I'm using Speed Pro cast pistons in my 355, not cheap pistons, still ran me $300 + for the set 5 years ago. Their part number is H100CP 30 and has 1/16" rings. My CR is very close to 10:1 and I run well with it on 93 octane, I have used an octane booster with it too.
If you go to KB's website and actually look that piston up, you'll find it is listed as 11.3;1 only with a 58cc head. List says 11.3:1 w/58cc, 10.7:1 w/62cc, 10.5:1 w/64cc, 9:1 w76cc. By the way, KB's number appear to be figured with the common .041" thick x 4.166" bore composition gasket and an undecked block....if you either zero deck the block or leave it stock height and use a .015" shim all those listed ratio's go up by 3/4 of a point. Listed as -5cc total volume, .100" tall solid dome.. With the KB 2 valve relief flat top #KB156 listed as a +7cc valve relief volume, that means that the .100" tall dome is -12cc different than the flat top. This gives you a fairly easy approximation of about every .0083" of dome height = 1cc. Rough figure for 4" bore based 327-383" engines is every 1cc =0.1 points compression. If you use the KB 157 dome, and you want 10.:1 with a uncut block, 64cc head and the typical Fel-Pro composition gasket, you'll need to machine off 4cc, or roughly .034" of the dome. Want to do it with uncut block and the .015" shim gasket to preserve good quench for better detonation resistance, you'll need to remove 7cc/.060" from that dome to get 10.2:1, or 9cc/.078" for 10.0:1 On another note, uncut block, .015" steel shim gasket, 64cc head and the KB 2 relief flat top #KB157 will give you 9.67:1. Uncut block and a composition gasket plummets this to 9.05:1 but rotten quench clearance of .063" Same flat top piston, zero deck block and composition gasket at .041" thick x 4.166" gasket bore gives 9.5:1. qeuch would be .041"(in good range)
Yep, 9.5:1 compression with composition gasket....can't use a .015" thicksteel shim though, minimum piston to head is .035" unless you are willing to gamble....an .026" composition gasket is available from GM and Mahle/Clevite(#5746) that will push compression ratio to 9.9:1 zero decked block, but let the RPM's get away from you on a missed shift and the piston could hit the head.
I should probably add you can juggle all these numbers with head milling....on a closed chamber SBC head like your traditional Hump, Fuelie or Power Pack every .006" flat milled removes 1cc/adds 0.1 point compression on 4" bore 327-383 engines
Figure your quench, .045? seems to be acceptable. You will have to tune the ignition, 4.88's will help a lot. Really depends whay you want out the the combo. With 4.88's, not feeling a DD here
Where at in East Tn. are you ? I live in Athens and maybe can help you. I have been building hot small block chevys for over 40 years. PM me if you want some help. I mostly build Fords now but haven't forgotten how to make a bowtie run.
I Thank You all! You have given me lots to think about. I use to build some hot engines back in the 70-early 90's, but switch things to '90s stock running sbc & 4.3's. I don't think I want to cut the pistons, I can do it myself, I was in Tool & Die for about 40 yrs, and I have accesses to my neighbors lathe. But if it's the way to get good 10:1. I don't think going the way of thin gasket to get to 9.9:1 with a stock bore, which mine is +40 A zero deck, I have to look to see if he did cleaned the deck or not. But I didn't have it decked, just cleaned if I did. I was going to have the heads have clean up cut also. Maybe I should go through the hassle of cutting domes down .06-.078 of the .100 dome off, to get 10:1-10.2:1. But I don't think I want to run thin head gasket, So I suppose I'd have to cut a tad less off for the difference. Ericnova thanks for the cutting the dome info, it gives me lots more to think about, as if I didn't have enough already. lol As with you all that gave input!
I'm in Deer Lodge, about 60 miles nw of Knoxville. (just south of Jamestown), about 75 miles north of you. Right now I'm in the getting parts together, and all the machining done.
Sorry for not getting back to you guys. My wife has been in & out of the hospital, and I have not worked on getting pistons yet, my mind has been on my wife. I'm still not sure which way to go. I don't think there's a difference in valve to piston clearance with flat tops, or cut down domes. I want to run a decent lift cam, not sure on which one to run yet, but I need to get the pistons figured out first. I'll be running a tunnel ram on it also. I'll have to re-jet the Holley 600's to make them work, or find some rebuildable Holley 450's. Thanks, Pat
Hope things go well for you and your wife, that's always a priority. If the flat top and the dome have the same diameter and depth of valve notches, having a dome there doesn't effect valve to piston clearance. As far as your minor reluctance to cut down a solid dome piston, look at ti this way....there are engine assemblers, guys who buy parts, take them out of the box, wipe them off, and stick them in...and there are engine builders, who take used or new parts and modify them if needed to meet their needs....guess who the guys who make more power are. On the tunnel ram, my advice would be to avoid the 450's, they are poser tunnel ram carbs, not power makers. If you want Holley's, modified 600 vacuum's, 600 or 650 Double Pumps, or probably the best for power the 660 Center Squirter's. No 390 vacuums or the 450 mechanicals that have only a single pump. i have yet to be impressed by anybody's 450's.
