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Old 11-22-2007, 12:02 PM
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Compression on street tunnel ram

Hi,can anyone tell me the highest compression for 102 octane fuel. Could 12.5 with a big cam do it or not?
The edelbrock street tunnel ram,does it need a high compression?

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Old 11-22-2007, 02:05 PM
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There is no magic formula to come up with an absolute compression ratio limit for a fuels rated octane.
The rated octane of a fuel is a broad number based on the average of two different lab tests on a specially build motor under two different lab test conditions. The octane rating is a average of the two tests.
Every fuel acts a little different. Every engine is a little different.

All engines will make more torque with a high(er) compression ratio.
If you want to build for the street keep the compression ratio within what will work with street pump gas.
A street tunnel ram will work very well with 9.5 to 10:1 compression and 92-94 octane pump gas.
Just don't get carried away with the camshaft duration. Pick a cam that makes good power from 3000 to 6500rpm.
Use a 3500+ stall converter for an automatic. Use a good bit of rear gear ratio.
4.10 or more is good. 2.73 is not going to cut it.
Keep the carb cfm size reasonable. 900-1000 combined cfm is plenty for a street small block.

Don't try to crutch fix a motor with a excessive compression ratio by overcamming it. That won't fix it, or make it run on a certain fuel.
You'll just end up with a motor that is a dog.

Last edited by F-BIRD'88; 11-22-2007 at 02:15 PM.
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Old 11-22-2007, 05:45 PM
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F-Bird is right. A huge cam with a lot of compression isn't really any fun just to run pump gas. I just went through the same crap with a small block 350 bored .030 and domes. I ran a huge cam and it was lazy until 4,000 rpm. I just stepped down from a camshaft that is 310/320 In/ex. duration advertised and 262/270 in./ex. @.050 To a comp cams 294s grind number 12-224-4 in hopes for more bottom end and streetability. There isn't a need of high compression for a tunnel ram because the create a lot of velocity going down the intake runners which helps the engine rev quickly.
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Old 11-22-2007, 09:03 PM
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A comp cams 294S is a real good cam to use with a street tunnel ram. Needs around 10:1 cr. Needs a 3500stall converter and some gear. I"d pass on the 12:1 compression idea. You'll get real tired of buying race gas for the street. Needs a modified distributor advance curve.
Add a pair of 450 to 500cfm carbs and it will perform very well and drive nice on the street. A tunnel ram will need a longer warm up period to get the some heat in the manifold plenum for good drivability but once warmed up will run and drive fine.
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Old 11-22-2007, 10:40 PM
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So the street ram don't need the compression the high rpm rams do.
You reckon 600cfm carbs would be a overkill. At just over 7000rpm
would it still be?
The car is a strip car and would not see road time,if it does ones a month.
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Old 11-22-2007, 11:21 PM
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The hi rpm prostock type tunnel ram has larger and shorter runners. Its tuned to get busy at 5000rpm and up. It wants a very long duration, high rpm camshaft which requires a high static compression ratio to make any cylinder pressure and torque.
A street TR is tuned much lower (longer/smaller runners).
The torque peak point and usable rpm range will be similar to what a Vic JR does. but the torque range is actually a little broader with the STR. It's a mid rpm manifold 3000 to 7000rpm is best. It will make more torque and power than a Vic JR.

You can use a pair of 600's as long as the minimum WOT rpm on launch or gear change is high enough to meter the fuel properly enough to get a decent AFR at that low rpm point. You need a minimum amount of venturii velocity to get the mains started flowing fuel. The higher the minimum rpm (stall speed) the better the motor will tolerate big carbs. I would use a minimum of a 3500 stall converter.
A 4000-4500 stall even better. A bud if mine runs two 750's on a chrysler 440 TR but runs a 5000+ stall. Vac sec/air door carbs will add some flexability.
Are these 600's Vac sec carbs..or D pumpers?

Last edited by F-BIRD'88; 11-22-2007 at 11:31 PM.
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Old 11-23-2007, 05:55 AM
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On the street ram ,if a cam gets used that makes peak power above 7000rpm,
would it still make good power there? Edelbrock said its for under 7500rpm motors.
I would like to make 1.4-1.5hp per cubic inch.(383)
Can it be done with this setup? I need to choose the rotating assemblies compression and cam.
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Old 11-23-2007, 06:37 AM
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Quote:
Originally Posted by 383
On the street ram ,if a cam gets used that makes peak power above 7000rpm,
would it still make good power there? Edelbrock said its for under 7500rpm motors.
I would like to make 1.4-1.5hp per cubic inch.(383)
Can it be done with this setup? I need to choose the rotating assemblies compression and cam.
It appears to me you are building an engine from the manifold down. That is kind of backwards to the way that I think it should be done. Depending on those components that you have yet to choose, it shouldn't be hard to get the 1.5hp per cube....with just a 4 barrel.
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Old 11-23-2007, 07:41 PM
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Quote:
Originally Posted by 383
Hi,can anyone tell me the highest compression for 102 octane fuel. Could 12.5 with a big cam do it or not?
The edelbrock street tunnel ram,does it need a high compression?
The isky Z-60 grind cam is old school but it works great with a tunnel ram and 10.5 compression. I used it in a .060 over 327 with 4-speed and a 4:56 gear.

Here's the cam specs. High performance. Street/strip. Lopey idle. 3200 Stall. 4:56-4:88 axle ratio. Up to 800 CFM Carb. 10.5-11:1 compr. RPM-Range (3500-7500) Valve Lift (.548 .548) Valve Lash hot (.016 .016) ADV Duration (292 292) .050 Duration (259 259) LC 108...The motor flat out beat the ground (sounded to nice) and it wasn't to bad driveability wise either. Probably wouldn't be as much fun with an automatic.
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Old 11-23-2007, 07:58 PM
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If you are building a track ride you need a real bottom end to handle 7500 rpm all the time. Get loose clearances on the mains and rods, Tight clearances on the pistons, lots of camshaft and heads to match. When all said and done you will have a radical 383 12:1 compression or higher and 2gs in the heads and valvetrain just to make the motor last for the long run. 1.5 hp per c.i. is great but its gonna take more than just an intake.
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Old 11-24-2007, 02:23 PM
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Quote:
Originally Posted by 383
On the street ram ,if a cam gets used that makes peak power above 7000rpm,
would it still make good power there? Edelbrock said its for under 7500rpm motors.
I would like to make 1.4-1.5hp per cubic inch.(383)
Can it be done with this setup? I need to choose the rotating assemblies compression and cam.
Yes the STR will have a very strong top end and works beyond 7000rpm. It will not hold you back from making the power you want to make.
The cylinder heads/ headers and camshaft are going to be the determining factors.
You'll need a very good cylinder head to make this amount of power.
AFR195-210 ,Brodix T-1, IK200 ,Edelbrock Vic JR etc. 1-3/4" headers. 248++ duration cam 4000+ stall, big gear. If pump gas (94) use 10.5:1. max or less. If strictly race gas/track motor use as much cr as you can 13:1+ and run 110+octane racing fuel.
If you have 102 octane fuel readily available to you and will be running it all the time, I would build a 11.5-11.7:1 motor to use that fuel.
Build the motor to have proper .040" quench clearance.

Last edited by F-BIRD'88; 11-24-2007 at 02:33 PM.
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Old 11-25-2007, 12:27 AM
383 383 is offline
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Thanks for all your input on my questions.
I think 11.5 is what i will use.
Thanks for a great forum.
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