.................Return to Sumner's Home Page ........................ Return to Tech Info Index
..............- DCR Combinations That Have Worked -
............................................................- For Small Blocks -
The purpose of these pages is to helpfully show what DCR (Dynamic Compression Ratios) and SCR (Static Compression Ratios) have worked with what Octane gas.
You have to realize that there is more to this than just the DCR. Other things that will effect the octane you can run are altitude, load, quench, timing, combustion chamber shape, piston top shape, etc.. So use the following as a guide for what has worked for others and go from there.
If you know your combination and would like to share it please e-mail me your information (see this page for e-mail address). Use the examples below to compile your data. The more we have the better it will be.
Note: Here is a link to a DCR & SCR Calculator. Please try and use this calculator so we are comparing apples to apples. If you use a different one please let me know. Also if you can fill in all of the fields then we can double check each others calculations.
...........................(I'll try and keep these in order of lowest DCR to highest DCR)
sgian (on http://www.chevytalk.org/): This cheap engine build from mostly spare parts was a dog that needed lots of advance to get decent driveability. Gas mileage was often around 13 mpg city, 14-18.5 mpg highway in a Nova with a TH350.
DCR = 6.82 SCR = 7.80 Octane = 87 (or lower) Heads stock iron smog heads 76 cc Chambers 110 Lobe Separation 106 Lobe Centerline Cam Comp 252
12-205-2206/206
@ .050Lift =.425/.425 Advertised Duration 252/252 Pistons 16 cc Dish 355+ cu. inches Bore 4.040 Stroke 3.48 Rods 5.7 inch stock exh. Piston to Deck
.030Head Gasket
.041Initial Timing
20*Total Timing
40*Induction
Q-jet on
GM Cast Iron
Intake
1FATGMC - Sumner (on http://www.chevytalk.org/): This is the motor I run in my truck (1FATGMC). I only run 86/87 octane and have never had any detonation in 130,000 miles. About 40,000 of that is towing a "heavy" teardrop trailer with a combined weight of around 5800 lbs. I get 20 mpg at 75 mph without the trailer and about 16-17 with it. 3.50 rear-end with 28 inch tires and a 700R4. Does not detonate even in overdrive pulling a hill.
DCR = 7.44 SCR = 8.52 Octane = 86 Heads World SR 76cc Chambers Lobe Separation 110 Lobe Center line 106 Cam Comp 252
12-205-2206/206
@ .050Lift =.425/.425 Advertised Duration 252/252 Pistons Cast Flat Top 4 valve reliefs 7 cc dish 355 cu. inches Bore 4.030 Stroke 3.48 Rods 5.7 inch 1 5/8" Headers Piston to Deck
.025 I thinkHead Gasket
.040Initial Timing
12 degreesTotal Timing
?????Induction
Carb -Q-Jet
Weiand Action+
sgian (on http://www.chevytalk.org/): With the same lower end in the same car as above (see sgian's other motor further above "This cheap engine build from mostly spare parts was a dog that needed lots ............... in a Nova with a TH350.), this engine gets 14-16 mpg city and 16-20 mpg highway with a TH350. Octane = 89 (after a couple of tanks of 87 oct it develops a knock, and with cheap brands of gas it loses power and several mpg). Now that I'm at sea level, I'm running 6*-8* initial timing and city mileage is slightly lower.
DCR = 7.77 SCR = 8.9 Octane = 89 Heads swirl port
heads64 cc Chambers
(some say 65cc)110 Lobe Separation 106 Lobe Centerline Cam Comp 252
12-205-2
206/206
@ .050Lift =.425/.425 Advertised Duration
252/252Pistons 16 cc Dish 355+ cu. inches Bore 4.040 Stroke 3.48 Rods 5.7 inch No Headers Piston to Deck
.030Head Gasket
.028Initial Timing
8-10*Total Timing
29*-31*Induction
Q-jet on
mild Aluminum Intake
DragRacer383 -- Glen (on http://www.chevytalk.org/): In my 84 Silverado with a 350 and 3.73 gears and 2,000 stall. It ran a 8.95 in the 1/8. It will cruise all day in any heat pulling a Trailer and car and run on 87 Octane. loads of Torque.
**Note: all the volumes were cc'ed to give accurate figures, Glen
DCR = 7.616 SCR = 9.122 Octane = 87 Heads Dart SS 165 heads 74 cc Chambers Lobe Separation Lobe Centerline Cam Crane 266 energizer .210/.210
@ .050Lift =.440/.440 Advertised Duration 266/266 Pistons Flat Top 4 valve reliefs 6 cc dish 355 cu. inches Bore 4.030 Stroke 3.48 Rods 5.7 inch 1 1/2"Headers
Piston to Deck
.025
Head Gasket
.020
Initial Timing
12Total Timing
34* total in at 3,300 RPMInduction
600 Edelbrock
RPM intake
Brain55 -- Brian (on http://www.chevytalk.org/): This is the engine in my '55. Its best power was made at 33 degrees total timing. I have had no detonation problems, even on the chassis dyno. I am very happy with it, I can't wait to get it back on the road. See the chassis dyno results at www.brians55.com/dyno.html (look at his dyno results and comments -- good stuff).
