Squish!

[D3VST8R96GT]

This is why I love building engines. Each combo is infinitely special. Hell the weather can play a role in detonation
All the systems working together each playing a decent role/factor in power and efficiency.

 

[96blak54]

Absolutely! So why waste potential? Why waste the opportunity to gain 20hp or potentially more depending on design.

 

[chris91]

Stickied! Love seeing great info like this being posted.

 

[96blak54]

So im looking back at old threads and sort of criticizing myself of what I wrote and in this thread occurred to me,...I never stated how to achieve the .020" squish....or less. Lets dig into it!

Remember squish is the amount of space between the piston crown and head deck surface when the piston is at top dead center (TDC).

The length of rod, the distance from wrist pin to piston top/crown, head gasket crushed, piston rocking in the bore and the material type of each one made, greatly affect the squish distance when into the rpm's....running squish...so to speak.

Stock 4.6l modulars nominal(not running) squish distance floats around .045 and doesnt change to much from this measure when running. Stock modulars consist of powdered metal rods and casted hypoeutectic pistons, both of which are known not to stretch or expand greatly when heated and stressed.

All types of steels have the ability to expand and stretch when stressed,... return to its nominal state when not, and be completely reliable. Known as tensile. Cast iron, powdered metal, aluminum have very limited tensile strength, will retain damaging shape when stressed, but will expand when heated just like steel. Knowing these veriables will greatly improve your build.

We look back at that stock modular and realize the stretch from the rod when running or expnsion from the piston will be very little, because of their own material make up....Without so much mathmatics and pure speculation, im guessing the factory considers the rods expansion/stretch to be .005" and piston swelling maybe .005"( all because of material make up and stress) putting the squish distance at a comfortable manufacturer stand point of .035" while running high rpm's. Nominal .045"
• -.015" piston deck hight(the pistons distance down in the hole)
• .030" head gasket crushed
= .045" squish

Take in the speculated .010" of materials used when the rpm's are high, subtracting from the nominal .045" and you come up with .035". Can we do better? Absolutely! The closer we can get while running safely, the more static compression we can run, the better auto ignited fuel control mechanically, and detonation resistant it becomes.

Their is a rule of thumb used for steel rods stretch/expansion. For every inch of rod concider .002" for stretch. For forged pistons consideration we mathmatically derive the amount but bore size and compression distance affect the outcome. And then the gasket thickness when crushed. Take these veriables in your build and up that compression!!!

 

[96blak54]

Its a proven fact that 1point of compression equates to 4% power increase with any internal combustion engine...period! 200rwhp x 4% = 208rwhp. That dont sound like much improvement!! But lets say you deside to go from 9:1static to 13:1static....thats 4points! That equates to 232rwhp. Can that be done with pump gasoline? Of course!

The biggest issue of an internal combustion engine is detonation. Detonation is a shock wave of auto combusting fuel mixture. Im not refering to the total mixture auto combusting, im refering to very tiny pockets of that mixture auto combusting while piston is TDC and mixture is compressed into head chamber, creating a shock wave before the piston starts to travel down. Detonation destroys! (I have yet to hear of a naturally aspirated performance 2v modular experiance detonation) What level of detonation depends on the destroying level. We know cars today detonate when cruising down a highway, maintaining the same speed, the computer leans the mixture out to detonating/knocking to aid in as much mpg as possible. Thank you knock sensors!

Take a 2000 crown victoria, its known to squeeze out 32mpg on long trips that empty the tank on interstates. 32mpg's!!! Our same 2v's can bairly touch 24mpg on a good day with inflated tires, but mpg's are not what im getting at, detonation resistance of our 2v modulars is my point.

Bore size, rod length, chamber shape, fuel injection, stoke length, squish distance, 2valves swirl homogenous mixture alone aids the best, ...all play a big roll in detonation resistance and our modulars canidate well!!

Long rod, cammed 350ci cheby guys and their 4" bores while carbureted can run 11:1 87octane with newer style aluminum heads, we modular guys have a greater advantage with smaller bores, fuel injection, chamber shape, long stroke and long rod,.....much like the Honda guys running 16:1 in their 4cyl.

[emoji6]

Happy building!

