Building a 283 SBC! Need help!!

My grandfather built this motor and he passed away 10 years ago. His wife has all the paper work and wont give it up. Thats why i need help. The motor's bored out .30 over, Mild Cam, 12:1 or 10:1 Pistons, performer rpm intake. Everything is high performance on this motor. I think the heads are L98 heads? Cfm for carb? One more thing, after it is completed how much hp do you think? Thx for the help, I really appreciate it!! Heres some pics! Also, talking to my dad he said it might be 10:1. How can i check this? Thx

 

A 283 bored .030 is now 288 cubes. A far as a carb probably about 750 cfm. and The carb size is also determined what you are gonna do wiith it. is it gonna be a stick or automatic. and the cam had a lot of bearing. brand of carb dont really matter. horsepower is a sketchy thing to accurately measure. where are you gonna measure it at. the rear wheels? the flywheel? at what rpm ect, ect. oldwolf

 

Forgot to mention it has a mild cam. I'm not really sure, I'm up for suggestions. Thx

 

The camshaft is the brains of the engine. Without knowing the cam specs, it's hard to get a horsepower figure. As far as carb size, there is a formula for that. Take your cubic inches X your max r.p.m. that your engine will see, then divide that answer by the number 3456 and that will give you your carb size. 288c.i. x 6500?/ 3456= 542 cfm. A 600 Edelbrock or Road Demon should work just fine.

 

Not nearly enough info to even take a WAG at what HP it might be. The CR, heads, and things you do know make it sound like a great build, but with nothing more than "mild cam" I could begin to know HP. If you're really curious you might pull it apart and either hope for a number on the cam, or take it to a local cam grinder to have them tell you what it is.
A 750cfm carb is pretty big for a 288 with a mild cam, even if it's 12:1 cr. If you do go a 750cfm, then be sure to do it with a vacuum secondary 750cfm, so it wont be over carbed at lower rpm's.

 

If that engine has been sitting for 10 years with half of the valves open and no spark plugs you might want to pull the heads and check the cylinder walls for any rust or corrosion.

 

And replace the valve springs...

 

600 cfm max--for street and strip---why would anyone use a mild cam with that kind of compression?---good advice on the springs and oil

 

I am with the 600 cfm carb guys. Detonation will be your biggest problem with today's gas and 12/1 compression. Start with one step cooler spark plug.

 

That's what I was wondering. There's no way you're going to get away with running 91/92 pump gas with 12 to 1

 

And yet the 56 chev 265 with factory 2 fours used two 380 cfm carter WCFB carbs for a total of 760 cfm. So why is a 750 four bbl too big for a 283? Ive found that due to the good design and breathability a small block chev can make use of a larger carb than other makers engines of the same cu in. Just my opinion OldWolf

 

Why not ask her if you can run copies of the paperwork?

 

@hotrod40coupe
We asked but she said no.

 

The heads are 86-87 Corvette L98 heads. Aluminum, angle plug with 58 cc chambers. Intake runner size should be around 160-165, this is the primary down fall of the heads. They only flow to around .500" lift and fall flat after that. 1.940" Intake valve and 1.500" Exhaust valve. The small 58 cc combustion chamber does help to raise static compression. They serve the purpose of a relatively low RPM head for the EFI Corvette which generally had very tall final gearing and didn't need to rev that high for optimum performance, TR

 

She sounds like a real winner.
On the heads here is the link to the Google search that you could have done on them yourself. It looks like they are late 80's Corvette.
https://www.google.com/search?q=141...c2134a814ceeeb&bpcl=40096503&biw=1047&bih=445

I'd agree that it would be wise to pull the heads and check things out. It will cost a gasket set but then you will know that everything is ok an have a better idea of what you have.

 

I have to learn how to type faster

 

There's a LOT of experience available on this site. TR is one with a lot of know how. I will also share a couple of recent experiences. Recently i bought a very nice blown SBC assembled and dyno run by Oddys in 1997, sitting until about 4 mos ago. I pulled the heads/rods and pistons. The cylinders needed a light hone job and the rings/lands were gunked up a bit probably from some oil left in the cyls. The heads were disassembled, valves lapped and spring pressures checked. All were still within 5lbs plus or minus advertised specs. Copper headgaskets were cleaned and reinstalled. Intake/exhaust ports/combustion chambers were CC'd just because I like to know exactly what is going on. A good cleaning and fresh lube, a few hours and about $70 (paid to a buddy for disassembling, CC'ing/cleaning the heads/lapping the valves) = time and money well spent. The other thing, I have a ZZ-4 350 with a Comp cam upgrade. On pump gas (premium) with a 625 street demon. This engine has run 5.94 @ 117 (eighth mile) in my FED. Lots of people think bigger is better and while I'll admit it took a bit of tuning, thats pretty good. This engine is currently installed in my (shame on me) 67 Camaro. Carb retuned as needed to match the dual exhaust (no zoomies). You can make a lot of different carb setups work, but sometimes bigger isn't better. I'd be looking at a carb in the 600 CFM range. Look up the formula and do the math on airflow requirements for your engine you may be surprised.

