear did not get changed to match the rear ratio. When I changed my TH350 out the new one had a gear in it that assumed a 3.55 rear. With my 3.08 at the time I had to change the driven gear to get the speedo to read right.

If you want to check your rear diff ratio. Jack up the rear and mark both the tire and the drive shaft. Then rotate the tire once and see how many times the drive shaft rotates.

 

Yeah I will do that, jack it up and see how many times it rotates... If they changed out the motor then they could have easily changed out the trans with it. I def would like to know what rear end is in there before I go with the manual swap. I'll let you guys know what its looking like when I get a chance to do it.

I thought it was odd the car gets close to topping out rpm wise around 95 ish on the gauge... but apparently its going a bit faster than that.

so on the to do list:
Figure out rear end ratio.
Get it tuned for this altitude / determine if motor is good.
Figure out cam/change cam if still down on power.
verify cylinder head part number.

I really wish the previous owner had taken note of some of these things... but then again I always learn alot when doing it the hard way. Thanks for the help and info guys!!