 

[D3VST8R96GT]

Alloy used will play an effect when it comes to pistons. But your usually aware of its expansion when you put to father the short block and attaining your desired piston to wall clearance..

But I'm not sure how to square that into the calculations for achieving the squish I desire.

 

[MustangChris]

We all know how much compression can be had with a pi swap and stock cams. Neighborhood of 10.5:1+..? By adding aftermarket cams the compression ratio will drop. By adding longtubes or a diffrent intake manifold ...again the compression ratio is altered greatly but the challenge is figuring out how to mathematically put a number to it so that we can keep are compression up. This is called Dynamic compression.

how is the compression ratio changed by headers/cams? I was under the impression compression ratio consisted of the value during the compression stroke (all valves being closed, and therefore intake/exhaust components being unable to effect anything going on in the combustion chamber.)

 

[D3VST8R96GT]

Your talking about static compression.

Piston
Head volume
Stroke
Compressed Hg thickness

 

[D3VST8R96GT]

Dynamic takes into account cam events

But also considering the engine is an air pump removing restrictions will alter airflow into the cylinder.

 

[96blak54]

A very sophisticated pump!

 

[The Electrician]

Would it be safe to wind the engine up to 7000 RPM with .020 squish, TFS heads 38cc, 11.51:1 CR, aluminator block, stock cast crank, boss rods and 2618 Alloy pistons with valve reliefs?

 

[96blak54]

Your asking a question with alot of variables. Tarket .020" squish in account with all the expansion and tensile of the engine running. Getting that piston to kiss the head is where you want to be ..."max effort" and to achieve this you must use available resources such as head gasket thicknesses or o-ringing the heads to use thinnest gaskets on top of your projected figures. Stock modular gaskets crushed is .039", your alloy pistons are going to swell .030"(assuming stock bore) and I haven't had any dealings with the boss rods yet, so im uncertain of the tensile growth, but I do know they offer more hp handling, so im going on a limb here to say they probably have more tensile than old rods, so more stretch is probable. The aluminum block grows more over cast and offers more compression capabilities just because its aluminum,....I this is why ford started the aluminum block engines at 10.5:1 static in the lincolns while still running 87octane.

You didnt specify the cams to be ran with this combo. Also a question for you,...and thank you for asking a question here,...why are you only running 11.5:1 static with a set of $2000 heads? I know your car is 4300#'s but youll have some nice rear gears back there.

 

[D3VST8R96GT]

Idk what kind of crank deflection you'll see at 7k rpm.....

I tried look at the boss rod specs and no one has published them that I could find maybe call some high end modular engine builders and ask

Tune would need to be dead on though can events happen so fast at 7k rpm

 

[96blak54]

Crank should be fine, ive witness 4v lincoln shortblock touching 7800rpm launches.

 

[The Electrician]

I went to 11.5:1 CR because the highest Octane available is 91

I'm going to use 3V FRPP head gasket which is 0.036" crushed (I think)

but the block is decked 0.023" so squish should be 0.036"+0.012"-0.023"=0.025" and if the head gasket is 0.030" then the squish would be 0.030"+0.012"-0.023"=0.019"

Victor Jr Manifold, Stainless Works 1.625" Primary | 3" Collector LT headers, 2.5" cat-back x-pipe, 3000-3200 stall TC and 4.30 rear gears



I'm worried about pistons will kiss the heads at 7000 RPM

 

[96blak54]

You should be worried! The rods will grow some from heat expansion as the pistons will too. Knowing exactly how much takes experience with each item. To achieve a tight squish, normally a builder starts will a workable scenario at a comfortable distance and works it in tighter by head gasket thickness changes after hard runs. My suggestion, run a thicker gasket unless you/someone have built that same senario multiple times and know where the limits are....run the thicker gasket.

Do you know what cams youre going with?. Judging by the stall im guessing a late IVC point with tons of overlap...?

