Jake, stock t iv cooling system limits ?

Jim Andritsakos · Post by **Jim Andritsakos** » Fri Jan 02, 2004 11:22 am

Happy new year Jake!

As for the question : up-to what engine displacement the stock cooling system can cool without problems ? I an 1974 412

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Fri Jan 02, 2004 11:25 am

Up to a 2316 with 10:1 in 914s no sweat..

cnavarro · Post by **cnavarro** » Fri Jan 02, 2004 12:47 pm

With Nickies, we've done a 2615cc with stock 914 cooling, with the addition of an external oil cooler only, and ran temps cooler than a stocker. I'm pretty confident that you could even do a larger engine, permitting that your transmission can hold up to all that extra torque.

Charles Navarro
LN Engineering
http://www.LNengineering.com
Aircooled Precision Performance

factman · Post by **factman** » Fri Jan 02, 2004 3:22 pm

Jake, why is my compression only at 9:1 for my 1971 if the stock cooling can cool a 2316 with 10:1. i know those are apples and oranges but just curious why the 2316 runs more compression? is it the cam that needs more. i guess if the combo is right then it wont create more heat right? thanks

SAM

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Fri Jan 02, 2004 3:26 pm

1500 bucks worth of head mods.... and my cam.

Its all in the combo!

Bobby74 · Post by **Bobby74** » Fri Jan 02, 2004 8:52 pm

Lumpy cams bleed down dynamic compression.
Large cams need large engines to be drivable at low RPMs.
Small engines with large cams have little bottom end torque (unless stroke is added, etc). Finally small cams, need Less compression to keep head temps happy do to the amount of heat produced by compressing gases.

Much like how an air compressor heats up, large cams "blow air past" the pistons if that makes sense. The valves are staying in closed position for a short amount of time. Small cams give the engine more "time" to burn the mixture (wich means more power per stroke), but this also results in more "stagnent" air around the heads. Small cams have more peak cylinder pressure, so that results in more heat.

Gross over-simplifications but it helps to see how cam and compressions relate.

-Bobby

raygreenwood · Post by **raygreenwood** » Sat Jan 03, 2004 10:54 am

Bobby, I'm not clear on how the cam profile will produce more or less "stagnant" air around the heads. The fan turns at a given rpm....and you may produce more or less torque on it a a given rpm in a given engine....but stagnant air around the heads has to do with restriction in the cooling system. Unless the torque transfered to the air at any given rpm is ...say...cut in half, I think its unlikely that cam profile will greatly limit or change cooling air. Unless...it causes a given fan to too heavily load the engine...but then that is simply producing more heat and dropping the rpm. Please explain. Ray

factman · Post by **factman** » Mon Jan 05, 2004 3:59 pm

i think he means stagnent air in the chambers and exhaust port. i dont agree with this. we are talking like nanoseconds on this issue. but if you run too much compression for the cam then it will create more heat than the optimal CR will.

SAM

raygreenwood · Post by **raygreenwood** » Mon Jan 05, 2004 10:59 pm

Ah....ok...I know what he is thinking of. Stagnant is probably the wrong word...but the thought iscorrect. If the cam is just wrong, the air column can be stalled with each valve closure to the extent that it causes alternating pressure and turbulence spikes. These are commonly known factors of varying degrees. Iwas just curious as to how they related to the fan. Ray

AlanU · Post by **AlanU** » Wed Jan 07, 2004 9:36 am

Bobby74 wrote:Lumpy cams bleed down dynamic compression.
Large cams need large engines to be drivable at low RPMs.
Small engines with large cams have little bottom end torque (unless stroke is added, etc). Finally small cams, need Less compression to keep head temps happy do to the amount of heat produced by compressing gases.

A large duration cam would have low static compression due to the delayed timing(open longer) of the exhaust valve. Lumpy would probably be used due to the nagative reversion through the intake valve/manifold/carburetor. Since the larger cam has a longer duration the exhaust valve stays open longer and intake opens sooner. I would say "bleed down" at lower rpms. THIS IS WHY large cams like more static compression. BUT for higher rpms the momentum of the a/f mixture will have such speed that if a cam (smaller) closes the exhaust valve too soon you stop short the filling of a/f charge....meaning reduce Volumetric efficiency at higher rpms. This is why the longer duration "opening" of the exhaust valve aids a motor in breathing/rpms and at the same time increases the "fill" of the cylinders. So I would say "lumpy cams" Does bleed down static compression. As for dynamic at high rpms it would allow more of a "window" to make more power. Bleeding sounds like your losing compression which in the "dyanamic" case you do not.

small cams have more static compression at idle. The probem with small cams is that once the a/f charge gains momentum at the top end of the rpm scale the cam stops short the high velocity of the charge. As the exhaust valve closes much sooner than a "big cam" you loose volumetric efficiency. The gains is torque and more useable power band for driving applications.

Big engine with a large duration cam has the advantage of the additional torque of the larger stroke. Torque gets you going, HP keeps you going. By saying this the larger stroke can get away with a big duration cam but still may have a soft bottom end. A smaller crank with same cam will have a terrible driveability but will scream at the top. The larger displacements will have both - better driveability and topend get go.

