help with a 273 build

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bamacuda

bamacuda

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I am building a 65 valiant that has a 273 commando 4bbl. I had the motor to a builder who rebuilt my 904 tranny with a mild shift kit. I pulled the heads and he rebuilt them. When he disassembled the rest of the motor, he informed me that it had been rebuilt recently and was .30 over. He suggested that I have the crank polished (I did) and get a new cam-(stock grind*) and just put it back together and go. ( He recognized I am on a budget) I want some advice on whether or not I should go this route or not. Should I get it built at a shop, trust a friend that has built a handful of motors, or do it my self ( I am good with tools, just don't have the expertise of what is best) . Also, in any event, what are some recommended things to do to make this a dependable warmed up 273, (cam, etc..)

* he said that a new stock grind would actually perform better than original due to todays manufacturing techniques.

Any advice is welcome! David pm me, or [email protected] or 205-908-0868
 
bamacuda said:
I am building a 65 valiant that has a 273 commando 4bbl. I had the motor to a builder who rebuilt my 904 tranny with a mild shift kit. I pulled the heads and he rebuilt them. When he disassembled the rest of the motor, he informed me that it had been rebuilt recently and was .30 over. He suggested that I have the crank polished (I did) and get a new cam-(stock grind*) and just put it back together and go. ( He recognized I am on a budget) I want some advice on whether or not I should go this route or not. Should I get it built at a shop, trust a friend that has built a handful of motors, or do it my self ( I am good with tools, just don't have the expertise of what is best) . Also, in any event, what are some recommended things to do to make this a dependable warmed up 273, (cam, etc..)

* he said that a new stock grind would actually perform better than original due to todays manufacturing techniques.

Any advice is welcome! David pm me, or [email protected] or 205-908-0868
Click to expand...


I would make sure it is someone that has good engine building experiance. And most of the newer stock cams I would disagree with his statement in part;

Most stock cams are a reground lode cut out cams, I would look at a cam that is not an autoparts special gippo cam. Comp cams, Crane etc make good cams. On a small 273 in you budget I would look for a cam that is short duration and a little more lift, That is what the 273HP 4v engines used. Also what valve springs are in the heads? You need to make sure springs match the cam too. I am sure many folks here will chime in with what the reccomend. Also the stock pistons back then on the 4v engines were 10.5 to 1 , most all replacements are only 9 to 1 and hurt low end torque on the 273, especially if the cam is to long on duration. You may need to have the heads milled a little to to bring the compression backup if you do not have the higher compression pistons. But if ou only go with a stock 2v cam it does not really matter as much.

good luck!
 
If it was rebuilt at .03 over it may have lost the dome top commando pistons. If whatever pistons are in it now still mic good I"d re ring it and go. I'd bet your car gets driven about as much as mine (3000 miles a year at very most). Let an experienced builder put it together right and it'll probably last forever.
I'll have to quote someone about those exhaust manifolds though, "like poopin through a straw". If there is any way to improve that short of headers that would be great. I'll paste a link to his article but I can't say it works as easy as he says...
http://www.geocities.com/lars_an_artist/durango.html
 
Stock 2bbl cam is mech 240/240 and .395/.405
Stock 4bbl cam is mech 248/248 and .415/.425
D-Dart cam was a mech 284 with.500 lift (radical for a 273, idled like the full on race car it was)
I think you will have a tough time finding a stock replacement cam for the 4bbl 273.

I had good luck with an Isky E4 mechanical cam in a 273 4BBL. Part number 390144. 260 (216 @50) with 425/425. It's close to stock with a slight power improvement and still very nicely mannered on the street. A little head work helps the 273 and, as previously mentioned, a less restrictive exhaust path works wonders.
Stock compression was 10.5:1 so (also as previously mentioned) make sure yours has the domed pistons or mill your heads to get the compession up close to that if you want it to perform like a true Commando.
 
Thanks for all this info. I really appreciate you guys for helping. I will have a better idea of what pistons, springs, etc. in the next few days. i will post what I find for your further evaluation, David!
 
Consider a stock 340 cam or comp 268/454. Both work great in 273/318 motors. I have used both in the past with very good results.

Bob
 
When I rebuilt my 273 I used a Hughes cam with good results. Don't remember the specs but it had a lift around the .480 range and had good vaccum.
 
I will be posting pictures of my car soon, I just set it in the driveway, covered in dust from the body shop. thanks guys for the help. ps if I have a cam, how can i tell what it is? lift, duration, etc. I have another engine that was built, it has well worked heads that are gasket matched to an ld4b, motor was a "hot" motor, but rear seal leaked. should i just get new stuff and take the guesswork out of it, or is there a way to tell what i have got?
 
You can get an idea of the lift and duration of a bare non identified cam using a degree wheel and a dial indicator. attach the degree wheel to the snout of the cam. Make a couple of V blocks from wood and rest the cam in them on the bearing surfaces, make a pointer from a coat hanger to read degrees of the wheel, rotate the cam and dial indicate the lobes to measure lift (total lift = dial indicator reading x 1.5), at the start and stop of lift, read the degree wheel at the start and stop of lift (total degrees = measured degrees x 2). You wont be able to figure out centerlines etc, but this will give you some ideas. Maybe you'll be lucky and the thing will be marked already with some part numbers, these are usually on the backside of the cam, on the flat behind the last bearing.
 
Just finished my 273. Egge 10 to 1's, 30 over and I love the cam, an Isky #390144. Mine is a 2V and I have stock cast iron manifolds. I bought a MufflerTech 2.5" mandrel bent dual exhaust system w/ a X pipe. Great combo, I'm getting 21 MPG with it. Here are some pics.
Jim

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Cool! Great mileage, that's new-car territory.

I like 273's, very underrated engine. Heavy duty stuff from the factory in a small package.
 
I was looking at my pile of parts, and just realized that the pistons are stamped .030 over, but they are still the domed pistons like the originals. They also have stamped L2222N next to the .030. What will this do to the compression and should I stay with these? I have a shot at a 273 with the original stock pistons. Is it worth the trouble, or just have this one built... Thanks for everyone's input!
 
so where does one go to get decent pistons for these? (sorry to hijack)

As australia never got any options other then the basic 2bbl 273, they were usually traded for 318s and 360s, the cranks and rockers were usually taxed for larger engines, thus leaving few 273s left here, and not many performance tricks are known.

I'd also like to keep mine in my vc, but cost is really pushing me towards dressing my 360 in 273 trim and biffing that in, but fuel at $1.60 litre has me hesitant :)


Dan.
 
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