Thread: How much is to much?

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I'm building a 350 for my Camaro. Right now the block is bored .060 over. I am running 76cc cast iron heads with 2.02" intake valves. I'm trying to figure out what compression to run. The pistons that I have picked out are going to raise the compression to 10.88:1 ratio. I think that is a little much for 87 octane. I was wondering what compression I should go with. I could run higher octane fuels but they cost more per gallon. I don't want to break the bank everytime I go on a drive. I also want to have good power. Maybe I could meet in the middle, go with a higher octane fuel and a slightly lower compression ratio. I don't know what the octane to compression ratio is. Anyones input would be greatly appreciated.

10:1, you should use a 92 octane minimum, you could get away with it maby if you had aluminum heads. with 9.5:1 you could get away with 89. why get a lower compression and higher octane, you use higher octane for a higher compression. higher octanes are less prone to pre ignition than with the lower octane fuels that's why there used. when you build an engine/ car, always figure that speed costs money, how fast do you want to go?

I would never use 87 in any type of hod rod its just pointless,,,,use the good stuff 93+,,87 can and will cause spark knock,valves to rattle,,,etc... now a computer controlled vehilcle like all these new cars and truck its ok ,but the old stuff and built motors usually over 9 to 1 compression "need" higher octane,,,if you want power keep the compression up but you have to run good gas...try aviation gas its 100 octane and here in Tennessee its just $3.20 a gal also make sure you use good spark plugs,,you cant go wrong with Iridium plugs

......well I don't believe there is a compression ratio to octane 'chart'. There are way to many 'variables'. Plus two engines built exactly the same could react differently to the same octane. Different shape combustion chambers, quelch area, alum/steel all affect this.If it were my motor I would not go with a 10.88 to I compression ratio with iron heads. Why take the chance??? Now here again there are no exact figures but I've read that you have a 3% HP loss for every point that your compression ratio is lower. If your motor were to put out 300 HP with 10:88 to 1 compression then it put out 292 HP with a 9:88 to 1. Your not going to feel that difference in a seat of the pants feel. Take a look at the GM crate motors. The iron headed 350's don't go over 9.40 to 1. Even the aluminum headed ones don't go over 10 to 1 {I just pulled these examples out of a the
www.SDPC2000.com catalog}...... bill

So your saying that I should just run the higher compression and put in 92+ octane? My uncle says that it can run on 87 just fine, but I doubt that. I'm also trying to figure out a transmission and rear end setup. Right now it has a 4.11 and I think that is a little low. I was looking at maybe a 3.73. I still don't know if that is low enough or if I should just consider an overdrive transmission. It has a 350 right now, which is a pretty tough trans. I want it to be a very driveable car. To drive down the highway at 70 and the engine be running at a reasonable speed. I was looking at some 700R4's but I don't know if they are tough enough to withstand the engine. We are planning on getting 500hp out of it, so it needs to be tough.

....No, what I was saying is; I would LOWER the compression ratio AND plan on using the 92 octane gas. The 400 small block that I had ran aluminum heads, had 9:75 to 1 compression AND I used 91 octane {that's the Max octane in Calif}{.... Remember the new cars that have compression ratios in the 10 to 1 & 11 to 1 range have; aluminum heads, fuel injection, computer controls to retard timing {knock sensors}, combustion chambers that are designed for low octane/higher compression......

disregard what your uncle tells you, your engine will run on 87 with the 10.88:1, but you will find your cleaning pistion material off the sparkplugs, and eventully the need for new pistons when a hole is burnt through them. go to 9.5:1 comp ratio, and instead of using the 76cc heads, get some smaller 64cc heads, Dart Iron Eagles or somthing like that, still 2.02/ 1.60 valves. If you want a very drivable car, look at 400-450 HP, 500 hp will be very touchy, and require a lot of extra's to make the car hook. and for reinforcement

I found a set of pistons that would bring it down to 9.79:1 or should I even go lower yet? Is 9:1 the ideal number that I am looking for? I could also go with a set of aluminium heads. Thanks for keepin me in line. I'm new to this and just trying to get a feel for these things.

....Example; I know a guy who built the motor in his Ford p/u. It was a while back so I don't remember the exact details as in engine size, compression ratio, etc, etc... BUT what I do remember is he built the motor with the compression ratio to the high side of what was recommended, it pinged AND he used to have to dump a can of Octane Upper in every time he filled up. Trust me, it became a real pain in the a**, REAL QUICK..... WHY take the chance??? bill

Originally posted by dillspy
I found a set of pistons that would bring it down to 9.79:1 or should I even go lower yet? Is 9:1 the ideal number that I am looking for? I could also go with a set of aluminium heads. Thanks for keepin me in line. I'm new to this and just trying to get a feel for these things.

....Alright, now your listening ...... Yep, aluminum heads with 9:71 compression..... I know you'll be 'safe' there. And what Matt said about the 64cc heads. I believe they 'burn better'. But remember with the 64 cc heads you'll need different pistons than with the 76 cc heads...... Also listen to what Matt said r/e 500 HP. In ANY motor the HEADS are the MOST important part in the motor. Well, it's all important but without good heads you'll never make good power... And plan your ENTIRE motor out before you start buying parts..... bill

....Oh, for a street motor build it for Torque! and let the HP just follow......

9.5:1 would be the highest compression I would build to run pump gas. use a 10cc dish pistion and a set of 64cc chambers, you should net around 9.5:1.

Which brand should I go with for heads? I no jegs and brodix make good ones, but what would you recommend? And what Intake valve size. I heard that 202 intake is good but I dunno what i would benefit from.

...there is a compression ratio calculator at www.campbellenterprises.com ..... just put in the bore, stroke, deck height, head cc, etc and it gives it to you.......
Also there is a web site but I don't remember what it is that gives examples of different engines with the HP/TQ. Tells the parts to use, PROVEN combinations. Thats the 'key', build your motor to where you KNOW it'll put out what you want.. Oh, someone elso on the board will remember that web site r/e engine builds..... bill

Originally posted by dillspy
Which brand should I go with for heads? I no jegs and brodix make good ones, but what would you recommend? And what Intake valve size. I heard that 202 intake is good but I dunno what i would benefit from.

....on my 415 small block I used AFR {Air Flow Research} 195 cc, 2.05 intakes, 1.625 exhaust..... So I like AFR's but everyone has there favorites. Dart are good..... Make SURE that your heads match your cam/converter/compression ratio, etc.....