>Date: Mon, 27 Dec 1999 08:54:47
>To: land-speed@autox.team.net jyturbo@onelist.com
fordnatics@lists.best.com alpines@autox.team.net
>From: "Lawrence E. & Cathy R. Mayfield" <lemay@hiwaay.net>
>Subject: Compression Ratio Calculations & Comments?
>
>It is time to get serious about building the motor for the Sunbeam land
speed car. Right now I have a DSS short block which has been bored 0.030 to
4.030. It has 1/2 inch studs, so I would like to use it if it is still
good. And it is a roller cam block. Now the problem: at 4.030 bore, it is
just a tad to large in displacement for the class I think the car/engine
belong in. Currently it is 306.134 CID. The max allowed is 305 CID.
>
>Good solid racers have suggested that I offeset turn the crank, destroke
it, just enough to get it into the class. This is doable and may be
considered. It would require grinding the crank, naturally, but possibly
requiring new rods also. SO this might not be inexpensive (but what in
racing is?).
>
>Another thought is to run a block which is only bored 0.020 over. This
yields 304.616 CID and is also doable requiring new pistons, rings and of
course boring the block. But it also requires that I prep the block to
receive the 1/2 inch head studs which I assume is not cheap either.
>
>Yet another possibility is the use of a 289 hipo crank, which I have
buried in an old engine. I understand that the crank will have to be
modified by removing the oil slinger at the rear main and that rebalance is
also required. But here is the part that interests me the most: use of the
289 crank with the 5.0L rods and piston give me a pretty low compression
ratio. I believe this to be of considerable benefit in a turbocharged
motor. Also, the displacement fits well within that allowed: 292.87 CID.
Now I need some help in validating the compression ratio.
>
>1) Block height is 8.206 inches
>2) Rod length is 5.090 inches
>3) Compression Height on Piston is 1.605 inches
>4) Gasket thickness is 0.040 inches
>5) Chamber volumn is 64 cc's (3.9055 cubic inches)
>6) Stroke is 2.87 inches
>7) Boer is 4.030 inches
>
>With the assumptions above, the CR is calculated as follows:
>
>a) swept volume V = Bore x Bore x PI/4 x 2.87 = 36.608 cubic inches
>b) Clearance volume = Bore x Bore x PI/4 x {8.206 - (2.87/2 + 5.09 +
1.605)} = 0.89
> cubic inches (note that this is the volume of space above the piston
but within the
> bore)
>c) Head gasket volume = Bore x Bore x PI/4 x 0.040 = 0.51 cubic inches
>
>So adding the combustion chamber, the clearance vol and the gasket vol =
5.3086 cubic inches.
>
>Compression ratio is then 36.608/5.3086 = 6.896 to 1. There is a small
additional amount of static vol that might be considered to lower the ratio
even more: The gap between the piston wall and piston down to the top ring.
But, I think for now that I wont consider it.
>
>Now I need comments: Did I do this right? I know that there are many
calculators on the web but I try to go back to basics so that I undestand
what it is I am doing. Is this a really good CR for a blown motor? My
thought is that lowering the CR allows more charge into the engine
resulting in a higher overall chamber pressure with more fuel, resulting in
more power output. IS this right? Could some of you who have done things
like prep a block for 1/2 inch head studs let me know the costs involved?
Ditto for balance operations? What kind of heart attack can I expect when I
carry all this to the engine shop? Do I need to take my nitro pills? Or rob
a bank? Or is one of the other alternatives I mentioned better?
>
>I really need you help. Please respond off list unless you feel that the
information or flames would be appreciated by the list.
>
>mayf (in the dark)
L.E. Mayfield
124 Maximillion Drive
Madison, Al. 35758-8171
1-256-837-1051
old >>>>>>>> http://www.hsv.tis.net/~mayfield
new >>>>>>>> http://home.hiwaay.net/~lemayf
DrMayf@AOL.com
lemay@hiwaay.net <<<<preferred
Sunbeam Tiger, B9471136
Sunbeam Alpine Bonneville Land Speed Racer,
'66 Hydroplane Drag Boat (390 FE)
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