Oops, 6.123 - 6.125

14ish years ago I bought diamond forged dished pistons for use with magnum heads, chevy 6.125" eagle rods and stock stroke crank.

Most here are telling me to throw the rods I have in the trash.
For some reason these eagle SIR rods have small pin size and also have the stock width of a sbm.

First thing I would do is measure the crown thickness of the dished Diamonds you have. If they started life as a regular flat top, and were milled to get the compression down... they could be thin and not suitable for the power you're talking about...

Ask me how I know...

IMG_20140104_121106_840 (1280x720)

I think 700 HP is going to detonate your bottom end... you can try a stud girdle that may be some insurance. It might stay together with only an occasional blast down the hwy but won't last under any serious boost over 7-8 lbs. Mopar cranks are strong but they have their limits.

My 13.5-1 SBM has been o-ringed. Used Fel-pro gaskets.

Big end width is not a big concern to me. A bit narrower won't hurt anything. Stock rods will last at 6500 rpm's. My oval track motor tossed a rod when the former driver ran it with thick oil and no engine warm-up...

You can bush the small end of a stock rod... finding a shop that will work on this may be a little tuff... so many only want to do belly button engines and are afraid to bend the rules.

As mentioned before... mine is a girdled 1991 360 block, 1/2 fill, with a stock cast crank, h-beams, and custom diamond pistons. Non-intercooled on E85 I've run mine at 23psi. From the ET/MPH/Weight, that is somewhere in the 850hp neighborhood at the crank when it's turned up that high. Most of the time I run it around 9.90 which is 700~750hp range since it doesn't have a cage in it.

I made around 700hp on stock rods, before putting the h-beams in it. That was with a pretty small cam though, and never went over 6K. I've heard lots of bad stories about SIR's, but never seen one break myself.

If you can't afford to replace the parts it's going to kill if it breaks a rod... better to save up for something better now then be disappointed later.

I would say if you're going for big power that you'd want to put a girdle on it. I know that you could see really strange things on the main bearings, where the main caps were moving around a lot. The girdle definitely helped that situation.

The tune needs to be pretty good to make big power without hurting stuff.

As this is your first turbo build, you should expect to break some stuff along the way if you're going to shoot for big power (especially with low-buck parts). Just make sure you're prepared financially, mentally, and have the time to go through that WHEN it happens.

The small block is a real good platform to build 600hp out of pretty easily. 700+ is pushing it, and going to get expensive unless you have a very good handle on tuning it.

How would a person measure the piston top thickness?
Ramblings on a few things.
Stock rods look bulkier.


Old combo.
#7 was blowing air out into the crankcase when pulled apart.
Cam specs were 505/515 lift 224/230@50 110lsa
2.02 valve with 75degree deep bowl cut.
Silv-o-lite pistons blah blah

A note on the half fill, I was looking into it pretty deeply for my build (also same goals, 650-700hp for a street car while attempting to keep the RPM's low only I'm using a blower instead of a turbo).

Hughes told me don't bother with it.
My machinist, a very knowlegable NHRA super stock record holder said don't bother and stated there was plenty of meat in the lower bores of my 340 block. I had actually paid him for it and he called me up asking if I wanted a refund telling me he didn't think it would provide any benefit.
I have also talked to a few people making 600-700hp with lower rpm forced induction builds who did not half fill and had zero issues.

There were, of course, a lot of guys that I found who DID half fill and had SBM's living at 650+HP. I'm still on the fence on whether or not I did the right thing by not doing it, but I do know that it probably saved me from some potential oil temp issues.

I just don't think I've seen anyone yet who had a high HP, low RPM forced induction SBM fail because of issues that could be attributed to lower bore distortion or anything that a half fill could have prevented. I've never seen anyone talk about problems they had with a turbo/blower motor that were solved with a half fill.

Did you use a girdle? What about all the others you talk about?

I'm pretty confident in the block, crank, and pistons.

2 bolt mains make me think I need a girdle because you don't have the same clamping force as 4 or 6 bolt blocks but not sure if they really help on a sbm. I've read on here otherwise.

The rods I have unless they are made of some seriously good material seem sketchy. But who has actually seen them fail in a low rpm engine?

I know the LS guys are bending the piss out of their skinnier rods at 700hp+

I did use the girdle with mine, most of the guys I talked to making 600+hp used one.

I have heard some debate of whether or not a girdle that doesn't tie into the pan rails actually helps, but I've spoken to a few well known engine builders who say it definitely does and also have talked to guys with first hand experience using them on mopars or other brand motors where the girdles mount the same way who have fixed or at least greatly improved bearing wear issues they were having as a result of cap walk.

Many of the guys who told me it it was just a gimmick on a motor that doesn't have the girdle tie into the pan rails had no first hand experience to back up their claim, so I decided to go for it.


I have heard some good cases made for using billet caps, and if I had an unlimited budget but for some reason needed to stick to an LA block I probably would have used them. The reason I used an LA block was because I didn't have an unlimited budget though, and with the cost of buying billet caps/having the block machined for them I would have just gone R block.

I tossed the Eagle I beams I had in my 340 and went with Eagle H beams and ARP2000 bolts.

Thanks for your input 1mean340.

I've been in contact with SD-Concepts in RI and will see what they have to say.

Looking at these as next choice unless they say differently.

https://www.ebay.com/itm/331624224300

I also see this for sale:

https://www.ebay.com/itm/371660576728

I'm reading the book
MOPAR SMALL BLOCK HOW TO BUILD MAX PERFORMANCE
After skimming through and then reading up to the rod selection section it appears I will learn very little.
Not much new and less technical than the original How to hotrod small block mopars I read back in the early 90's.
A little disappointed actually.
Maybe I'm just dense.

Demand a refund!

You might go to www.moparchat.com & scroll down to & click on "circle track chat" & then read thru Sanborns' oiling/cooling mods that are in a sticky at the top of the page. it'll take you a good hour at least. definitely worth it.

Ok, I read the oiling mods link.
8k rpms is outa my league.
Also just finished reading this book @ 6am this morning.
I learned a couple things about auxiliary injection systems for cooling intake charge.
Back to the basics by Larry Shepard.

I'm putting my 383 SBM back together with 340 rods... it's had them in there for two seasons @ 575 HP and they work well unless you spin a rod bearing and keep the hammer down...

O-ringed the deck and use a copper head gasket along with good fasteners. The rest you've been already told. A spot on tune will definitely be needed.
My mostly stock 318 went from 160hp on the Dyno to 536hp on back to back pulls. Stock 2bbl and exhaust to GT45 turbo and a 800 cfm Thermoquads using C 12. The only failure was the head gasket. I O-ringed the deck and installed copper head gaskets it has held up to 26lbs. of boost at the intake.
If it See's detonation at those power levels bring a shovel and a bag. Dave

My 383 used o-rings and old style steel shim gaskets with 13.5-1 on methanol... todays MLS gaskets are pretty good.

Thanks for all the opinions and experiences shared.
Just finished reading this book.
It had a decent section on durability mods.
Really enjoyed the history of turbos section.

Charmed life of a boosted engine.
Via Supercharging performance handbook circa 2016

15psi of forced induction creates ONLY a 8% increase in rod compression forces.

6k to 7k rpm jump using standard N/A tricks to produce more HP increases rod bolt/rod forces by 36%

That is true...if and only if you have enough octane, no detonation, and the timing backed WAAAAAAAY down.

There is a reason people run o ringed blocks and cometic gaskets, and I assure you it's not only for that 8%!