240Z Turbo Posted December 16, 2003 Share Posted December 16, 2003 The thinking behind the dual pass is water will travel twice as far through the radiator as opposed to a single pass. The further it travels the more heat that is discipated. Also, the longer the coolant stays in the heat exchanger the more heat is discipated. However, just like intercoolers there is a max efficiency. A trick shown in the how to hotrod the datsun book was to restrict the outlet from the engine coolant system. This slowed down the flow of coolant through the radiator giving it more time to discipate heat before returning to the engine. Quote Link to comment Share on other sites More sharing options...
pparaska Posted December 16, 2003 Share Posted December 16, 2003 The thinking behind the dual pass is water will travel twice as far through the radiator as opposed to a single pass. The further it travels the more heat that is discipated Also, the longer the coolant stays in the heat exchanger the more heat is discipated. Agreed. There's convection happening in the tubes, and if the flow is very high, it doesn't have enough time to happen efficiently. The extra length a daul pass radiator has allows for more time for the transfer to happen. Too much time is not helpful either. For different flow rates, time and tube length (doubled with a dual pass) are somewhat interchangeable. But there are limits, and only a window where the flow rate or tube length can be varied. One issue is that after the coolant has reached something closer to ambient, the transfer rate drops off added time (slow flow rate) or more tube length gives diminishing returns. But if the tube length and flow aren't optimal, a longer tube (go to dual pass) or slow flow rate will help move more heat out of the coolant. The down side to slowing the coolant flow too much is that it may not allow efficient heat transfer from the engine parts to the coolant. Leave your WP belt off and you can see what happens (BTDT). Quote Link to comment Share on other sites More sharing options...
JMortensen Posted December 16, 2003 Share Posted December 16, 2003 I thought the restriction in the How to Hotrod book had to do with keeping the water pump from cavitating at high rpms. Has anyone run a 510 pulley on their L6? Seems to me that their pulley was quite a bit larger than the Z, IIRC. I also seem to remember some of them running the Euro damper, so it sounds like the pulley offset would be correct. Jon Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted December 22, 2003 Share Posted December 22, 2003 I think there's some confusion regarding the "system pressure" (SP) in the cooling system and the force needed to move coolant through the radiator and engine. Yeah, what John said. The pressure drop across a heat exchanger is referred to as head loss. The system pressure John refers to is the average pressure throughout the entire cooling system. This is one of those things that it is hard to speculate on. You have to work the numbers, or better yet conduct a test to see what works. The amount of heat a radiator dissipates can be computed from the temperature drop across it times the mass flow rate through it. The specific heat capacity of the coolant and radiator surface area also comes into play, but they could be the same for both radiator types. Thus keeping the coolant in the radiator longer will most likely lower the output temperature, but if the flow rate is reduced more than the temperature drop, you will lose cooling capacity. Think thermostat. A thermostat restricts the water flow through the radiator to reducing cooling (raise temperature) and opens up to increase cooling. Also most people don’t realize what a poor heat conductor water is. If water isn’t moving it is actually more of an insulator. Thus smaller coolant passages and higher flow rates will generally improve cooling capacity, up to a point. The last item to consider in a double pass radiator is the air cooling the second pass (or first pass depending upon the configuration) will be preheated by the other pass. This obviously affects cooling capacity and is why intercoolers are put in front of radiators. Raising the overall system pressure (by using say a 20 pound radiator cap instead of a 15 pound cap) really doesn't increase the cooling capacity of the system. The heat capacity of water doesn't change much with temperature, especially at the low systems pressure in a car cooling system. What it does do is raise the temperature at which the coolant will boil. You need to make the system pressure high enough to avoid boiling at the lowest pressure point (or hottest point) in the system. If the pressure inside the water pump drops too much, then steam bubble form inside the pump (called cavitation). This greatly reduces the flow of water through the pump. Also hot spots (say in the heads) can be significantly hotter than the rest of the system. If these points go above the boiling point for the given system pressure, then steam bubbles can form in the heads, and steam doesn't cool as well as water. So if you go to a more restrictive double pass radiator, the water pump will have to produce more head to drive the same water flow rate. This may require a higher system pressure to avoid cavitation. Interesting discussion. But go with what is known to work. Keep in mind that street cars don’t seem the same level of maintenance that a race car does and also in many ways see a wider range of driving conditions. So you probably want more margin (i.e. excess capacity) for a street car than a race car. Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted December 22, 2003 Share Posted December 22, 2003 Yes' date=' I was talking with a radiator man who is himself a racer and he said he regularly fixed problem overheaters by modifying single pass radiators to double or triple pass. And that modification alone will usually fix the problem, if the radiator is big enough in the first place. But he did say that the baffles so used must be very securely fixed in place.[/quote'] Yes, "if the radiator is big enough in the first place". No amount of flow modification or internal pass length will fix the problem, unless the frontal area is large enough. It sounds like for the Z radiator there is enough area. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted January 30, 2004 Author Share Posted January 30, 2004 Well i finally got some free time to let you guys know how everything worked out. Radiator is more than ample enough to cool a Z with two 10" fans. Ran it 600 miles with no problems. Actually cooled it off too much! lol need to put a warmer thermostat in it... cooled so much that i couldn't get hot air from the heater untill i came to a stop light and let it warm up a little. btw.. did the whole trip without the fans on. Anybody looking to do the conversion i would highly recomend it... very easy and looks great. Quote Link to comment Share on other sites More sharing options...