Don't get wrapped around the axle over thinking it..... EricNova72 has the best advice....zero deck motors are always better...a standard 0.040" ish composition gasket is the most forgiving for deck finish (and gives the corrected quench) and, as several folks have mentioned, the flat top 327 is a very happy motor. With a baseline of 9.5ish:1 you've still got plenty of wiggle room on any milling the heads may need (or already have had....should cc the chambers) and still keeping the motor under 10:1. Keep the heads simple too. Nothing wrong with a cleaned up port and 1.94 valves. There are many instances where the 2.02 valve isnt neccesarily better....especially if they're just stabbbed in without a fair amount of the **correct** work to realize any gains. With a tunnel ram you want to keep low and mid range air flow up and let the top end take care of itself. Dont over cam the motor. Sent from my SM-G950U using The H.A.M.B. mobile app
Thanks again! I have no problem with cutting the piston domes, if I go that way. I am use to building an engine with 10:1, 10.5:1, 11:1's, and that was more years then I can..............What was I saying? lol I'm after a good street/race type engine, and thought 10:1 would be a good place for pump gas. I was just looking at some forged 11:0 pistons designed for milling the dome down. But it say's their for a destroked 327. What is the stroke on a destroked 327, what's used for the crank? I just don't want to build an engine that looks like it has hp. but can back it up also on the street. So Do I want a strong 10:1-10.2:1, or go with flat tops, and get about 9.5:1 -9.9:1 Wouldn't they still run the same gas? How much difference would there in torque? It seems like you guys are for going with the flat tops, saying it would be a happy engine, and run fine. But I want it to be a pissed off Mother&#@&*^! when I need it to be, also. I do have the 194's and thought of having 202's installed, but not sure of it. I am going to clean up the ports and match them. Someone already worked on one of the heads. Plus I'll put it screw in studs. My plan was to use my Holley 600's Most likely sticking with them. Thanks, Pat
I can't say without actually knowing the compression height(pin height) of the pistons you are looking at, but generally I've found that pistons in online listings referred to as 327 "destroker" pistons are for using a stock 283 crank to make a 302 out of a small journal 327 block. If your planning to stay with the factory 5.7" rod length and not going to use longer aftermarket rods like 5.85", 6.0", or 6.125" then you need to make sure the pistons you look for have a compression height of 1.675". Compression height is the distance from the centerline of the wrist pin bore to the top flat area on the quench pad side of the piston(on a flat top it is the entire top, on a dish piston it is the top of the rim around the dish). if you want a motor that gets up and sounds angry with a bite to match and plan to only use pump gas you need to push compression ratio as high as you dare. With cam duration up in the range of the old "30-30" cam with more modern lift amounts I wouldn't be afraid of an honest 10.5:1, especially since your short stroke limits piston dwell time around TDC in that .100"from the head distance that is the prime detonation zone. Would not surprise me to find out 11:1 would work, but I can't say for sure as I only mess with the 3.75" stroke 383 stuff in a 4.00" bore block anymore, or 400" 4.125"+ bore based stuff. I do 10.5:1 with them on pump gas anytime.
Not to worry! She is truly my best friend. She had a surgery 10 years ago. They hit her Vagus nerve, and paralysed her stomach. It's been getting more & more, and there's nothing that can be done. I have sold off all my car parts, and my R/C hobby, which was alot. I sold it all for her, to get he med's the insurance still won't pay for, and I'd do it all over again. That is why building this 327 has taken some back seats at times. Thanks, Pat
I totally must have had a dead brain cell or something pop! I built a 302 back it the late 70's. But I don't know anything about them, and the outlet selling them only know what the paper work tells them. Their not auto people at all. They are forged solid dome 11:1 new in box for $149.95 With how to cut the ratio you want. But I know of someone that has some 327 +040 11:1 dome also. I have to find out if their solid dome first. That puts it right back to what I was thinking about. 10:1 -10.5:1, with around 10.25 being a goal. It has to have a growl, and a as you say, a bite. I don't want a thumping piss ant, that won't bite back. Thanks, Pat
All around a Flat top 327 with modern thicker head gaskets will run nice at 9.5:1.ish Favorite cam is still 350hp 327 hyd...0.447in/0.447ex long duration..the original tire burner thru the mufflers..The 327 like a 283 is a very smooth running engine as well.
The amount of money that you will spend on the 3 angle valve job + porting on the iron heads you can purchase some new double hump aluminum trick flow heads and paint them orange. You could then run the 11.1 pistons because the aluminum forgives about a point of compression = 10.1 and they would flow better.
I run an L-79 cam in my 355. They are a good street cam and you can make play with the same timing a little bit and make lots of zot with one. Where you run into trouble with the thick head gaskets is that you cannot run as much compression as you can with the same fuel with a thinner gasket. The modern thick cometic (SP?)gaskets work fine but you can create a stronger mill with the same parts if you play with your quench a little bit and it works backward to what you would think. At this point we are getting deeper into tuning theory than most of us want to think about.
All of my sbc motors that I have built/build here in Denver, I run with final compression ratio of 10.6 with no problems. Pump gas and altitude. Go for the pistons and adjust compression with head cc's or gasket thickness, or both.
Well I just saw a rule of thumb for this as I am going thru the same thing with a 327. For every .025 you raise or lower the head you will gain or lose roughly .5 compression. I purchased 11-1 speed pro pistons and Summit has a great calculator right in the piston specifications of the pistons you would be purchasing. You have three regular choice of off the shelf gaskets .015-.026-.039 (roughly) or Cometic as jimmy six said.
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