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Old 10-15-2006, 11:06 PM
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Radiator for my 75 V8 Vega??

Hi all. I'll give you all a quick breakdown of my car first. Car is a 75 Pontiac Astre GT, though it's identical to the Vegas. I've built a 440 horse 355 with Dart Pro I's, and running 10:1 compression with a 268H, and full MSD ignition. I've got a built TH350, and a temporary S10 rearend with 3.73's.

Obviously I'm having cooling issues. Well here's how it goes. My first V8 in there was a stock motor with a 256H cam. Never drove it on the streets, but then again it never idled hot. That was with a Summit high flow water pump, and a custom Vega 3/4 core radiator made several years back I got off ebay. It followed the stock dimensions which were tiny, like 24" by 12", but it cooled that fine. Well that engine had ring issues, so I built a new engine that should be good for 440 horses. Well now I'm running a "tad" higher than I was before. The old 3/4 core radiator didn't cut it, I'd drive a mile before I'd get to 230* plus. This was using the same water pump, plastic flex-a-lite fan, and 10" pusher electric fan as before.

So then I decided I can make a Ron Davis radiator work that was 26" by 19". The tech line said it was good to 700 hp. I thought I was good! I was thinking that I could be running too cool! WRONG! I went 2.5 miles before I got to the same temps as before, 230* and climbing. It would get warmer whether I was cruising, or idling, didn't matter. The other thing I was thinking was my radiator cap. Ron Davis recommended 17-19lbs, and my 17lb Moroso cap tested out to be more like 13 lbs. So I replaced that with a new cap that tested at 18lbs, and replaced the low flow plastic fan with a steel flex fan, but I wasn't able to find out if that helped any since the fan ate my brand new Ron Davis radiator.

So I talked to some people, and it sounds like the first problem is my pulleys. I have a 7" crank pulley, and a 7.1" w/p pulley, so that's underdriving my water pump (why this is important is that V8 Monzas used a 5.5" w/p pulley to keep cool). So that's one thing I'll track down that should "help".

So I'm getting to my question in a few sentences. Now I'm going to run a Ford Taurus electric fan behind the radiator since I've heard good about those. Which means my .5" of clearance I had between the radiator and pulley will be no good. So now I'm resolved at building a new core support, hacking it all away and building from scratch. I will be able to fit the bigger fan in, as well as get rid of the 3" tall section that was in front of the bottom of my last radiator, then I can build shrouding to direct air in.

Anyways, based on my engine, what should I do for a radiator? I liked the Ron Davis I had before, but going up to a much larger size didn't help a ton, so I think relocating it will help. I've noticed Jegs sells radiators for $180, are they worth it? Or should I just step up to the pump and pay another $230 for a Ron Davis radiator again? Do I need to stay 19" tall, or can I go an inch or so shorter so it doesn't hang down as much? Or does anyone on here recommend a good brand of radiator at a decent price? (I am a broke college student, lol, but I don't want to buy junk). I'm mainly concerned with what everyone on here thinks, since I will be custom mounting it, I just need to know what will work with my setup. I will also be fabricating a new latch setup to prop the back of my hood up 4" to vent hot air out.

Thanks in advance.

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Old 10-16-2006, 05:41 AM
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I have a 87 S-10 with a 350, Good for 390-400 hp. without the nitrous. Sound like the problems I had with cooling. I went with a rad. from a 88 vette and a steel flex a lite fan and a fan shroud from a 77 camaro and run a 170 thermostat and that made all the difference in the world. On the highway it runs at 175 and in traffic idling, the highest i have ever seen it get was 210 and that's here in Tn. on a 96 degree day. The Taurus fan is a good fan if you use it as puller as you plan to do, I know a few guys that have them and they work real good for them but they also had fitting issues too. The rad I had before was a monsterous 4 core brass rad that looking at it, You would think it would cool anything but it wouldn't cool this motor, Had a 305 in it at one point and it worked for that but that was a stock motor, When I bought the Vette rad, I took it out of the box and looked at it and said "no way" because it was a single core rad. Installed it, been happy as hell with it. Good luck with the Taurus fan and I hope this helps,,Perry.
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Old 10-16-2006, 07:35 AM
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Forgot to add, The rad is for a stock vette motor with air cond. What style water pump are you running? long or short? Perry.
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Old 10-16-2006, 11:59 AM
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I had a Monza years ago with the old style LT-1 in it. I used a 4 core radiator from a Buick Skylark. It cooled it just fine and dropped right in the Monza, without any mods. I'll try to remember exactly what it came out of.
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Old 10-16-2006, 01:50 PM
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check the front of the vehicle for anything that will block airflow, I had a v8 vega and the bumper assy. blocked 1/2 the radiator(the spring behind the bumper). also ditch the flex fan and go with a gm 4 blade as sold at circle track supply houses. Also use a good shroud.
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Old 10-16-2006, 11:24 PM
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Thanks for the suggestions, but I'm very sure I want to use a large aftermarket radiator basically since this is AZ, 120* is not uncommon and I would like to even be able to drive in that on a Friday night. Also, with aluminum heads and other goodies, I can't put another plain radiator in it, gotta have the eye candy!


As far as the fan, I think I'll try the Taurus electric fan still, since I like the dual speed feature, and I'll have the room. Besides, I don't think the fan was my whole problem since I would overheat while moving at 45mph also.


I think a big part of the problem was my thermostat. My Moroso cap was actually at 13lbs, when it should have been above 16, but my radiator was destroyed before I was able to find out. I thought it was the cap before, but now I'm really curious since the 87 Chevy car hauler we have at the shop used to overheat if idling for a couple minutes. The cap was looking a little old, so we replaced it and now the temp gauge doesn't move!


So I guess I'm just gonna order a 26"x19" Ron Davis radiator again. Unless someone thinks a Jegs unit, or some other brand the same size will cool as well.
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