Got my '68 400 ragtop a couple months ago. Rebuilt a pair of "62" heads, added hardened seats(one of the originals was cracked)...Crane Cam No.283901(mild...came with the car)...stock Quadrajet and intake...longbranch ram air exhaust manifolds... The car runs well,BUT... It feels like there is some power left in her that I can't quite get to. The carb seems to be adjusted properly. Nice low idle(600)The plugs are a nice light brown color. I've played with the timing a bit but, it doesn't make much of a difference. Any ideas on how to get a little more goose out of the old girl?
I'm a hobbyist. Not a professional. Don't be hatin'!
Welcome to the site! I would check to make sure your mechanical distributor advance is working. You could buy a timing tape for the balancer if you don't have and advance style timing light. The other thing I would do is to make sure the secondaries on your carb are opening. You can check the lower plates mechanically and then play with the spring tension on the vacuum operated plates. It's been a long time since I've done this, so perhaps someone else can chime in too.
I have read that the stock 750 Q-jets for the FGF were made to not open the secondaries all the way due to GM self imposed HP restrictions for vehicle weight. The Tempest/GTO and big car Q-jets were not as restrictive.
At the very beginning of my Pontiac experience, I had to start my engine, then crank in some more timing to get the power that I knew had to be in there. I had installed a distributor curve kit that didn't quite work right, but once I took the time to recurve it, it pulled hard everywhere. I'll second the timing check.
I did not notice if you mentioned your intake manifold, but please save some money and MATCH your intake to your carb! Buying a bigger Carb won't solve your problems (your desire for more punch) unless you match a bigger carb to the right intake manifold.
Obvously Robert found the right carb for his intake and cam setup, but slapping a bigger carb on the car is not the answer unless you've done alot of studying what you've got first. I bet you have the power right under the hood, right now, just need to check things out a little more.
'68 428 HO M3 Monster, 4-on-the-floor! Need I say more?
Well, how fast is it? If it's an automatic with stock stall converter and street tires I would expect a 14 second quarter with that setup. Maybe 13's if it's well tuned.
Don't spend money on new parts. You have a good setup. Take it to a dyno shop and have them dial it in.
Sounds like you don't have an advance style timing light. You're after the total timing with the vacuum disconnected. I believe this car should like about 35° total which should be in around 3,500 rpm. You can get a timing tape for $5.99 here: Pontiac Timing Tape Once you install this, you will not run out of marks. If getting your total timing correct makes your timing at idle too high, you will need to get a recurve kit - a liklihood if it's the stock distributor.
The factory Q-jet is 750 cfm. The factory restricted the power by inserting a small clip on the passenger side linkage. It could be removed in less than a minute, hence most of them have already been removed. If you could mechanically open both sets of secondary air valves, I doubt that it could be installed on your car. Go easy on those spring adjustments, a little goes a very long way.
Greg, I would talk to someone at Crane Cams about the cam you are using & find out what type of advance curve needed for your cam. Then find someone to re-curve your distributor, then time it up to what Crane recommends & see what she does! I built a '69 428 using a Comp Cams High Energy cam, run OK just putting aroung but was a dog trying to romp on. Found out that the distributor wasn't set up right for that cam. Ended up my vacuum advance was not used, it then ran it's *** off! Worth your time just to call.
Spoke to a tech at Crane. He advised 34 degrees total advance at 2800 RPM. I bought a good timing light and will dial this in this weekend. I'll advise all how it turns out. Again, thanks for all the info.
I'd post a photo of my toy if I could figure out how!
I set the timing as advised earlier in this thread. It wasn't even close! Also...
there was a slight stumble upon lght acceleration. I pulled the air filter and noticed there was a very slight leak at the accelerator pump. I thought there might be some dirt stuck in there so I disconnected and plugged the fuel line. Then I ran the fuel out of the carb. I blew some compressed air through the fuel inlet, then, reconnected everything. This resolved the leak and the "stumble".
With the 400 and 62 heads, you have no detonation at that timing? Are the #62 heads stock volume?
I have a similar setup, stock '69 400 with stock intake, carb, 067 cam, #62 heads, but stock exhaust manifolds. I get significant detonation on anything over 24 degrees total timing or 9 degrees initial timing if I run anything less than 100 octane R+M/2.
I will be rebuilding in the spring, just curious as to why two similar configurations act so differently. Any idea what the lift and duration are on your Crane?
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching
Yes, heads are stock volume. No detonation at all. I asked the machinist if it would be wise to the shave the heads when rebuilding. He warned not to do this for the reason you mentioned. So, we didn't.
Disclaimer: I am not an auto mechanic. I may not have the timing set correctly. My timing light says I do but, its a cheapy I bought at Sears. If I missed the mark, its a good miss!
sounds like the cam is retarded about 8 degrees from an 067 on the intake side, about 5 degrees on the exhaust side, and just a hair more duration and lift. What octane fuel do you run?
A "Cheapy" timing light is not an advance timing light, which is the only way to set total timing without a timing tape or marking the balancer. Balancer drift is always a possibility as well.
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching
Greg's Garage from what i have read, synthetic lube in the engine, the tranny and rear end can increase horsepower by up to 5%.... dont know if that is a fact but it seems to work well
I spoke to Brian at Ebert's Engine Service in New Orleans(ebertsengine@msn.com). He did the machining on the heads installed on my 400. He explained that he DID mill down the heads, deburred and polished the interior surfaces, added hardened seats, multi angle valve job, added bronze guides and polylocks, standard rockers, lifters, and standard size valves for the #62 heads. He expected the compression ratio to be right at factory spec.
He also added that the deburring and polishing goes a long way as far as avoiding detonation, especially on Pontiac heads. I run pump premium with no problems. I'm sure he'd be glad to answer your e-mail directly if you have any specific questions. I definitely recommend his work!
I'm a hobbyist. Not a professional. Don't be hatin'!
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