[GTOJOE228]

Define ported vacuum as opposed to manifold vacuum. Thanks.

[george kujanski]

Manifold vacuum is as the name says, the vacuum of the intake manifold. It's characteristics are: at idle, vacuum will be high, at wide-open-throttle, it will be very low.

Ported vacuum is taken from a port inside the carburetor which is slightly above the edge of the throttle plate when the throttle is closed. It's characteristic is: at idle there will be little or no vacuum, at partial throttle, the throttle blade is higher than the port so the vacuum becomes that of the manifold. At WOT it is the same as manifold.

Ported vacuum becomes available at part-throttle cruise conditions to advance the timing for better economy. Manifold vacuum does the same except it is available at idle also.

That's why timing specs are stated "with vacuum advance disconnected and plugged" because using manifold vacuum advances the timing at idle.

GM typically used manifold vac until the emmissions years where they started playing with the vac advance control systems. Upside of manifold vac for advance use is the engine may run cooler at idle and part throttle, but may be harder to start if your static timing is already advanced.

George

[Trips4me]

***** (Originally posted under "Valve/rocker and cooling issues" dated July 16.)
"Interesting topic.. It just so happens that I just put my 389 back together after retrofitting my #76 heads to an adjustable valvetrain, Rhoads lifters and Comp Magnum roller rockers (+ new valves, etc). Before it never got over 190 now its' running 190-210. Is there something up because of the valvetrain??? I thought it may be because I was producing more HP but now I wonder?? "

July 19 response....
Did the divider mod, installed a new 160 t/s and the temp did not change much. I checked the radiator while it was out and it seemed to flow very well. I also adjusted the valves once again and the idle A/F. ...it's 97 degrees here today also. I'm running a rebuilt 8 bolt water pump w/ cast impellor as well as a stock fan and fan clutch.
I'd like to get it cooler than that so what's next... a RR radiator??? Do they fit into the stock 1965 GTO mounting brackets??

[convbird]

WC, Try this web site for pulley part numbers and sizes. Don't know if it will help you since it is for 67-69 firebird and tempest.

http://1968firebird.org/illustrated/...ullybelt1.html

[A1Judge]

Well after installing a cast impeller pump and checking the divider plate the engine still seemed to run a little hot. To the point of giving me the hot start problem last weekend.

I modified the thermostat the other night, cutting the guts out of it so I just had the ring.

At idle I can now see great flow through the radiator, temp appears to never get over 190 as I drove it and it was in the high 80s here.

Brought it home and although it was a littl slow on starting it back up it did start much better.

I have the heat shield and hot soak spring coming from PY. Hopefully that will help with the semi-slow starting when hot.

[aerosmyth]

Cooling and Cast Impeller Forum Freinds;

Aerosmyth back from a 1300 mile test drive to the GTO Ntls in Pontiac,MI. Yup, took the chance and went for the longest test drive to date with this 389 tripower. What a fine event, magnificent turnout (~500+ FINE GTOs) and relatively perfect (cool) weather!!

I gotta tell ya that it was a nervous drive but all the tweaks did lower temps to about 190-200deg. Results and conditions: 75MPH, 3400RPM, 80 degree OAT, 92/93 Gas, NO OIL consumption (viton stem seals), Amsoil 10W40, #70 center jets (tan plugs - no carbon), that three pass 4 core radiator baffle scheme (see note below), 30/70 glycol/water, 15psi cap, 160 TS with 6 extra 1/8" holes, new hoses (not colapsed, R44S, 8deg initial, 32 max mechanical plus 10degree manifold vac (made limiter bushing)returned to standard distributor cam/weights (though think springs are too strong) AND....continued use of the AEROSMYTH closed volute cast impeller pump (aka flowcooler see earlier posts).

Id still like to get less heat generation out of this beast so am looking at the dynamics of compression and cam relationships. My "straight- up" XE262 is milder than the GM-068 that was OE. Could also retard the cam (later intake closing = less volume).

Learned from many at the meet that camshaft, ignition curve relationship with todays fuel is really an overlooked (and misunderstood) aspect of getting control of combustion temperatures. Also ran on to this site with a fine JAVA calculator.

http://not2fast.wryday.com/turbo/com...pressure.shtml

Regarding the radiator: My 4 core 180 tube Harrison is in perfect condition, though the
misguided baffling scheme tripled the flow velocity causing aeration of coolant (foaming), likely pump cavitation at higher speed (higher discharge head pressure), and trapped air in the new second top tank area (baffled off from filler). SO....Im going to return to the radiator GURU and resturn to the original design.

All for now on this long-winded post. Keep kool

aero

[wheelspin]

George,

I don't know if it has been mentioned in this thread yet, but Jim Hand's new hi-po Pontiac book has a page with pics and dimensions on the water pump mod that runs thru this topic.

Additionally, I recommend, but have no proof of temp reduction, that you DO NOT run the rubber a-arm water shields as the superheated air behind the radiator needs all the escape paths it can get. This is demonstrated by how cool an overheating engine runs with the hood removed.

Les

[KS circutguy]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>I have the heat shield and hot soak spring coming from PY. Hopefully that will help with the semi-slow starting when hot.
<HR></BLOCKQUOTE>
Buy a PowerMaster Mini starter and be done with the hot start problems for good.
Best $149.00 I ever spent, of course, that is, if you don't count my Rodney Red radiator.

