Not only was my compression ratio measured,,,,it was planned.

My cam was obtained first(Comp 264s....free). I built the head with larger valves (1.72/1.50)and changed the shape of the chambers(which made them larger and consistent in volume). When I sent the block out to be done I already knew my chamber volume. We dummy installed the pistons(60 over), measured how far the pistons were in the hole (compression height) and milled the block to get the CR I thought would go with the cam and 87 fuel. (turns out I did OK.....but then my machine shop and some of the sages here were a big help).


not true.....if you ran a stock cam and 10.5 you might have trouble anyway.... regardless of running 93.

Another issue is during new engine break in. I have seen new motors be prone to running hot and detonation. Being conservative in the first place reduces the potential for damage during breakin or times when good fuel is not available.

To be frank I would not build with 93 in mind....there are a lot of places you cant get 93. Build for 91 and use 93 if you have to.

How much HP you get is about combination,,,,,not CR.

I wish you were closer,,,,Id take you for a ride in the Valaint with its conservative build ......you would be surprised at the performance,,,,,and the cost......and the drivability. I can idle at 600rpm in 2nd gear....floor it and have it pull away smoothly till it gets on the cam.....

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Yeah....Im the one who destroyed this rare, vintage automobile.....

How did you decide what you wanted your CR to be?
Here in Florida 93 is everywhere.

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

You know the talk can you walk the walk. Ron Parker











Bagels Juiced Im Bamboozled
The Slanted Family

The "2 HP" figure was nothing but hyperbole, exageration to make a point. The point is that you can tweak and tune for that last little bit but it is so small as to be meaningless in the big picture. It's all about balance and synergy - chosing parts and setting things up so that they all work together in the best possible way. These guys are pretty smart, lisen to them. If you do that and decide you want to try something different then go for it but at least you will have heard from some of the best. If everyone did everything the same way, well Hell, we'd all be driveing Chevys with small block motors so do what you want to do but be smart about it and listen to those who have walked the road before you.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

My motor has a compression ratio of 10.9-1 as it is built now. It will run all day long on 87 octane, and I race it on 91-93. I spray it on 100+, but if I run all motor on anything more than 93 it will slow down in the quarter. I have run 12 teens spraying on 91 too.

I run a cam with lots of duration, and have timing limited to 30* total max on motor, and cut it to 25* on the hose. It starts out with almost 20*. I have the slots welded in the distributor to accomplish what I want. Slants by nature do not want a whole lot of timing.

Most people who run 95-110 octane in their Slants have no clue that it is slowing them down and costing money they do not need to spend. Leave the race gas to the race cars.

Yeah, Putzie was using an additive from Price Fuels. Picked up 3 tenths, but collapsed the tops in all 6 pistons. Haven't heard from him in a while either. Hope he is doing well.

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Official Cookie and Mater Tormentor.

Humm. Some say 93 octane will support 10.9:1, some say no. Is there anyone here that thinks 10.4:1 is to high for 92-93 octane?

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

Come on Brennen, this has been answered. It depends on others factors, also. With a stock cam, yes. With a "big" cam, maybe, depending on the other factors, already mentioned.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Keep asking the question till you get the answer you want. It may take a while though.....

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Yeah....Im the one who destroyed this rare, vintage automobile.....

If you ask a dozen more times, maybe someone'll come along to say you can run 11.645:1 compression on 87 octane gasoline as long as you tint the windows illegally dark.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Why do you keep trying to push the limits of pump gas on something that you seem to want to drive more on the street than anything else? The .0000000000000000000000001 improvement you'll see isn't worth the headache you are causing yourself. Just build the car for 91 octane or whatever is common in your area and stop trying to get the answer you want when you and everyone else knows its a shot in the dark.

Brennan, I asked the same question some time ago and got the same answers.

just as surly in some cases too.

exact answers just can't be had without knowing every little detail about your combo. even then your just going to get a "best guess".......and a lot of people that don't agree with anything your doing anyway. remember, to some people here, "headers are overkill for the street".

with my set up I am running 10.4 comp and probably 93.....thats according to the guy who helped me build it so it is possible (with big cam....4 barrel.....etc...).

I'll let you know when I get the money together for headers and a dyno run, probably won't be possible for a couple months though- too much house stuff to do.

I love the "just build it for 91 octane." OK - what CR will that support? I'll keep asking until I get an answer. I have not gotten an answer. Who here doesn't know my combination. At least 10 of you have been following my build, But in case you have forgot -
It's a 258 cu stroker with oversized valves, lots of head work, bore 3.591, 470 cfm 4-barrel, Dutra Duals, and a .518 lift 240 duration cam. Am I forgeting any needed info for a best guess?
Read this post again and you'll find that the question has not been answered. If you don't have enough info tell me what I need to know and where to find the answers.

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

You've gotten a true and correct answer from a lot of different people. You just haven't gotten the answer you want.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

With that cam, I would run 10:1 comp for 91 octane. You can run higher, but with a decent advance curve 10:1 should be safe.

Lou

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Home of Slant6-powered fun machines since 1988

I have finally gone two answers that are the same.
Thanks for the help.

PS I am tinting if two days. Dan maybe you should visit Orlando.

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir