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#1
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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?
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"I only ride 'em, I don't know what makes 'em work." Last edited by FlyJS41; 10-28-2020 at 01:43 PM. |
#2
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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?
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1967 Firebird 462 580hp/590ftlbs 1962 Pontiac Catalina Safari Swapped in Turd of an Olds 455 Owner/Creator Catfish Motorsports https://www.youtube.com/@CatfishMotorsports |
#3
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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...
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"I only ride 'em, I don't know what makes 'em work." |
#4
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Quote:
My brother's '73 was recently put back on the road; I has:
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?
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1970 Formula 400 Carousel Red paint on Black standard interior A no-engine, no-transmission, no-wheel option car. Quite likely one of few '70 Muncie three speed Formula 400's left. 1991 Grand Am: 14.4 @ 93.7mph (DA corrected) (retired DD, stock appearing) 2009 Cobalt SS: 13.9 @ 103mph (current DD; makes something north of 300hp & 350ft/lbs) |
#5
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Quote:
__________________
"I only ride 'em, I don't know what makes 'em work." |
#6
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I would also suspect a flat cam, that car should easily be able to break the tires loose with a 3.23 gear.
There may be a host of tuning issues that could be adding to the lack of performance from a standstill. If everything is as it should be you are correct in assuming that the performance is substandard. I'm curious if the cam timing was checked upon install for a mistake in timing components. Trusting the manufacturers to not have any variances in the cam components is a blind leap of faith. Many possibilities in hunting down why performance has suffered in this build, it may take a qualified detective to track down all the possibilities. Two cross threaded studs would be a red flag in my opinion, to suspect the whole build. That is however my opinion, and you asked for advice, and opinions. |
#7
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Of course I have no proof, but I'm guessing it was simply installed dot-to-dot.
__________________
"I only ride 'em, I don't know what makes 'em work." |
#8
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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.
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1967 Firebird 462 580hp/590ftlbs 1962 Pontiac Catalina Safari Swapped in Turd of an Olds 455 Owner/Creator Catfish Motorsports https://www.youtube.com/@CatfishMotorsports |
#9
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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.
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"I only ride 'em, I don't know what makes 'em work." |
#10
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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.
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"No replacement for displacement!" GTOAA--https://www.gtoaa.org/ |
#11
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Quote:
__________________
"I only ride 'em, I don't know what makes 'em work." |
#12
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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. |
#13
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Quote:
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"I only ride 'em, I don't know what makes 'em work." |
#14
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There is some truth to the noise. While my 703 is quiet at idle and performs very well generally, the noise gets a little annoying at cruise over a fairly short period of time.
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65 Tempest, 400, TH400 86 Fiero SE 2.8 |
#15
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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.
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"Honestly the car will only be there for a few weeks, OK maybe a month at the most" |
#16
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Quote:
__________________
"I only ride 'em, I don't know what makes 'em work." |
#17
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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
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#18
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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.
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1967 Firebird 462 580hp/590ftlbs 1962 Pontiac Catalina Safari Swapped in Turd of an Olds 455 Owner/Creator Catfish Motorsports https://www.youtube.com/@CatfishMotorsports |
#19
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Quote:
__________________
"I only ride 'em, I don't know what makes 'em work." |
#20
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Quote:
Stan
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Stan Weiss/World Wide Enterprises Offering Performance Software Since 1987 http://www.magneticlynx.com/carfor/carfor.htm David Vizard & Stan Weiss' IOP / Flow / Induction Optimization - Cam Selection Software http://www.magneticlynx.com/DV Download FREE 14 Trial IOP / Flow Software http://www.magneticlynx.com/DV/Flow_..._Day_Trial.php Pontiac Pump Gas List http://www.magneticlynx.com/carfor/pont_gas.htm Using PMD Block and Heads List http://www.magneticlynx.com/carfor/pont_pmd.htm |
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