455 engine code

[Bruce]

HI I have a 455 that I need more info on the heads are number 15 and the block is 0147946yh. any info on what I have and a value Thank You

[SPRINT 6]

This site has good info;

http://www.pontiacpower.net/numbers/engine-codes/

[Frosty]

Bruce, welcome to FP. 

Your YH code and #15 head indicates that this is a 455 from a Bonneville/Catalina. It is the 360 HP version motor for these big cars. It has 1.96" intake and 1.66" exhaust valves and 87 cc combustion chambers. The ideal heads in 1970 were the Ram Air III and Ram Air IVs for the GTOs and Firebirds, which were #12 and #614 heads. They have 2.11" intake and 1.77" exhaust valves and 71 and 72 cc chambers.

All that said, the motor is worth whatever someone is willing to pay for it. I'd guess its worth between $200-$1000 as a core motor.

[Bruce]

So I've read a lot about 6x4 heads and 6x8. But no one really talks about #15 heads are they not a good pair to use. I'm not racing it just want a snorty  car for cruising 

[Frosty]

The #15 heads are a fine head and well worth rebuilding. It will be a stout cruising motor for sure. The only way you could do better is to find a pair of #64 heads (these are also 1970 heads). They have the bigger valves but retain the 87 cc chambers. If you are going for a total rebuild, talk to you machine shop. Perhaps they could re-size the heads out to 2.11/1.77. If not, don't worry about it. Many a GTO and Firebird were built with 400s with 1.96/1.66 valves. They are no slouches either.

The 6x4 and 6x8 heads came out on the 350 and 400 engines starting in 1976. I don't see any particular advantage getting a set of these heads over what you already have. Remember Detroit was already taking compression out of these motors to meet the (then) new emission standards.

So my recommendation is rebuild what you have and go cruising.

[Bruce]

Okay that's sounds good. I've read that the 15 has press in studs and the rods are a problem on the bottom end. Should I be addressing either of these? The thing is my motor has 60000 miles and if I don't need to touch it I wasn't. I thought after reading forums that a cam change might be wise and a performer intake to wake it up a little. Any suggestions. I'm putting at auto overdrive behind it with 342 or 373 gears 

[Frosty]

ARP stud bolts are certainly a stronger way to go and I would highly recommend them. That being said, for a stock rebuild the factory bolts or replacements are fine. Now, if you are going to tweak the motor with a beefer cam and such, then definitely go with the ARP studs, it's cheap insurance.

A new cam and performer intake will wake up the motor. Depending on your goals and budget, I might consider re-using the stock 4-barrel manifold since there is not a huge difference in performance between an Edelbrock Performer manifold and the cast manifold from idle to about 4000 rpm, where you motor is going to live most of its life anyway. I would definitely invest in a new timing chain, and a new high volume oil pump, water pump, and thermostat.

As for the rods, a competent machine shop should magnaflux and inspect them and replace any questionable rods with stock replacements. Re-using the stock rods on a near stock rebuild is fine. Remember Pontiac built these engines to produce close to 400 HP in stock form back in the day. There is no reason that is still not the case today so long as they have not developed any stress cracks in them.

I went with a Melling hydraulic lifter cam and high volume/pressure oil pump. The pushrods are stock but I have roller rocker arms for longevity. New matching springs were purchased with the cam and lifters as a matched set.

Consider installing a Pertronix III conversion kit in your stock distributor to eliminate the old points and condenser. Inspect your vacuum advance on the distributor and make sure it still works or if it needs to be replaced. How old is the coil? Is it time to change it too?

I am not clear on what overdrive you plan to use. If I had to do it all over again, I would get a TH 200 4R for my Lemans over the TH400 I currently have. They have the B-O-P (Buick/Olds/Pontiac) bolt pattern and they require no serious modifications to your trans tunnel. Only thing is a TV cable to replace the kick down cable and moving your transmission cross member back 2 more inches than stock.

There is a nice write-up elsewhere in this forum on the TH350/TH400 to TH200 4R conversion. I would recommend reading it.

Edited August 1, 2017 by Frosty