Tcheairs38655

The Racing Head Service 383 Magnum, Dart Heads installed in my 66 Convertible requires a BB hood. Still barely have clearance for the air cleaner and cannot use a wing nut hold down. Dipstick is on the drivers side. This engine was available from Racing Head Service in Memphis in the late 90s. I have volumes of specs and test info available if interested

6T5RUSH

I agree Tom. I'm going back 11 years ago when I decided to spend the money on my '461 heads. Very competent shop, Modern Cylinder Head owned & operated by Jeff Kobieski (sp?), RIP Jeff). Here's my bill on his efforts to make these 50+ year old heads breathe.



Here's how they flow:



Pics of assembled '461 heads with screw in studs and guide plates:







Very reliable! I've got 30,000 miles on these heads, no issues. Rockers are GM stamp steel 1.5 ratio.

Following along on this thread with interest. Do like the stealth approach

GearheadJoe

Hi Gerry:

Your timing is good, because I just recently figured out that this may be true for some '657 blocks. Just recently I saw a '657 on ebay that did not have the rod clearance notches. That block was cast in January 1967.

I have two '657 blocks that were cast in February, and they both have the rod notches. So, the notches may have been phased in after production started.

I see that the pad on your block has a November assembly date. What is the casting date of the block?

Your block does have the bearing tang notches for both small journal and large journal mains, so this is an interesting mix of features.

Regarding your question about just grinding in the notches, I'd be careful about how deep you go. I have assumed (but never verified) that when GM added the rod notches to the casting, they also added some meat behind them to maintain the wall thickness. It is possible that your block has less meat available for grinding. You can absolutely grind some amount in that area, but you may not be able to go as deep as you could go with a block that already had the notches.

I have a '657 bare block that has the notches, and I also have a 1964 '870 bare block that does not have them. I think it would be possible to carefully compare these two blocks to determine the wall thickness where the base of the cylinder meets the floor of the water jacket.

I have always intended to do that comparison, but never got around to doing it. The key question is whether GM changed the inside profile of the water jacked floor when they made a notch in corresponding area in the crankcase.

I will add this to my Corvette task list, but it may be a while before I can perform the measurements.

JohnZ

As the photo below shows, it can get frightfully expensive if you mis-judge and grind just a little too deep.

Randy G.

DZAUTO

I have ground notches myself, but I usually have my machinist do that. As long as you have .020-.030 clearance, you are good to go.
My machinist reduced a wrist pin for a just barely slip fit in a rod. Then he showed me how to do a test fit-grind-test fit-grind with the crank installed and one rod/piston installed on the crank in each location. Rotate the crank/rod/piston to check for rod clearance and ONLY GRIND AS MUCH AS NEEDED FOR CLEARANCE!!!! Time consuming? YES, but these little things are what can be done at home on the workbench (or engine stand) if you are on a tight budget and are trying to save every possible penny (ever heard of a cheapskate-----------I wrote the book!!!).

Here are 2 examples of minimal clearancing for rods.






Also, if building a 383 or 400, and using typical style 350 rods (with a bolt/nut configuration), then it is necessary to do some clearancing of the rod bolt head which FACES THE CAM. Again, I do this on the workbench at home using a die grinder and a sanding disc. Make the cut at about 45deg angle. Now, if using aftermarket rods which have cap bolts (NO NUT on the other end), then those have plenty of clearance for the cam lobes.



Last, why does a 350 rod bolt head need to be clearanced for cam lobe clearance and a 400 rod does not?
Here is why. The 400 rod has the lower pocket for the bolt head than a 350 rod. Thus, the 400 rod clears just fine. BUUUUUUUUT, the down side of the 400 rods is that they are shorter than 350 rods, thus, greater side loading of the piston on the cylinder walls. This is just fine for what a SB400 was designed for----low rpm, non hi-perf use.

GearheadJoe

Hi Tom:

I'm a strong advocate of doing the clearancing yourself, by hand. Most machine shops have a generic CNC program that provides clearance for a generic rod. If you carefully select your rod and then grind only the minimum amount necessary to clear *that* rod in *your* block, you will end up removing a lot less material than a generic CNC job.

In my 383 build, I used the Scat Pro Comp rod that has pretty good clearance for both the block and the cam. Attached are the before-and-after photos of the block clearancing. Note that my '657 block already had the cast-in notches, so I didn't have to make them much deeper than they already were.

Since doing my 383 build, I have continued to research rods to try and find some that have even more clearance than the Scat Pro Comp rod that I used. Rods such as the Scat Pro Stock, Eagle SIR, and Manley Sportsmaster all have .060" to .100" more block clearance than the rod I used.

I have not confirmed this yet, but I suspect that for a 383, at least one of these rods would clear the existing cast-in notches in any 327 or 350 block that has the cast-in notches. Older 327 blocks that don't have the cast-in notches would still need some degree of clearancing for a 3.75" stroke (383 CID), but maybe not for a 3.625" stroke (370 CID).

