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Discussion Starter #1
I’m curious as to what gains can be seen when going from 11.5 to 13.5:1 compression? What are your personal experiences? Just curious what other have experienced with similar setups.

408 SBC
Vic Jr Intake
750 CFM BG Mighty Demon (race gas)
AFR 220 heads (2.10 I/1.6 E valves)
Solid Roller cam, .682/.687 lift, 261/267 dur. w/1.6 rocker arm 110 LSA
3300 lb Camaro

Plan is to purchase domed piston and mill head to 62 cc chamber to achieve the compression increase. I’m guessing the carb will need to be upgraded as well but that is what I’m running at the moment prior to change.

Thanks
Brian
 

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It will help you torque more than you HP which may be just what you need. What is your gear/converter/tire combo? That engine combo could use more intake & carb unless you are gear/converter/tire limited which I am assuming is the case by your 60'.
 

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Discussion Starter #3
At the moment i'm using a th400, 8" converter (~4300 rpm), 4.56 gear, 28x9" slick.
 

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Not a great match with that converter & cam. A better intake & carb would make more power but would likely hurt you even more where you are already hurting, so you would probably run slower. Upping the compression will give you more torque down low but I think your money would be better spent on a converter now, then later you could step up the induction. I know you are somewhat tire/suspension limited, but you are still probably roughly 1500 rpm too tight on converter. The compression change will probably bring your flash speed up a little, but we're talking maybe 150 rpm not 1500. The last 406 I did was less lift than you & 253*/258* @ .050" on a 111 LSA/106.5 ICL (same heads/different induction), & it made peak torque at 5400 rpm & peak hp at 6500, so your torque peak is probably at least 250 rpm higher than that.
 

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Discussion Starter #5
I'm switching to a PG the same time I wanted to do the compression increase. The converter is from ProTorque and a re-stall on the list as well. I mis-spoke earlier, I have a Super Vic not the vic jr. I was mainly just curious about flywheel numbers and the affects the increased compression would have.

What Carb did you run on your 406?

Thanks for commenting.

BP
 

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I read in one of the Vizard books a while back that it's about a 3% HP increase with each point of compression with diminishing returns the higher up the compression you go.
 

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Yes i read that to and the power increase from 11:1 to 13:1 would be less than from 9:1 to 11:1. Something to consider with high dome is the combustion flame in the chamber has trouble getting over the dome. Enough trouble to take away the power the c/r increase gives. But longer rods help here and the longer rods make more dwell time at TDC for the combustion flame to deal with the piston dome.

Take it or leave it thats all i can say.
 

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I'm switching to a PG the same time I wanted to do the compression increase. The converter is from ProTorque and a re-stall on the list as well. I mis-spoke earlier, I have a Super Vic not the vic jr. I was mainly just curious about flywheel numbers and the affects the increased compression would have.

What Carb did you run on your 406?

Thanks for commenting.

BP
It was a carb the dyno facility had on the shelf that they said had been a great carb on a lot of combos, an old modified 780 nascar carb. I feel like we might have made more power with a 950 carb they had but the build exceeded our expectations anyway & was built for EFI, so the carb was just for the dyno session. When you get your compression & a looser converter you might want to try more carb but right now I don't think you would see much gain if any.
 

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You won't have hardly any dome in that scanario just going to 13-1.depends how it lays out to comb chamber.you may be pushing cyl pressure up into area that may not be beneficial to your combo.two point change in comp rarely likes same cam unless it was wrong to begin with.gona depend how it effects your ptv area too if much gain is seen.quite a bit to engine design to get all out of what is available. Good luck .if you get the right area together you should be pleased.if I have choice I like to angle mill head and stand port up and rework all of that to its potential.
 

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How did your car run at the track? Where were your shift points and where did the rpm drop too on the shift? :)
 

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Discussion Starter #11
Car runs 7.0x pretty consistently. I shift at 6000. Not sure what the tach drops to on the shift. Will have to check the next time out.
 

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Discussion Starter #13
steel town, did you have to modify anything to get that tire under there? the 9" tire rubbed so I had to adjust it with a hammer.
 

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The seat belt humps in the wheel well needed a slight massage but nothing else. The quarters and wheel wells were stock and uncut. I ran an 8" draglights with 4.5 Back space. I've ran 28x12.5 ET streets and 28x10.5 slicks they will fit without cutting and you won't need your car all jacked up.
Same thing I did when I had my 73 camaro, you can definitely get more than a 9" tire on that car.
 
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