cylinder cooling and tuning consistency


Staff member
One of the factors I see being consistently IGNORED or at least overlooked is that its almost a total impossibility to consistently get good results from tuning and engine if you can,t maintain consistent temperatures, now thats not easily done because both the ignition timing advance changes and the number of power strokes changes with the engines rpm levels even if you can maintain exactly the same fuel/air ratios in the cylinders.
one of the secrets of making consistently good hp is keeping the coolant and oil temps in there ideal ranges, and for oil thats in the 190F-215F range, for coolant thats in the 170F-190F range in most carburetor equipped performance muscle cars, and in some applications coolant temps just a bit higher for EFI equipped cars.
If both your coolant and oil temperatures rise noticeably when you start driving aggressively you should look into improving the cooling and lubrication system efficiency,
a multi level approach here may help!
one factor you may be having, if your engines running a bit warmer than you would like it too be, is that some coolants don,t contact the inner engines micro surfaces without a wetting agent added to the coolant ,and, I know you are sure you did a good job tunning the cars engine, but something may have changed,
Id start by verifying the fuel pressure, ignition timing, coolant levels , I'd look for vacuum leaks,and check the oil level, inspect the oil filter internally, and you may want to consider retarding the cam timing an additional 3-4 degrees and checking the piston to valve clearance, as this effectively reduces the dynamic compression, and moves your whole torque curve about 200 rpm higher and IF , anyone is reading this thread, and having a similar issue and if your car, does not have an oil cooler, transmission cooler,7-8 quart baffled oil pan, radiator fan shroud, and an adequately sized radiator,and oil temp gauge's that keep you aware of the fluid temps. you might want to install those, as those parts are all effective in reducing the thermal loads on the engine, keep in mind reducing the operational temps reduce the potential for detonation. you might want to recheck the ignition timing curve advance, has not changed, and a 160F t-stat with several air bleed holes added might help as a test, but as youve already proven , increased octane levels will potentially help avoid the issue, and filling the fuel tank with the highest level of octane fuel at the gas station ,may seem like its increasing the cost of vehicle operation, but its dirt cheap insurance spread over a life of the car, vs the cost of replacing a detonation damaged engine if you select lower octane fuel in a false effort to save cash flow.

the links and sub links will be helpful

Ive been asked how long it takes for an engine to reach operational temps,obviously outside air temps play a factor here and in Florida its generally in the high 70f-low 90F range,and keep in mind my engines got an 11 quart oil pan and oil cooler capacity so it may take a bit longer than average, but Ive timed my corvette a few times and sitting at idle it takes 6-7 minutes to have the coolant temp stabilize, at the operational 190F temp its set at if I just let it idle, If I drive it slowly, and keep the rpms below 3000rpm to allow the oil to warm up and the internal engine temps to stabilize, the times reduced to about 5 minutes.
keep in mind the corvette has sensor controlled electric fans that won,t kick in until the coolant temp is well above the t-stats 190f

Keep in mind the coolant flow thru the block and heads is not at a consistent rate in all areas due to the irregular shape and size off the coolant passages and slightly different pressure levels so an additive the breaks down surface tension in the anti-freeze helps the coolant contact a higher surface area., and a high volume water pump with a more effective impeller design tends to increase the coolant flow rates, which tends to increase the heat absorbency.
a high efficiency aluminum radiator of adequate size with the proper duct work and fan design can have a huge effect on lower the coolant temp of antifreeze entering the engine, just a few degrees cooler temps can easily prevent detonation.
as most experienced guys know the fuel air ratios in about the 12.5:1-12.8:1 range generally produce the best torque and ratios of about 14.7:1-15:1 produce the best mileage , so in most cases experienced tuners try to match the fuel air ratio to the most likely use, ie, below about 3500rpm your generally going to want to maintain decent mileage and avoid fouling plugs so the engine tends to be tuned to run a bit leaner for use in daily driving in the 14:1-15:1 range and as rpms build past the 3500rpm levels most experienced tuners tend to try to let the fuel air ratio slowly but predictably shift to a richer 12.5:1-13:1 range to slow the advent of detonation and increase torque because your generally trying to increase power output significantly when your rpms start to climb over that 3500rpm level
If your having cooling issues while the cars stationary but not when the cars moving theres an excellent chance that the problem is lack of low speed air flow rates, a larger more effective fan or a more efficient fans or adding a pusher fan or more efficient fan shroud would help. clear pictures of the car,s engine compartment, radiator fans, fan shroud etc would help here a great deal.
keep in mind oil does a good deal of the heat transfer, in an engine, so an oil pan with a larger than stock capacity and an oil cooler with a built in electrical fan can do a good deal to lower engine temps.
keep in mind automatic transmissions tend to add a significant amount of heat to radiators that use the lower section to cool the transmission, adding a large efficient trans fluid cooler to the car can also significantly reduce the heat loads on the radiator
BTW one frequently overlooked factor, in cooling your engine or adding an additional oil cooler, is your alternator size,in amps and wiring the alternator correctly, if your running a 70amp-100 amp stock alternator and using electric fans to cool the engine,its not going to provide the power required to spin the fans nearly fast enough to cool the engine like a better 200 amp alternator can, Ive seen several corvettes cure cooling issues by swapping to 200 amp alternators, that simply allowed the electrical cooling fans to spin significantly faster

