So long story short, I picked up a 455 out of a 1970 Delta 88 with 94,000 miles to be a cheap/temporary donor replacing my very tired 350 in a 1969 Cutlass. Although sitting for 18 years, I got the 455 running very well with almost no smoke, so my goal was to run it for a couple of years adding a few power adders now, holding off on a complete rebuild until later. I was excited to find a 70 because everything that I have read led me to believe that all 70's were high compression. I got the pan off tonight only to find that the pistons appear to be low compression. They have a part number cast into them (398591) which the one document that I found through Google, lists as 8.4 to 1 compression. Is this correct?


If this motor is low compression, what suggestions does everyone have for my next steps with the goal being having the car up and running in 4 weeks or less for the summer cruise season. The original plan was to leave the heads bolted to the block (still original shim gasket), but add the following:


FelPro Valve Seals - Purchased
Cam and Lifters - Working with Cutlassefi on this, not yet purchased
Comp Cams Magnum Roller Rocker Kit - Not yet purchased
Cloyes Timing Set - Not yet purchased
Stock Replacement HEI out of '76 - Purchased
GM HEI Module - Purchased
Edelbrock Performer Intake - Purchased
Holley 870cfm Street Avenger - Purchased
Hedman Elite Headers (1 3/4") - Purchased
New Oil Pump - Not yet purchased
New Water Pump - Not yet purchased
2,300 rpm Stall Converter - Not yet purchased


The rest of the specs are:


E Heads (assuming small valves)
TH400 (out of the same Delta 88)
3.42 Gears
27" tall N50 tires


Thank you for your help and expertise.

 

I should mention that the block ID confirms that it is a '70. The engine appears to be completely original outside of a well worn aftermarket timing set, fuel pump and water pump.

 

Personally I would leave it alone and put it in the car for this season. Maybe put the intake on so it will look pretty. The HEI is a good idea for reliability.

The piston crosses to a low compression piston in every interchange I have so you are correct on that point. Probably around 8.4 to 1.

I am almost certain you will have to at least change valve springs with a cam change and the low compression the cam probably wont help much anyway.

Save your money for a proper build and after the cruise season is over go to it

 

Based on what? The casting number or the VIN derivative? The only low compression 455 offered in the 1970 D88 line was the L30 2bbl motor with 9.0:1 CR.

 

Joe, based on the VIN derivative located on the block just under the head, driver's side. The code is 30M395621 which if I understand correctly, is a '70. The last six digits of that code match the VIN on the car. The engine had a 4 barrel stock manifold on it that appeared that it had been removed before, most likely when they changed the timing gears and chain. The original must have grenaded because there were plastic teeth everywhere in the oil pan. The heads do not appear to have ever been off. The casting on the block is 396021F. As mentioned, the pistons have a cast part number of 398591 in them. According to this link - http://beckracing.com/slvpg76.htm that is a 8.4 to 1 out of a 68-76 455. Any ideas?


The car is a 2 door 1970 Delta 88 with a TH400.

 

Well, my first recommendation would be to stop using aftermarket catalogs as a reference on factory part number.

The factory piston P/Ns are NOT the same for 1968-1976, so that immediately tells me that the Silvolite data is suspect. Keep in mind that the link you provided is intended to show what their product replaces, not what was factory installed.

As for the casting number, unfortunately the factory parts book only lists the P/N for the piston/pin assembly, which is not the same as the casting number on the piston itself. The 1970 Engine Assembly Manual only shows the piston/pin/rod assembly, so that's even less help. Bottom line is that for a 1970 455 from a Delta 88, there were only two piston options for cars sold in the US and Canada, the small dish 10.25:1 pistons and the large dish 9.0:1 pistons. The latter were only offered on the L30 2bbl motor. Export models got even lower compression pistons, but I really doubt that's what you have. It wasn't until the lower compression of the 1971 motors that the 8.5:1 pistons were used in US cars.

 

Joe, I am not sure if visually you can tell the difference between the low compression and high compression pistons. Below are a few borescope pictures of the pistons. I apologize for the quality, it is the best my camera was able to get.

 

Pretty hard to tell from those photos. See if you can find the notch on the piston. It will be towards the front of the motor. LC pistons have a rounded notch, HC pistons have a V-notch. This is an LC piston:

 

Joe, I had to switch cylinders as the notch was not pronounced on that piston. The piston has a single round notch as opposed to two like you image.

Also, I am not sure if this means anything but it does have the letter B stamped into it like your example.

 

Yup, that's a 9.0:1 piston. The single notch is correct for a 1968-70 motor. The 8.5:1 pistons in the later motors got the double notch.

