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Old 09-20-2017, 08:46 PM
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Default New Found Power

So this month makes it 2 years of ownership of the 70 GTO. After that amount of time, you feel like you should pretty much know you car inside and out. Well thanks to hurricane Irma, I think I got sold a tank of regular gas as premium (no big surprise) as I hammered the car, I got some detonation, ping, knock, whatever you know it as. I didn't at first think of the gas but I also know I hadn't heard the car detonate since I've owned her so now its time to check timing on the car. (something I should have done right after I took delivery) So of course a timing light is something few people outside of our circles owns, but those in our circle can and will loan them out. I was the loaner of a timing light and the loanee moved before I could get it back so now I was the loanee and today I put the gun to the car and was surprised to learn the car was running just under 14+ degrees of initial timing.....wow! No wonder! So now its back down to 4+ degrees and man talk about a boost in off the line torque! Of course the idle took a nose dive and after about a half a dozen adjustments I can really get a nice rumpety cam sound I knew this car should have had all along. Still drives smooth, stills idles with a nice side to side motion of the chassis at a stop light and a lot more push back in the seat on the butt dyno. I went ahead and tightened down on the screechy alternator belt while I was under the hood losing 1 pound a minute of sweat in this blistering Florida and engine heat. It might not be a bad idea to check the little things here and there, you might be surprised of what you will find.

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Old 09-25-2017, 01:47 PM
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Now I took the GTO to work this morning and wouldn't you know? I forgot to adjust the mixture screws so at every stoplight I would get a stumble and a stall. I also had a hard time keeping it running and getting it out of the garage even after the engine came up to full temp. So I got her home, adjusted the screws and it ran like crap. So then I got out MY timing light that has no inductor clip but an alligator clip so I have to stick a paper clip up in spark plug wire #1 and keep moving it into a position that doesn't short out on the block. The timing light I borrowed yesterday had a bad connection at the base of the gun and was intermittent. So I ended up adding back +4 degrees of initial timing and got rid of the idle and stumbling issue at operating temperature. So I guess I will see how it is to start and warm up on my next trip out. It's been years since I have had to "tune" a car so this stuff and the tricks of tuning are coming back to me slowly. I guess it helps to do this on a consistent basis to remember all that's needed to perform a complete tune .

So I've read on numerous car forums and have read from as low as 4 degrees initial timing to 15 degrees initial timing....anyone know for sure? And I know a lot of you will say "total timing is what counts" I get that but I don't have a fancy adjustable timing light just yet.

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Old 09-25-2017, 01:57 PM
tom s tom s is online now
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You can get timing tape to put on your balancer to help you find total,I run 12 into and usually about 36-38 with iron heads,9.5 CR and our 91 crap gas.Tom

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Old 09-26-2017, 01:09 PM
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Timing tape or just measure and mark your balancer(circumference divided by ten will mark 36 degrees etc). Lots written on it and very easy with a std timing light. 4 sounds extremely low for initial, I'm around 12/13.
Two biggest power gains I ever got were advancing timing on an old ram air three and adjusting carb linkage to fully open the secondaries. Two bonehead mistakes that woke the car right up.

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Old 09-26-2017, 09:22 PM
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Good advice guys, I see 12 degrees timing in my near future. I also see getting the timing tape on the balancer as well. I might also check with Harbor Freight as I hear they may have an adjustable timing gun on the cheap. Can't hurt to look into it. Thanks again.

Here is the cam card and I am running long tube headers, 3K stall convertor, 4:10 gears. Heads have some port work done or so I was told, forged internals. Holley 750 and an Edelbrock RPM Performer manifold.



Last edited by 360Rocket; 09-26-2017 at 09:41 PM.
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Old 10-09-2017, 03:29 PM
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That's quite a bit of cam for the street. I would bump it back up to 10-12 initial timing. Should idle much better than the 4 you had it at.

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Old 10-14-2017, 12:14 PM
Stuckinda60s Stuckinda60s is offline
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That cam's a perfect candidate for Rhoads lifters. I had several cams cut with 234-244 @.050, 110/113* centers with the intake at 108 and .462-.491 lift. I built a street 412 with that cam and Rhoads that would idle at 800 rpm and ran 12.80's at 109 mph in a '64 GTO.