bit of info from BDS SUPERCHARGERS
"The cooling system for a SUPERCHARGED motor should be in a good general operating condition. Inadequate air flow across the entire radiator at low speeds is one of the most common causes for overheating. Mechanical fans and shrouds are highly recommended. In a recent study of electric fans, especially anything from 18 to 20 amps with a 3000-4500 CFM capability, these fans seem to work efficiently on blower engines, but it may still require some experimenting with location to find the best operating position. A 180 degree thermostat is recommended. Water flow restrictors may also be used, however, you will have to experiment to find the size that works best with your system. Stock factory water pumps are recommended and required in most applications. After market "High Performance" water pumps work best in the mid to upper RPM ranges and therefore may not have adequate water flow at lower RPM's to keep a blower motor cool. Three core radiators or larger are recommended for most applications. Higher performance engines will require better cooling systems because of the additional heat generated by these types of engines."

read links
the t-stat controls COOLANT temps,
which are generally 15F-25F lower than peak oil temps,
obviously the coolant temps vary as the t-stat opens allowing flow ,
and closes as temps drop off.
your oil temp may read only 10F hotter than the coolant temps,
but its a fact that oil temps vary a great deal during the trip from sump,
oil pump, valve train,and bearings and back to the oil pan sump.
get out a high quality infrared temp gun, and scan the valve springs after 10 minutes of engine run time,
youll notice the oil temp on the rockers is significantly cooler than that flowing over the valve springs
this is the most consistently accurate I.R temp gun I've used for testing
42545.jpg Extech Products

Wide temperature range from -58 to 1832°F (-50 to 1000°C)
any time that your dealing with a potential temperature issue or a trouble issue where
, knowing the exact temperature vs what a gauge might say,
\it helps to have a handy and accurate infrared temp gun handy,
to locate and confirm heat, levels. ... ermometer/

having a good cross check tool like a quality IR temp gun, and a decent multi meter, sure helps find the truth as far as a defective gauge or sensor

think you may have a blown head gasket or cracked heads ETC??
have you tested for a cracked head or block with the reactive dye in the coolant that shows exhaust gasses contamination?

watch this link








not verifying the ignition advance curve, verifying TDC and using a marked and indexed timing tape or balancer is a VERY common mistake ,Id bet fully 50% of the cars I work on have not verified TDC nor do they have a correctly marked timing tape or indexed balancer
you can,t make intelligent changes until you know exactly what your currently dealing with







A principle problem in using a liquid to cool internal combustion engines is the fact that coolant temperatures vary within the cooling system components used, factors like but not limited too, outside air temperatures,air flow rates, coolant volume, radiator surface area, and coolant flow rates. This is generally the result of differences in the locations of heated areas in the engine that contribute to unequal temperatures. For example, metal surfaces nearest the combustion space and exhaust passages tend to be higher than elsewhere in an engine's cooling system. While reverse flow systems address certain aspects of temperature extremes and levels, localized "hot spots" can still contribute to detonation, lost power, and potential parts damage. this factor alone means that a great deal more consistency can be obtained with a very efficient cooling system that will maintain a stable and consistent engine temperature,if your cooling system has both the high coolant flow rate and rapid heat transfer ability to dissipate, changes in engine temperatures and the ability to prevent hot spots by simply overcoming the potential with high heat absorption rates, youll have much more consistent cylinder temperatures, this requires an accurate fast acting thermostat and a coolant system with the extra cooling capacity to absorb and rapidly dissipate rapid increases in engine cylinder temperatures, thru very efficient heat transfer and an understanding that the lubrication system , and additional oil coolers and high capacity oil pans also play a significant roll in engine temperature stabilization. You can,t have hot spots or rapid temperature changes and expect the engine tune to stay spot-on, or consistent, and you can,t have some cylinders running significantly cooler than others or detonation is the likely result when your pushing for the best possible power levels
so to maintain a consistent engine temperature range the cooling and lubrication systems must BOTH have the capacity to regulate their temperatures, even while the input temperatures vary rapidly

