mid year big block running hot

[Duke W.]

Re: mid year big block running hot

How about "mitigate".

Duke

[Anthony S.]

Re: mid year big block running hot

New radiator cap solves first car temperature, now back down to previous cooler range...

[Kenneth B.]

Re: mid year big block running hot

What is the root cause of the big block cars overheating issues? Right now I am trying to help a friend solve this issue.
Concern is that it is an engine design problem (from day one), rather than other causes (engine timing, bad H2O pump, radiator cap not holding pressure....etc.)
Any advice/insight appriciated Thanks Tony

I have been down this road for 30 years. i tried all of the quick fixes that have been offerd. NONE worked. Big block Corvettes did not overheat when new. The problem is the aftermarket fan clutches are 210 instead of 180. Find or reset it to 180. I can leave my 67/390 air or my 435 set out in 90+ temp & not get over 180. before the 390 would only make 4 stop lights before peging the temp.

[Michael J.]

Re: mid year big block running hot

Right, and I have a B26 and set the initial at 10 degrees. Never really gets over 210.

[Bill M.]

Re: mid year big block running hot

I'm pretty sure GM used a similar system beginning sometime in the early to mid-seventies, but I'm not sure what it was called. It may have been part of what was called CCS - Combustion Control System.

Duke

Close. (I spent the summer of '68 at the GM Engineering Staff working on advanced emissions systems.) GM used that coolant-temperature-switched vacuum advance device in the CCS system in 1968. Maybe earlier in California, not sure about that...

[Joe L.]

Re: mid year big block running hot

Close. (I spent the summer of '68 at the GM Engineering Staff working on advanced emissions systems.) GM used that coolant-temperature-switched vacuum advance device in the CCS system in 1968. Maybe earlier in California, not sure about that...

Bill-----

1968 was the first year for CCS, even for California. Corvettes did not get it until 1970 but most other Chevrolet models got it in 1968. However, for 1968-69 it was used only for automatic-equipped models; most manual transmission applications used AIR.

[Bill M.]

Re: mid year big block running hot

Bill-----

1968 was the first year for CCS, even for California. Corvettes did not get it until 1970 but most other Chevrolet models got it in 1968. However, for 1968-69 it was used only for automatic-equipped models; most manual transmission applications used AIR.

OK. Thanks, Joe. I remember a lot of emissions stuff was "49-state". CA was leading the way.

[Joe L.]

Re: mid year big block running hot

OK. Thanks, Joe. I remember a lot of emissions stuff was "49-state". CA was leading the way.

Bill-----

Unlike 49 state cars, most 1966-67 Chevrolets shipped into California did get exhaust emissions controls but it was all via AIR. There were a few exceptions for 1966 (like L-72 Corvettes and full size Chevrolets and L-78 Chevelles) but for 1967 virtually all were AIR-equipped.

While it's much maligned, AIR is actually a less performance-robbing exhaust emissions control system than CCS. I'm convinced that's why it was used for all 1968-69 Corvettes as well as 1970-72 LT-1 and LS-6. For 1970-71 Corvettes used CCS except LT-1 and LS-6.

[Kenneth B.]

Re: mid year big block running hot

Bill-----

Unlike 49 state cars, most 1966-67 Chevrolets shipped into California did get exhaust emissions controls but it was all via AIR. There were a few exceptions for 1966 (like L-72 Corvettes and full size Chevrolets and L-78 Chevelles) but for 1967 virtually all were AIR-equipped.

While it's much maligned, AIR is actually a less performance-robbing exhaust emissions control system than CCS. I'm convinced that's why it was used for all 1968-69 Corvettes as well as 1970-72 LT-1 and LS-6. For 1970-71 Corvettes used CCS except LT-1 and LS-6.

As we all know all the pump did was to add more air to the exhuest to dilute the gas. the same polution came out but with more air like adding watter to smoke ftacks to make the smoke look white.

[Bill M.]

Re: mid year big block running hot

As we all know all the pump did was to add more air to the exhuest to dilute the gas. the same polution came out but with more air like adding watter to smoke ftacks to make the smoke look white.

If that's all it did, Chevrolet would not have gone to all the trouble and expense to inject the air at each exhaust port...

[John H.]

Re: mid year big block running hot

As we all know all the pump did was to add more air to the exhuest to dilute the gas. the same polution came out but with more air like adding watter to smoke ftacks to make the smoke look white.

Ken -

That's not how it worked at all - read the second-to-last paragraph in this article, with the heading "Ported Vacuum":

http://www.lbfun.com/warehouse/tech_...101Article.pdf

[Duke W.]

Re: mid year big block running hot

Bill-----

While it's much maligned, AIR is actually a less performance-robbing exhaust emissions control system than CCS. I'm convinced that's why it was used for all 1968-69 Corvettes as well as 1970-72 LT-1 and LS-6. For 1970-71 Corvettes used CCS except LT-1 and LS-6.

Under normal driving conditions the AIR pump only consumes one to two HP, but it increases with the cube of engine speed, so at the top end it is more.

What really reduced power and increased fuel consumption was the retarded spark advance maps used with AIR to increase EGT.

Hot HC and CO are very reactive as long as they can find oxygen, and the hotter the better. Injecting air into the exhaust ports where the exhaust gas is hottest allows time for mixing and oxidation in the exhaust manifold and upper exhaust system and was a very effective aftertreatment method for the relatively high emission standards of the era, but it came at a cost in power and fuel economy.

As standards tightened, particularly the 1975 standards proposed by EPA in the late sixties, the OEMs knew that more than AIR would be required and, in particular, oxidizing catalysts would be required in addition to AIR.

High overlap cams require a richer mixture for acceptable igniteability due to the very high exhaust gas dilution than low overlap cams, which generated higher engine out HC and CO, so that's the reason why LT-1 and LS-6 required AIR when GM had figured out how to meet the standards without the expensive AIR system on many mainstream engines.

