The only thing I see missing is the piston volume + or - depending if it
is domed and how deep the valve notches are. But that is a less
important subject right now.. In my professional opinion, for whatever
it is worth, is #1 build an engine that is as close to stock bore as
possible. 4 inch would be ideal but i realize probably not possible. so
a good .010 over would be very nice. 2 reasons for this are you get a
chance to run it as is and later have some metal left for a few rebuilds
and still end up with a straight bore.. Can take it to +.015 and
+.020... The second reason is you can run the 302 crank which i suspect
is stronger in the first place. Although i have very little experience
with stock crankshats so i may be wrong here. I am not in favor of a big
regrind to destroke as it just makes the crankshaft weaker in the long
run, and you are going to have a lot of torque to consider. The largest
issue i see is the distance the piston is down the cylinder.. I come up
with about .076 plus the thickness of the head gasket. You are asking
for a lot of problems with this due to the lack of squish area. This
will cause a lot of troubles with detonation as it raises the octane
requirement of the engine a lot. If you have the luxury of it and they
make a piston with a cup in the center it is he way to go to get the
compression to 7/1 assuming you are planning to run enough boost to make
that practical at 5000 ft..The cup shape ala diesel style is the most
effecient design available .. but you do need an outer ring that is
approximately .045 from the underside of the head in order to maintain
the squish area..I would also condider filling the block partially in
order to stiffen the bore and help hold off cylinder wall cracking..
Hope this helps. If you have any other thoughts to bounce around on this
feel free to send them. Glad to help if i can..
Dave Dahlgren
Engine Management Systems
"Lawrence E. & Cathy R. Mayfield" wrote:
>
> >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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