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Dynamic Compression Ratio Calculator

CGT80 said:
I would have to look up the build sheet. My 383 had 350 rods, but with this block, the builder may have used 400 rods. He used Scat 9000 series rods and crank. Cam is Comp 270h magnum 224/224 @50 470 lift. Don't know the other specs of hand. TRW hyper pistons stick out of the cylinders by 0.005"
Quench should be 30-35 thousandths from combustion chamber to piston top. This head guy and my friend that has used his parts, said his engines require less advance than most due to the efficiency of his work. I don't have any proof one way or the other on that statement. You could be right about running less compression and more advance-I haven't heard much about one vs. the other.

I might still be able to run more centrifugal timing if I slow the rate of advance and/or limit the vac advance more. I think most people run less than 16 degrees on their vac advance for modified engines. I think I remember MSD stating that the dizzy I have is set for 10 degrees from the factory (I have a different can than what msd used-mine is adjustable too).
Click to expand...

.030" quench?! Wow that is pushing it, your aren't trying to win the pro stock nationals or anything. My engine machinists actually moves it up to .045" on some larger engines because he says sometimes he gets contact with the head. Probably barely, but still, can't be good for the bearings. It seems like your engine builder is trying to build a record setting engine for a street truck, then uses a 30 year old single pattern cam design, a little odd. And with a piston .005 above the head, I get the same numbers as you, I did confirm your intake valve closing as well. 11:1 with a 9.1:1 dynamic is high compression for pump gas, especially with old combustion chambers, a small cam, and a carb. I would of never went that high. So unless your pistons are a dish and not a flat top, I would be using E85 or race gas or something with that thing.
 
The engine builder was ok with the quench that the head guy specified. Head guy said that often quench is too low and the mixture heats the entire combustion area rather than being forced towards the spark plug, which causes the gases to move to the opposite side of the chamber, which in turn keeps part of the head and piston cooler. He has studied these theories quite a bit and says it is different from what many builders will do.

He chose the single pattern cam due to the extensive amount of work done to the intake area of the heads. He reshaped the heads enough, that bumping up the intake valve size from 2.02 to 2.05 (if I recall correctly) was necessary to give him room to work.

I wouldn't be surprised if my data is off on the head size or some other area that would effect compression. The engine machinist is used to building high HP engines, but definitely wanted to not go over 10:1 on compression. He was looking at practicality for the street.

The head guy does do work for engines such as what is used in NASCAR or drag racing and goes for every little bit of power. His race engines are supposed to be 2hp per cubic inch carbed with no forced induction. I would guess on race gas.

My heads are the bigger chamber Edelbrock performer. Intake is edelbrock performer egr. They wouldn't have been the first choice for the head guy, but they were left over from my 383. They flowed horribly when he got them. The intake had half the runners at good performance level cfms and the other half were no better than a stock iron manifold.

I would have loved to have more details on the engine, but I just didn't have the time to gather all of it. My friend picked up the heads when they were done (he knew the head guy). I dealt with the engine builder. The head guy and engine builder spoke on the phone to come to an agreement on parts and dimensions used. This was the best route I had at the time and the performance is awesome but I know there are a million ways to skin a cat with some being a little better.

Race gas won't happen, unless I take the thing to a drag strip. I am a bit curious about E85 though. Would I have to change anything on the truck or engine to run E85? I think the head guy I used had actually built some engines for E85 before due to it's advantages for a race car. He didn't say a lot about it. He actually never shut up and was a pain to deal with, but my friend had 100% confidence in his abilities and used him for his engines. One of them was in my friends yellow and black 67 ? fastback mustang. It was a 428 FE engine 525hp and 11.8 quarter mile at around 120mph. It was on the cover of car craft magazine around 2000 in the "looks stock hauls ass article". That engine was put on an engine dyno after it was built. My friend said it had great numbers for the time. I guess they are pushing better numbers from newer builds.

I wonder if E85 would be economical or readily available anywhere near me. I use this truck for towing to Ocotillo or the Bishop/Mamoth area. I also use it as a daily driver but plan to use the K5 more often now. I can't afford to run hard to get or real expensive gas in it at 10 mpg.
 
You'd have to change your fuel system and your carb or injectors, whatever you are running for fuel delivery, to use E85. And your mileage will go down with E85, but it is cheaper to buy. Not sure if it's worth the hassle for you or not. It'll keep your valves cleaner! ha ha

Also, that performer intake is a huge bottleneck for that engine. I'd ditch that thing before the next fill up. Get the RPM version, you gain considerable torque/power and lose nothing basically.
 
With the RPM intake I would loose the EGR (IIRC). That would mean failing smog in California. The manifold I have has been ported and matches the flow of the better intakes like the RPM. I was limited in choices due to building a smog engine.

I have a feeling that E85 would not be worth while and I have not seen it for sale at local gas stations. I remember that being the catch for E85-cheaper but uses more fuel, can build more power, but not as readily available for a street engine-Might be great for a drag car that doesn't see DD status.

Thanks for all the insight though.
 
Its been awhile since I used this and its not working for me now. Anybody else having issues with it?
 
I clicked on the original link and it came up, but I had to put in my google password. I didn't try to put any numbers into the spreadsheet though.
 
It opened up in google. There is a file menu on the web page toward the top left. Choose "file" menu and then download. I was able to download it to my desktop and then open it in excel.
 
FYI, this may not be your problem, however, the "protect sheet" is turned on in the review menu, so people don't accidentally overwrite any equations. This will only allow you to change the cells that need to be changed to use it, so if you are trying to change the input cells, then something else is wrong. If that is your problem, you will get a pop up saying that the cell is protected.

However, there is not a password to "protect the protection", so if you want to turn it off you can simply just turn off the "protect sheet" (when it asks for a password just leave it blank) and it will allow you to modify your copy any way you like. I did this so people wouldn't accidentally modify the calculators, but if they really want to modify them they can.
 
I just fixed the link, it may not have been working for a couple weeks, sorry about that.
 
I recently updated the calculator to include a couple more items like max connecting rod angle, average piston speed, valve overlap, etc. I updated the link on the 1st post.

I also put an example 350 on the left side and an example 454 on the right side, both with flat top pistons and a small cam.
 
Hello, I recently updated this file to also include turbo sizing calculators as well as fuel pump and injector sizing. Just look at the different tabs on the bottom of the spreadsheet. Thank you.
 
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