If you were running unleaded before, you should be able to run the Rhoads and run at least 8-10 initial without issues. Advancing the cam 2* degrees would help bottom end and idle as well, but might limit the initial timing you could run. Remember, you might not be able to hear detonation. Pontiacs are less prone to it than most engines, but they can have problems with it. You can jet the carb a little rich to help reduce the tendency to detonate. I ran an 800 Spread-Bore, Double-Pumper Holley that I'd done quite a bit of work to. Response with 3.55 gears was more than impressive. You would have thought that it had vacuum secondaries rather than mechanical.

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Last edited by Stuckinda60s; 10-14-2017 at 12:33 PM. Reason: Added carb
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Old 10-14-2017, 02:40 PM
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I may have missed it, but I didn't see the size of this engine. I assume it's a 455, by the size of the cam. To me, an intake lobe of 240° @ .050 is too big, even in a 455, for a mild to moderate 455 street build. I definitely wouldn't attempt it without Rhoads lifters.

But, after doing more lookin, I see that it is an XE284. So, the Rhoads may not be a good idea. The Rhoads, along with the steep closing ramps of the XE would probably make lots of tickin & clickin noises.

https://www.summitracing.com/parts/cca-51-225-4

There are much better cam choices. But, I realize that the OP didn't ask for cam opinions.


Last edited by ponyakr; 10-14-2017 at 02:58 PM.
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Old 10-23-2017, 08:14 PM
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so some follow up.
Car is still running like crap but I am closing in on it. So with some research I've learned that my HEI between vacuum and mechanical is accounting for a total of about 35 degrees advance. With an initial timing of now 12 degrees a total of 50+ degrees of timing. Way too much. So I have capped off the vacuum advance and the car is running much stronger and I heard no pinging. I still don't know total timing as the timing tape I applied the other day fell off somehow on my way to work today. I need to get a new tape to confirm total timing and then the idle mixture screws and idle itself is kicking my ass. I'm trying to set those using a vacuum gauge with no luck so far.

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Old 10-24-2017, 08:47 PM
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Well she's now dialed in to @36 to 38 degrees total timing and running fairly smooth. I tried to get it down to 32 degrees but I just couldn't get the engine to smooth out and give me a good idle. Feel like I got the idle mixture screws and idle where it needs to be. I need to let her completely sit and cool and then start it again to see how the cold start characteristics work out. I wouldn't think that the timing, or mixture screws would effect cold start and I wouldn't think I would need to re adjust the electric choke either? Thoughts?

Oh and I guess they don't make timing tape like they used to. after about 20 minutes of the engine running while I was tuning the tape melted and came flying off in 2 pieces. lol.


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Old 10-25-2017, 01:51 PM
Stuckinda60s Stuckinda60s is offline
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I would say that 36-38 would be where you should be running. Have you been setting your initial without the vacuum hooked up? You should. total timing should also be without vacuum advance. If you aren't running vac. advance at all, you need to richen the idle mixture, open up the air bleeds and usually go richer on the main jets. Basically, the carb needs to be gone into by someone who knows what he's doing. you have a choice, a rich mixture where the fuel molecules are closer together, promoting rapid burn; or advancing the timing because the flame front moves more slowly and idles poorly. Low compression particularly needs a lot of initial timing or a rich mixture because the compressed mixture isn't dense enough to promote rapid burn. I've seen a several low compression Pontiacs that loved to have initial timing at 16-18 degrees initial and still could tolerate vacuum advance.

It would help a lot if we knew what engine/head combination you're running.

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Old 10-25-2017, 06:07 PM
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455 motor and worked(ported/polished) heads. So much worked that they ground off the ID #'s on the exhaust ports. I don't know the compression ratio but I figure it would be near impossible to get detonation on 93 pump gas with a 9:1 compression so I figured it would at least be in the 10's. I was setting initial timing with vacuum advance off. I the hooked it back up to get total and when I finally did that with timing tape, that's when i discovered the 50+ degrees total timing. Its getting difficult to find anyone that tunes carbs anymore and its been over a decade since I've messed with them myself so its trail and error or stumble across someone who knows.

Total timing should be set WITH vacuum advance hooked up shouldn't it?

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Old 10-25-2017, 07:44 PM
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No, set with advance unhooked & hose plugged.

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Old 10-25-2017, 08:19 PM
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So then why is it called total timing? Total timing should be initial+mechanical+vacuum right? The vacuum line should be unhooked from the distributor and blocked on the carb side to establish initial timing at idle and then hooked back up to attain total timing .

I have initial set at @16 degrees BTDC and the mechanical is covering the other 20 degrees with no vacuum advance hooked up.. If I hook up the vacuum advance i get 50+ degrees of total timing.

