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Discussion Starter #1
I have a ZZ4 Short block I am building for my truck with a Vortec blow throw supercharger with holley's super sniper EFI at 5 pounds of boost. trying to get close to 9:1 Compression to run on 91 octane. can someone help me calculate the Compression I will have with my current setup? I have listed the parts below that I currently have

Comp Blower Cam part# CL08-301-8

Intake Valve Lift (in.)0.502
Exhaust Valve Lift (in.)0.52
RPM Range2000-6000
Int. Duration @ .050 in. (Deg)224
Exh. Duration @ .050 in. (Deg)236
Int. Duration Advertised (Deg)276
Exh. Duration Advertised (Deg)288
Engine Make/SizeChevy Small Block (262-400)
Advertised Duration276 int./288 exh.
Advertised Exhaust Duration288
Advertised Intake Duration276
Basic Operating RPM Range2,000-6,000
Duration at 050 inch Lift224 int./236 exh.
Exhaust Duration at 050 inch Lift236
Exhaust Valve Lift with Factory Rocker Arm Ratio (0.52
Intake Duration at 050 inch Lift224
Valve Lift with Factory Rocker Arm Ratio0.502 int./0.520 exh.
Lobe Separation (Deg)113

1:6 Roller Rockers (Comp cam)

pushrods

Chevy 262-400ci w/Retro-Fit Hydraulic Roller Cam
5/16'' Diameter
7.266'' Length (Stock Length)
End Type: H-H
16/pkg.




HEADS

225 Series Aluminum Cylinder Heads
Small Block Chevy
100% CNC Ported
225cc Intake Ports
64cc Combustion Chamber
2.08'' Intake / 1.60'' Exhaust Valves
3/8'' Rocker Arm Studs
.600" Max Lift
Steel Retainers

Head Gasket Fel-Pro

Steel Wire Ring Head Gasket
Small Block Chevy
Bore 4.080''
Compressed Thickness .039''
Compressed Volume 8.2cc


COMP Cams Hi-Tech Roller Race Timing Set part #3136
 

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Discussion Starter #3
Bogie i tried the link you provided but it doesnt help since i have no idea what swept volume, piston volume ect is..
 

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What I think you're saying is that you know you can run pump gas at 5 psi if the static compression ratio of the motor is 9.0:1 or less.

In order to figure static compression ratio, you need 6 values.....
1. Bore size carried out to 3 places.
2. Stroke length carried out to 3 places.
3. Piston deck height (crown of the piston in relation to the block deck with
the piston at top dead center) The blueprint figure of a Gen I small block Chevy 350 is 0.025", but manufacturing tolerances will vary this figure. Plus, if you are not the original owner of the motor straight from the factory, you have no idea who took a cut on the block decks and how much cut they took. In this case, you must measure the block deck height to find out if it is stock at 9.025"
4. Combustion chamber volume in cc's.
5. Head gasket volume in cc's.
6. Piston crown (+) or (-) cc's (eyebrows, dish or dome)

Here's the chart from Blower Drive Service that shows allowable static compression ratio limits for use with pump gas. These results can be altered somewhat with the use of water/alcohol injection and/or reduction of ignition timing.
Technical Charts

If I had to take a wild guess at your static compression ratio, based on a piston with 1.625" compression height and 2 valve eyebrows, with a piston compression height of 0.025", I would say that the motor has a static compression ratio of 9.49:1.

I would never build such a motor for use with artificial aspiration. First off, I would want the static compression to be 8.0:1 or just a few tenths more and I would want a zero piston deck, so that the head gasket thickness described the piston crown to head measurement. Such an arrangement (with a 0.035" to 0.045" head gasket thickness clearance) will offer maximum detonation resistance.

.
 

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Discussion Starter #6
R1 thank you for that info im not trying to race the truck just want it for more cruising and show but based off your numbers i think ill benefit more with 72cc heads to lower the compression as you mentioned
 

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With no other changes, 72cc heads would put the static compression ratio at 8.75:1.

If piston deck height is stock at 0.025" and head gasket thickness is 0.039", then the squish/quench will be 0.064", which won't contribute much to minimizing detonation. Luckily, the blower rotors will flail the incoming air/fuel into a finely homogenized mixture, so that detonation shouldn't be a huge problem.
 

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Discussion Starter #8
Thanks for your help on this, i think going 72cc, decent head gasket and 4 pounds of boost and having the timing on safe side should help avoid denotation 91 octane fuel
 

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Thanks for your help on this, i think going 72cc, decent head gasket and 4 pounds of boost and having the timing on safe side should help avoid denotation 91 octane fuel
Should be good until you get a bad load of fuel. Buy it at the busiest station in town, no matter the price.
 

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Bad slug of fuel or reving it high and the fuel pump not delivering. That is if you dont loose a head gasket. I would lower the boost levels down to around 2-3 psi for driving around mostly for show. Then turn it up on track day with some 100/104 in the tank.
 

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Discussion Starter #12
It wont make it to any track will only be for car shows, should i maybe get some smaller intake ports like 185 or 200 instead of the 225?
 

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Discussion Starter #14
Awesome sounds good, Vortech tech support recommend the 225.. will post pictures once i get the truck back together.
 

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Discussion Starter #15
I started looking into menthol/ water injection as you recommend and order new heads with 72cc when looking at the snow Performance kits what kit would you recommend? The holley sniper does have a Nos progressive controler i can use to control meth/water injection or should i use a separate controler?
 

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I started looking into menthol/ water injection as you recommend and order new heads with 72cc when looking at the snow Performance kits what kit would you recommend? The holley sniper does have a Nos progressive controler i can use to control meth/water injection or should i use a separate controler?
I would see no use in using more than this initial unit......
https://www.snowperformance.net/Stage-1-Boost-Cooler-Water-Methanol-Injection-Kit-p/sno-201.htm
I would not be swayed to use steel braided over nylon line. If the nylon works, it works.
 
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