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Topic Review (Newest First)
01-15-2014 09:42 PM
crussell85
Quote:
Originally Posted by oldbogie View Post
Sounds like a solution to me.

An Offy Dual Port, here I though I was the only person to purchase one of those.

Bogie

PS you got me to thinking. I never, nor have I read about, a head swap to Vortecs that also included a piston swap to idealize the squish and quench characteristics of the Vortec head. It's always been a Vortec head strapped to whatever bottom end was already there whether the pistons had round dishes or not before and after. So your comment on greater compression tolerance got me thinking that I need to build a stock Chevy small block with those round dish pistons and pre Vortec heads, then put Vortec heads on it and redo the dyno run, this is what we usually see for data. Then take the engine apart and put D dish or flat top pistons in it, idealize the deck clearance to run the compression up and maximize the squish/quench of the head taking the SCR to the tolerance limit of the existing timing to see how far the SCR can be pushed before the chamber pings. Then test to see if the usually seen lost bottom end torque of these heads is recovered while the top end gains are either improved or at lest not compromised. I've never done it quite that way in back to back tests nor have I seen it done. hummmm!

Bogie
I know this thread it's old.....just curious if bogie ever did these build?
09-03-2010 02:42 PM
Uncle Buck
Quote:
Originally Posted by oldbogie

Go look at Chevy High Performance magazine, a few years ago they did an article titled "Agent 87". It gives a lot of clues as how to get a higher compression 350 to live on 87 octane
Found it online: http://www.chevyhiperformance.com/ho...075/index.html Thanks!

Quote:
Originally Posted by techinspector1
If you would like to research other ways of controlling detonation, google for "Singh grooves".
I did google "Singh grooves," read a little bit about them.... now I need a drink! Some guys call it "snake oil" while othes swear by the grooves. I did see a 14-page thread on this forum, although I haven't had a chance to go through it yet.

Looks like I have some readin' to do over this long weekend......
09-02-2010 08:22 PM
techinspector1
Quote:
Originally Posted by Uncle Buck
Here's the problem I keep running into: if I bring quench to something acceptable I drive CR up
Yeah, but what you gain in squish far surpasses the additional SCR.

You may or not know that I run quite a few DynoSim software programs and have been doing so for a while. I really enjoy it. Well, anyway, I had this one in storage, so I pulled it out to post the results here.
331 (0.030"+ 327)
L31 heads
9.00:1 SCR
600 carb on standard Performer intake
1 5/8" long tube headers
CompCams 12-234-2 cam. I don't like suggesting flat tappet cams anymore, but you could use these timing numbers to have a cam grinder cut a roller for you.
http://www.summitracing.com/parts/CCA-12-234-2/
These pistons make 9.0:1 with a 64cc chamber and have a nice, wide squish pad....
http://www.kb-silvolite.com/kb_car/p...etails&P_id=43
RPM HP TQ
1500 90 314
2000 140 368
2500 187 393
3000 225 394
3500 267 401
4000 304 399
4500 332 387
5000 347 364
5500 341 326

Pulled the heads off, replaced them with Racing Head Service cast iron Pro Torkers, 170cc intake runners, 64cc chambers. Installed 1.6 rockers int and exh. Pulled flat tappet cam out, installed hydraulic roller retrofit, Crane 119811, installed straight up. All else the same.
http://www.summitracing.com/parts/CRN-119811/
http://www.summitracing.com/parts/RHS-12410-01/
RPM HP TQ
1500 95 334
2000 145 381
2500 193 404
3000 232 406
3500 272 408
4000 303 404
4500 335 391
5000 350 368
5500 352 336
6000 312 273
Torque curve is as flat as a table. The 1.6 rockers only added a few hp and a few ft/lbs. I probably knew that before running the combination, but did it for grins. Not worth it if you don't have them on hand and have to buy them. Use 1.5's.

If you would like to research other ways of controlling detonation, google for "Singh grooves".
09-02-2010 08:13 PM
oldbogie
Quote:
Originally Posted by Uncle Buck
Here's the problem I keep running into: if I bring quench to something acceptable I drive CR up.

Maybe you can help me approach this from a different direction. I plan on using Vortec heads, and I know these heads are more compression tolerant- but how much? I'm rebuilding a carbureated 327 for use in low-geared 4x4 (Toyota FJ40). I plan to install a "torque cam," but haven't even started spec'ing one yet (does that help or hurt DCR?). Can someone give me a geneal idea of the max "safe" CR for this combination running plain old 87 octane?

