I didn't do enough research before rebuilding my 350 and had the work done by a shop that didn't know enough about Pontiac's so the advise I did get was not as solid as I hopped for. Admittedly all rookie mistakes now I need advise on how to correct what I have. I think I have some decent parts (not heads) I just need to make some key changes to pull it together..
The car starts and runs very well. it just doesn't pull like it should (probably the low compression or the big cam or both) . Although the carb is big I assume it is adjusted well because the plugs have good color.
What I am looking for is a weekend driver with some good power and decent mileage (doesn't need to be great) I'm thinking changing the heads or the cam or both. If I change the cam I' thinking 066 or 067 pontiac type cam (I know there a plenty good new grinds to consider) . If I go with heads Im thinking 17, 18, or 46's. I did find a set of 67 143's heads, can I use these on my 1970 350?
Thanks in advance, be nice
Build Spec: 1969 Firebird 1970 350, 30 over Deck not zero'd out 068 cam 11 heads, 93cc, pressed studs 8.3 compression Doug's headers and duel exhaust 2R4 Trans with OD 2400 Stall 800 Qjet 3.73 posi B& M quick silver
sounds like you're mixing stock parts with high perf parts. You need to make up your mind which way you want to go. Using mismatched parts doesn't usually work well and you will end up with disappointing results.
Agree carb way too big...068 cam too big for those 93 cc heads. Optimal cc should be in the 72 to 75 cc range.
My calculations based on your setup is 7.59 to 1 compression.
My first change would be a set of 72 cc heads...1968 #16 1969 #48 #12 1968 #18 350 HO. You need compression brother...you are pathetically over carbed, over cammed and under compressed. Changing the heads only at first will alleviate most issues...then if still dogging, change to a smaller 750 q jet.
Si Vis Pacem Parabellum
1967 Starlight black PMD Engineering 400 Auto 1968 Alpine Blue 400 4 speed 1968 Verdoro Green 400 HO 4 speed 2013 1LE 2SS/RS Inferno Orange Camaro.
I don't know how you got the 8.3 CR number...but even at 8.3 with those gears and converter, 8.3 is dismal for anything. What pistons are used? Stock is typically 6.7 cc reliefs...and if so...again, my plug in numbers show you are only at 7.6 CR.
72 CC heads will bring you up to 9.12 safe for pump gas...and with proper carb and tune, you would be safe with 66 CC heads which would be 9.7 to 1 and require 91 to 93 octane.
Si Vis Pacem Parabellum
1967 Starlight black PMD Engineering 400 Auto 1968 Alpine Blue 400 4 speed 1968 Verdoro Green 400 HO 4 speed 2013 1LE 2SS/RS Inferno Orange Camaro.
If you search long enough, rebuilt heads could be had ready to bolt on for less than $800.
I also forgot to mention the venerable 670 closed chamber head. If your block has the chamfers on the cylinders for valve clearance...consider those.
If you need any help locating heads or have any questions, send me a PM.
Tom
Here is a nice set of #16 heads..date matched. For the Buy it Now price and free shipping..I see no reason that they can't be used as is. If you would feel more comfortable, have them pressure tested and checked for guide leakage/wear.
If they do need work, I see no reason why any work needed would cost more than $400
And as another side note...those #11 heads were rated at 265 HP on a 400 block. considering the 350 block is 17% smaller in CI, With the #11 heads, theoretically (and optimally with proper cam and carb) you are looking at 220 net HP on paper...and with overcamming, over carbing and poor flow..likely in the 160-170HP range.
Si Vis Pacem Parabellum
1967 Starlight black PMD Engineering 400 Auto 1968 Alpine Blue 400 4 speed 1968 Verdoro Green 400 HO 4 speed 2013 1LE 2SS/RS Inferno Orange Camaro.
BTW...I don't think your problem (low compression, miss-cammed, oversized carb,...) has anything to do with Pontiac specific knowledge. Not sure what your builder was thinking...if at all. It's just CR calcs and engine geometry. Pretty generic stuff...but can all be fixed.
I'm a hobbyist. Not a professional. Don't be hatin'!
The 143 are marginally below decent. They are small valve press in studs. You have a big cam in the block. You need 2.11/1.77 valves.
You also have an OD trans with 3.73 gears.
You do have access to 143 heads..but why use them? You asked how to rectify a botched build and using 143 heads IMO, is a band aid.
Could they work? Yes. But considering everything else in your build, the heads will still your weak point. If you are trying to rectify someone else's botched build and may have to rebuild heads...consider getting large valve, screw in stud 72 cc heads.
I only say this because I have made the same mistakes when I was 17...low on money, and quick to fix. I built a 400 with a lunati 245 single profile cam with 110. 850 caddy q jet, headers..3.55 gear..and 5C heads. Dismal 8.1 compression. Switched to #46 press in small valve heads. Spring seat pressure too much for the studs.
But wtf do I know...
Si Vis Pacem Parabellum
1967 Starlight black PMD Engineering 400 Auto 1968 Alpine Blue 400 4 speed 1968 Verdoro Green 400 HO 4 speed 2013 1LE 2SS/RS Inferno Orange Camaro.
Why would a 3:73 contribute to the lack of acceleration? The higher numerical value, the lower the ratio aka loose screw. A 2:56 is a slug, a 3:08 loosens it up some, a 3:55 loosens it even more, and a 3:73 loosens it more. Out of the listed selections of ratios, the 3:73 will make the car accelerate the fastest. And a 3:73 screw is perfect for an od tranny. You seem to imply that the 3:73 will slow it down, and a 3:55 will make it accelerate faster. Am I misinterpreting something?
I was going to leave it alone, but it’s something that needs to be addressed. After all, years ago, you were a super stickler about correct information, even to the point of semantics and spelling; in fact, you suggested that poor spellers be banned from posting ‘because they undermined the quality of the board.’ Remember? I remember lots of stuff that people posted. My short term memory may suck, but my long term memory is top shelf.
Anyway.
It’s physically impossible for any Quadrejet to be too much carb for a v8 engine. If someone has strong mechanical aptitude, this illustration is self explanatory that’s it’s physically impossible for a quad to be too much carb for ANY v8 engine.
Not my opinion, but it’s my guess that you consider yourself as having a strong mechanical aptitude. If so, it should be easy to use the posted illustration to show how a quad can be too much for a v8.
I can use the illustration to explain to anyone why it’s physically impossible for a quad to be too big for any v8 engine, but I’ll let you go first.
OP: One thing you didn’t mention was timing. Spark advance is beyond critical for acceleration. You can do what you want, but before you start tearing things apart, try advancing the timing some. You can start with small increments or lay into it. Note where it’s set before you experiment. Don’t be shy because low compression engines love lots of timing. It may be so retarded that advancing the distributor 15’ to 20’ may wake it up like you wouldn’t believe, and if it starts, not wwwwuuummmmppp, wwwuuummmpp, wwwwuuummmpp when you start it while hot, you’ll be good to go.
Pontiac didn't think 800 cfm Q-JETwas to much for 301's. Holley to much for sure. Agree on heads. Unless the block is an HO, cylinders should be(must be? Only had 1 350 HO, and it was) chamfered on intake valve side for 2.11 valves. 068 cam would work well then.