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Staff member
the big block chevy engine has gone thru several versions and the early mark IV has had the cooling system improved with a different head gasket and three extra holes in the block for coolant flow,
I think it is 80 & up mark IV big block engines that has the later improved cooling with the three extra holes.
(look at the gasket info below)
ITS Real easy to drill the holes in the earlier blocks if you don,t have then with a 3/8" drill , using the gasket as a pattern as it was found to increase cooling.

BTW fritz1990 posted this info

Top gasket pic is one with the extra cooling holes. Can use this gasket as a template to drill these 1/2" holes in the deck of the block. All heads already have these holes just some blocks don't.

The holes are the three on the bottom side of the gasket right below the ones between the cyls. The ends of the gasket are also different.

Just don't use the top gasket on your block without drilling the holes. I have to run to work and I can explain the difference later. The top setup is suppose to give you a lil' better cooling but there are many like yours running around, not a real big issue, just better to do it now.

If you have the three holes in the block you can run either gasket.

There are gaskets made specifically for this swap. Use other gaskets at you're own risk- these are what you want (from a V/R press release, presumably prior to the Gen 6 engine release):

General Motors 7.4L Head Gasket

General Motors (GM) 7.4L (454 CID) engines use two types of engine blocks: the Mark IV and Mark V. The Mark IV is found on 7.4L engines in model years from 1965 to 1990, and the Mark V is found on 7.4L engines in model years from 1991 and newer.

Often, installers will attempt to adapt a Mark IVcylinder head for a Mark V block. This conversion can be made if attention is paid to the coolant circulation. Mark IV and Mark V have different coolant flows and were originally designed for different head gaskets. If the conversion is not performed correctly, the engine will overheat, causing premature engine wear and damage.

Victor Reinz has designed two Nitroseal® head gaskets to specifically allow for this conversion. The installation requires Victor Reinz part number 4918 be installed on the right cylinder bank to maintain proper coolant circulation, and part number 4923 to be installed on the left cylinder bank for the correct coolant flow.

Victor Reinz part numbers 4918(right bank) and 4923 (left bank) are available for GM 7.4L (454 CID)
The bottom gasket is the one you will need to use if you don't drill the holes.




MARK V- coolant passages


MARK IV- coolant passages

Three types of gasket materials are generally available, steel shim, composition and copper gaskets. Cast iron heads can use all three types of gasket materials. Aluminum cylinder heads require the use of composition or copper gaskets. Various compressed gasket thicknesses are offered. Remember that you should have a minimum clearance of .035"-.040" between the top of the piston deck and the deck of the cylinder head when using steel rods. Aluminum connecting rods typically require a larger clearance.
Fel-Pro composition head gasket (PN-8180-PT) for 4.250" bore Mark IV engines. It has two additional holes for head bolts that go into the lifter valley found on some high performance Bowtie and aftermarket blocks.

Different head gasket bore sizes are offered. Mark IV head gaskets have different coolant core hole passages than gaskets for Gen.V engines, blocking some passages and opening other coolant passages. Some block deck coolant core holes are round, while on Gen.V production blocks the holes are irregularly shaped on the block deck. Mark IV heads and head gaskets should be used on Mark IV blocks. Likewise Gen.V style cylinder heads and gaskets should be used on Gen.V blocks. There are exceptions. Mark IV heads can be used on Gen.V "Bowtie" and on Gen.VI HO blocks because the core holes in these block decks will seal the water core holes found on Mark IV heads. If you build this combination then use a Mark IV style head gasket and plug the core hole in the Gen.V "Bowtie" block deck located near the front head dowel pin location (see photo). Otherwise coolant entering the front of the block can bypass the rest of the block and exit out thru the head and intake manifold.

Steel shim gaskets and copper gaskets require the use of head gasket sealant. Composition gaskets do not require sealant.

