[mrennie]

Regarding Skips post, I have upgraded 30 spline axles and and Truetrac for the differential.

[tom s]

I would let your machinist tell you which one HE would machine and build.Tom

[Dragncar]

Sorry to hear about your wife. I would be a mess, she is everything to me.
I run a 73 stroked 400 block and all is good.
71s bore numbers do look nice though.

[mrennie]

Originally Posted by tom s

I would let your machinist tell you which one HE would machine and build.Tom

Thanks Tom.

When I picked up the 73 block and we reviewed the numbers, the machinist said he was most concerned about the #7 wall with a .107" thickness (non-thrust side) knowing I would be using a .040" overbore. He said if I was filling the block (I am), and shifted the bore over to keep as much wall as possible, I should be OK and we could probably keep it at .100". But that still leaves other bores (#4 & 6) with a finished thickness of .110" and .108" on the thrust sides unless I relocate those bores. If the bores are shifted, around .120" is the most I can get on the thrust side.

Maybe I should ask this a different way:

-what is the minimum recommended wall thickness on the thrust side when building a 500-550HP bracket motor?

-has anyone encountered block issues such as broken or cracked main bulkheads with the style of casting that this 71 block has, at this power level?

I should clarify that I don't see anything "wrong" with the 71 block, it is not a bad design like the 557 block, but in comparison to the 73 block it does have this different design with some thinner areas. Interestingly, not only are the cast surfaces smoother, but the block seems more dense in some way, tapping it has more of a ring that the 73 block does. I have read many posts that the blocks got thinner and lighter as time went on in the 70's, but that is not the case comparing these two examples.

[mrennie]

Originally Posted by Dragncar

I run a 73 stroked 400 block and all is good.

Thanks. Do you know or recall if your casting is the same as the one I have? Having only these two to compare, I am not sure if there were other mold styles used in 73 or if what i have is the only type.

[steve25]

Just use hard block to fill the water jacket up to just below the front of the block water pump holes and then the machine shop can bore away without off set boring .

You will gain ring seal and better cooling from this mod.

[tom s]

Hard block will raise oil temps!Tom

[Dragncar]

Originally Posted by mrennie

Thanks. Do you know or recall if your casting is the same as the one I have? Having only these two to compare, I am not sure if there were other mold styles used in 73 or if what i have is the only type.

I will take a look when I get a chance.
Few pics of my block.

[mrennie]

Thanks for the pics Dragncar, my 73 casting is the same as yours. The identifying feature is the parting line from the casting and how the main/cam area is one piece.

I came across these pics below in a post from GRX back in 2006 that was about block differences. They are representative of my 71 block on the left and my 73 block on the right.

[Tandyman]

Michael, my machinist always told me that he would not recommend starting a performance build with less that .180" on the thrust side. Your machinist was OK with your numbers?

Also, what airport races do you plan an doing. I've done 7 or 8. Raced at Kirkland Lake, Northbay on the hill , and Elliott Lake. Been over 10 years since I did one.
They were all a blast. Just a totally different environment than racing my local track (Shannonvlle). Have always wanted to go back to another

Glenn

[mrennie]

Hi Glenn,

I specifically plan to do Kirkland Lake as it is just under 2 hours away, and perhaps Bonfield (close to North Bay), both are 1/8th mile. K.L is two weekends a summer and Bonfield is 3 or more, so if I can do 3-4 weekends a year, that would be very satisfying.

The machinist (Beatty and Woods) was not thrilled with the first block, but he was not aware I had a second one and we were both more pleased with those results, so I am glad I made the second trip down to have it checked. I only have these 2 blocks so will likely go with the 71 and have a few bores shifted to maximize the thrust side, it appears the thinnest two would be ~ 0.160".

My winter goal is to rebuild a TH400 I picked up and install new clutches, 4L80 drum and 34 element spragg, case saver, RMVB, and to get the engine close to complete. Next summer/fall will be the chassis stuff, so hoping to take it out for summer of 2027 which coincides with when I can retire.

[Tandyman]

I hope the build goes smoothly for you Michael.

My experience at the airport races is that the Friday night gamblers race is usually a petal fest (which can be an advantage if you are good at that sort of thing) and the first rounds on Saturday can be sketchy . Bigger bias ply slicks are a big plus. I found that radial or dot radials were not my friend in that environment .

Bonfield is just as close for me as Shannonville (3 hrs) but its schedule has always been in conflict with Shannonville so haven't made it there yet.
It would be nice to see and another Pontiac racing. My 69 Firebird more times than not is the lone entry at most of the races I go to.

Glenn

[mrennie]

Block/crank/rods/pistons for my 462 build are going to the machine shop next week for bore/hone & balance.

The I-beam rods I bought for this project were advertised as having ARP2000 bolts which I thought would be a bonus. Turned out the rods have ARP8740 bolts installed, and 16 x ARP2000 bolts were shipped with the rods in another package...so if I want to use the better bolts I will likely need to have all the rods resized

As they are now with the 8740 bolts installed, the bores measure on the low (tight) side of the range and OOR and taper is good.

Engine will have around 530HP and 600LB of torque. I plan to limit RPM to around 6000-6250.

Are the 8740 bolts sufficient at this power level/RPM, or should I invest in the machine work to upgrade to the 2000's?

[ChiefCrazyCanuck]

Are the 8740 bolts sufficient at this power level/RPM, or should I invest in the machine work to upgrade to the 2000's?[/QUOTE]

More than adequate.