Engine builder questions

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Here's a thought..........

Is the year of the block important? If not, look for a 1955 Poly 301........3.91 bore, 3.125 stroke, or at least look for the crank, do a 318 block, custom pistons and have fun.

Just an idea.
 
The older cranks had a different rear flange
 
273 have you looked at any solid rollers for this combo? If I keep it factory bore and stroke run more gear then I want it to be able to scream. :D
 
JBurch said:
Here's a thought..........

Is the year of the block important? If not, look for a 1955 Poly 301........3.91 bore, 3.125 stroke, or at least look for the crank, do a 318 block, custom pistons and have fun.

Just an idea.
Click to expand...

Those poly motors are big and heavy. Thanks for the input though. :wink:
 
Badart said:
Those poly motors are big and heavy. Thanks for the input though. :wink:
Click to expand...

That is not entirely true. Some where here at the site I have put next to each other a "LA" shortblock and a '66 poly shortblock. I took pictures to be illustrative on the exact differances of the two.

I'm at work on my I-phone, so forgive me for not finding or repostings the pictures. I'll just restate them here in short.

There is NO size differance between the blocks!

Please read that last sentence again.

LA heads will fit and bolt on the Poly block BUT the Poly blocks water passages will not match the LA head at all.
There are less freeze out plugs on the block. Notably on the front.

The Poly block will only be heavier due to the thicker cylinder walls and extra metal due to the lack of freeze out plugs.

You can swap cranks around between the Poly and LA engines. As said before, the flange at the cranks rear is the issue to contend with per application.

Unless the "301" cube engine was around the corner, I would not search for one. Or the smaller 277 Poly engine.
 
rumblefish360 said:
That is not entirely true. Some where here at the site I have put next to each other a "LA" shortblock and a '66 poly shortblock. I took pictures to be illustrative on the exact differances of the two.

I'm at work on my I-phone, so forgive me for not finding or repostings the pictures. I'll just restate them here in short.

There is NO size differance between the blocks!

Please read that last sentence again.

LA heads will fit and bolt on the Poly block BUT the Poly blocks water passages will not match the LA head at all.
There are less freeze out plugs on the block. Notably on the front.

The Poly block will only be heavier due to the thicker cylinder walls and extra metal due to the lack of freeze out plugs.

You can swap cranks around between the Poly and LA engines. As said before, the flange at the cranks rear is the issue to contend with per application.

Unless the "301" cube engine was around the corner, I would not search for one. Or the smaller 277 Poly engine.
Click to expand...

Thanks Rumble.
 
Here's a rod that might be usefull http://m.summitracing.com/parts/esp-6300hj it's a 6.3" Chevy rod with Honda bearing size 1.89" I don't if you can turn a 340 crank down that much but if you can and bore the rod out to a .984 dodge piston pin you could get a 2.91" stroke with a 6.3" rods with 4.07" piston with a pin height of 1.804" = 9.559" and mill about 0.040" and you'll have a zero decked 303 CID.

I'm interested if this would work I might have to change my 273 build plans to a 303 :)
 
rumblefish360 said:
That is not entirely true. Some where here at the site I have put next to each other a "LA" shortblock and a '66 poly shortblock. I took pictures to be illustrative on the exact differances of the two.

I'm at work on my I-phone, so forgive me for not finding or repostings the pictures. I'll just restate them here in short.

There is NO size differance between the blocks!

Please read that last sentence again.

LA heads will fit and bolt on the Poly block BUT the Poly blocks water passages will not match the LA head at all.
There are less freeze out plugs on the block. Notably on the front.

The Poly block will only be heavier due to the thicker cylinder walls and extra metal due to the lack of freeze out plugs.

You can swap cranks around between the Poly and LA engines. As said before, the flange at the cranks rear is the issue to contend with per application.

Unless the "301" cube engine was around the corner, I would not search for one. Or the smaller 277 Poly engine.
Click to expand...

I have only seen a couple of them old poly in my life but i though it was a lot Bigger!

Not saying your Wrong, Just surprised :-&
 
Seems I was off on my math, Honda bearing would give you 3.11" stroke and with a 3.94" bore would be a 303, and with a Chevy 2" bearing would give you 3.21" stroke and with a stock 3.91" bore would be a 308 both under 5.1L, Still trying to find out if either possible.
 
Badart said:
SCCA Solo racing rarely gives you a chance to get out of second. They really like to limit speed. It's more tight and technical racing. Cars like this Mustang would be the competition. Most courses are actually tighter than this.
Fox Mustang Autocross SCCA C Prepared CP - YouTube
Click to expand...

That looks like alot of fun. Reminds me of the sand dunes but without the whoops, uphills and drop offs.
 
News Flash!!!!! I have been over at the Grassrootsmotorsports.com with my build thread and found some info. Most of these guys are tied into the SCCA and here is a quote that I am researching. "I know CPDave here petitioned the SCCA to allow 318's to be substituted for 273's, but I can't remember for what classes. IIRC, they allowed it. He's built a pretty stout '66 Dart with that 318. If you've seen pics of a zebra striped '66 Dart, that's his."

If this is true and they allowed him to run a 318 in the under 5,100cc class then this is a game changer. That would be awesome, because we could build a killer 318 IMO.
 
Badart said:
News Flash!!!!! I have been over at the Grassrootsmotorsports.com with my build thread and found some info. Most of these guys are tied into the SCCA and here is a quote that I am researching. "I know CPDave here petitioned the SCCA to allow 318's to be substituted for 273's, but I can't remember for what classes. IIRC, they allowed it. He's built a pretty stout '66 Dart with that 318. If you've seen pics of a zebra striped '66 Dart, that's his."

If this is true and they allowed him to run a 318 in the under 5,100cc class then this is a game changer. That would be awesome, because we could build a killer 318 IMO.
Click to expand...

That would be great if you could use a teen. It's so much easier to get 400 horse out of a 318 than out of a 273.
 
Mad Dart said:
Hey John! Will be xlnt news if you can use a 318. You can make them scream real easy!
Click to expand...

I'm not holding my breath. I think it for racing in SVRA (SportsCar Vintage Racing Association) and not SCCA. SVRA is really strict about anything that you run. Must be period correct stuff.
 
Well I just received a message from a long time racer in SCCA CP and he informed me that it is not worth it using a 273 even if stroked. He claims even with the 300lb weight break it isn't worth it. The torque of a 318,340 or 360 stock stroke or stroker torque more than makes up for the weight penalty. Plus if you get your car down to below 3,000 you can add ballast weight anywhere in the car as long as the rear axle doesn't weigh more than 51% of the total weight of the car. Many mustangs run in this class and have 300 lbs of lead in the trunk and kick ***. I may just use the 360 on the engine stand that was going to go in the dart. We will see.

Thanks for all of the information guys.
 
I ran a 273 with "72" 340 "J" heads. The 1.88's worked, but I centered the chambers over the bores with offset dowels and it took .040 to clean up the cylinders. I never notched the top of the cylinders. I'd mock everything up and check it real close to run 1.88's in a 273. I ran a stock 340 Cam. It pulled real strong.
 
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