ok i am planning on building a 598 for my 67 and i would like get about 7:1 dynamic out of the motor. now the question i have is running at 7 dynamic, is running high octane fuel going to crush my motor or should i just run pump gas? i know that running high octane fuel is "good" for performance, but where do you draw the line? i used to be a ford guy so high comp motors are easy to obtain and i have noticed with chevy bb its very common to run at about 9-10 static when you have flat tops. i plan on having a blower later in life so i dont want to run domes, but i also dont want to destroy the motor before i get to put the blower on. thanks so much!!

kev

 

You seem to be a little confused regarding compression and octane. Higher octane than needed does not cause engine damage, except perhaps to cause exhaust valve damage, as the fuel may still be burning when the exhaust valves open. Higher octane does not make more power unless you have the compression to utilize the extra octane. Higher octane fuel burns somewhat slower than lower octane stuff, and has less BTUs per unit of volume. However, it is less prone to detonate and allows more compression to be used, and possibly make more power.

Dynamic compression depends upon the relationship of static compression and intake valve closing, and makes a good theoretical talking point but is of little value when building an engine.

If you are going to run a blower on a big block, make sure the internals can take it and you will need to plan the compression ratio based on how much boost you intend to use.

 

ok i decided that i want to run high comp, like 13 static so i know that a high octane will be needed, however i did not realize that higher octane doesnt cause undo damage. the way i've had it explained to me was that if you run higher octane then you run into issues of too slow burn off resulting in major wreckage to your vavles, but that could have also been me reading to much into it. now i understand the basics of CR and know that to get the most out of the decreased burn rate you need more comp, so i've decided that when i'm ready to switch to a blower then ill get the new pistons and cam to support it. the other thing is whether i should run a large cam with domed pistons? i'm currently looking at dart pro 2s and a comp cams 321a-r12 cam with +33cc pistons. the lift is 806 intake and the closing point is at 70. i want to run 1.8 rockers to get lift up to 850 and get my CR at about 12.5. with the 124cc CCs and 33cc pistons i'm seeing 12.4 CR on the calculators. i'd like to get this motor started but i want to take the safe route and try to plan as much out before i start buying parts. thanks for the help and more input is wanted!!!

kev

 

What use are you going to put the engine to. The 13:1 compression is going to require racing fuel, not practical for street use, but OK for racing. That big cam is going to punish the valve train, so get the best possible parts.

 

ok i am going to be using this for racing so the race fuel is not a concern. i plan on running a modded tremec t56 from promotion powertrain with 373 in the rear with an eaton posi. but everyone has said to run an auto, i say no only because i will still take it out for sunday drives. as far as the vavletrain......already on it i'm planning on running a solid roller so lifters are from comp cams as well as pushrods. im going to run 1.8 rockers 7/16" stud mount from crane so i can get my 850 lift on intake and 800 on exhaust. the heads are 380cc intake with 144cc exhaust runners from dart they have 1.625 double springs. valves are 2.3 and 1.88. i think i have a pretty stout setup but i'm not 100% yet there are still a few things here and there that i cant make my mind up on. oh and yes i know that a cam that big will put the hurtin on valvetrain and i'm prepared to do the necessary adjustments every week to keep the car in tip top. but thats also why i'm building the car the way i am....for sheer mechanical enjoyment....i want to have to work on it all the time. that's what i like to do work on cars. but if you've got anything else for me pete, please tell me i'm always lookin to learn more and get advice from those more knowledgeable than myself, as i am still "wet behind the ears" at 23. thanks

kev

 

and i just did a little more research on the heads to find out they only run to 790 lift with the 1.625 springs. so i'm thinking of going with the bare head for these and getting some 1.68 triple springs from comp cams that will handle the 850 lift.

 

With that much lift, be careful to check the springs for coil bind before cranking the engine over, to avoid broken parts

 

hey thanks Pete i appreciate all the help!! i am constantly researching and learning as much as i can, as often as i can. i'm only 23 and have lots to learn. i have a pretty good knowledge of motors and the mechanics of cars so i like to learn more and more. if you have anything else to add please do!! also if anyone else has any pointers or ideas for this please write, i want the best for this motor!! all input is taken into consideration and researched, so let me know what you got!!!

Kev