BTW, I know you are a fan of using 400 blocks that have the larger bore so that the stock 3.75" stroke yields 400 CID. I have noticed that the 400 blocks have MUCH larger cast-in rod clearance notches than the 350 blocks. I bought a '509 400 block to look at, and I think it could easily go to 427 CID with a carefully selected rod. I'm toying with the idea of giving that a try.

This "stroker disease" is incurable.....

Vitaminmopar

OK call me late to the party. One cylinder block not mentioned in this thread is the 3933180 used 68-69. This was a large journal 327 and has the rear ventilation provision and drivers side dipstick location. There is one for sale in my neck of the parking lot for $200 with rods and pistons. Price might be a bit steep but I do not know how common this block is today.

https://denver.craigslist.org/pts/d/...439775754.html

Vettrocious

John, that's not pretty picture. As I add clearance to my 657 block, that pic will be etched in my mind

DZAUTO

For those folks who may not be familiar with the SB400 blocks, here is what the foundry as-cast notches look like in a 400 block. Only for a 4in stroker (427-434 with 6in rods) might it be necessary for some additional clearancing.
BUUUUUUT, for Tom Parsons, going out to 427-434 in a dependable, long lasting street/performance/driver engine, is more than I feel comfortable with. A 420 is max for me (3.85 stroke-.040 bore).

DucatiDon

I had mine (a CE 512 block) clearanced at the machine shop, but had to finish clearancing by hand anyway. I used a zip-tie to measure. Its about the correct thickness.

I also had to clearance the factory windage tray, but the stock pan fit fine.

68hemi

My 657 block needed to be notched for clearance when building it into a 383. I had my machine shop do it by HAND. Sorry, I don't recall the date of this block.

GearheadJoe

Wow, thanks for pointing that out. I did not know about this casting.

The nice thing about 1968 production blocks is that all of them were machined for large journals. In 1968, even the 327 had a large journal crank.

I thought that the only 1968 production casting that had the rear vent (sort of) was the 3914678, which has most of the casting material for the rear vent, but the holes are not machined, as shown below.

There is actually a little bit of material missing inside the bell housing flange, in the area where the "tomato can" oil separator would poke through the back wall of the lifter valley. However, I think this problem could be overcome by slightly raising the height of the hole.

For people who only want a suitable casting and don't care about the casting number, the 3959512 casting was used as a generic service replacement block for 327 and possibly 350 engines as well. Lots of these were installed as warranty replacements, and their pads often have the "CE" stamping associated with warranty repairs.

This block has the rear crankcase vent. Depending on the specific warranty application, GM machined the 3959512 raw casting for either small-journal or large-journal cranks, and for either 2-bolt or 4-bolt mains. The small journal versions had the large-journal bearing notches already present.

Contrary to what some web sources say, I do not believe that the 3959512 casting was ever used in production. This makes it a great starting point for a stock-appearing C1 or C2 383 build, since it has the rear crankcase vent and is otherwise not a desirable block for numbers-matching applications.

68hemi

That is interesting, I did not know there was a block that late with the old draft tube hole. A good block for someone that want to build an engine that will allow them to run there original no hole PCV valve covers without having to do a bunch of mods.

JohnZ

That's correct - the 9512 casting never had ANY production application, and most of them were cast at the Saginaw Service Foundry.

Mike C#2

Looks like you have a chrome aftermarket drop filter base? The GM air cleaner for a 365hp 327 (or for a 67-69 Z/28 for that matter, LT-1 Corvette, etc.) has more drop than any of the aftermarket solutions. If you need more clearance, that's the way to go. It also is for a Holley application so is designed to align correctly on the float bowls.

Vettrocious

Here's pic of the clearance notches on my 657 block...

Vitaminmopar

I had to search eBay for photos so I could see what gearheadjoe was referencing on the back of the 678 block not having the lower cast provision for the crankcase vent. Photos are from eBay.


3892657 rear of block



3914678 rear of block

GearheadJoe

Thanks for posting those photos! Some time back I promised to post similar photos using a couple blocks I have stored in the garage, but it would be hard to pull them out for photos, so I just kept putting it off. You saved me some work.

At one time I thought it would be a neat trick to machine a 3914678 block for the rear vent tube, so I got a sample block to study. The missing casting material isn't a deal-killer, but it makes the conversion a bit more complicated.

Now that I know about the 3933180 that Vitaminmopar told us about, I think that's probably the go-to block for people who want the rear vent provision and don't care about the numbers matching. All of those blocks had large-journal mains, while only some of the 3959512 were machined for large-journal mains.

Note that the 3959512 replacement casting (and later production 1967 3892657 castings) have the required material to support large-journal mains, so it's just some extra machining cost to make them equivalent to the 3833180 block.

DZAUTO

EXCELLENT, EXCELLENT, EXCELLENT!!!!!!!!!!
I'm saving these pictures! This is an issue which frequently arises and today's young pups don't know what we're trying to explain about the rear vent hole casting for crank case ventilation, which permits using a PCV valve without having to use valve covers with holes!!!!
Thanks for those pictures!