DCR = 8.1 SCR =10.1 Octane = 91 Heads Vortec's
Ported-Polished65 cc Chambers Lobe Separation 110 Lobe Centerline 106 Cam Comp XR276HR
hyd roller
224/230
@ .050
Lift=.535"/.544" w/1.6 rockersAdvertised Duration
276/282Pistons TRW forged flat-top 4 reliefs 6.1 cc 355 cu. inches Bore 4.030 Stroke 3.48 Rods 5.7 inch 1 5/8" headers Piston to Deck
.012Head Gasket
.028Initial Timing
18 BTDCTotal Timing
33 BTDC in by 2500 RPMInduction
TPC Holley 750DP
Edelbrock Super Victor
DragRacer383 -- Glen (on http://www.chevytalk.org/): This engine in the same Silverado with just the stall changed to 3,000 went 8.58 in 1/8 on a shake down run. It will go faster with tuning. The way it is it will run on 91 Octane. The slightly low compression was so I could add 100 shot of nitrous with out backing off the timing or mixing in a higher fuel. It went just as planed. I have used 2 bottles on it with out a problem. No good track times on it yet. just the shake down run on motor. it will run in the 7's with the spray. On motor and street tires if you stomp it from a stop, no power brake it will burn the tires to 6,500 in all 3 gears. Mileage Sucks. Idle sounds nasty. WOT sounds like any race car, with mufflers.
**Note: all the volumes were cc'ed to give accurate figures, Glen
DCR = 8.12 SCR = 9.97 Octane = 91 Heads ProTop line
Aluminum Lighting200cc Intakes
74cc ChambersLobe Separation Lobe Centerline Cam Comp Xs274 lashed at .010 236/242
@ .050Lift =?? Advertised Duration 274/280 Pistons Flat top 2 valve reliefs 6 cc Dish 383 cu. inches Bore 4.060 Stroke 3.75 Rods 5.7 inch 1 3/4"Headers Piston to Deck
0.000
Head Gasket
.040Initial Timing
12Total Timing
35* total in by 2,800Induction
750 Edelbrock
Rpm intake
DragRacer383 -- Glen (on http://www.chevytalk.org/): This engine ran on 93 octane. With a 100 shot of nitrous you didn't have to change the timing or add booster to the fuel. The car was light weight though 2,700#. In the 2,700# car (86 mustang) With a 350 and 3,000 stall, 4.10 gears it ran 6.67 in the 1/8 at 100.3 mph with 100 shot of nitrous. It had a 1.49 60' time.
I have built more pump gas engines using the Calculator, but these I owned and can verify the info is correct.
**Note: all the volumes were cc'ed to give accurate figures, Glen
DCR = 8.38 SCR = 10.27 Octane = 93 Heads Edelbrock RPM 70 cc Chambers Lobe Separation Lobe Centerline Cam Comp Xe274
230/236
@ .050Lift =?? Advertised Duration 274/286 Pistons Flat Tops 4 valve reliefs 6 cc Dish 383 cu. inches Bore 4.030 Stroke 3.75 Rods 5.565 inch 1 5/8" Headers Piston to Deck
.025Head Gasket
.015Initial Timing
16Total Timing
36* total in at 3,000Induction
750 Edelbrock
RPM intake
SteveStreeter -- Steve (on http://www.chevytalk.org/): This has been runing well at 5000feet, better at 2000ft and great at sea level for more than 50,000 miles. Got 23 mpg at 80 mph in the 79 Bu on the way to Reno's Hot August Nights last summer. Running 700R4 with 308 gears and a locker. 25.7" tires and a 2400rpm converter stall makes for lots of fun.Note: 92 octane with the A/C running at 115 degrees F. -- 89 octane in the winter. 1.6 Crane roller tip rockers i/e for .485" theoretical lift and about 1 degree more duration.
