Advanced Engineering Tech - 13:1 c/r on pump gas?

ok let me lay out my situation, just picked up an ls2 block, stroker 402 with 10cc domed diamond pistons. with the 66cc combustion chambers on the afr's the compression is appx. 13:1. now the previous owner of the short block claims to have run on pump gas with some kind of tune and a special cam. my plan is to mill the pistons down to 5cc and run a 12:1 ratio on pump gas. the question is what would be required and what are the effects of running either one of these ratios on a street driven car. The cam I plan on using is an ms4, 239/242, .649"/.609".

Free bump for you, i'm interested in this as well as i am wantin to do a high compression build but dont have e85 real close by.

yeah it seems people are more interested in perpetual motion, hope somebody can shed some light on this situation.

Years ago I ran 12.2:1, and 25 degrees of timing in a 422ci stroker... On pump gas.

its not the 12 to 1 ratio i am so much worried about, im confident a modern fuel injected engine could handle a ratio like this, I just want to know how you could run a 13 to 1 on any engine with pump gas, at least not without taking all the timing out and loading up on fuel.

you can on these motors you need a spot on tune and the timing needs to be perfect the fact that having non iron block and heads helps alot also

The cam should be specifically designed for the compression and head. I don't know that an off the shelf cam that small will work without moving it around a great deal. Then you might end up with less than optimal valve events. We have a 12.5:1 427 with ET LS6 heads that will run on pump gas...

Shane

the cam was actually bought for my stock bottom end and afr heads, the short block was an after thought that just kind of presented itself. So I guess my next question would be has anyone had any experience with this ms4 cam on higher compression engines?

I wouldn't see a problem with it. It will be all about a lot of overlap and keeping your dynamic compression around 8.5. if the dynamic compression gets any higher with 13:1 or even a 12:1 build you will have to run high octane

I wouldn't see a problem with it. It will be all about a lot of overlap and keeping your dynamic compression around 8.5. if the dynamic compression gets any higher with 13:1 or even a 12:1 build you will have to run high octane

??? If he wants to avoid detonation it'll be easier with LESS overlap.

Heres thing, theirs what works in theory and what actually happens.

418ci flat top pistons, AFR heads, .045" quench, 251/259 camshaft, TR6 plugs, timing @ 20º
SCR: 12.4:1
DCR: 8.5:1

pinging its nuts off at 4000 rpm in 3rd with a load on it

93 octane BP, in Chicago we're supposed to get best quality 93 octane, BP fuel is pipelined from BP's Whiting, IN refinery directly.

100 octane unleaded, fine, made 520rwhp though auto.

I know a few 13:1 LS builds even SBC street cars running 100 unleaded, in Chicago we have 100 octane available
in most suburbs on the pump. If you consider that pump fuel you're fine.

must be nice we only have 91 at the pumps :(

Heres thing, theirs what works in theory and what actually happens.

418ci flat top pistons, AFR heads, .045" quench, 251/259 camshaft, TR6 plugs, timing @ 20º
SCR: 12.4:1
DCR: 8.5:1

93 octane BP, in Chicago we're supposed to get best quality 93 octane, BP fuel comes from Whiting, IN BP refinery directly.

pinging its nuts off at 4000 rpm in 3rd with a load on it

100 octane unleaded, fine, made 520rwhp though auto.

I knew a few 13:1 LS builds even SBC street cars running 100 unleaded, in Chicago we have 100 octane available
in most suburbs on the pump. If you consider that pump fuel you're fine.

Is the 100 octane your speaking of still unleaded? :secret2:

??? If he wants to avoid detonation it'll be easier with LESS overlap.

Wrong. As in exactly backwards wrong. Less overlap = more dynamic compression = more detonation.

Is the 100 octane your speaking of still unleaded? :secret2:

unleaded 100 octane, CAM2, Sunoco etc. ; only down side its normally $5-$6 gallon.

ok so back to the original question, with the 111 lsa and specs posted above for the ms4 cam im assuming its a higher valve overlap camshaft, what would this do to the engine with 13:1 compression pistons, if it lowers the static compression would it still have problems on the top end?

ok so back to the original question, with the 111 lsa and specs posted above for the ms4 cam im assuming its a higher valve overlap camshaft, what would this do to the engine with 13:1 compression pistons, if it lowers the static compression would it still have problems on the top end?

camshaft doesn't affect static compression, only dynamic compression which I showed is over analyzed.

We've also run a 418ci engine with 12:1 SCR 9:1 DCR and had no problems on 93 pump fuel.

If it helps at all I ran a 388cid sbc with world products iron heads and a mild sollid roller with a static compression of 13 to 1 and it ran and drove fine at 32 degrees of timing but definately ran it's absolute best when id mix 2 gals. of vp c16 fuel and about 20 bucks of 93 pump gas.