Head bolts should be completely cleaned and then torqued down in the proper sequence and to the correct torque values. Head bolts or studs, used on aluminum heads, need to have a hardened steel flat washer (PN-3899696) under each bolt head or nut, to prevent damage to the aluminum head surface. Head bolt threads going into water passages should be coated with sealant and head bolts going into blocks with "blind" holes should be coated with moly lube or oil. Some head gaskets do not need retorquing, but it is a good practice to retorque all of the head bolts after the motor has been heated up the first time and allowed to cool down. Remember, do not try to put Mark IV heads on a production Gen.V block and visa versa. You can use Mark IV heads on the new Gen.VI 454 and 502 HO blocks or on "Bowtie" blocks.
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Staff member
Can running a tad rich on jetting avoid detonation using my bone stock 396 325 as an example? Besides the obvious issues with small cam, high compression and backing off on the timing for today's fuel, would fatter jetting help? "

the answer depends on how close your pushing to getting into detonation, but the richer mix in the 12.7-13:1 range tends to produce a bit less heat that a emission friendly 14.5:1015:1 range so it tends to delay detonation very slightly, keeping your coolant temps low,having a larger more effective radiator etc., slowing your ignition advance curve and using a higher octane fuel will obviously help


Staff member

Black or brown specs: This is an indication of detonation usually caused by too hot of a plug, drop one or two heat ranges and it should go away. The plug gets so hot that it will start to detonate the fuel before the ignition fires, this cause a double flame front and reduces the efficiency of the combustion process as these two flame fronts battle each other in the combustion chamber. The black spots are the result of the fuel deposits being burned onto the porcelain by the double flame front. Once you cool down the plug and remove the secondary ignition source you can re-set your timing to produce the correct combustion chamber temp for optimum power.

I've heard 100's of so called tuners and engine builders tell people that this is normal and nothing to worry about......WRONG. Do not underestimate the damage that this condition can do to your engine, drop the plug heat range.

BTW swapping to a colder plug and increasing the fuel octane DID prevent this. below is a colder plug after the changes from the same engine

the answer too what cooling system is most likely to both cool the car/truck efficiently and fit your budget,would mostly depend on your budget limitations,
but a large 3-4 tube aluminum radiator with a a 140-to-200 amp alternator


I'd point out that a 7-8 quart baffled oil pan helps cool an engine.
and dual or a large single electric fan with a matched ducted shroud and the ability to move,
2500 fcm-3000 cfm of air should provide adequate cooling for most engines.
adding an auxiliary oil cooler certainly helps

and if you have an automatic transmission Id add a electrical fan cooled trans fluid cooler

if coolant in the engine gets hotter faster at idle than when your cruising the cause is frequently related to either a lack of air flow (not the correct fan or shroud)
or not enough functional radiator surface area,as the car speed increases it obviously has the effect of increased air flow that results in more efficient heat transfer rates
yes the idea of a larger radiator with increased surface area helps.
most of us are forced due to clearance limitations to select a radiator with specific width and height limitations you can frequently select a radiator thats a bit thicker,
or has a higher fin count per square inch of surface or more efficient inner coolant tube designs.