 

[The Electrician]

Bore: 3.572"


Cams: MHS TFS N/A Stage 3

Here are photos of the cams found them on the web

Duration Advertised : 273 / 275
Duration at .050" : 233 / 236
Lift : 550 / 550
Centerlines : 106 / 112
LSA : 109

http://www.classictiger.com/mustang/CamChart/CamChartCandDr3-1.htm

Intake Opens BTDC: 10.5
Intake Closes ABDC: 42.5
Exhaust Opens BBDC: 50
Exhaust Closes ATDC: 6
Overlap: 16.5



The block is not decked yet, I'm waiting for the parts to be delivered


According to MHS article "Recession Buster Combo"

http://www.modularheadshop.com/recessionbustercombo.aspx

Decking the block.012~.015 is safe


I planed to deck the block 0.023" after reading this replay by nickmckinney of MHS at corral

"If you zero deck the block or better yet run the piston slightly outside the deck you not only gain compression you also at the same time gain resistance against detonation (sounds backwards but its very true) Race engines that are forced to run on pump gas have the pistons just about touching the heads at higher RPM. You can run the pistons to within 0.025" of the heads on these motors if you blueprint everything (and some race motors go 0.020" I know of but they have bigger cahonas than me)"
http://forums.corral.net/forums/10311459-post14.html

and this replay by him at modularfords

"Quench on a PI head is worthless unless you can get the piston to the head clearance down to 0.036" or closer. Since the head gasket is 0.036" compressed you need the piston right at zero deck or slightly out of the block. I have seen 0.025" used up to 7500RPM without a problem on these. Those hyper pistons have a lower compression height so it means you have to deck almost double off the block to be able to quench it (remember I said on my piston design I wanted the compression height "raised" as an option or else I wouldn't sell it) Try to deck that much off a block get ready for a serious bill at the end and also getting the timing cover and valve cover rails to line back up nicely."
http://www.modularfords.com/threads...-quench-area?p=1769820&viewfull=1#post1769820


but to be safe I think I should deck the block 0.018"~0.020"

What do you think about that?

Also, Do you think 4.30 is too much?

would 4.10 gears ratio be better?

 

[96blak54]

You are absolutely correct. And this follows along any engine build for max effort power. Ill follow up with the cam specs.

 

[The Electrician]

I found this interesting article on Hotrod magazine


Combustion Chamber Dynamics
A cool charge may be the first step toward utilizing a higher CR, but what happens in the combustion chamber can make or break any such efforts. A prime factor here is never to loose sight of the fact that the faster the charge can be burned the higher the compression the cylinder will stand. Chamber cavities between the piston and the cylinder head between about .060-inch - .0120-inch appear most likely to be the site of detonation. Speeding up combustion mixture motion/agitation is vital. This means maximizing the quench action. On a small-block Chevy with a stock block height, a stock compression height piston is typically .025-inch down the bore. With a .040-inch gasket this makes the static quench clearance .065-inch, which is way too wide. By cutting the quench clearance the burn rate and quality improve to the point where the motor gains compression and is less likely to detonate even at the higher ratio involved.
So how closely can the pistons approach the head face? Although it comes under the heading of "don't do this at home" I have run the static piston/head clearance down to as little as .024-inch in a 350 with stock rods and close-fitting hypereutectic pistons. The pistons just kissed the head at about 7,000 rpm. As far as power is concerned, an associate of mine ran some tests in a nominally 450-horse 350 and found that each 10 thousandths of quench reduction was worth approximately 7hp. If you are building from scratch, make maximizing the quench your number one priority toward achieving compression and avoiding detonation.




Read more: http://www.hotrod.com/events/coverage/0311em-power-squeeze/#ixzz3YEWMpAcI

 

[96blak54]

Good read! Writen by David Vizard, no surprise their. Thanks for posting it. .024" is close with a 4" bore!! Piston rocking prohibits such a tight squish, but if the engine it built right it can be achieved. David Vizard has some good stuff and may be worth checking into his books which I have never done. I only know of his name.

I agree maximizing the quench is where its at, but you have to know your components. Repeated builds, reducing the squish each time gets you aquainted with the components.
Back to your cams, im not degrading your cams used, only enlightening your thoughts.(maybe I should explain modular camshafts in detail for another thread) Combustion starts as soon as the intake valve seats! Not .050" before the seat closes. The big lodes of a modular camshaft can hang the valve open under .050" for a number of duration, unlike the old in block cams of our ancestry. Knowing exactly when the valves open and close is very important to power with any engine, but especially with a mud motor. You would be very surprised at the open/close points of a pi cam. Ramp rates and the ramp rate lobe seperations are what sets cam apart in a modular.