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Old 10-25-2017, 08:31 PM
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Well, it can be confusing. Total is your initial timing (what you set at the balancer) at idle. Would be around 10-16 degrees. ,+ The mechanical advance built into the distributor. Vacuum advance isn't counted in total. I suppose because it changes with conditions.

So you usually hear something like 36 degrees total that is with the vacuum unhooked & plugged & the engine reved to about 3000 rpm or so. If the vacuum advance was hooked up you would see around 50 degrees, IF the engine was producing max vacuum. Like at light throttle cruise. As the throttle is opened up the vacuum advance pulls timing out. At WOT you would see the mechanical total of around 36.
I hope that helps. I don't splain things very well.

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Old 10-26-2017, 12:12 AM
Stuckinda60s Stuckinda60s is offline
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Total timing should be set with vacuum disconnected and plugged. Fifty* total timing at cruise with vacuum advance hooked up isn't unusual, particularly with low compression. The first thing for you to do is get an adjustable vacuum advance such as Mallory sells. Determine what total timing is at what rpm and then you can adjust the vacuum can for best cruise without surge.

What is the engine code? What is the date code on the heads and do the heads have screw-in studs?

You can get detonation with low compression, depending on circumstances. .

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Old 10-27-2017, 03:14 PM
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If anyone here is learning "How to tune 101" at my expense I have cut and pasted why I need vacuum advance as these guys are helping me with:

Now connect the vacuum advance from the carburetor to the distributor and read the timing on the harmonic balancer while revving the engine to 2,800 rpm. This number will now be greater than 34 degrees with the addition of the vacuum advance. Let’s say it now reads 49 degrees, which would mean the vacuum advance is worth another 15 degrees. These are typical numbers.

First, let’s look at the mechanical advance portion of the timing—the 34 degrees total. This is determined by the weights and springs spinning around inside the distributor. This establishes the amount of timing the engine will see at wide open throttle (WOT). As you are probably aware, at part throttle the engine will create a certain amount of vacuum in the intake manifold. This is because the throttle is mostly closed and the engine is pulling against this restriction. Because the throttle is mostly closed, very little air is moving into the cylinders. So at light cruise, such as running down the highway, the engine is making much less power than it would at this same rpm at WOT.

With less air and fuel in each cylinder, the air-fuel mixture is not as densely packed compared to WOT. This less-dense mixture requires more ignition timing to complete the combustion because it takes longer to complete the combustion process. So we need a way to increase the amount of timing based on the load on the engine. This is how vacuum advance works. At part throttle, high manifold vacuum moves the diaphragm in the vacuum advance canister on the distributor to add more timing. But at WOT, the vacuum drops to near zero and vacuum advance is removed and the total timing then is established by the initial plus the mechanical advance.

So there are significant advantages to retaining the vacuum advance on your distributor.

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Old 10-27-2017, 06:15 PM
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Quote:
Originally Posted by Stuckinda60s View Post
Total timing should be set with vacuum disconnected and plugged. Fifty* total timing at cruise with vacuum advance hooked up isn't unusual, particularly with low compression. The first thing for you to do is get an adjustable vacuum advance such as Mallory sells. Determine what total timing is at what rpm and then you can adjust the vacuum can for best cruise without surge.

What is the engine code? What is the date code on the heads and do the heads have screw-in studs?

You can get detonation with low compression, depending on circumstances. .
Well, that's what I tried to say. Sorry if I was confusing. I've been told I have that effect on people.

Murf

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Old 10-27-2017, 08:29 PM
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Quote:
Originally Posted by Murf View Post
Well, that's what I tried to say. Sorry if I was confusing. I've been told I have that effect on people.

Murf

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No problem, you didn't do too badly. I didn't see your posting because I had started mine and left the computer while I did some things. I came back not knowing you had posted in the interim and finished my post. When I posted I saw yours and considered removing mine, but I figured that mine might serve to make yours a little clearer while adding some detail. Not trying to step on your post.

We still need to know Rocket Man's engine code.

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Old 10-27-2017, 09:16 PM
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Quote:
Originally Posted by Murf View Post
Well, that's what I tried to say. Sorry if I was confusing. I've been told I have that effect on people.

Murf

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I think you did great Murf, you can never get too much input. Lemme go see if I can spot that code. It looks like a "YC" It has 455 on the bottom side of the block..

Stuck....I actually slipped in engine size in post #12...lol.


Last edited by 360Rocket; 10-27-2017 at 09:24 PM.
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