reading links helps



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Staff member
Chevy reversed the flow direction in the LT1-LT4 engines to direct the cooler coolant from the radiator into the heads first, before in flowed into the block in an effort to reduce cylinder head temps because high cylinder head temps tend to increase the potential for detonation with lower octane fuels, and most modern cars run at higher average temps and have restricted air flow rates thru the radiators,
keep in mind an LT1 or LT4 production engine made well under 400hp in factory form, needed to pass emission testing and was designed to operate for years mostly spinning well below 5000rpm the vortec head design took the basic LT1 intake port and used it in a standard flow head design, reverse flow was a band-aid cure for a problem that better heads and a larger cooling system can easily over come. the direction of coolant flow is not nearly as important as keeping a rather consistent and controlled low coolant temp, in the cylinder heads coolant passages, if you have an aftermarket high capacity multi core aluminum radiator, and a high flow water pump and several other mods that maintain consistent coolant temps the direction of coolant flow is not critical, what is critical is moving the coolant under pressure at a fairly fast rate of flow thru the heads so the coolant can absorb and transport heat out of the heads to be dispersed in the radiator to air flow.
if coolant is not moving rapidly thru the heads steam pockets can form reducing the coolants ability to extract heat.
Ive tested dozens of engine combos, and for awhile that deal of running extra coolant ports at the rear of the intake and several more between the center exhaust ports, and the result is that, If you have aluminum heads and you use thermal barrier coating on the combustion chamber and pistons,and if you have a fully functional high volume water pump and a radiator capable of dissipating much more engine heat from the coolant than the engine produces, rather rapidly and your using a surface tension destroying additive in the coolant like purple ice or water wetter and a fully functioning oil and transmission fluid cooler with auxiliary fans and with a t-stat that keeps the trans fluid at 180F and the oil at 215F-220F the potential gains of reversing the coolant flow are minimal at best.
the effort required simply is wasted in my opinion ,time and money best spent else-ware, if you've maximized the cooling capacity and maximized the heat transfer rates.
the object is to remove heat from the heads to reduce the potential for detonation, and to increase cylinder pressure, a correctly designed cooling system can do both.
I've had good results with a 200 deg F rated T-stat with the holes drilled (READ THE LINK) but many guys select a 180F t-stat
yes that should be just fine!
In an ideal world your coolant temp never exceeds 210F and spends most of its time around 180F-190F , oil MUST reach 215F occasionally during your cars operation, to burn off moisture and acids but should be at about 10 degrees hotter than the coolant, most good quality oil easily handles 240F for limited times, If I was you Id stick a 180F- or -190F T-stat in the car with several holes, ID custom drill in the flange, to allow some coolant flow at all times, this does slow the time required for the engine to reach operational temps but it alst tends to almost totally reduce the temperature swings as the t-stat opens and closes
buy a new 190F t-stat but before installing it drill 6 3/32" holes in the flange this mod usually prevents that problem and results in stable temps





img212.gif ... Code=Therm





drilling a couple small air bleed holes in the t-stat is almost mandatory in corvettes,
to allow filling the radiator with coolant easily ,
and it tends as stated earlier to minimize engine temp swings, it can't hurt and in my opinion helps.

if you have the room mounting the coolant temp sensor in the radiator t-stat housing location with a custom spacer for the sensors, is a good option as it tends to read more consistently than sensors mounted in the cylinder head.
some chevy race intakes have rear coolant ports to allow rapid coolant extraction from both ends of the cylinder heads

using a surface tension destroying additive in the coolant like purple ice or water wetter can significantly reduce or prevent this, which is one of the reasons the 400 chevy has extra steam holes in the heads and gaskets.
pumping cooler coolant that has a higher capacity to absorb heat also reduces cylinder head temps as does increased oil flow thru the valve train if your using an oil cooler that maintains consistently lower 215F oil temps

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busterrm said:
Hey grumpy,
What would it do if you ran the hoses and fitting on one of those manifolds to recirculate the coolant back to the radiator, would it cool better?
IF your running the rear coolant port hoses to the radiator t-stat spacer, you ARE running it directly back to the radiator if those rear manifold coolant ports have fittings and hoses routed to the spacer under the t-stat, all water flows out or the t-stat spacer and upper radiator hose directly into the upper radiator

keep in mind the openings in the head gasket restrict coolant flow till all the area around the cylinder walls are full and only then does the coolant flow up into the heads coolant passages and back to the radiator, the holes are designed to restrict coolant flow so its more or less equalized as it moves up into the heads and back to the radiator, if the holes in the head gasket were not slightly restrictive the front cylinders would be much more effectively cooled as coolant would take the fastest and easiest route of least resistance, having a restrictive head gasket makes all coolant flow paths roughly equal in the crappy diagram below the blue shows the head gasket


some intakes don,t require the adapter as theres already 4 ports designed for the coolant re-routing modification , like the edelbrock #2925



putting some thought into selecting the correct high flow capacity fans and matching shroud, and carefully measuring the clearances available ,
and installing and using ,a high fin count aluminum radiator goes a long way towards increasing cooling efficiency, ideally you,ll want an aluminum radiator
and ideally with a multi pass design with large coolant transfer tubes.
yes its VERY LIKELY your current radiator size is woefully undersized and the area its mounted in can,t be easily increased, if you have significantly increased your engine power out put! 3-&-4 row aluminum radiators that hold more coolant volume, allow the liquid to transfer heat more efficiently, and allow the coolant to pass thru a bit slower.
adding an auxiliary oil cooler with a powered electrical fan can reduce the heat load on the radiator



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