When I built my 455, i had no idea what years were better than the others and i cam accross a 1975 455. Well i picked it up, tore it apart, and brought it to the machine shop, we installed stage 1 valves in it and some bowl blending. No port work done. I know now that these heads wern't the best choice. Is there anything i can do to these heads to make them better or is it a lost cause. Car runs super strong. The motor is really strong and pulls all the way up to about 5800. JE 10.1 -1 pistons, stock crank and rods. I run a crower cam 230/ 244. .507/.526 lifts. Elderbrock intake, holley 750 carb, headers and all the goods. with this setup, would i be gaining much putting like a 72 head on it or will it be just a little differance. This is strictly a street car not a race car, should i leave it alone? i am kinda torn both ways. just an estimate, will this setup run 12's with 3.55 gear, and 28" slicks?:3gears:
Your heads were very low compression heads. Having them shaved would help compression some, but to get the compression way up, you'd need to zero deck the block, and shave the heads to the point that you'd also need to take some off the intake to get it all to align properly. I would say leave it alone if it's running good and you're happy with it. I put your engine on DeskTop Dyno and then in Desktop Dragstrip. Assuming 8.5 to 1 true compression ratio, your combo should be good for 12.7's at about 105 mph. Good luck. Phil
thanks alot yeah i thought about taking the heads off am bringing them to work and milling some off the face. The only problem is i don't know how much to take off? the other question is i thought with a 10.1-1 piston it would bring the compression up around 9.-1, not sure though? acording to the destop dyno what kind of hp and torque will it make thanks
381 HP at 5000 rpm and 435 lb.ft. of torque at 4000 rpm. Bumping the compression to 9.0 to 1 bumps numbers up to 392 HP/448 torque.
Assuming the cam is properly degreed and the timing is correct it should go well into the 12's...... I've gone 12.20's with less cam,and Iron Intake,And a Q-jet.
Sounds like the compression is assumed. You know what that gets you! Before you do anything with the heads... you need to 1) cc the heads -- find a graduated cyringe and a piece of clear plastic with a hole off to the side of it. grease the perimeter of it and and stick it to the clean face of your head insert colored water or any other colored substance with low viccosity until you have filled the combustion chamber. record that cc. I don't give you a link to find out how many cc's are in your heads. this is because you have already installed the stg 1 valves the size and unknown installed hieght may have change that number from stock. These referances are of no use to you. 2) Bring a piston to tdc (as close as possible -- this is critical) do the same thing to that cylinder as you did to the head record those cc's. if the motor is in the car this can probably still be done just put the hole in your plastic at the top. grease the plastic well. 3) use an online compression calculator (they are every where)plug in those numbers with your stroke, bore, and head gasket thickness. With those 10:1 pistons and valves you may have more compression than you think. this brings other questions to my head: 1) what head gasket are your running. the stock is less than half the thickness of the felpros(.038" i think). this will have an effect on your compression 2) did the machine shop deshroud the larger stg 1 valves or did they just cut them in. stg 1 valves don't do much unless this is done. I believe there is also a cut in the throat for those. deshrouding will bring the compression down althou with taht head they may not need it(huge chambers) 3) what bore do you have? boring the block will raise compression. I know that seems like alot of trouble but will be the only way to know what you re dealing with. I don't know what your pistons are like.. but if you go to earlier heads you need to check valve clearance too. You also need a different head gasktet. I believe there was a change in the coolant ports or somthing to that effect with the 75-6 stuff. Hope this puts things in perspective. :TU: :TU:
ok let me think the motor is 1975. about .01 was milled off deck. we bored and honed it .038 over using a torque plate. we used stock crank and rods with stock stroke(3.900) pistons are JE 10.-1 We used fel-pro head gaskets. Heads were shaved for cleanup. Heads were installed with stage 1 valves, and we did deshroud them. I always thought that was nessary. i know as stock the heads were around 78 cc now i have no idea. hope this will help
probably will have to go with the above formentioned techniques unless somebody knows the relieve cc's fo those pistons and how far they sit in the hole. o No:
Bryan, I have the same heads as you. What did you do to deshroud them. I am also installing stg1 valves. I did not think there was a need for deshrouding because of the open chamber design. The valves are a good 4-5mm from the edge of the valve to the edge of the chamber. What are your thoughts on this? Royden
Don,t use desk top dyno as the numbers you will get the program is a what if it will lead you in the wrong direction in cam timing. mike
I 'm finding the best way is a machinist with a serdi machine. My sources are telling to take the cut to the cylinder wall.
computer programs The two programs i use are Dynomation this is a wave action simulator and the other is Engine Expert it works on ve and some other stuff.These two programs are what nascar and pro stock teams use they work togeather.They are $60.00 dollars each. There is a nother program by Recardo that is $60,000 dollars none of these programs can predict acuale HP they can only model the engine and get you close.You have to watch the garbage in and garbage out Desk top Dyno is what the call an empty and filling model. There is to much in the way of pulses in the intake and exhuast tracksto predict HP but they are coming close.Chyrsler use ,s spark plugs made by champion that are $2500.00 a pice to look at cylinder presures. i don,t type good engouh or spell good to keep going on but i study and read a hell off alot. mike
What kind or real-world comparison have you done with Dynomation? I have had it for quite some time, but have no real-world experieince to back up the cam timing recommendations it has made. Sometimes they are somewhat off the wall compared to conventional wisdom (very wide LCA, for example). I can spell OK, but my typing makes it look like I can't!
The wave action pressure graphs that are in dynomation will help you determine your cam timing it is no good for ex. timing so don,t even try some of your best engineers can,t figuer out the ex. waves.Use you your conventinal wisdom on the ex.Now if you have engine expert you take what you have gotten from dynomation and apply it to engine expert after you get about 5 pages of numbers out and your brain is ready to melt you can figuer out you beginning runner area and your minimal cross sectional areas for the intake and ex.As for real world numbers i talked to the guy who wrote the program and he told me if you can get the peek numbers wright in the program for HP and TQ that match your combo on the dyno your are 80% of the way there.This subject is quite complexed to hash out on the bulletin board. mike