 

and use .040 head gaskets if it don't allready

 

OK, I tried to have paragraphs, what happened..................

 

Thx for the help! Anyone else:

 

Only thing I can add that hasn't been said already is the cam grind number can likely be accessed easily by pulling the timing cover and chain. Just a few minutes work and you can look up what you have.

Also if you haven't already, roll the motor over (if it will) to make sure your valves aren't hitting the edges of the bores. Those heads were designed for a 350 with a larger bore and I don't know if the chambers are wider.

Devin

 

I think you're in better shape than one would think with this little motor. First, getting 12:1 in 283 is not easy even with a 58cc head. It would need somewhere in the ballpark of .500 worth of dome.It should have a composite head gasket with the aluminum head which means it is thicker than the original and is probably made for a 4"+ cylinder bore. Both of these are going to more than likely reduce compression ratio. Looking at the photos, someone knew what they were doing when they put that thing together. There are little clues that indicate that the motor may be fairly mild. You did not mention whether you had loosen the rockers but no valves apperar to be open so the springs have not been compressed. The exhaust valves had standard sheilds and rotator type retainers indicating that the cam profile is mild.The intake is just sitting on the motor this could be because someone intended to adjust the hydraulic cam in the future. If you in fact did not back off the rockers then someone did and I would assume that it was because the motor was intended to sit a while and makes me wonder what other precautions may have been taken.Whole lot a maybes and just my 2 cents. Good luck with Grandpas motor.

 

Run either a 500 or 600 cfm on it if you are going to street drive it. Carb brand is strictly a personal choice.........mine would be an Edelbrock as I find them a little more forgiving for street duty. You do not need more than 600 cfms.

It must be an interesting story about Grandpap's wife.......you could get the motor but not the paperwork? I'm guessing you two won't be having Christmas dinner together.

Don

 

It looks like your grandpa had that engine sealed up good with plastic wrap. I didn't see any rusty areas on the steel parts. Don't tear it down unless it feels tight. The valve springs also don't look more than z28 size and they should be ok. I noticed there is no 1\8 inch plug installed above the timing cover. It is possible that is not a 283 block. I checked 6 283 engines in my shop and they all have that plug. Check the casting number behind the left head on the block and take a photo of the crank flange. Maybe grandpa built a sleeper. CJS

 

Thanks everyone for your help!!!! Also, talking to my dad he said it might be 10:1. How can i check this? Thx

 

Guy's the heads fit and work with the 1.940"/1.500" valve sizes.

Remember the difference between the 283 and 350 bore sizes is only .125", divided by two is only .0625" on either side of the cylinder. This engine is purportedly .030" over making it a 3.905" bore size. Now only a .095" difference, divided by 2 equals .0475" per side, about the gap of some spark plugs.

Adding the valve sizes together for a total of 3.440", now subtract this from the bore size of 3.905 is .465". That would leave you a available .1325" on either side of the 2 valves and another .200" between the 2 valves, which of course is exagerated over what they actually are quite a bit.

Please note that this is NOT how we Blueprint engines, only a exercise to help understand how this can work.

 

Karkrazy, as a engine builder I strongly suggest tearing the engine down and checking everything over. If you are not comfortable with the procedure a small investment by a engine builder could save you from disaster and pay big dividends in the long run.

Then and only then after KNOWING and NOT quessing the compression ratio{ calculated }, cam specs, etc, would I make a suggestion for carb sizing for this engine, all the best, TR

 

There is also the chance of spark plug ground strap and piston dome interference with this combo. The piston domes might require notching/relieving for the ground strap due to the now Angle Plug heads that are on this engine. Another reason NOT to quess and speculate here on what may or may not have been done, TR

 

I would slow down on pulling it apart.
Who actually built the engine?
If they knew what they were doing like a shop, don't mess with it.
Pour oil over the valves. Put some in cylinders, hand turn over a bunch.
Are the Harland Sharp roller rockers loose?
They are probably 1.65 ratio instead of 1.5 which give you cam more lift when you find out what cam it is.

 

why does she want paper work, what good is it to her?