350P Expectations
 

Some folks here may remember me asking questions about my 1968 350P rebuild. Well, the rebuild is complete and has been on the road about 18 months (2000 miles). It was done by a builder at a local shop with a long history (40+ years) and a good reputation. Long story short, it was a fairly difficult process and I'm pretty underwhelmed with the performance of the finished product. The engine is .030 over with a Summit 2800 cam and lifters, OEM 4v intake, claimed CR of 9.13:1, No. 17 heads, Ignitor 3 distributor & coil, log manifolds and OEM style true dual exhaust. It pulls 14" of vacuum at idle. Car is a '68 Tempest convertible, TH350 w/1700 stall (TCI Street Rodder) , and "Safe-T-Track" 3:23 rear gears. Overall, she's been running okay, just not as strongly as I expected. Only real trouble I've had thus far is the shop installed the incorrect (late style) intake manifold gasket and two of the Summit HFT lifters are bad. As I've been prepping for the lifter replacement job, I've found several of the ARP rocker arm studs cross threaded. Perhaps I'm just being paranoid, but such basic errors make me wonder what else might have been goobered up in the assembly process.
As a disclaimer, I'm not a hot rodder, I'm simply interested in a strong power plant for an antique car. I am I being overly optimistic in my expectations?

I would be concerned about the cross threading, but "butt dynos" are notoriously inaccurate. If you had some dyno numbers or track times it would be more reasonable to try and diagnose if it seemed normal or not.

What are you deeming as not running strong? Will it not break the tires loose from a stop?

Perhaps it's a bit juvenile, but this is what really got me wondering. Any mildly built 350 from the other GM marques I've driven will easily light the tires from a stop. This one not so much. I can break-torque it, but I could do that with my old Dodge 318 2bbl...

Yeah I would think it should be roughly 1 hp and TQ per CI so I would also think it would break them loose. But you did say you had two bad lifters. If you arent getting any lift in two spots that would hurt performance a lot.

Fair point. So far, I don't know how "bad" the lifters are. One doesn't push any oil, the other is very low volume and they make some noise. I'll be replacing the whole set with the USA made ones from Butler/Comp. It'll be interesting to see if it makes a difference.

Two things: I wonder if the claimed compression ratio of 9.13:1 is actually much lower than that. I've found over the years that low compression engines tend to feel "soft". We used to own cars of the early '50's in high school with 7.5/7:1 compression and merely shaving the heads would bring alot more powwer to them. The Summit 2800 should have a higher compession (on a compression gauge) than the 2801/2802 cams and should have a higher vacuum than you have. We both live in areas where the elevation is about 1100 ft. I used a Comp 274H cam in a SBC 350 and with a 3.08 rear it would smoke the tires. That cam is 230* at .050 and had a vacuum on my autometer vacuum gauge of 16". I think you unfortunately need to go back behind your builder to find where something is awry. Jeremy is right if you could dyno the engine you might well find the problem. Possibly timing curve is off as is air/fuel. Hopefully others with more experience willl chime in and give you some good ideas.

If I ran a compression test in all cylinders, is there a way to extrapolate those numbers into a CR formula?

I see your running an oem 4bbl manifold which is good for your combo. What carb are you running? and was it tuned for your combo? If it's a part store bought rebuilt carb it may need to be gone thru to get the right adjustments, same thing with your ignition. The right or wrong curve and carb tune can really effect performance. On a lower hp engine it can really make it a noticeable.

What happened to user Squidward? I miss his posts. He had a lot of experience with 350s and shared a lot of useful stuff. For example, I did a quick search and found this:

"I ran the 2800 in a 47 headed 350. It was an awesome street cam for cruising and lots of driving. Made lots of vacuum, and was good enough to push that motor into the 14's with 3.23 rear gears."

This isn't apples to apples with your engine but is impressive to me.

I also have a 350 with 2800 cam but it isn't drive-able so can't help. But I am interested in what you learn.

There are lots of threads about 350 performance that suggest your intuition is good.

First carb was a Q-Jet. It was built for my combination by one of the better known, online retailers. It never ran quite right, so I replaced it with a Holley 4175. Performance has noticeably improved with that change. Timing is 12 degrees initial, 20 mechanical all in around 3000-3500. I've played around with the one spring lighter (bronze for my application) and various mechanical limiters. This seems to be the most effective setup I can get with street tuning. I'm not adverse to a dynotune, I just want everything dialed in close enough before I spend that money.

Too funny. That quote from Squidward is what got me thinking about the 2800 cam. I originally wanted a Voodoo 250 or 256 cam, but the old-timer building the engine said those cams were "good for nothing but noise." I'm sincerely doubting his opinion based on what I've read online.

Just my 2 cents,I ran a 366 pontiac with smaller vales than you but used a 2801 and it ran great,lots of lowend and pulled great.Never ran it down the tack it also had the 2 speed auto with a fairly tall gear like a 3.08.Been years so the mind gets foggy.Tom

Are you saying you have 32* total timing or 20* total? I would have guessed mild compression would want probably 36* so 32 would be fine, but if its only got 20* total on the crank, thats not enough.

Also if you are concerned about oil in lifters I might also be concerned about flattened cam lobes. Which would also kill performance. In general if a new engine is significantly under performing, I think my first thoughts would be the cam flattened on break in.

32 total. She's a pinger with much more than that. FWIW, I've experimented with 30-36 total. 32 seems to be the happy spot.

My old 68 Lemans with a 350 picked up a lot of power just from headers and a carb swap. But I did have single exhaust with the stock exhaust, so I can't really say if it was the headers or going to a full dual exhaust with a crossover that made the difference.

I'd be incline to think that something is off.

My brother's '73 was recently put back on the road;
I has:

• numbers matching short block (cannot recall the overbore)
• stock #46 heads (milled to make somewhere around 9.0:1 compression)
• and a cam just a little smaller than a 068 (cannot recall the grind)
• a 1968 intake with the cross over removed
• a 1973 400 Quadrajet, stock metering
• 3.08:1 posi rear (3.42:1 in the works)
• M22 (2.2 1st gear)
• shorty headers
• Jegs(?) 2.5" exhaust kit with a crossflow muffler (iirc)

... is able to break tires loose

His car bone stock (350/2bbl & TH350 c/w open 2.73:1 rear) was a real one-wheeler-peeler.

How much was milled off your heads?
(I type that knowing that #17's should be decent, as I have run them on my 400)

How far down the "hole" are your pistons?

As far as I know, the heads were milled to 77cc's. They were at 81cc's as cast from the factory. Again, as far as I know, the pistons are .022 in the hole.

I ran a 2800 cam in a 350 with 48 heads. Ran good, sounded great. Did not start to pull until 3500RPM though. Ran mid 15s in a "as is" 69 Le Mans. Never go into 3rd gear in the 1/4 mile. Well, shifted right before the stripe.

Do you figure that's a function of the bigger valves (2.11/1.77 vs. 1.96/1.66)?

I will admit, mine does fine dropping into second for passing traffic.

Please do a cranking compression test and post up the numbers.

Stan