Also, from a straight cost standpoint, is it cheaper to buy new pistons or have the block zero-decked?
Buying pistons over decking the block is something you'll have to look at since prices can vary quite a bit from place to place.

My tendency would be to go with pistons for two reasons.

1) Thinning decks whether head or block reduces strength and in this age of thin wall castings you want to preserve as much of that as you can to insure against gasket leaks and casting cracks. I don't mill OEM castings anymore than it takes to get a straight surface.

2) Piston selection when everything else is dimensionally known will let you dial in the compression and optimize the squish/quench. Flat tops as you have make for ideal squish/quench as their flat crown surface will close opposite the squish/quench deck of the head optimizing that area with the possible exception of the valve pockets (2 being better than the usual 4 but even 4 is way ahead of the OEM style circular dish. But as you see, you quickly get into CR trouble with tight chamber heads. The next best solution is choosing the so called D dish or D cup piston where the dish is kept under the valve pocket and a flat area not unlike that of a flat top piston is presented to the squish/quench deck. These let you maximize the squish/quench effect like a flat top while dialing in the SCR by selecting the dish volume. These type pistons can be had in cast or forged hyper-eutectic. Hyper-eutectic is nice stuff as it's very thermally stable which lets you run tighter clearances which reduces oil consumption, thus preserves the octane rating of the fuel you buy. you will want to hit a DCR between 8 and maybe 8.5. So you have to play with SCRs and the cam's intake closing event in the formula. One of the easier formulas to get at is at Keith Blacks house of pistons. So you'll have to get some data together on the dimensions that make the SCR and some specific cam candidate info and fit this stuff into the equations. Have link on me; http://www.kb-silvolite.com/calc.php Cam data you can get from the various cam stores like Comp, Edlebrock or Howards to mention a few. The KB link will want intake closing degrees After Bottom Dead Center (ABDC of BDC) and rod length which is 5.7 inch for 302, 327 and 350 Chevy's.

Go look at Chevy High Performance magazine, a few years ago they did an article titled "Agent 87". It gives a lot of clues as how to get a higher compression 350 to live on 87 octane while pumping out power in the high 300s to about 400. This was reprinted in a book by them titled "Small-Block Chevy Engine Buildups: How to Build Horsepower for Maximum Street and Racing Performance" This book has a lot of detail build info and dyno power graphs. While it's a lot more difficult to get an engine once in a vehicle to duplicate the kind of performance you can get on a dyno; it does lead you in some directions to max the amount and type of performance you're looking for without having to use your hard earned dollars on researching for yourself the effects of parts by guess and by golly. By performance between a crankshaft dyno and installed I mean more than the power numbers but how it reacts to detonation resistance, ignition timing, fuel ratios, power effects in different gears, etc. kind of stuff. This can be quite different once the motor has to haul around something with weight, gears and tires as opposed to exciting a generator or pump attached to the end of its crankshaft. I see people get all excited about numbers off a chassis dyno which are usually lower than expected. The purveyors of these things like to sell installed power looses as being around 15 to 20 percent. My experience says that upwards of nearly 50 percent loss isn't all that uncommon. So that 400 horse on the crank engine someone bought and had test feels cheated when the chassis dyno numbers read 260 corrected to 312. When in fact the installation may actually be loosing 50 percent off the crank which would make his 260 into 390, which is a lot closer to what was advertised by the seller of the motor.

OK its 7 something PDT and the ole' lady wants to do dinner so I'm out and down for tonight.

Bogie
09-02-2010 07:45 PM
Duntov
Quote:
Originally Posted by techinspector1
Don't know what Cr is, but the measurement you describe is compression height or CH. Also, piston deck is the distance from the piston crown to the block deck surface with the piston at TDC. Perhaps you meant to say:
CH is measured from the wrist pin centerline to the piston crown.
Good Catch TI

Was a miss-statement. I'm getting old

Miss-structured the sentence contextually.
09-02-2010 07:43 PM
Duntov
cheapest way to stay in 87 octane IMHO

Quote:
Originally Posted by Uncle Buck
Here's the problem I keep running into: if I bring quench to something acceptable I drive CR up.
Can someone give me a geneal idea of the max "safe" CR for this combination running plain old 87 octane?

