thenewkidz28

Ok so I thought I was getting close to finishing my build (383 lt1) but have hit another bump.. a big one. I purchased a short block from a member on this board that was advertised with 16cc inverted dome pistons. however upon further inspection I found out they are 26cc pistons and its now thrown my whole build outa whack since, this will be a na motor for a year or 2 while I save for heads and a procharger. The cam is a hyd roller cc 282/292(adv), .579/.576, 110 lobe, 106 incl. Combined with modified stock Heads*EDIT*. Long story short my heads are at the machine shop being milled from 53.25cc to 47cc just to bring the dcr to only 8.3:1! Also I was told the valve seats have to be raised as well... Combine that with the resurface on the intake manifold and it equals me not happy. I know its my fault for not verifying the pistons when I purchased it and I'm not trying to start any drama here. That's between me and the seller. I just want this to run right. I've been working on this for almost 2 years and already got burned the first remanufactured block I purchased.


Ok.. so anybody want to chime in? Do you guys think I can make this setup work ok? its just going to be a street car for now so I'm ok with the compression. it should like pump gas right? Thanks everyone for reading this.

DrewHMS97SS

I think I am missing part of the plan, so set me straight if so.

If you have 2 engines, I would personally build the second engine for the SC and leave it on a stand until the project is complete. I would not swap in a low compression engine with a cam designed for a blower to run NA.

If you are an audio guy, it's like buying amazing speakers and running them on a stock radio with the intent to buy amplifiers later. The speakers are done a dis-justice because they are not designed to run on such low power, and will most likely not sound as good as the stock speakers.

For the engine in process, I am really confused about the numbers. If this is a 383, with a 26cc dish, and a 47cc chamber, the CR is rounding out to close to 11.5:1; how are you getting 8.3:1?

Can you clarify what is happening with each engine and what are the goal specs for the interim and final engines?

thenewkidz28

what how did you get two engines? no I have ONE forged 383 that was HAD a boost cam that I swapped out with a cam I was using in the previous short block that I wasn't happy with and is now SOLD..... I am still using the cam/ valvetrain setup. And im not sure how you figure your numbers but my STATIC compression will now be 10.6:1, and the DYNAMIC compression will be about 8.33:1 if you reread my post I abbreviated dynamic compression ratio with dcr.

DrewHMS97SS

I was thinking two engines because you had the car, and bought an engine. I'm on the same page now.

https://www.summitracing.com/newsand...ion-calculator

What are the specs you are entering (some of this is guess work on my side because I don't have details of your engine)?

What goals are you trying to hit in regard to CR? Dropping to 16cc on the piston pushes what I am seeing over 12:1, which is not ideal for boost.

thenewkidz28

again no. there wont be any boost for a good while, and when I do boost it, a different cam will go in, possibly the old one I took out. The specs I provided are for the cam to be used while the motor is naturally aspirated, until I can afford the mods to supercharge.. does that make sense?

I'm also using the pat Kelly compression calculator but heres the specs you need for the summit calc...
Bore: 4.0305
stroke: 3.75
CC: 47cc
Dome volume: 26cc*
Deck clearance: 0
Gasket: 0.039

DrewHMS97SS

10.65 with those numbers.

So what are your actual goals for the engine pre-boost? If the piston was actually as 16cc dish, your CR would be just over 12:1. That isn't normally a place builders try to go as it is just high enough to be sketchy on pump gas. Because of the need for richer fuel after 12:1, builders go higher in CR to optimize power for the fuel that is needed. 12:1 is sometimes called no mans land because why not 13 or 14:1?

That said, what were you trying to do with the 16cc piston that the 26cc piston is messing up? If your plan was to swap heads and a cam and add the boost, the 16cc piston would have been a poor fit anyhow for your boosted application.

thenewkidz28

My goals are to have a smooth running 383 that lasts a long time..*Edit* OK and ill also be driving it like I stole it occasionally. and plan to hit about 6400 rpm here and there.

You're not using the right numbers for the calculations. The static compression is a little over 11:1 and about 8.7:1 dynamic with the 16 cc dish piston and the 53.25cc heads that I had/have (I only have one pair of heads, they're currently at the machine shop getting the axe. So if it sounds like I have 2 different pairs that's why.)

I feel like you still don't get what I'm trying to say. I'm only milling the heads so much because 53.25 cc heads with 26cc pistons doesn't even get me 10:1 static compression I only picked this short block because it was supposed to dial right in to the head and cam specs that were ready to go on the 355 I was originally building. Sorry if all this is misleading.

Injuneer

Drew:

He THOUGHT he was getting 16cc dish pistons, and that would be good to go with 53.25cc heads. But he found out he had 26cc dish pistons, so he’s having the heads milled to 47cc.

My concern would be quench. Is the “dish” in the piston a full circle, or does it have a “D” shape, allowing the flat area on the crown to effectively meet the flat area of the head? I'm no expert with quench, but it appears to be important in avoiding detonation. Just sounds like a strange combination, with the potential for issues.

thenewkidz28

Mostly the questions I have are:
What happens when you move the combustion chamber further into the piston?
How does that effect timing?

Wouldn't the spark be more centered in the combustion chamber? (a good thing?)

Has anyone ever milled this much off (1994)lt1 heads? if so did you have to raise the valve seat? what about the alignment dowel pin holes?

thenewkidz28

its like a D shape with some squish zone. mahle SBC125030I26 pistons

DrewHMS97SS

Got it, and we are quickly beyond my depth.

#EatingPopcornWaitingForSomeoneWithExperience

Has the machine shop you are working with provided any decent advice?

thenewkidz28

Not really. They (Noland's Cylinder head repair) are always busy and the work to be done is sometimes split between the machinists there, so I normally talk to them more after the work is done. But I consider them the best machinists in KC MO from my experience, so I know the job is going to get done right if he told me it would work.


Stay tuned. I guess this will be my new thread for the build since all my other posts got deleted somehow.

Chimera96

IDK if this helps, I searched the part #

well per OP's part # post...Summit shows this pic (although also saying pic is "representative" of item)

Jegs pic just shows 2 D shape valve relief...Summit ones shows a recessed dome with D shaped relief..so IDK what the piston top actually looks like

Agree this combo does sound strange with possible issues. All above my ability to advise. My concern is if that much is taken off the heads....and this doesn't work...the heads are done

https://www.summitracing.com/parts/MLE-SBC125030I16/

thenewkidz28

after he reseated the valves and decked it .015 it only got me to 52cc so I just told him to stop and match the other cylinder head. So ill just have a 10:1 motor for now I guess. It should love pump gas now right? Do you guys think I could run 87 octane??

DrewHMS97SS

I think 87 would work with 10:1, but plus/premium is such a small cost difference, that I would just pony up. It wouldn't hurt to test it out though.