here's the question: how do heads "make compression?"
here's the other question: with 11.9:1 pistons, will my car still run on pump gas? (93).
here's one more question: due to higher temps from the higher compression, should i use a 160 t-stat? i would like to stay with a 180, but not at the risk of detonation.

here's how these two questions relate: joe (the guy building my 355 LT1) says that my final compression for the motor will be higher than what is stated for the pistons (11.9:1), because "the heads make compression too." i didnt argue, because, i didnt know how to argue with that...so i'm asking you guys how heads can make compression?? i havent gotten the heads flowed, but they're ported/polished stockers (so, assume average flow #'s). if they DO make compression, how much more will the compression be?

with 11.9:1 pistons, CC306 cam, ported/polished heads, is it reasonable to assume that it'll run on pump gas without hella-tuning it?

any and all help is greatly appreciated,

shokor

 

O.k.
Ask him these questions then come back:

1. What is the volume of the chambers (in cc's)
2. What gasket are you using?
3. 4.030" bore right?
4. What are the pistons? and how much dome volume do they have?


That's what we need to know to give you an acurate figure on the compression.

11.9:1 is high for street gas. You might want to change your pistons to a flat top design and closer to 11:1

Bret

 

If you search this forum you'll find quite a bit of information on static compression, dynamic compression and the calculation of these.
I know for a fact I've posted the complete calculations probably 10 times. Why just give an answer? This is an advanced forum and to me that means.... if a guy comes in here and isn't well versed, then he needs to do some research.
Your question is not particularly advanced, with about an hour of research/studying you'd have the concepts down no problem. Then you can amaze your friends with your knowledge. They'll think you a genius.
Then again, there are always spreadsheets/calculators... but it's always better to learn the math!

Teach a man to fish or give him one.... give him one and he always comes back for another.

Chuck Riddeck
Progressive Race Engine Development

 

Just curious, why do you say that? With a cam that size one would think he could get away with more compression than 11:1. For example the factory LT4 ran 10.8:1 on a much smaller cam than the 306.

Also after calculating the DCR on his combo I get 8.83:1 which sounds pretty high for a normal SBC but probably ok for an LT1 according to the info here.

Are there other factors in selecting a compression ratio that I've missed?

I'm not trying to call you out or anything, just trying to understand your reasoning.

Thanks!

 

well, chuck, you're absolutely right!!

i read a few of your previous articles, and also went to a tutoring website about dynamic compression...after reading and reading and reading, my brain hurt, but just wasnt much closer. one particular reason was because i didnt have the proper info for the calculations. after reading post after post, and article after article, i decided to ask for some help. i'm constantly learning to answer my own questions, but this one was one i didnt know how to answer.
as far as it's "advanced section" requirement, i dont know, you still havent answer the question about ideal coolant temp. you said you'd have to look into it before u could answer (u didnt say it to me, you just mentioned it another post, on the subject of t-stats/coolants.)
shokor

 

i read the thread you linked before i decided to post my question. IMHO, that thread's answer was "it depends," but from the jist of it, it basically said that if you have a bigger cam, and more timing, then it's ok to run more compression...well, that's what i thought it said. but i'm still trying to determine what the overall effect of low t-stats is. so far, ppl seem to believe that a 160 t-stat will help, but it's also damaging the motor...still, big debate on that.

thanks for the help, i'll come back tonight with more info,

shokor

 

thanks, bret! i'll ask, and then be back tonight.

 

Tell me, how does a 160 t-stat damage the engine?? NOT running one with most programs WILL hurt the engine.

 

well, ponyhntr, that's where the heated debate is. some ppl believe that by using a 160 t-stat, you're not letting the oil heat up enough, and also, you're not letting the parts expand to their full potential, to give a good seal.

others believe that running a 160 t-stat is good because it keeps parts from heating up too much, and therefore, decrease thermal ware.

so, it's not fully determined which is better...it pretty much goes to what you THINK is better.

shokor

 

I routinely see 210-220 deg on oil temps. I run a 160stat. I think the dissenters have more of a problem with coolant temps not being hot enough....than anything else.

Common acceptance seems to point towards 170deg coolant/220deg oil as the near ideal to make power.

 

If you check again, the man did answer the question. I don't think it's as black and white as everyone wants to make it out to be. I kinda think that applies to everything automotive though cause it seems that the more you learn, the more you see that one answer is not always the right answer for everyone.
Having spoken to Chuck (he's working a set of my heads right now) I can see more of where he's coming from. He builds endurance engines and does alot of R&D. What he's after is likely a little different than what me and you are after. I think he explained it well though and I hope he can elaborate a little more on the subject??

-Mindgame

 

This thread is deteriotating into a discussion of what belongs on Advanced Tech, and whether the answers to other questions are adequate. If it deteriorates any further, it will be locked.

Fred