Also, from a straight cost standpoint, is it cheaper to buy new pistons or have the block zero-decked?
If you don't want to bore and buy pistons, it would be cheaper to deck. If you buy pistons for your existing bore which have the correct pin height (CH), the top ring will travel past the wear ridge, whether visible or not. Your existing bore/build would have to be very low mileage for me to feel good about a new top ring passing that point.

IMO I would take it down, deck the block .025ish and have the intake surface on the heads cut /012" for every .010 off the deck. Might be hard to find a shop who can do that on Vortec heads, because of the configuration, but easy to find a shop who can take it off the intake.. $150.00 around here.

With your CR you could go to a decent set of 993s and get all the juice a low cr 327 has. Probably cheaper than vortec and easy to find. Not prone to cracking and also 75cc. They flow very well when window matched and cleaned up, and allow a good quench and lower compression to where you want it. I buy every 993 set I see at the core supply.
09-02-2010 07:35 PM
techinspector1
Quote:
Originally Posted by Duntov
Cr is measured from the center of the wrist pin to the top of the piston deck.
Don't know what Cr is, but the measurement you describe is compression height or CH. Also, piston deck is the distance from the piston crown to the block deck surface with the piston at TDC. Perhaps you meant to say:
CH is measured from the wrist pin centerline to the piston crown.
09-02-2010 07:21 PM
Uncle Buck
Quote:
Originally Posted by oldbogie
Your quench distance is much too great at .084 inch, it should be half that, and certainly not more than .060. As the quench distance becomes larger the tendency for detonation increases. This forces compromises in one or more of several other things which ends up sub-optimizing the engine for power and fuel efficiency. The compromises can be high octane fuel without taking thermal advantage of the fuel, this is lost power, lost fuel mileage often a large number, this hits you on the ET slip and in the wallet. Other compromises would be lowering the ignition advance, richening the mixture which again sub optimize the power and cost excessive fuel burn. Excessive fuel burn not only costs you at the pump, but reduces engine life because the excess fuel washes the upper cylinder wall lubrication away speeding the rate of wear on the piston, rings and cylinder wall.

Simple solution for you is to disassemble the engine marking everything as to where it came from so it goes back together the same way, assuming there is little wear on the pistons, rings and cylinder walls. Take the pistons out of the bottom will be better if there's any ridge on the top of the cylinder walls cylinder after smoothing and lower glaze from the cylinder walls with sand paper. Break any ridge at the top of the cylinder. Do a light hone on the walls to remove any glaze. Deck the block to zero. Clean everything super well and reassemble.

Bogie
Here's the problem I keep running into: if I bring quench to something acceptable I drive CR up.

Maybe you can help me approach this from a different direction. I plan on using Vortec heads, and I know these heads are more compression tolerant- but how much? I'm rebuilding a carbureated 327 for use in low-geared 4x4 (Toyota FJ40). I plan to install a "torque cam," but haven't even started spec'ing one yet (does that help or hurt DCR?). Can someone give me a geneal idea of the max "safe" CR for this combination running plain old 87 octane?

Also, from a straight cost standpoint, is it cheaper to buy new pistons or have the block zero-decked?
09-02-2010 06:08 PM
oldbogie
Quote:
Originally Posted by Uncle Buck
Bogie, that's one of the things that has me confused about 327's. I always thought the factory standard deck clearance for SBC's was .025. But stock style 327 flat top pistons with 4cc valve reliefs have a compression height to 1.654, which puts the crown .046 in the hole (assuming standard 9.025 deck).

With 64cc heads and a standard .040 gasket that gives me a SCR of 8.8 put a quench of .084!
OEM piston pin to crown is 1.678 for the 327, not 1.654. 1/2 the 3.25 stroke is 1.625. The rod is 5.7 inches center to center of the holes. This makes the OEM piston crown 9.003 inches above the crank centerline. That puts the crown .022 inch below the head deck. Pistons made for rebuilt engines often lower the pin to crown by .020 inch to restore the factory clearance after zero decking the block to 9 inches or thereabouts. These pistons in the case of the 327 would measure 1.658 inch from the pin center to the crown.

Your quench distance is much too great at .084 inch, it should be half that, and certainly not more than .060. As the quench distance becomes larger the tendency for detonation increases. This forces compromises in one or more of several other things which ends up sub-optimizing the engine for power and fuel efficiency. The compromises can be high octane fuel without taking thermal advantage of the fuel, this is lost power, lost fuel mileage often a large number, this hits you on the ET slip and in the wallet. Other compromises would be lowering the ignition advance, richening the mixture which again sub optimize the power and cost excessive fuel burn. Excessive fuel burn not only costs you at the pump, but reduces engine life because the excess fuel washes the upper cylinder wall lubrication away speeding the rate of wear on the piston, rings and cylinder wall.

