[shaker455]

[QUOTE=dhcarguy;6384264]

Originally Posted by shaker455

Has your distributor been built for your combo?
Was your carb dialed in with a wideband?
How hot does you car run?.. ever get over 190 degrees?
Are your exhaust crossovers active?[/QUOTE

1- stock dizzy with Pertronix ignition.
2- correct tripower carbs., bigger than stock jets and opened venturi tubes slightly. 1/4" phenolic spacers on all three. Adjusted with vacuum gage.
3-Only runs above 190 when on the highway driving over 60mph. will get to 205degrees. Rear gear is 3:90 with NO overdrive. ,4sp Muncie.
4- crossovers are not blocked.

Car will stay under 190 degrees all day long around town ,even in traffic in 90degree weather.

Is your dist mapped out?
Initial timing
Degrees of Mech advance
amount of vacuum advance and ported or non ported source?
Total timing
Also, I would not exceed .050" on head gasket swap as proper quench will be diminished.
High CR can live on the street but tuning has to be right on
Depending on your pistons a small D-shaped dish can be machined in to get you lower CR and maintain proper quench.

[4dblnkldude]

All things being equal, if all is properly tuned why don't you switch to the proper cc heads. Aluminums would be nice.

[Jay S]

Some guys unshroud the chambers to around 76 cc. Here is a thread you can look thru that talks about that. See post 24.

https://forums.maxperformanceinc.com...=839932&page=2

Combining that and going back with a bit thicker head .050” head gasket would drop the compression about a point. Keeping the quench in that .050” or less range would for sure be better.

The newer heads have a different valve inclination angle,the valve reliefs don’t line up to a 389 piston. I think it would work with the cam that is in it, but valve clearance would be fairly tight with it zero decked.

[dhcarguy]

Originally Posted by 25stevem

The pistons have to have at least 2 valve notches if there aftermarket.

Please when you have time and before making any changes do a cranking compression test and report back .

Steve,
The last time I did a compression test was July of 2020. Nothing is any different as far as how the car runs since then. this is with the engine cold.
I will check it soon with the engine warm.
July 2020 test:
#1- 160 #5 - 155
#2- 165 #6- 150
#3- 155 #7- 150
#4- 150 #8- 150

[Jay S]

Originally Posted by dhcarguy

Steve,
The last time I did a compression test was July of 2020. Nothing is any different as far as how the car runs since then. this is with the engine cold.
I will check it soon with the engine warm.
July 2020 test:
#1- 160 #5 - 155
#2- 165 #6- 150
#3- 155 #7- 150
#4- 150 #8- 150

Those numbers with the cam the engine has are indicating the compression is closer to 10:1 than 11:1. The octane blend you have been running calculates out to be about 95. Appears you have some things to work out with the engine tune, those are pretty low pumping numbers for 95 octane.

[Formulajones]

Agree with Jay, those numbers are low and shouldn't have any problem at all running on even a straight 91 octane diet.

Generally an engine doesn't start to get sensitive until you get up into the 180's or more. That's my experience anyway. When they get close to 200 I find they get super finicky and need a blend of race gas.

[tallrandyb]

Originally Posted by Formulajones

Agree with Jay, those numbers are low and shouldn't have any problem at all running on even a straight 91 octane diet.

Generally an engine doesn't start to get sensitive until you get up into the 180's or more. That's my experience anyway. When they get close to 200 I find they get super finicky and need a blend of race gas.

Agreed, I'm cranking 190-200 on my 65 389 and I'm staying on the high side of octane range at this point, beginning to work my way down.

[Skip Fix]

We tried doing a 0.100 down deck to lower compression on a 455 in the late 80s to lower CR down to 10:1 . Ran good but had to have race gas or was a rattling fool!

[Formulajones]

Originally Posted by Skip Fix

We tried doing a 0.100 down deck to lower compression on a 455 in the late 80s to lower CR down to 10:1 . Ran good but had to have race gas or was a rattling fool!

Yeah that starts to get into more technical things like mixture motion and poor combustion. Lots of things at play here whether something will live and work on pump gas or not. But you already know that.

One of the 455's built for dad's car was .030 over and zero decked with a flat top piston. Ran a set of #12 heads that were milled quite a bit (.030 if I remember right) and I believe compression cam out around 12:1. It had tight quench with just the .038 head gasket.

Ran a solid flat tappet cam from Ultradyne. Can't remember the specs off hand but it was healthy (in a box here somewhere)

Anyway, that thing would pump 195-205 cold, had a bunch of cylinder pressure. But on the street I could get away with running 94 Sunoco pump gas. I'd just run the total timing down to 30-32 degrees. Alot of that was due to good quench, keeping engine temps in check, etc.....but I will admit it's not for everyone, it was a finicky engine and the tune had to be spot on.
At the track we mixed a 1/2 tank of 110 race gas and I'd bump the timing up to about 34-36 degrees. It was a decent running combo.

Did this to keep the street driving costs to a minimum because he did drive it on the street a bunch. Drove it for about 4-5 years like that and it survived fine.