rc's240z Posted January 30, 2004 Share Posted January 30, 2004 remind me what radiator you finally bought? wasn't it a Ron Davis? Quote Link to comment Share on other sites More sharing options...
Brad-ManQ45 Posted January 30, 2004 Share Posted January 30, 2004 How much for the rad? Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted January 31, 2004 Author Share Posted January 31, 2004 The radiator costs 248 then 25 for each inlet outlet size change... had them changed to 1 3/8" to match the engine so with tax and shipping etc. payed 298. And it was worth everysingle penny! Once i get my card reader back for my camera i can post some images of what i did. Really clean install i think. -Ed I forgot to mention... yes it is a Ron Davis. Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted February 4, 2004 Share Posted February 4, 2004 You guys are all nuts (but you knew that)! The idea of restricting the flow of the radiator to increase the amount of time the coolant is in there seems misguided. If it's spending more time in the radiator getting cooler, it's also spending more time in the ENGINE getting hotter! Also, the faster the fluid flow, the greater the convection, in the engine and in the radiator. As for 16x the pressure theory, with half the tube area, and twice the length, wouldn't that be 4X? FWIW, I'm using a parts store 3-row 260Z radiator, stock plastic fan, no ducting. No problems! Quote Link to comment Share on other sites More sharing options...
Phantom Posted February 4, 2004 Share Posted February 4, 2004 Heck Fire boys! - I just converted my stock Datsun radiator to a four row, bolted up the Camaro fans & shroud and let 'er go. Works fine in Texas with AC on. No problems. Also no concern about the wieght, PMOI, etc. It's a daily driver, not a track car. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted February 4, 2004 Author Share Posted February 4, 2004 well i'm glad that worked for you guys but the upgraded 4 row i had in there with electric fans didn't cut the mustard, got too hot in traffic. But hey if it works for you guys that's great. Fact remains, I bought it, It looks absolutely gorgeous, cools like an ice queen with a cold heart. I'm happy and nobody can bring me down Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted February 5, 2004 Share Posted February 5, 2004 well i'm glad that worked for you guys but the upgraded 4 row i had in there with electric fans didn't cut the mustard' date=' got too hot in traffic. But hey if it works for you guys that's great.Fact remains, I bought it, It looks absolutely gorgeous, cools like an ice queen with a cold heart. I'm happy and nobody can bring me down [/quote'] I consider that a good recommendation, and I, for one, learned more because of this discussion. My 4 row also overheats a bit in traffic, but I considered it the fault of my weak electric fan. Quote Link to comment Share on other sites More sharing options...
pparaska Posted February 5, 2004 Share Posted February 5, 2004 You guys are all nuts (but you knew that)!The idea of restricting the flow of the radiator to increase the amount of time the coolant is in there seems misguided. If it's spending more time in the radiator getting cooler' date=' it's also spending more time in the ENGINE getting hotter! Also, the faster the fluid flow, the greater the convection, in the engine and in the radiator. As for 16x the pressure theory, with half the tube area, and twice the length, wouldn't that be 4X? FWIW, I'm using a parts store 3-row 260Z radiator, stock plastic fan, no ducting. No problems![/quote'] But Dan, you're making 255 hp. Others here are making twice that. I submit that a 3 row copper radiator may not be enough if you have 400, 500 hp and use it. Also, adding more rows to a radiator gives diminishing returns, especially in the copper core radiators, that have more thremal contact resistance than aluminum cores that have wider flat tubes that are better thermally bonded to the fins. 4 core copper is a heavy, inefficient design compared to a 1 or 1.25 inch 2 row high quality aluminum radiator. Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted February 5, 2004 Share Posted February 5, 2004 I wasn't trying to say that a stock-type radiator is all anyone needs, or that more rows in a copper radiator is better than flat tubes in an aluminum radiator. That's why I said "FWIW"! Just a data point. I know a good aluminum radiator would be lighter/better, but it might be good info for some that it's not required at or below my power level. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.