compression ratio
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Re: compression ratio
I agree with the heads being too big for that. Do you have epoxy etc in your vic jr to make it match up? What does the port alignment on that look like? I wouldnt bother with the half point compression myself.
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Re: compression ratio
F-BIRD'88 wrote: ↑Tue May 22, 2018 2:03 am The SBC victor JR is not a vortec head style intake. Thats why it lacks torque.
Get a "vortec" intake that matches the vortec heads raised intake port.
Change to a RPM air gap dual plane vortec intake. It will make a lot more torque and match the power of the MIS matched vic JR because the port alignment is better. Play with the valve lash a bit.
Looser valve lash shortens the duration. enhances low end torque
Move the cam to a 99deg intake C/L and adjust move >>>retard as needed.
Combine these changes with the compression ratio bump.
For what you are doing he is right the intake is the big problem the air gap should be very close to the height of the VR jr and it will recover better for you ...
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Re: compression ratio
A common racing folklore. Absolutely not true. Fuel octane alone has not effect on power. Its purpose is to avoid engine destruction.
Two fuels with the same octane can perform quite differently while two fuels with different octanes can perform the same.
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Re: compression ratio
How much HP loss by running the air gap?
I know the Vic is just port matched, thats all.
I know the Vic is just port matched, thats all.
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Re: compression ratio
At peak maybe a few but going to be way better below the curve because torque will be better ... on short track you have little use of your peak number you need it to be more of a flat power curve so you can just drive and instead of fight to get up-to your peak..
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Re: compression ratio
If I get an air gap, does it make sense to run a 1" spacer? I gather from previous post that on the duals you want to get a 4 hole spacer, mill the center out on the short side but on the tall side keep the primary and secondary side separated, allowing transition to be easier on the short side so its not going straight at the plenum floor.
Re: compression ratio
You will not "give up" power.. You will gain overall useful power, especially as you come off the corners. Faster car acceleration.
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Re: compression ratio
Sure about that? Obviously not a 355" street motor here with a 255 degree cam and the DP manifold has a sweet spot below where this engine will likely torque peak. Not to mention nobody even asked about current gearing and rpm range the engine typically operates in.
IMO, the OP will be down on average power in the 5000-7000 rpm range using a dual over a single plane. So unless the gearing and track length pulls the engine down much below about 4,500 rpm I think a dual plane is a mistake that no amount or type of spacer will ever be able to fix.
Re: compression ratio
How much ignition timing? These heads are "fast burn" and do not need or want as much advance as is commonly used with other Chevy heads.
Re: compression ratio
Use a the rpm dual plane, non air gap, for use with a spread bore carb, mill the divider down to match the air gap, adapter to the holley, 1" open spacer, 1" 4 hole spacer, advance the cam to 106. Should have at least 20ftlbs in the middle and match or make more on the top.
BORN RIGHT THE FIRST TIME
Re: compression ratio
Not to de-rail this thread... I think this is on-topic....
In your experience, what total advance generally works best with Vortec / fast burn style chambers? I'm running mine at 33 total, and I guess I've never really tried using less total advance. Maybe I should?
Re: compression ratio
I have found significant power increase with less than 30 degrees, in fact mid 20's at the torque peak. If you can get on a chassis dyno you may find your engine wants the timing to advance from the torque peak to the power peak. Recent experience is a dirt oval track 355, 13.8/1 comp ratio, 100LL w/MMT, GM marine DP spread bore intake that fits the large port head, Qjet carb, GM 140 cam, likes 24 at 4000 with the advance slope to 29 at 7000, the advance will go to 30 at 8000. With this advance setup the torque is flat like a billiard table and the power is still climbing at 7000 but it doesn't need to turn more than that to win. More than 24 at 4000 hurts the torque. All the stuff interwevbzsez don't work, ports are too big, dual plane has no power at high RPM, Qjet is junk, HEI has weak spark above 4000, 140 cam has too much duration and not enough lift, etc. etc. ….... ha... joke's on the intervbez and the rest of the field. They hate the Qjet. When they come over to see what yards them 1-1/2 lengths from the flag to corner entry they just walk off mumbling and shaking their heads. LOL Answer truthfully what cam is in it and get accused of lying. The internet has people's heads so screwed up it is almost impossible to have an intelligent conversation at the race track nowadays. Did you know race engines are supposed to idle all slobbery and stink up the shop and foul plugs if you drive them too much in the pits?
Re: compression ratio
Tuner
I could not agree more!
In many racing situations the advise and comments always seem to be what a racer and how his engine should be changed to really work and not to pay any attention to things that don't go along with convention but ACTUALLY WORK !!
It must have been built by aliens !! HA!
I could not agree more!
In many racing situations the advise and comments always seem to be what a racer and how his engine should be changed to really work and not to pay any attention to things that don't go along with convention but ACTUALLY WORK !!
It must have been built by aliens !! HA!
The Older I Get, The Dumber I Get
Re: compression ratio
So your comparing a 13.8 355 to the OPs 9.4 355 with close to the same in, duration @.05Tuner wrote: ↑Tue May 22, 2018 5:14 pm I have found significant power increase with less than 30 degrees, in fact mid 20's at the torque peak. If you can get on a chassis dyno you may find your engine wants the timing to advance from the torque peak to the power peak. Recent experience is a dirt oval track 355, 13.8/1 comp ratio, 100LL w/MMT, GM marine DP spread bore intake that fits the large port head, Qjet carb, GM 140 cam, likes 24 at 4000 with the advance slope to 29 at 7000, the advance will go to 30 at 8000. With this advance setup the torque is flat like a billiard table and the power is still climbing at 7000 but it doesn't need to turn more than that to win. More than 24 at 4000 hurts the torque. All the stuff interwevbzsez don't work, ports are too big, dual plane has no power at high RPM, Qjet is junk, HEI has weak spark above 4000, 140 cam has too much duration and not enough lift, etc. etc. ….... ha... joke's on the intervbez and the rest of the field. They hate the Qjet. When they come over to see what yards them 1-1/2 lengths from the flag to corner entry they just walk off mumbling and shaking their heads. LOL Answer truthfully what cam is in it and get accused of lying. The internet has people's heads so screwed up it is almost impossible to have an intelligent conversation at the race track nowadays. Did you know race engines are supposed to idle all slobbery and stink up the shop and foul plugs if you drive them too much in the pits?
Tom