Simple solution for you is to disassemble the engine marking everything as to where it came from so it goes back together the same way, assuming there is little wear on the pistons, rings and cylinder walls. Take the pistons out of the bottom will be better if there's any ridge on the top of the cylinder walls cylinder after smoothing and lower glaze from the cylinder walls with sand paper. Break any ridge at the top of the cylinder. Do a light hone on the walls to remove any glaze. Deck the block to zero. Clean everything super well and reassemble.

Bogie
09-02-2010 05:18 PM
Duntov
Quote:
Originally Posted by Uncle Buck
Thanks, very useful site. Just curious, when you CR's listed like that, are they based on a .040 head gasket?

I now realize that I was looking at the specs for rebuild pistons and didn't realize they were .020 shorter than stock. Now I get what Bogie was warning about....
Cr is measured from the center of the wrist pin to the top of the piston deck.
09-02-2010 04:51 PM
Uncle Buck
Quote:
Originally Posted by Duntov
http://www.flatlanderracing.com/
This site is a good reference for minor specs.. select pistons//TRW/forged/ Chevrolet and go from there.
Thanks, very useful site. Just curious, when you CR's listed like that, are they based on a .040 head gasket?

I now realize that I was looking at the specs for rebuild pistons and didn't realize they were .020 shorter than stock. Now I get what Bogie was warning about....
09-02-2010 04:40 PM
Duntov
Quick Reference for CH

http://www.flatlanderracing.com/
This site is a good reference for minor specs.. select pistons//TRW/forged/ Chevrolet and go from there.
09-02-2010 04:36 PM
Duntov
327 Ch

Quote:
Originally Posted by Uncle Buck
Bogie, that's one of the things that has me confused about 327's. I always thought the factory standard deck clearance for SBC's was .025. But stock style 327 flat top pistons with 4cc valve reliefs have a compression height to 1.654, which puts the crown .046 in the hole (assuming standard 9.025 deck).

With 64cc heads and a standard .040 gasket that gives me a SCR of 8.8 put a quench of .084!
I'm sure that 1.675" ch is more typical with 327. If memory serves it's factory, or maybe 1.671" was factory. I think you're dealing with what I call machine shop pistons. I'm not sure who they older machine shops order from, but they have access to .080" pistons for283, 307, 327, 350and lots of other stuff I assume. The availability of 080 makes me feel a little better about an 060 bore.
09-02-2010 04:17 PM
ericnova72
Quote:
Originally Posted by Uncle Buck
Bogie, that's one of the things that has me confused about 327's. I always thought the factory standard deck clearance for SBC's was .025. But stock style 327 flat top pistons with 4cc valve reliefs have a compression height to 1.654, which puts the crown .046 in the hole (assuming standard 9.025 deck).

With 64cc heads and a standard .040 gasket that gives me a SCR of 8.8 put a quench of .084!
Actually, stock blueprint compression height for 327 pistons is 1.675", you have the typical .020" reduced height that many rebuild pistons are. Only way you are going to get it right is to deck the block or replace the pistons with real 1.675" height models.
09-02-2010 04:09 PM
Uncle Buck
Quote:
Originally Posted by oldbogie
One has got to watch for those 1.54 inch compression height pistons when rebuilding. They are designed for zero decked blocks that retain the original piston crown to head deck clearance, thus I guess it's safe to say some semblance of original compression ratios. If they are used in a stock height block the piston crown will around .040 inch below the head deck instead of .025. Or even zero if the intent of zero decking was to gain compression by having the head deck and piston crown the same distance from the crankshaft center line. Many builders, hobbyist and professional, get skunked by these pistons which between the pin and the crown are .020 inch shorter than stock production units.

The first thing is to carefully check the dimensions for the piston being ordered to be sure they are dimensionally what is needed for the desired results.

Bogie
Bogie, that's one of the things that has me confused about 327's. I always thought the factory standard deck clearance for SBC's was .025. But stock style 327 flat top pistons with 4cc valve reliefs have a compression height to 1.654, which puts the crown .046 in the hole (assuming standard 9.025 deck).

With 64cc heads and a standard .040 gasket that gives me a SCR of 8.8 put a quench of .084!
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