The letter is simply the code for which size piston it is. Olds used four different sizes (labeled A to D) to account for machining tolerances in the block. It doesn't really mean anything for your application. The "select fit" W-30 motors all used "A" size pistons in "D" sized bores for greater clearance, but the regular assembly line motors just matched up "B" pistons with "B" sized bores, etc.

 

Joe,
Thank you so much for your help! I wonder if someone did an intake swap on this motor at some time placing the 4 barrel intake on it? Either way thank you!

 

I'd say that was likely.

 

Learned something new today. I knew about the stampings on the block for bore. I didn't realize same type of stamping was on the pistons. Thanks Joe.

So, what was the clearance on the piston to wall on the W30?

 

The A size piston is 4.1240 - 4.1235
The D size bore is 4.1265 - 4.1270 (0.0025 - 0.0035 clearance)

Normally, the A piston would be used with an A bore of 4.1250 - 4.1255 (0.0010 - 0.0020 clearance)

 

Thanks, If I really had thought about it the piston stamping makes sense. I just didn't think about mix and match. Now, I think the marine/replacement block I have has the D stampings on it, but never had the pistons for that one. I have no idea what it was out of.

 

Of course, this was all done to get acceptable piston-to-wall clearance in the mass production environment. For a rebuild, you'll obviously just have the machine shop hone each cylinder individually to match the specific piston, so the stamping is sort of a moot point.

 

Buy the Engle 18/20 cam, lifters, springs. I put it in a 72 455 and was quite satisfied. Do a valve job. Headers or manifolds? After removing the heads you could have tbe center exhaust port divider brazed up. The headers or W&Z manifolds would work better.

 

Android, I am working with CutlassEFI on the cam right now. Machine shops are backed up around here with circle track racing starting soon. In order to save the cruising season, heads are staying on for now. I did already get a set of Hedman Elite Headers for it (1 3/4"), Edelbrock Performer Manifold, Holley 870 Street Avenger, and HEI distributor.

 

The advance curve on the HEI should be checked. If it came out of a parts store or off a junkyard car it is lazy and the vacuum advance not optimum.

 

Thank you for heads up! I have been reading up on HEI's on here, so expected as much. Do you have a recommendation for a spark plug and gap for a 455 with HEI?

 

Whatever is recommended except one range colder. If an engine is on the edge of ping then colder plugs are one of the things that can be done to help. 9:1 meant regular gas in '70 but today I would use 93 or at least 91 if thats all you can get.

 

Mark will treat you right. As far as ping, some of that depends on the cam profile. As an example, my 455 with aluminum Procomps, built at 10.25:1 ran 91 and no ping. I bought heads,cam,lifters,rockers, pistons from Mark. (Understanding you are running a stock bottom end and heads right now and your results would be different. Just thought I would throw that illustration your way.)

 

Android and Troy, thank you for your suggestions and insight.

 

Something I learned from Brian, 507Olds. By the distributor there's a large number then 2 or 3 smaller numbers. The larger is the year it was cast. Being they started making 455 blocks in 1967, hence large 1. Small numbers is the day of the year. Aka 01 would be January 1. And so on. I tried this out with a 455 I pulled from a rusted out 1968 Delmont 88 convertible, Big 2 smaller 193. July 11, 1968, it was a Thursday. This car was probably at the end of the 1968 production. So if this works a 1970 could be a large 3 and higher day numbers or a large 4 and probably under low 200's. 1970 was the "peak" for different HP options in 455 engines. They had lo-comp 2 barrel 310 hp and a hi-comp 320 hp 2 barrel. I have one on the engine pile. Supposedly they the hi-comp 2 barrel had the red air cleaner vs the lo-comp black air cleaner. What's your numbers from the distributor area.

 

Let's just say that there is some disagreement in the community over this. There are too many documented blocks where that doesn't make sense. For example, there are documented 455 blocks with a "1" and a day number of like 57 or lower. Considering that 455s didn't go into production cars until the start of the 1968 model year, a Feb 1967 production block is unlikely. By the way, this block came out of a car with a Mar 1968 build date. Similarly, there are 455 blocks with 1976 VIN derivatives but a "6" for this year code. That would mean that a block cast in 1972 got used in a 1976 model year car. Again, unlikely.

 

We just pulled the heads on a 455 I picked up. here's a picture of it with a notched .030 over piston from a type F block (no Fa). It came out of a 1978 jet boat. The vin derivative indicates its a '73 with the 6-digit serial number for a car which is odd for a type F block. It has E heads (1970?). So don't really know what I bought. Can anyone tell what the pistons might be and why a type F block was stamped for a 73 auto?

Type f block

V notch .030 over. Super clean looks like never run.

Vin derivative stamp 33M plus serial num

E heads