DCR = 8.38 SCR = 10.26 Octane = 92/89
See Note aboveHeads S/R Torquers with unshrouded and polished chambers/crowns 80cc
ChambersLobe Separation Lobe Centerline Cam Crane 100052 Energizer
216/216
@ .050Lift =.452/.452
1.6 rockers see note aboveAdvertised Duration
272/272Pistons speedpro 5 cc pop-up 360 cu. inches Bore 4.060 Stroke 3.48 Rods 5.7 inch Headers Piston to Deck
(.040 Quench)Head Gasket
(.040 Quench)Initial Timing
12Total Timing
10 degrees vacuum can, (Full manifold) 20 centrifugal all in at 2000rpmInduction
rumrumm -- Lynn (on http://www.chevytalk.org/): Here is another one which works well with 92 octane
DCR = 8.46 SCR = 10.6 Octane = 92 CompCams ProMagnum roller rockers (1.52) Heads AFR 190's 68 cc Chambers Lobe Separation 110 Lobe Centerline 106 Cam CompCams Magnum 280 hydraulic cam 230*/230*
@ .050Lift =.480/.480 Advertised Duration
280/280Pistons SRP forged flat top pistons 5 cc 355 cu. inches Bore 4.030 Stroke 3.75 Rods 6.0 inch Sanderson 1 3/4 inch block hugger headers Piston to Deck
0.000 (zero)Head Gasket
FelPro .039Initial Timing Total Timing
32* total timing; MSD distributorInduction
750 Edelbrock Edlebrock RPM intake
Ricktpi -- Rick (on http://www.chevytalk.org/): 93 octane zero ping in a 383 roller block. I used the Silvolite calculator (for DCR) from Grumpy's post above on Chevy Talk Performance Board). (With Pat's DCR calculator I get 10.2 SCR and 7.75 DCR -- Sum)
Note: The lift #s have been recalculated for 1.6 rockers.
DCR = 8.790 SCR = 10.405 Octane = 93 Heads AFR 195 heads 68 cc Chambers Lobe Sep Angle 110 Intake Ctr Line: 106 Cam Lunati 74756 cam w/1.6 rockers 232/242
@ .050Lift = .544"/.560" Advertised Duration 290/300 Pistons KB122 Hypereutectic flat top 2 valve reliefs 7 cc Dish 355 cu. inches Bore 4.030 Stroke 3.75 Rods 6.0 inch Headers
Piston to Deck
.010
Head Gasket
.039 FelproInitial Timing
20*Total Timing
38*Induction
Holley Stealth Ram EFI
Boogie (on http://www.chevytalk.org/): No clatter,very responsive with lots of low end torque in a '74 Nova with a TH350 and 3.08's. No time slips,spins too much anyway with the open dif.
DCR = 7.65 SCR = 9.04 Octane = 87 Heads Vortec 64cc Chambers 110 Lobe Separation 106 Lobe Centerline Cam Comp Cam XE262
218/224 @ .050Lift = .462/.463 262/270 Advertised Duration Pistons Dished 11 cc Dish
H423P360 cu. inches Bore 4.060 Stroke 3.48 Rods 5.7 inch Headers .037 Piston to Deck -- .077 quench .040 Head Gasket with 4.166 bore Initial Timing 36 deg. Total Timing Induction
Boogie (on http://www.chevytalk.org/): Same engine as above only with H345P -6cc 4 valve relief flattop pistons. This is in a '84 SWB truck that ran 14.50's with a TH350, 28" drag radials and rear gears that I cannot remember. Clatters a bit under load on pump gas but, it is still running today and was build least five years ago (in 2006).
DCR = 8.03 SCR = 9.50 Octane = 87 Heads Vortec 64cc Chambers 110 Lobe Separation 106 Lobe Centerline Cam Comp Cam XE262 218/224 @ .050 Lift =.462/.463 262/270 Advertised Duration Pistons Flattop 6 cc 4 valve reliefs H345P 360 cu. inches Bore 4.060 Stroke 3.48 Rods 5.7 inch Headers .037 Piston to Deck -- .077 quench .040 Head Gasket with 4.166 bore Initial Timing 36 deg. Total Timing Induction
Joe C. (65TripleBlack on Chevytalk.org). A 327 (331) that makes 353.7 RWHP, SAE corrected @ 6300 and 323.03 ft-lbs torque @ 4500 and has a 90% torque bandwith between 3300 and 6300. An image of the dyno run ( HERE ).
DCR = 8.205 SCR = 11.116 Octane = 93 PON Heads Chevy 461 ported, 2.02/1.6 Int/Exh 65 cc Chambers
185 cc Ports110 Lobe Separation 106 Lobe Centerline Cam Comp Cam 12 - 772 - 8 with 1.6:1 rockers 248/254 @ .050 Lift =.600"/.606" 286/292 Advertised Duration Pistons Speed Pro L2166NF-30 Domed 5.3 cc 331 cu. inches Bore 4.030 Stroke 3.25 Rods 5.7 inch Headers=Hedman 1-5/8" primary tubes Piston to Deck +.004 out of the hole with .034 Quench .038 Head Gasket 20 deg. Initial Timing 37 degrees @ 2500 RPM Total Timing
14 degree vac advance @ 5
in-hgInduction = Ported LT1 dual plane with QFT 750 mech. secondaries
Put your combination here...................
DCR = SCR = Octane = Heads cc Chambers Lobe Separation Lobe Centerline Cam
@ .050Lift = Advertised Duration Pistons cc 355 cu. inches Bore 4.030 Stroke 3.48 Rods 5.7 inch Headers Piston to Deck Head Gasket Initial Timing Total Timing Induction
............Return to Sumner's Home Page ........................ Return to Tech Info Index