|07-15-2008 11:44 AM|
a 12CC dish and 75CC is less than what you want.. its at best 8.75:1 with conventional gaskets to get 9.1 you will need a shim style headgasket...
|02-26-2008 07:48 PM|
I not sure but I think the 4% general rule for compression ratio/power difference refers to peak hp. Torque at the low end can be effected more.
Take it as a general rule of thumb.
Even at that if you were limited to running economical 87 octane gas (and the limited cr, you'd still have a pretty good motor. Mostly because the cam is fairly mild as cams go and the heads are pretty good. Should work well.
|02-26-2008 06:41 PM|
|techinspector1||ok, point taken. But since my idea is to make good torque on junk gas, and since power is reduced by about 4% for each point in c.r., could we say that we might make 451 ft/lbs at 9.15 with 1.6 rockers? (470 X 0.96).|
|02-26-2008 06:13 PM|
Take the combos in the Ryan web site for what they are. Basic ideas, without specific details, drawn for the most part from old hot rod mag articles that are famous for missing critical details and spec errors (editing errors).
That combo (the real combo) probabily had more actual compression. You'd want to maximise the net valve lift to take advantage of the AFR heads with that mild short duration cam. (use 1.6:1 or higher rockers) you'd want to run as close to 10:1 actual compression unless you are restricted to junk 87 octane fuel.
You might want to start with a 600cfm carb body but modify it for more airflow while keeping the small venturii size for good fuel mileage etc. Engines are all about airflow.
|02-26-2008 05:49 PM|
Pump gas street motor
There is always a question coming up here asking about engine combinations. I came across this combination #11 on ryanscarpage and thought it looked like a real good combination for a pump gas street motor. I couldn't find the rest of the info on the cam from AFR, so don't know if it is still available from them, but would like input from you guys about another cam or cams from different manufacturers that would work with the rest of this combination, as well as the correct carb, etc. There are members on this board who know way more than I do and I would appreciate your input. What I want to do is direct the next "pump gas street motor" inquiry to this thread and be done with it. Or maybe post it on the wiki and be done with it. I figure it's hard to go wrong with 470 ft/lbs of torque at 3,500 rpm's.
Here are the details I came up with.......
350 block. Assuming you're starting with a virgin block, bore it 0.030" and cut the decks 0.017" to arrive at a final block deck height of 9.008". With a "stack" measurement of 9.008" (crank radius, rod, piston), this will result in a zero piston deck height.
Pistons. KB197 hypereutectic 12cc dish. Clearance piston to wall at 0.0015" to 0.002". Gap top ring at minimum 0.026". Gap second ring at standard 0.018" to 0.020". With 75cc heads, 0.041" compressed head gasket, zero piston deck height and these pistons, static compression ratio will be 9.15:1
Rods. 5.7" 350 rods. Usual clearancing on a 383 includes grinding at the rod bolt heads for cam lobe clearance, grinding at the oil pan rail of the block for big-end clearance and paying attention to the clearance of the pin end of the rod on the balance pad at the underside of the piston crown. Also, there are cams which are ground on a reduced base circle to circumvent the need to grind on the rods, but must be used with longer pushrods. I don't like 6.000" rods in a stroker because it puts the pin up into the oil ring. Also, I consider longer rods much ado about nothing. This opinion is shared by Iskenderian. Click here and scroll down to Tech Tip 2005......
Crank. Use the 3.750" crank of your choice. You can cut the main journals of a stock 400 crank to fit into the main saddles of the 350 block or you can buy a specifically-made aftermarket crank or complete and balanced rotating assembly. Your choice. If using an aftermarket crank, pay attention to the fillet radius. You may need to use bearings with a wider fillet to clear at the corners of the journals to avoid interference.
Heads. Air Flow Research 195 street heads with 75cc chambers. Straight plug part number 1036, angle plug part number 1038 depending on header interference and your personal choice. Screw 'em onto the block with Fel-Pro #1003 head gaskets (AFR #6800). (0.041" compressed). This will put the squish (piston crown to cylinder head at TDC) at 0.041".
Intake. Airflow Research #5028. This is the manifold listed in combo 11, but I would talk to AFR about using the #5030 to find out if it might work better on this relatively low-rpm motor.
Carburetor. Holley 600 CFM. I'd talk with AFR to determine the specific model to use in this application.
Headers. Equal-length, 1 5/8" primaries, 2 1/2" tubing to the back using an "X" pipe right before the mufflers. Don't get caught up in all the muffler hype. There's probably not 5 hp difference in any of them when the dust settles. I like to use 36" long glasspaks myself.
Cam. I don't know if AFR still offers the cam shown in combo 11, but if they don't, I'm sure they could give you the detailed specs (LSA, installed centerline, etc.) to use to arrive at the hp and torque figures shown. The short lift is gonna be easy on valve springs too.
Ignition. I think it's hard to beat an HEI, especially if revs are limited. KB doesn't like advance to exceed 34 degrees and I suspect AFR would tell you the same thing. Put 12 in at the crank and configure the weights, springs and stops for an additional 22, all in by 2,800-3,000 rpms. Also use vacuum advance.
NOW HEAR THIS!!!!! I don't want to hear any carping about the cost of AFR heads.