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Old 05-16-2005, 10:46 AM   #1
Big-Daddy
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Default FAQ - Olds forged rods and olds pistons questions

Ok guys- I need a definate answer on this one.
I'm tearing my 472 down this week. Planning a budget buildup, and hoping for about 600 hp. Got a chevy friend who is gonna port match, clean up, and blend the bowls on my heads. Also match my new edelbrock intake.
My question is spacifically on the swaping of the Oldsmobile rods, and pistons.
I'v been around caddy's long enough to have heard that stock 'olds rods and 403 pistons will go into the engine, but I need more spacific details.

Which rods work with what combinations? 6 3/4 or 7 inch rods, 472 or 500 crank? What kind of compression will I end up with using my '71 472 heads? What oversized 'olds piston sizes will be needed?

The engine will receive a 200 hp nitrous shot, and I'm hoping for about 450 hp on engine, so about 600 total hp. At these levels, forged rods are a must.

But I need definate answers on the rod lengths, piston compression, and cylinder quench so I can select the proper cam, or have it ground [maybe reduced base circle if I need to mill the block for quench]?????????

Really apreciate whatever help someone can provide...

Daryl T.
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Old 05-16-2005, 12:37 PM   #2
KJC
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7" rods, 403 pistons and a 500 crank will go together and you'll have to deck the block for decent quench, 30-50 thousandths, I think.
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Old 05-16-2005, 01:41 PM   #3
Caddycarlo
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why do you feel that forged rods are a must? ..... I have been as high a 808 hp on stock pistons and rods though the piston life is questionable the rods did fine ...... I also have run a stock motor with just arp rod bolts a cam and intake and 250 cheater plate .... ran bottles and bottles thru it to the tune of 4 to 6 a week for a very long time and never had any trouble ........ the stock rods with a good bolt and resized with ALs new piston would be a easyer match ...........
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Old 05-16-2005, 07:48 PM   #4
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I am with CaddyCarlo all the way. The Olds combo you have in mind will work but you wind up with a deck height of 10.765 (.049 cut ) which will limit your options of rod/piston combination in the future.
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Old 05-17-2005, 04:57 AM   #5
dave_brode
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Default Re: Olds forged rods and olds pistons questions

Big-Daddy,

The TRW 403 pistons [in std 4.351" or 4.381"] with 7" olds rods was more popular before the "for caddy" KB pistons existed. As others said, they are too short, but afaik, they were the only non-custom piston option for a pump gas 76cc head 500. Using 1.910" as the stock C.H., the .250" longer rod would want a C.H. of 1.66 to get back to "square one", so the 1.615" tall 403 pistons are at least .045" too short. If the block ins't cut, the quench would be in the .080"-.100" range. Not good, according to most experts.

The 7" olds rods work well with 454 chevy pistons, since most are 1.645" tall. Flat tops can give close to 9-1 with a 120cc head, if the quench is kept tight. You can also buy dished blower pistons for the 454 that *may* work for a pump gas 500 with 76cc heads and a 7" rod. Note - I said *may*. Valve to piston clearance issues may arise, if the valves don't clear into the nothces, but I believe that they will.

They 403 piston/7" rod deal would not work in a 472, since the stock C.H is 2.010" or so. I know of no off the shelf non caddy piston that'll work in a 472 with 7" rods. KB makes a dished caddy 472 piston for a 10-1 CR with 76cc heads, but they are hypers, like the KB dished and flat pistons for the 500. Most experts feel a hyper isn't a good choice for N20.

As far as the 6.735" olds rods, they'll work to replace the 6.75" long caddy rods, with a "for caddy" piston if .015" is cut from the block to get the quench back to where it would be with 6.75" rods. The olds rods must be reamed on the small end to fit the caddy pistons. Eagle olds 6.735" rods are also often used.

Note - most experts feel that the olds rods should be turned 180 degrees when used in the caddy, due to the chamfer on the rods' big end, and the fact that the caddy front to rear head offset is opposite vs the offset on an olds engine.
Dave



Quote:
Ok guys- I need a definate answer on this one.
I'm tearing my 472 down this week. Planning a budget buildup, and hoping for about 600 hp. Got a chevy friend who is gonna port match, clean up, and blend the bowls on my heads. Also match my new edelbrock intake.
My question is spacifically on the swaping of the Oldsmobile rods, and pistons.
I'v been around caddy's long enough to have heard that stock 'olds rods and 403 pistons will go into the engine, but I need more spacific details.

Which rods work with what combinations? 6 3/4 or 7 inch rods, 472 or 500 crank? What kind of compression will I end up with using my '71 472 heads? What oversized 'olds piston sizes will be needed?

The engine will receive a 200 hp nitrous shot, and I'm hoping for about 450 hp on engine, so about 600 total hp. At these levels, forged rods are a must.

But I need definate answers on the rod lengths, piston compression, and cylinder quench so I can select the proper cam, or have it ground [maybe reduced base circle if I need to mill the block for quench]?????????

Really apreciate whatever help someone can provide...

Daryl T.
[/quote]
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Old 05-17-2005, 06:37 AM   #6
Al from MTS
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I see it alot like Caddy Carlo does. I think stock 500 rods get trash talked more than they should. I have not hit em as hard as he has. I've used them in 600hp N.O.S. sprayed engines and never hurt one. I never spin them past 5200 RPM.
Every time I broke a rod, it was from RPM failure. IMO 5500 and up is gambling big time. 5200 and under has in my experience been bullet proof. Even with a good dose of spray.
For the most part I only use the 455 Olds rods in engines that will be spun past 5500 RPM.
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Old 05-17-2005, 12:46 PM   #7
MilesO
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Here is a link to the KB site
http://kb-silvolite.com/performance.php?action=diam

A 7" Olds rod (6.998") on a 472 crank will need a comp ht of 1.772". If you will look up KB-206, KB-137, & KB-138 these will have the desired comp ht, but, will need the pin bore diameter of the rod enlarged to fit the piston pin dia.

Also, the question relating to valve / piston top clearence must still be answered as this is not a 'made for it ' combination.

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Old 05-17-2005, 04:21 PM   #8
cadillac512
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Al,have you experienced rpm related rod failure with stock rods fitted with ARP(or equivalent) bolts? I can hear the "time bomb" engine in the T ticking its life away out there in the shed as I type this..... :roll:
Terry
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Old 05-17-2005, 05:31 PM   #9
Big-Daddy
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I apreciate all the help everyone.

IMO, forged rods are simply the way to go if the option exists, and all other things being equal. I see both the 6.735 and the 7.0 olds rods for sale all the time, and at very reasonable prices on some of the olds web sites... Why not go with them?????

I had my share of pontiacs "back in the old days", and wasted more than one of them due to the cast armasteel rods. Sure, there fine up to a certain power level and RPM, but it's always there in the back of your mind that those darn rods are the weak link in your pride and joy. I just dont want that costing me any sleep.

My local machine shop is where my chevy racer friend works, the one who will be doing the heads and intake for me. He will also be handling the assembly as well. They cut valve releifs in pistons, and we have already discussed these issues.

While were on the subject, am I going to run into any oil supply issues with a reduced base circle cam?

Again, thanks for the help.
Daryl Torres
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Old 05-18-2005, 08:49 PM   #10
smalltruckbigcid
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Default Don't be shy Terry

Remember, for many of us your doing the CSOB R&D work, so that ticking is all in your imagination......tick tick tick
George
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