[george kujanski]

Aerosmyth: Good to hear from you and your data.

Les: I received the book last week and gave it a glance. I'll be reading it this weekend.

On the subject of cooling mods: In my mind I've had the mindset of trying to solve the riddle of why Pontiacs today have these heating issues when they probably didn't exist years ago.

I believe we have all seen some of the reasons: different impeller designs, clearances, etc.

The technique of purging the underhood hot air may also help, especially for the members with performance improvements where the already mentioned improvements have reached a limit.

I'd still like to know how grandville455 managed to run cool with the 'wrong' parts.

George

[WCWhitey]

Also regarding the book a mental note was made at the success with the 160 degree T-stat. It does stand to reason that if the coolant temp is held lower at most operating speeds the overall job of cooling and underhood temps fall as well. As far as the A arm covers. I have been led to believe that they help to create a flow towards the firewall and down, similar to sealing the radiator. They were installed mainly on A/C equipped cars to aid in cooling. I have to do some driving with my new open scoop to see if that shows any improvement going with the cool air in theory, have not been able to do any work the last week or so due to some minor surgery. Will get back with those results.

[grandville455]

Same way I can run mid 13's in 4800pds + george...it's a secret ...j/k.I have no idea why it runs the same with the good pump or the stamped one

[PMDRACER]

I'd be willing to attribute Grandville's success with what Les has said about air movement out of the engine compartment. That big car has lots more room to let the air out.

Simple dynamics. To get more air in to cool the radiator, you have to be able to get the hot air out.

[wheelspin]

Thanks to the EPA and their stepchild agency CARB here in SoCal, hotanking these 35 yr. old parts will never restore the original water passage size and volume. Realizing this, when I built the GTO's 455 I used rubber plugs and muratic acid (pool acid) to clean the head and block passages, AFTER two hot tank passes. I also dug and scraped layers of rust and corrosion out of these parts as this material acts as insulation keeping heat in and coolant away from the superheated metal core.

What I see is a lot of us "stacking" add-on fans, beefy radiators, improved water pumps, and oil coolers in addition to the factory cooling system to compensate for parts that cannot be restored to original internal dimensions. Add the increased hp that we are making with the available "fuel" (is there any GAS left in this stuf?) and we need to shed the additional BTUs produced @ these elevated levels.

Don't expect any huge improvements by adding alloy heads as E-heads, KRE, etc mimic the factory heads external dimensions with larger bowls and runners, leaving less space for coolant passages.

Les

[matrix]

I installed a new pump with the cast impeller this weekend. Used a block of wood and hammer to "adjust" the backing plate for a nice fit. Looked to be light years ahead of the stamped impeller that was over a 1/4 inch in clearance and the blades were also recessed away form the center hole in the backing plate at least another 3/8". Unfortunately it didnt seem to make much if any difference at all. Cheap piece of mind though.

[Malky]

Another strikeout. Damn - I thought we had it .

[george kujanski]

Matrix: with all that clearance, I can't believe your pump was efficient B4. It's got to be better now, but sounds like you possibly still have something limiting your flow. with the cap off, and running the engine until the t-stat opens, how does the flow volume look?

George

[guentherjohn]

Thanks George and others for the help fixing the cooling problem with my 67 Bird. I quit driving it for about ten years thinking I had a motor or head problem (it all started when I upgraded to a set of #62 heads because mine were shot during a rebuild. The Autozone water pump every one said to get is also pot luck as I ran into a stamped. I ended up using the Milodon which I bought before I read this post, but the cast impeller was only 1 1/2" long. I changed my pulley to a 6" from an 8" and I think the biggest help at idle was buying a junk yard 7 blade and new clutch. Everyone thinks a clutch is good if it has a little drag but that is not true. I tried the junk yard clutch that had drag and it didn't move much air. I replaced the clutch and it was 300% better. I also closed the water pump gap from the original 1/8" gap which I think solved the highway heating problem. I used to run 210 highway and 240 and climbing at idle. I now run 180-190 highway and not over 200 idle. Thanks for the help. I will replace the water pump with a full 2" vane cast when I get one.
Does anyone ever run into carb heating problems? Now that the motor stays cool, the carb still gets pretty hot from radiant heat and seems to stall when starting from an idle. Any help out there for this?
I am getting rid of the headers and going with Ram Air III long branch. This may help get rid of some of the heat and definatley the exhaust leaks.

[wheelspin]

The most effective ways to reduce carb heat are spacers (watch the hood clearance, especially on Birds), blocking the exhaust cross over, and feeding the carb outside air. Insulating the underhood portion of the gas lines can't hurt.

Hesitation from idle sounds more like a accelerator pump action/timing issue.

Les

[guentherjohn]

what is the exhaust crossover and how can it be blocked?
If it can be blocked, what was its original purpose?

[wheelspin]

The exhaust crossover is the center passage on your intake manifold (the runners with the paint cooked off) that allows hot gasses from the cylinder head exhaust passages to heat the carb plenum, producing faster warmups and less time running with the choke on.

In warmer climates, like SoCal, you can block off the passages between the heads and the intake manifold with an appropiate gasket like Mr. Gasket's #502 or Fel-Pro's # 1233, both of which contain metal backed plugs. This mod has the side benefit of permanently stopping the engine paint from burning off the intake crossover runners.

Les