383 or 406

by ia bhtr Thu Feb 18, 2016 11:16 pm

Picked up nice 74 with a 408 built off of a 400 gm block , cant keep it cool in the summer and sides that it needs 91 gas which is hard to find in my part of the world ... got local engine builder working up a couple different motors for me , a 383 based off a GM block looking like 425 horse close to 475 torque , also a 406 based off a DART SHP block sitting 500/500 or close , both motors designed for 87 octane horse p fuel we have around here ......... mostly just a driver with a little " fun time " throwed in ........ anyone have any experience with the Dart block in a build like this , still a siamesed block , so a little nervous with heating , builder assures me it will cool much better than the GM block I have now , should cool much like the 383 ........... will it ??????? 406 is couple grand higher than the 383 , which is and isn't an issue ....... motor will be setting ahead of a built TH 350 , 373 gears in the back

>>==================> THOUGHTS ?? <=======================<<

by bracketchev1221 Thu Feb 18, 2016 11:24 pm

Dart block is a good piece. If you can afford it, go for the dart 406 combo. But either way is fine.

by Joe73 Fri Feb 19, 2016 12:58 pm

If your 408 is in good condition with no issues, I'd address the cooling aspect. No sense in throwing money away on another engine. Theres no reason that it cant run nice and cool in the summer. There are 700+ hp big blocks running 180 degrees in the summer with the a/c on in traffic.
First thing I would check is ACTUAL timing. Yes, you can run a little lower timing to handle your lack of octane. Not a big deal.
When you have time, I'd read and follow this thread about cooling small and big blocks. Really good read with part numbers and everything. Simple stuff to do.

http://www.chevelles.com/forums/32-heating-cooling/606465-cooling-101-setup-keeps-old-school-bbc-sbc-motors-nice-cool.html

And starting at post #20 in this thread. http://www.chevelles.com/forums/32-heating-cooling/736874-anybody-tried-radiator-2.html

Theres no reason your motor shouldnt be running cool. Somethings wrong.
But if you decide to swap engines (and I'd still do the recommended stuff in that thread) then either combo you mentioned would be great.
But I'd address your cooling system first. All the tests I've read show that an aluminum rad with (2) 1" cores out cools any 3 or 4 core brass stock type rad. A rad that fits this bill and is a bolt in for our cars is the Murray 433322. Just check the dimension on that one. And best of all, the rad is only around $100 and usually available locally.

Just my 2 cents.

by testpilot61 Fri Feb 19, 2016 1:41 pm

My 2 cents worth.
I built a LARGE small block and ran into cooling issues when our weather in Okla got warmer(Hot). My fix turned out to be buying a 4 core aluminum radiator and 2- 14" shrouded electric fans and a 180 thermostat and water wetter.

I'm now able to idle in traffic with A/C on or just cruising on down the old hiway with nary a problem.

by Joe73 Fri Feb 19, 2016 1:47 pm

Another thing I would check before anything is that your timing is around 16 degrees WITHOUT vacuum advance AT IDLE. Then hook up the vacuum advance and it should give you no more than 10 more degrees (around 26 total) AT IDLE. That will make a huge difference in cooling your engine down.
If your not running vacuum advance (which you should on the street) you can go a little higher but not much since it will overwork your starter. Vacuum advance gives you the additional timing to run cooler and increases your vacuum which you need with a larger cam.

by pila Fri Feb 19, 2016 7:24 pm

I have a 408 in my '74 Malibu. They do tend to run hotter than the 350 etc. My Malibu has a 4-core copper radiator in it, so cooling hasn't been a problem in summer. A 7-blade fan & a good fan clutch may be part of the answer....

by ia bhtr Sat Feb 20, 2016 5:31 pm

Some good thoughts there guys , I know money wise playing around with the current motor is the prudent way to go , just not sure I trust the motor , some really good reading on cooling , car currently is running a 2 row aluminum radiator ( don't know what brand ) 2 electric fans ( cyclones - wrong sp ) and an Auto zone 180 stat ......... timing was going to be my first item to get checked , was planning on that anyway , Thanks much for your thoughts

by chevellelaguna Sat Feb 20, 2016 5:53 pm

I have a 355 small block and was running hot in the summer. A good quality aluminum waterpump, in my case from edelbrock helped a lot.

by pila Sat Feb 20, 2016 8:02 pm

I couldn't agree more, late timing can really make an engine cook, but not in the way we like to think of it. Very Happy

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