T4 heads are big and they have tonnes of surface area due to the fins. having an exhaust valve that is open longer will reduce heat. The cam bandaid for the t4's probably does this. But still cannot compensate for "better quality" of flow. If the exhaust port wasn't so horrible with that tight bend of the exhaust port there would be no need to manipulate cam timing of the exhaust. Better volumetric efficiency is created with Jakes $1500!!!!!!!!! dollars of T4 head mods. MORE VE means MORE POWER. More power = more efficiency. More efficiency = Less heat. T4's size and surface area is also a bonus!!! Why do T1 potentially run hotter?? YUP smaller physical size head with less surface area. But the efficiency will keep the temps cooler.

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Wed Jan 07, 2004 9:37 am

Yep...... Surface area is the key..

And then the combo..

AlanU · Post by **AlanU** » Wed Jan 07, 2004 9:49 am

MASSIVE TYPE IV wrote:Yep...... Surface area is the key..

And then the combo..

Jake, I think in time when you get the aftermarket head going you will see less heat due to the efficiency of the newly designed ports. NOT to mention the huge surface area of the t4 head helps it a bunch. And of coarse with the better VE you'll get WAY MORE HP!!

Bobby74 · Post by **Bobby74** » Sat Jan 10, 2004 3:50 am

raygreenwood wrote:Ah....ok...I know what he is thinking of. Stagnant is probably the wrong word...but the thought iscorrect. If the cam is just wrong, the air column can be stalled with each valve closure to the extent that it causes alternating pressure and turbulence spikes. These are commonly known factors of varying degrees. Iwas just curious as to how they related to the fan. Ray

Ray,

Thats what I meant, but lacked the vocabulary to fully explain my logic. Thanks, you hit the nail on the head!! Nothing to do with area around the engine, I mean area in the combustion chamber.

Factman,

Yes cam selection makes a WORLD of difference when it comes to how long a cylinder is exposed to heat EXCLUDING head design. If the heat continues to move out of the heads (long durations) then it will keep heat from transfering to the combustion chambers from the burning gases - as fast. Constant cool intake charge is key. Valve overlap also can cool heads from spitting cool fuel out the exhaust and "internally supercharging" the engine by the velocity drawing fresh air/fuel in..

Long rods will also cause the piston to "dwell" longer and that can build cylinder pressures and head temps from the lack of piston speed/movement. (wich can be a good thing if you have free flowing heads)

That being said, the factory cam is "bad" design (especially Vanagon) because it has low lift AND low duration from a head temp point of view. The engine is so choked off that it can never breathe and get air moving through the heads properly.

When you have lots of heat, combined with Heavy loads, you get dropped seats (especially if they were installed at only .003" interference fit). I have yet to find a "vanagon" head that isn't cracked severely (exhaust ports) or has dropped seats..... well I have ONE, but thats an exception.

Sorry for taking so long to reply but I skipped over this thread. I thought it was important enough to clarify.

Also, the "perfect" cam would have a lift that was gentile, slow acceration from the seat, fast lift, and then a slow decent towards close to prevent valve float and extend valvetrain life. At least 3 "profiles", if you will. I've heard of 5 profile cams to keep from having the piston slam the valves and allow the duration/lift desired. Keep it below .500" lift and More than 240 duration and it should be happy with head temps. Long durations give the valves more time to react, wich also stops valve float because the valve isn't forced to slam open and shut.

Sorry, I went on a tangent, but cam design is still looked at as "black magic" on this forum and I've been doing a lot of studying and talking to engine builders outside of VW engines. I thought I'd like to share a little info...

-Bobby

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Sat Jan 10, 2004 9:30 am

Bobby is absolutely right.... He hit all the key facts in one post..

With a TIV, the cam is a huge piece of the puzzle.

raygreenwood · Post by **raygreenwood** » Sat Jan 10, 2004 10:03 pm

Yes...the cam is a huge piece of the puzzle. Puzzle is the right word. Many people have a hard time thinking in more than one dimension at a time.

Alans explaination was very correct....but if you will...think of this.
Many times I hear the explaination of if the exhaust valve closes too soon it chokes the velocity of the intake charge. It can be very true. It can also be false.

You have to keep the timing of the cam with its position to crank and piston, in your mind when your are thinking about the relationship that Alan described. If the exhaust valve closes....its not automatically choking off the velocity of the air column. You are forgetting the reason the air column is moving at all. The piston...during valve open point should still be moving downward. This is still drawing in charge.

Not mentioned, but of huge importantance...especially with fuel injection is TIMING. If the closing exhaust valve is going to start any reversion characteristics at all....just be damned sure that the complete injection sequence that was needed for this particular "dose" of air fuel mixture...is complete before the exhaust valve closes. If reversion is planned for...and does not disturb the needed vacume signature and flow rate too much...its okay. Its when it disturbs the ingress of part of the fuel charge, that you get lean spots and problems.

When the injection happens with relation to the open valve ..and the moving piston are very important. You also have to be sure that if the exhaust valve overlap is being used to augment intake flow, there must be enough fuel adjusted into the injection dose to make up for any that may get lost into the exhaust before the exhaust valve closes. That happens a lot. It causes high exhaust temperatures due to combustion in the exhaust manifold immediatel outside the valve pocket. Ray