Historical clarification on BBC rod designs

**Warren F.** · March 1, 2006, 06:44 PM

Re: Historical clarification on BBC rod designs

Steve,

I am assuming you have as reference material or have read the information pertaining to BBC rods in both these books, How To Hot Rod Your Big Block Chevrolet Engine by Bill Wilson. Also Corvette by the Numbers by Alvin Colvin.

I can only comment that the 7/16ths dimpled rods were used on production 1970 & 1971 LS-6 engines, the rod bolt however has a knurled shank, and not quite as strong as the boron bolts used with the ZL-1's.

**Mark #28455** · March 1, 2006, 09:11 PM

Re: Historical clarification on BBC rod designs

The 3/8" bolt dimple rods were used for the solid lifter engines through 1968. In 1969, they were also used for the L71 and L89 through the year, and for the 1st design L88 (closed chamber "IT" engine).

The 3/8" rods CANNOT be converted safely to use the 7/16" bolts.

The 7/16" rods with boron bolts and a coplated pin bore for floating pin were used on the second design 1969 L88 (open chamber LO or LV engine) and the ZL1.

The same 7/16" forging was also used on the 1970 and later LS6 but with the cheaper knurled bolts and no coplating as they used a pressed pin. This same rod was used in the service engines for about 20 years so they are COMMON on e-bay and can easily be upgraded with a fancier rod bolt if you want.

I believe that about 10 or 15 years ago, the basic forging for this rod was upgraded - the beam has a slightly different curve to it - but they continued to use the same part number.

If you are thinking of coughing up the $$$ for a set of original 7/16" floating pin rods, you may want to consider a set of the Eagle racing rods as they are a better rod and are cheaper too.

Mark

**Steve Antonucci** · March 1, 2006, 10:40 PM

Re: Historical clarification on BBC rod designs

Mark,

Thanks for the clarification.

If the 1st design L-88 used the 3/8 dimple rods as you indicated, were they
set-up for floating pins? Has the use of 3/8 dimple rods on 1st design L-88
engines been verified by any L-88 owners/members here?

When approximately did the 2nd design L-88 & ZL-1 come into production? I
know that the first ZL-1 Camaro's came into being in late December 1968, but
I don't know about the L-88's. Were the L-88 Vettes available throughout the
entire 1969 model year? BTW, did the open chamber 2nd design L-88 & ZL-1
engines use the '074 aluminum heads?

Lastly, the coplated rods you mentioned; are these the babbit dip rods I have
heard about?

Steve

**Warren F.** · March 2, 2006, 11:57 AM

Re: Historical clarification on BBC rod designs

Steve,

L-88 production ran thru the model year 1969. After strike, approximately June 16th 1969, second design L-88's came through with '074 open chamber heads. As I heard, approximately 44 L-88's of the 116 built for 1969 model year production used the open chamber head.

**Mark #28455** · March 2, 2006, 10:53 PM

L88's all used floating pins *NM*

**Michael H.** · March 3, 2006, 09:38 AM

Re: L88's all used floating pins

First design 67 L88 rods, #3893260, were pressed pin. 2nd design 67 and all 68-69 were floaters.

**Clem Z.** · March 3, 2006, 10:25 AM

Re: Historical clarification on BBC rod designs

8 of the 3/8" bolt rods are about 1 pound lighter than 8 of the 7/16" rod bolt rods so we always used them to save rotating weight and in big HP drag race engines that we ran at 7500+ RPMs we never had a rod failure. the stock bolts were the weak part so we used after market ones.

**Steve Antonucci** · March 3, 2006, 10:35 AM

Re: Historical clarification on BBC rod designs

Clem,

I have no reason to doubt you position on the weight/strength issue with
3/8 rod bolts. However, why did Chevy go to the 7/16 bolts if this was
the case. Just more of the "bigger is better" culture back in the day?

Steve

**Steve Antonucci** · March 3, 2006, 10:43 AM

Re: Historical clarification on BBC rod designs

Steve,

L-88 production ran thru the model year 1969. After strike, approximately June 16th 1969, second design L-88's came through with '074 open chamber heads. As I heard, approximately 44 L-88's of the 116 built for 1969 model year production used the open chamber head.

