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..............- 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
12-205-2
206/206
@ .050
Lift =.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

.030
Head Gasket

.041
Initial 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
12-205-2
206/206
@ .050
Lift =.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 think
Head Gasket

.040
Initial Timing

12 degrees
Total 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

heads
64 cc Chambers

(some say 65cc)
110 Lobe Separation 106 Lobe Centerline  
Cam  Comp 252
12-205-2 

206/206
@ .050
Lift =.425/.425 Advertised Duration

252/252
Pistons       16 cc Dish
355+ cu. inches Bore 4.040 Stroke 3.48 Rods 5.7 inch No Headers
Piston to Deck

.030
Head Gasket

.028
Initial 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.

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
@ .050
Lift =.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
12
Total Timing
34* total in at 3,300 RPM
Induction
600 Edelbrock
RPM intake
**Note: all the volumes were cc'ed to give accurate figures, Glen


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-Polished
65 cc Chambers   Lobe Separation 110 Lobe Centerline 106
Cam  Comp XR276HR

hyd roller

224/230
@ .050


Lift=.535"/.544" w/1.6 rockers
Advertised Duration

276/282
Pistons  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

.012
Head Gasket

.028
Initial Timing

18 BTDC
Total Timing

33 BTDC in by 2500 RPM
Induction

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.

DCR = 8.12 SCR = 9.97 Octane = 91    
Heads ProTop line

Aluminum Lighting
200cc Intakes

74cc Chambers
 Lobe Separation Lobe Centerline 
Cam Comp Xs274 lashed at .010 236/242
@ .050
Lift =?? 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
.040
Initial Timing
12
Total Timing
35* total in by 2,800
Induction
750 Edelbrock
Rpm intake
**Note: all the volumes were cc'ed to give accurate figures, Glen


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.

DCR = 8.38 SCR = 10.27 Octane = 93    
Heads Edelbrock RPM 70 cc Chambers   Lobe Separation  Lobe Centerline 
Cam Comp Xe274
230/236
@ .050
Lift =?? 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
.025
Head Gasket
.015
Initial Timing
16
Total Timing
36* total in at 3,000
Induction
750 Edelbrock
RPM intake
**Note: all the volumes were cc'ed to give accurate figures, Glen


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 above
   
Heads  S/R Torquers with unshrouded and polished chambers/crowns 80cc

Chambers
  Lobe Separation  Lobe Centerline 
Cam  Crane 100052 Energizer
216/216
@ .050
Lift =.452/.452

1.6 rockers see note above
Advertised Duration

272/272
Pistons  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

12
Total Timing

10 degrees vacuum can, (Full manifold) 20 centrifugal all in at 2000rpm
Induction


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*

@ .050
Lift =.480/.480 Advertised Duration

280/280
Pistons  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 .039
Initial Timing Total Timing

32* total timing; MSD distributor
Induction

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
@ .050
Lift = .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 Felpro
Initial 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 @ .050
Lift = .462/.463 262/270 Advertised Duration
Pistons  Dished     11 cc Dish

H423P
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


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 Ports
  110 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-hg
Induction = Ported LT1 dual plane with QFT 750 mech. secondaries



Put your combination here...................

DCR = SCR = Octane =    
Heads   cc Chambers   Lobe Separation  Lobe Centerline 
Cam  

@ .050
Lift = 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



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