When I visited the GM Tech Center while a grad student at the U. of Wisconsin Engine Research Center in the summer of 1970 one of the engineers told me they had run an engine with an old mechanical lifter camshaft through the EPA certification test. HC and CO were very high, but NOx was low due to the high overlap, which yielded essentially a full time EGR system.

In fact, increasing overlap (along with an even more retarded spark advance map) was one method used to control NOx when standards were first estalished (1971 in California and 1973 in the rest of the country), but as NOx standards tightened with time, EGR was required for many engine configurations. EGR is only required under "cruise conditions" when the mixture is lean, so high overlap is not a very elegant method because it results in poor idle quality and a big hit to low end torque and fuel economy.

Duke

[Joe L.]

Re: mid year big block running hot

Under normal driving conditions the AIR pump only consumes one to two HP, but it increases with the cube of engine speed, so at the top end it is more.

What really reduced power and increased fuel consumption was the retarded spark advance maps used with AIR to increase EGT.

Hot HC and CO are very reactive as long as they can find oxygen, and the hotter the better. Injecting air into the exhaust ports where the exhaust gas is hottest allows time for mixing and oxidation in the exhaust manifold and upper exhaust system and was a very effective aftertreatment method for the relatively high emission standards of the era, but it came at a cost in power and fuel economy.

As standards tightened, particularly the 1975 standards proposed by EPA in the late sixties, the OEMs knew that more than AIR would be required and, in particular, oxidizing catalysts would be required in addition to AIR.

High overlap cams require a richer mixture for acceptable igniteability due to the very high exhaust gas dilution than low overlap cams, which generated higher engine out HC and CO, so that's the reason why LT-1 and LS-6 required AIR when GM had figured out how to meet the standards without the expensive AIR system on many mainstream engines.

When I visited the GM Tech Center while a grad student at the U. of Wisconsin Engine Research Center in the summer of 1970 one of the engineers told me they had run an engine with an old mechanical lifter camshaft through the EPA certification test. HC and CO were very high, but NOx was low due to the high overlap, which yielded essentially a full time EGR system.

In fact, increasing overlap (along with an even more retarded spark advance map) was one method used to control NOx when standards were first estalished (1971 in California and 1973 in the rest of the country), but as NOx standards tightened with time, EGR was required for many engine configurations. EGR is only required under "cruise conditions" when the mixture is lean, so high overlap is not a very elegant method because it results in poor idle quality and a big hit to low end torque and fuel economy.

Duke

Duke-----

The really bad initial timing settings for cars with AIR were pretty much limited to 1966-67 Corvettes with AIR. For example, the base engine spec for those years without K-19 was 6 degree BTDC. For base engine with K-19 it was 4 degrees ATDC. For 1968-69, all of which were equipped with AIR, base engine spec was 4 degrees BTDC. So, there really wasn't that much difference between the non-K-19 66-67 base engine and the 1968-69 (all AIR) base engine.

Strangely, 1966 L-79, with or without K-19, was 10 degrees BTDC. For 1968, though, L-79 initial timing spec dropped to 4 degree BTDC.

[Duke W.]

Re: mid year big block running hot

But as you go into the seventies you find that centrifugal curves were shortened and initial timing was less than antecedant pre-emission engines. Vacuum advance was often more, but only at very high manifold vacuum llevels.

The '74 Califronia L-48 automatic, which probably represents the worst of the lot, is speced at 4 deg. initial and has nominally 18 degrees full centrifugal at 4200, so at WOT high revs total advance was only 22 degrees vs. the optimum of 38. That took a huge hit on peak power!

I don't think it had to be this way as WOT, high revs was never a part of the emission certification test procedure, but as Dave McClellan said in his book, sometimes they were up against the wall to get an engine/drivetrain configuration certfied in time to have a product that could be sold on announcement day, so the goal was to get the car certified whatever the cost in power.

That goofy setup on the '66-'67 327/300s with AIR (initial 4 deg ATC with a total of 40 centrifugal) was only applicable to Powerglide. Below about 1500 advance was severely retarded, but above 1500 the initial plus centrifugal was about the same as non AIR.

Why this was "required" on Powerglide is mysterious to me as automatics are typically easier to control emissions than manuals because manuals have a big HC spike when you lift the throttle to shift. This was the reason why some later model year Corvettes sold in California were not available with manual transmissions.

Also, that early California-only AIR system did not use lean carburetor calibration. The idle mixture was set in the normal pre-emission fashion, which yields about a 12.5:1 A/F ratio and about 6 percent CO.

That was the starting point, and the learning went on from there.

Duke

[Clem Z.]

Re: mid year big block running hot

But as you go into the seventies you find that centrifugal curves were shortened and initial timing was less than antecedant pre-emission engines. Vacuum advance was often more, but only at very high manifold vacuums.

The '74 Califronia L-48 automatic, which probably represents the worst of the lot, is speced at 4 deg. initial and has nominally 18 degrees full centrifugal at 4200, so at WOT high revs total advance was only 22 degrees vs. the optimum of 38. That took a huge hit on peak power!

I don't think it had to been this way as WOT, high revs was never a part of the emission certfication procedure, but as Dave McClellan said in his book, sometimes they were up against the wall to get an engine/drivetrain configuration certfied in time to have a product that could be sold on announcement day, so the goal was to get the car certified whatever the cost in power.

Duke

to pep up your smogged corvette buy a timing tape for the harmonic balance and with the vacuum disconnected with a timing light rev the engine till the timing stops advancing and turn the dist till the 38 degree mark on the timing tape lines up with the "0" mark on the timing tab. reconnect the vacuum advance and enjoy the power