Warren, so early to mid year 1969 L-88 production used the 3919842 heads?
These were obviously the closed chamber design. So, when the '074 heads
were added in late production, did the L-88 also include an open chamber
piston design to go with the head?

Steve

**Steve Antonucci** · March 3, 2006, 11:19 AM

Re: Historical clarification on BBC rod designs

OK,

So here is what I have gathered thus far from this thread:

- 1st design 67 L-88 rods used pressed wrist pins and 3/8 bolts. 2nd design
67 and all 68-69 L-88 rods used floating wrist pins. I assume they still
used 3/8 rod bolts?

- 7/16 dimpled rods with boron bolts and a coplated pin bore for floating
pin were used on the second design 1969 L88 (open chamber) and the ZL-1.
Would that be all ZL-1's?

- 7/16 dimpled rods were used on production 1970 & 1971 LS-6 engines.
The rod bolt has a knurled shank and used pressed in wrist pins with
no coplating at the wrist pin bore. This same rod forging was used
in service engines for many years thereafter. Would this include the
"over the counter" crate engines sold ( like LS-7 )?

- 3/8 dimpled rods can not be safely converted to 7/16 bolt sizes. I'm
fairly sure I've seen shops advertise this service.

Questions:

Is is safe to assume that the 7/16 rod bolts were not used until mid-year 1969
production ( L-88 & ZL-1 )?

So exactly how many different BBC dimpled rod designs were there anyway?
3/8 pressed ( L/71, L/72, L/78, early 1967 L-88 )
3/8 floating ( Late 1967 L-88 up to 1969 1st design L-88 )
7/16 floating, coplated, boron bolts ( 2nd design 1969 L-88 & ZL-1 )
7/16 pressed, non-coplated, knurled bolts ( LS-6, service, etc. )

Did I miss anything or get something out-of-whack?

This has been interesting reading.......

Steve

**Michael H.** · March 3, 2006, 11:28 AM

Re: Historical clarification on BBC rod designs

Steve,

Not 100% sure but I believe all 69 L88's used the new 7/16" bolts, not just the 2nd design engines. I'll see what info I have on this.

**Michael H.** · March 3, 2006, 11:51 AM

Re: Historical clarification on BBC rod designs

Near as I can tell, the first L88 rod, # 3893260, was used in early 67 with pressed pins and 3/8" bolts. It was replaced during the 67 run with a full floating design, #3909846, also with 3/8" bolts.

The 846 was used for the balance of 67 and through the end of the 68 model year.

According to paperwork, and the 69 parts book, a new 7/16" full floating rod, #3959187, was released for the entire 69 model year. There's no mention of 1st design or 2nd design for this application so we have to assume there were no 69's with 3/8" bolt rods.

The early release pressed pin 67 rod, 3893260, would actually have been a release for the 66 L88.

Most of the additional weight that was added to the 69 rod with 7/16" bolts, was added to the bottom end so it would be considered flywheel weight, not recip weight. For this reason, there would have been no reduction in horsepower or durability because of this additional weight.

**Mark #28455** · March 3, 2006, 10:41 PM

what's really a 1969 L88 engine?

It wasn't too long ago that all of the common sources listed the LO and LV codes for 1969 and didn't list the IT code at all. In fact, the L88's used in the early part of 1969 were in effect "left over" 1968 parts if you consider the date codes on many of the parts. My October 1968 L88 used a distributor from way back in the 1968 run, and the most common dates for the 4054 carbs are Dec 1967 and Apr 1968.

The 1969 service manual states ALL 1969 L88's used the 927 distributor.

I'm just not sure how accurate those sources really were.
Mark

**Mark #28455** · March 3, 2006, 10:43 PM

open and closed chamber pistons

There was a totally redesigned piston for the open chamber head and the CR was lowered to 12:1.
Mark

Historical clarification on BBC rod designs

Historical clarification on BBC rod designs

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