This was the engine that pushed me and my father to stick to strictly pump gas builds and learned that we didn't have to sacrifice power in doing so. As we tend to drive the cars more than race them, the whole mixing fuels thing just became way too much trouble and was getting more and more expensive. It's much easier, and more convenient, not to mention a hell of a lot cheaper, to just be able to roll into any gas station and fill the car and be on my way without worrying about how the engine will react or dinkering with the tune. Especially when towns are 100 miles apart in the middle of the desert. Not like I can carry that much fuel with me.

These days many of us have learned how to build higher compression engines and run fine on pump gas with all kinds of tricks we didn't know 30 years ago. I now run an 11:1 iron headed engine as a daily driver on 91 octane pump gas and it loves 36-38 degrees of timing. Don't even have to band aid it.

[track73]

Changing head gaskets will involve the cost of intake and exhaust gaskets. oil and filter and anti freeze plus the head gaskets which are pretty expensive themselves,Probably around $300 for 090's. So have you calculated the cost of extra race fuel opposed to the cost of redoing your top end, assuming the block and heads have the correct finish?

[Tom Vaught]

Put the Butler gaskets on it and drive it another 10 years.
Cometics have had issues, at times, with a grove in the gasket (wrong spot) causing
gasket water sealing issues. Otherwise they seem to be good gaskets in the .042" thickness.

Tom V.

[geeteeohguy]

I have the same rough combo in my '65 GTO on the 389 I built in 1981. It has about 50,000 miles on it. Forged flat top pistons, milled heads (about 11:1) cranking compression 175 all cylinders, #77 heads, Sig Erson cam with a lot of overlap and lift. I need to run race gas to keep out of detonation. Sounds like me, you simply have too much compression. You can: run race gas, disassemble and install dished pistons, or, install bigger chambered cylinder heads or 72 cc aluminum heads. Lots of people seem to think a bigger cam will get you out of detonation, but it will not. It will only change the rpm and load it detonates at.

[Jay S]

I did 91 octane pump gas 64 389 engine with flat tops, stock 716 heads, and log manifolds earlier this year. It would be great to know what the Erson cam is in the last 389 example.

My highest compression we have done is 12.2 on 91 octane with iron heads. Pontiac’s the highest is just over 11:1 in 91 with iron heads. Highest on 87 octane with iron heads is 10.5 SCR with 500+ cid’s. Most instances the those high compression pump gas car’s would be quicker with race gas and a different cam. If your content with how the engine runs, and don’t mind adding race gas like the Jeff “geeteeeohguy” , then leave it alone, no reason to change things.

The term bigger cam is usually associated with more overlap, more overlap with a bigger cam will just “move” were the engine has spark knock. That last post was exactly right on that.

With only 150 to 160 crank pressure, the engine may have a tuning issue. But it does not appear at 150-160 that the cylinder pressure needs to be spread out more and lower by using a different cam. As is, with the cam in it, lowering the compression, you would have to drop the cranking pressure down another 10 points to get down to 93 octane. Lowering the compression with thicker head gaskets is probably the worst option. The thicker head gasket fairs a little better than putting the piston down in the deck .100” like what Skip mentioned. But not a lot better, I am not totally sure what that is, my guess is the improvement is mostly because of a difference in turbulence.

Steve25 really nailed some of the issues with this engine in post #9. Read #9 again, start by reading the plugs. The pumping numbers are really pretty low for as much compression the engine has. Dropping the compression will lower the pumping number more yet. That isn’t necessarily good with the cam in it. I attached events for the Lunati cam in it. It has a lot of seat timing, and as much overlap as a Melling SPC-8 (041) cam. It would pump similar compression also. But the SPC-8 opens the exhaust valve up 10* earlier. Those early 389s need help in that area to run well on pump gas. That is worth about 2 point in octane on this engine with the same compression. That would get it down to around 93 octane with no other changes and you should not have add race gas anymore. I am not suggesting that is what it needs, it is just a basic example. There are MUCH better cam solutions that that. The Lunati cam was a pretty poor pump gas cam pick with the 77 heads and 10+ compression.

[geeteeohguy]

Originally Posted by Jay S

I did 91 octane pump gas 64 389 engine with flat tops, stock 716 heads, and log manifolds earlier this year. It would be great to know what the Erson cam is in the last 389 example.

My highest compression we have done is 12.2 on 91 octane with iron heads. Pontiac’s the highest is just over 11:1 in 91 with iron heads. Highest on 87 octane with iron heads is 10.5 SCR with 500+ cid’s. Most instances the those high compression pump gas car’s would be quicker with race gas and a different cam. If your content with how the engine runs, and don’t mind adding race gas like the Jeff “geeteeeohguy” , then leave it alone, no reason to change things.

The term bigger cam is usually associated with more overlap, more overlap with a bigger cam will just “move” were the engine has spark knock. That last post was exactly right on that.

