# Need Help determining engine Cubic Inches and HP.

Discussion in 'The Garage' started by Erich_in_AZ, Mar 24, 2002.

1. ### Erich_in_AZ1/2 ton status

Joined:
Mar 23, 2002
Posts:
237
0
Location:
Tucson (it\'s a Dry heat), AZ
Hello everyone,
I took on the task of removing the heads on a 350 4-bolt main that came free with the free truck I am building. (Actually, I'm more like taking it apart, but making it run at the same time). My question is this..... 2 of the 8 pistons are marked as .030, and are noticably different than the other 6.

Now I have been told that a .030 over 350 is actually a 355 so.... Please check my math here.... If I take the 5 extra ci gained at .030 over and divide it by 8, I get .625ci per cylinder that is .030 over. So, if I multply that times the 2 overbored holes (Cyl#1 and #3 in case it makes a difference) then I come up with a 351.25ci engine.

If I figure that my suburban was rated at 165hp with the 350, and divide 165 by 350ci, I get a whopping 0.47142857142857142857142857142857 hp per ci. That means that I have gained 0.58928571428571428571428571428571 hp by having this configuration. Watch out NASCAR! I wonder how this will affect my fuel economy.....

My other issue is the compression ratio on these cylinders. I understand that the bore size affects the compression ratio, so when someone asks me, should I just give them an overall average, or break it down to theoretical CR by each cylinder, or better yet, by cylinder pair?

Maybe later we can discuss what kind of cam I should run to take advantage of my additional 1.25ci!

2. ### NoRulz1/2 ton status

Joined:
Feb 6, 2001
Posts:
388
0
Location:
Mesa, AZ
uhm...
dude...
your thinking WAY too much into this...

3. ### Erich_in_AZ1/2 ton status

Joined:
Mar 23, 2002
Posts:
237
0
Location:
Tucson (it\'s a Dry heat), AZ
Well, I need to know these things. I mean, what do I tell the guy at Checker when he asks what size engine it has and if its an automatic or manual when I need a new headlight switch or something like that?

:-)

4. ### jimmyjack1/2 ton status

Joined:
May 11, 2000
Posts:
2,290
0
Location:
Tucson Az
When I had my 350 rebuilt I was told boring it "30 over" would make it a 362. That'll smoke the Checker guys shorts!!

5. ### Erich_in_AZ1/2 ton status

Joined:
Mar 23, 2002
Posts:
237
0
Location:
Tucson (it\'s a Dry heat), AZ
Now you completely messed up all my math. Damn, gonna have to do it over again!

6. ### Thunder3/4 ton status

Joined:
Jul 20, 2000
Posts:
8,946
1
Location:
You need some stuff from these guys:<a target="_blank" href=http://www.motionsoftware.com/>Motion software.com</a>
Should provide you with hours of entertainment. /forums/images/icons/laugh.gif

7. ### jimmyjack1/2 ton status

Joined:
May 11, 2000
Posts:
2,290
0
Location:
Tucson Az
But thats all 8 cylinders, not just 2. That's just what I was told, doesnt make it right

8. ### 4X4HIGH1 ton statusPremium MemberGMOTM Winner

Joined:
Dec 14, 2001
Posts:
22,063
70
Location:
Pleasanton, CA.
A 350 chevy bored .030" oversize is a 355 ci. The mathematical formula is as follows. ( bore x bore x stroke x number of cylinders x .7854 ) For instance, 4.030" x 4.030" x 3.48" x 8 x .7854 = 355.11 rounded to 355.

9. ### Erich_in_AZ1/2 ton status

Joined:
Mar 23, 2002
Posts:
237
0
Location:
Tucson (it\'s a Dry heat), AZ
Hey Everyone...
When I posted this I was VERY bored and a little surprised that 2 of my cylinders were .030 over and 6 were not. I guess this is proof of what you get when you buy a "reman" engine. I pretty much meant this post as pure sarcasm.

:-)

Has anyone else found out they have only a couple of cylinders bored over in a reman engine? I had heard of this happening, but this is first time I have seen it in person.

10. ### m j1/2 ton status

Joined:
Dec 28, 2001
Posts:
4,606
0
can anyone explain why that formula works?
I am missing where the .7854 comes from.
I always use the 'PI r^2 x stroke x #cyl'

11. ### Blazer791/2 ton status

Joined:
Feb 17, 2000
Posts:
1,816
0
Location:
Guatemala, Central America
I did some algebra, and I found out that the 0.7854 is just pi divided by 4. Someone took the time to rewrite the formula so it would be easier to remember.

If you really want it, I can type the equation and its simplification.

12. ### m j1/2 ton status

Joined:
Dec 28, 2001
Posts:
4,606
0
thanks
I knew it was 1/4 pi but was missing why
when you write the squared out long it becomes evident
just looks goofy. must be for calculators without squared and pi keys

13. ### Ddragggon1/2 ton status

Joined:
Apr 25, 2001
Posts:
2,657
0
Location:
Hartford, WI (formerly Etiwanda, SoCal)
I think everyone's missed what caught my eye: Why does your engine have only 2 overbored cylendars?
\
do you realize what kind of hell this is going to play with your cam selection? you're going to have to get one custom ground so you can best take advantage of the 2 overbored cylendars. I certainly hope they're either in a pair, or exactly oposite of eachother in the fireing order, otherwise you're going to have some lopsided power coming out of your engine, and have to time your launches with that .5214324523423451162163563432 HP gain you've got going on, to help throw you off the starting line. if oyu were to convert it to a 383, you'd probably end up wiht like a 384 or 385, with some really weird mechanics going on there... ( good luck balancing that thing, with offsized pistons)

ugh, my brain hurts now.

your best bet is to smack a Type R sticker on the ass end of your truck, and count the HP gains from that....

-Rich

14. ### Erich_in_AZ1/2 ton status

Joined:
Mar 23, 2002
Posts:
237
0
Location:
Tucson (it\'s a Dry heat), AZ
I had the very same concerns with the cam. Luckily the 2 overbored cylinders are across from each other. I had thought about getting the correct cam for the .030 over bore and using my angle grinder to take a little off of the top of the other lobes to make up for the displacemant difference. Hey, do you know where I can get an "Type "R sticker? I really want to find a "Harbor Frieght Tools" sticker too! That would throw the HP right out of the roof!
Seriously, can you believe that they only bored 2 of the cylinders?

Joined:
Apr 25, 2001
Posts:
2,657