70newport

So I am building a 383 for my Newport. The block was taken to a shop to be machined and them put a short block together for me so I just have to throw heads etc on. They bored it .030 over and did KB162 pistons and reworked my e street 84 cc heads and supposedly decked them .004. In the end before they started we had decided it should be built to 10.25 compression ratio.

Doing the calculations now of what they gave me back without looking at the reduction in head volume as I'm not sure exactly what it ends up at now, it looks like they built it to be 9.75..... I am going to talk to them either way but is it worth making them re do it? How much am I loosing with that difference?

Thanks,

Gary

Coronet 500

If you searched this you will find the percentage of increase per point of compression is very small. I would prefer the 9.75 for a street engine myself.

RacerHog

I think that is a safe C.R. for a heavy street car and today's fuel's
Run it on one of the build calculators and see what it comes up with?
I like the Wallace performance one.... but there are others to help you.

Hope there was not a miss under standing that you wanted the short block at 9.75 and then you add the heads and the compression ratio move up 1 more point... that would mean you are over what you wanted?
Better to check twice....

Was there something about the build you wanted that compression for?

70newport

Thanks Dan. I do realize that compression affects overall power very little but I'm curious as to why a large number of people told me to go 10.25 not 9.75... I guess even with my readings I don't quite get why 10.25 would be better or worse.

70newport

Thanks racerhog. I have run it through a couple calculators.

I'm just trying to make sure that I am not loosing something being at 9.75 because the shop I used decided to do what they felt like. $4000 is a lot of money for me to spend and want to get every pony I can for my money.

RacerHog

I see... Add the compression in will allow you to use a larger duration cam and bleed off some of the compression. so to say that there is no trade off, is not all the truth. But it can be very minimal if you get my point of it?
So... Sure... I might just go back and get the to refigure the build to get what you asked for....

Coronet 500

My only concern would be deck height and gasket to get correct piston to head clearance for some quench turbulence.

Iowan

If it's got iron heads I would prefer 9.5 myself on street motor with today's fuel.

70newport

So I went back to the shop and they aren't happy with me for double checking their work but are admitting that it is under 9:1 compression and are planning to swap out the KB162 for kb400 pistons and are planning to shave .020 off my heads to get it to 9.8.

Would you guys agree with what they are doing or are they "cutting corners" because they screwed up?

Also I was wondering how to calculate quench? I can't find a calculator for that. I feel like I'm over thinking it.

Coronet 500

Boy I'd be worried, I say that because my machinist works WITH his customers, as it should be.

To get upset that you did research or calculations then admitted they did F'd up would make me take it apart and check bearing clearances and correct cam bearing installation, which no one should have to do.

Some say I'm a perfectionist, I'm not, there is just right and wrong, which way do you want me to do this job? Right or Wrong.

Coronet 500

I did a quick calculation with zero deck, .040" gasket and (unmachined) 84cc head.

162 piston: +5 dome = 9.06 to 1

400 piston: -6 dome = 10.07 to 1

how far down in the hole is the piston and what gasket thickness.

Something is not adding up man.

70newport

Sorry guys. I realize I forgot an update for you guys.


When I used a straight edge and a feeler gauge with the 162 Pistons they were .024 below deck height, the gasket they sold me was a bore of 4.410 and a thickness off .044. With those numbers I get 8.54.

I had made a mistake with my 9.75 calculation. Please correct me if I'm wrong because I have little confidence in my calculations and NONE In theirs!

Coronet 500

Your calculation is correct.

Your previous question about quench is the finished distance between the flat of the piston and flat portion of the head. Space or gap of .025" in a race engine, .040" is a good average, any more than .060" there is no gain.

Compression height is the first thing to look at when designing an engine and choosing a piston. Many Chrysler engines have the piston "down in the hole" the C.H. is much smaller than aftermarket pistons which try and bring the piston close to the deck so you can cut the block a minimum amount to square the block and get zero deck if desired.

The C.H. of the KB pistons is 1.908" leaving .0265 for block clean up cut. So lets say you cut the block .025" leaving .015"+.025" gasket = .040" quench. you can manipulate the numbers like cut .0305" piston is .004" above deck with that .044" gasket = .040" quench. I hope you see what I'm getting at.

Anyone building this with a new piston .024" in the hole then say they will add a domed piston and cut your head .004" then another .020" to raise compression is an idiot and not a good engine builder.

70newport

Thank you so much for all of that Coronet 500!!! That makes perfect sense!

What would you suggest as a proper solution at this point?

Coronet 500

My answer is based on #1 hearing on forums the large amounts of money guys have spent trying to correct a bad engine build and #2 being a tradesman building and fixing things my whole adult life. This is not advise to you but what I would do.

Knowing that I would have to pay for work already done and I will likely lose money and would not want to get into a physical fight or get the police involved, I would:

1- Go there with 1 or 2 people and a truck.

2- Have a pocket full of money to settle the same day.

3- Ask for all of my stuff now with a report of work done, if they will provide one.

4- Load up, take my lumps and get the Farg out of there!

Myraman

I'm gonna chime in on compression ratio. The other guys have added their thought on the machine shop, which I agree. Anyway, I just finished a 512 stroker out of a 400 block. I was shooting for high 9's compression ratio. I came in at 9.7. Zero deck with cnc'd alum heads.

http://store.440source.com/Stealth-A...fo/200%2D1080/

At that CR, I couldn't be more happy. It runs on pump gas (93 octane) and it freaking screams! I'll need new tires soon! Sooner if the weather cooperates. For a street car, I think you'll be fine if you can get the CR into that 9.5 to 10.0 range. Any higher than 10, your getting close to not using pump gas.. That's my thought anyway..

Good luck with your build!

70newport

Myraman I'm hoping it ends up decent in the end. It's going back into the shop for new Pistons and machine work again. Shooting for 9.8:1 now. Running comp cams 23-223-4 cam with my e street heads etc. I'm hoping I end up needing new tires soon! 😀

Coronet 500

How does you machinist feel about cutting the block to get some quench rather than cutting your new heads for a second time?

70newport

I was actually curious iF that would be the "proper" way to go.

I am waiting for them to call me saying they have the new Pistons and then I'm going to ask what the odds are they just give me my deposit back so I can go to a shop I trust but I feel like that won't go over well.

If they won't do that ( I'm sure they won't) I'll ask about decking the block properly instead.