With only 150 to 160 crank pressure, the engine may have a tuning issue. But it does not appear at 150-160 that the cylinder pressure needs to be spread out more and lower by using a different cam. As is, with the cam in it, lowering the compression, you would have to drop the cranking pressure down another 10 points to get down to 93 octane. Lowering the compression with thicker head gaskets is probably the worst option. The thicker head gasket fairs a little better than putting the piston down in the deck .100” like what Skip mentioned. But not a lot better, I am not totally sure what that is, my guess is the improvement is mostly because of a difference in turbulence.

Steve25 really nailed some of the issues with this engine in post #9. Read #9 again, start by reading the plugs. The pumping numbers are really pretty low for as much compression the engine has. Dropping the compression will lower the pumping number more yet. That isn’t necessarily good with the cam in it. I attached events for the Lunati cam in it. It has a lot of seat timing, and as much overlap as a Melling SPC-8 (041) cam. It would pump similar compression also. But the SPC-8 opens the exhaust valve up 10* earlier. Those early 389s need help in that area to run well on pump gas. That is worth about 2 point in octane on this engine with the same compression. That would get it down to around 93 octane with no other changes and you should not have add race gas anymore. I am not suggesting that is what it needs, it is just a basic example. There are MUCH better cam solutions that that. The Lunati cam was a pretty poor pump gas cam pick with the 77 heads and 10+ compression.

Jay, I did some digging on-line and got in the ballpark. My cam is a Sig Erson Hi Flo II from 1979. The later Erson cam specs are similar, but slightly different.
It's a single pattern cam with a lobe center of 106, lift of .479, and overlap of 306/306 int. and ex and 235/235 @.050. Spec'd for power with 10:1 or higher CR, headers, and 750 CFM or more with power from about 2200--6400 RPM. At the time, I was planning on bracket racing the car, so I had the rods shoot peened and polished, the whole engine magnafluxed and balanced, heads milled, good valves and bronze guides, forged flat top pistons, etc.
And it did (and does) run hard with tripower and tubing headers with a 4 speed and now, 3.36 gears. I am hesitant to 'tear down' a good running engine that I built at age 20 41 years ago for the sake of lowering the performance to run on pump gas. That said, I sure would like to drive the car more. I lowered the compression on the '67 I have and I drive the wheels off of it. Bolted a set of #15 455 heads on it and that totally fixed my issues.

[dhcarguy]

OK, I have learned a lot so far. So this winter I am going to try to get this much done:
-- find someone local to calibrate my distributor.
--Take off my carbs. Rebuild and replace my jets with all .70"s
--I will post pics of my plugs soon, and again when I get the rest done and run the car until up to temp.
I won't replace the head gaskets for now. I will soon be 70 yrs old, so if doing this much helps , I'm stopping there. It is getting hard on me physically to work on my pride and JOY.

Thank you for taking time to help, I REALLY do appreciate It.
I will keep you all up to date., Dave

[geeteeohguy]

Dave, that is a solid plan. You may pull it off with a sharp tune. The timing and jetting may just be enough. Location matters, too. My cars detonate in dry, arid, hot central CA where they would not on the foggy coast. Humidity and temps play a part.
Messing around with the head gaskets is a zero-gain option. Don't do it. If you DO pull the heads, replace them with 72cc aluminum or 87-97cc iron GM parts. (aluminum can run a full compression point higher than iron on the same octane because it is less thermally efficient).

[dhcarguy]

[QUOTE=shaker455;6384278]

Originally Posted by dhcarguy

Is your dist mapped out?
Initial timing
Degrees of Mech advance
amount of vacuum advance and ported or non ported source?
Total timing
Also, I would not exceed .050" on head gasket swap as proper quench will be diminished.
High CR can live on the street but tuning has to be right on
Depending on your pistons a small D-shaped dish can be machined in to get you lower CR and maintain proper quench.

I am going to PM you shaker455.
Dave

[Matt Meaney]

While it is essential to have the distributor mechanical / vacuum advance itself known and spot on, don’t overlook the number one piston to timing mark on the balancer to timing mark on the engine relationship. it needs to be spot on as well. An accurate known base timing is the corner stone for a correct timing curve / total timing.

[mgarblik]

Originally Posted by Matt Meaney

While it is essential to have the distributor mechanical / vacuum advance itself known and spot on, don’t overlook the number one piston to timing mark on the balancer to timing mark on the engine relationship. it needs to be spot on as well. An accurate known base timing is the corner stone for a correct timing curve / total timing.

Pontiac engines are better than others with just a sheet metal tab on a timing cover, (like a SBC). But it does need to be checked and verified as balancers can have a slip on the outer ring or just be wrong with aftermarket parts. My experience is Pontiacs are generally +-3 degrees of true Zero. But that is a 6 degree range. Could be the difference between perfect and melted pistons in a race Pontiac engine.

[dhcarguy]

Did not forget about everyone's help. Wife and I had some sad family issues lately. I did not get to my car since I asked for help. Now it is getting very cold, but hopefully get to it soon.
Thanks again, Dave