If your engine has very poor VE you can run more compression. This is the opposite of what you want. You want great VE which is what makes Tq and power and the right amount of compression to go alonmg with it and your fuel.

If it's a solid dome have it lathed off. Call Diamond if you are unsure about the piston. If it's a hollow dome you are probably screwed. I wouldn't screw up the engine to try and run higher compression than what your local fuel can handle.

If you need to lower the compression it'd probably be easier to have 5cc added to the combustion chamber volume of than tearing down the bottom end, milling pistons and rebalancing.

The heads will likely flow better as well.

I doubt hes thinking of taking his motor apart just to low compression. And if he were don't you guys think a head gasket spacer or just a thick head gasket would be a lot easier and cheaper way to lose some compression?

Dude spray the car!

According to him he was planning on tearing into it

my plan is to mill the pistons down to 5cc and run a 12:1 ratio on pump gas.

From page 1:

Can someone explain how overlap effects dynamic compression?

As in, that's not accurate at all...

Erik would be correct in stating a poor breathing engine can benefit from
more compression to restore some of the 'punch', however you can run
all the compression you want until you're blue in the face... if you don't
have air and fuel combusting to provide the energy, the engine is a dog.

It is better to have a good flowing setup with less compression to arrive
at the same cylinder pressure.

Having a 13:1 SCR with "pump gas" means that IVC is going to happen later
to keep the dynamic compression within a window that is efficient for the
fuel you intend to run.

It also means the engine will be tuned for a higher RPM, and the torque and
HP will generally peak later in the band (high compression with late IVC).

I was wondering about having the heads combustion chamber pushed out 5cc but wasnt sure of the effects on the afr heads, still looking for some solid info on this. as of now the plan still stands at cutting the pistons down, I already verified the pistons will be good for this route and its a short block now so Im not to far into it as to be a hassle to tear it down at this point.

Your idea to reduce comrpession is much better than adding a thicker head gasket. Increasing quench height is not a very efficient method of reducing
SCR;it's fast and cheap, but hardly efficient. Raising quench height also promotes detonation.

Heres thing, theirs what works in theory and what actually happens.

418ci flat top pistons, AFR heads, .045" quench, 251/259 camshaft, TR6 plugs, timing @ 20º
SCR: 12.4:1
DCR: 8.5:1

pinging its nuts off at 4000 rpm in 3rd with a load on it

93 octane BP, in Chicago we're supposed to get best quality 93 octane, BP fuel is pipelined from BP's Whiting, IN refinery directly.

100 octane unleaded, fine, made 520rwhp though auto.

I know a few 13:1 LS builds even SBC street cars running 100 unleaded, in Chicago we have 100 octane available
in most suburbs on the pump. If you consider that pump fuel you're fine.i am a 408 with 12.1 with 20 degrees of timing on 93. i think i got it cleared up. but with 23-25 degrees over 4500 it would ping like hell.:eek2: i started at 27 and that sounded like someone was using an air hammer on my pistons!!

Your idea to reduce comrpession is much better than adding a thicker head gasket. Increasing quench height is not a very efficient method of reducing
SCR;it's fast and cheap, but hardly efficient. Raising quench height also promotes detonation.

Explain more please. Removing the dome off of a piston is exactly opposite of what its intended to do. Which is to go into the main combustion chamber of the head were spark nucleus, hatching out, and flame front all originate and make the air fuel ratio more vollitile thus allowing higher octane fuel to be more efficient and more easily ignited allowing for more ignition timing and ultimately more efficiency and power. Reducing the dome is fine but seems a bit extravagant. Not to mention exspense. Why not leave the short block alone and go with a custom ground camshaft?

Actually, reducing the dome is beneficial to flame travel. A dome impedes the
flame front from moving across the piston. If you can achieve the compression
ratio without using a dome (IE: reducing quench, or chamber cc), it's the
better scenario.

As for quench height, increasing the distance between the head and piston
reduces the quench effect. It also leaves air/fuel in an area furthest from
the spark plug.

http://racingarticles.com/article_racing-10.html

In a running engine, the .035" quench decreases to a close collision between the piston and cylinder head. The shock wave from the close collision drives air at high velocity through the combustion chamber. This movement tends to cool hot spots, average the chamber temperature, reduce detonation and increase power. Take note, on the exhaust cycle, some cooling of the piston occurs due to the closeness to the water cooled head.

If you want more advanced discussion on these topics, I'd recommend
going to Speed Talk forum and register an account there. You will have
access to the advanced forum and discuss these tuning tips with seasoned
engine builders in the industry.

As for using a custom ground cam to dial in the compression I would agree
that's a better alternative than sticking in a thicker head gasket.

From page 1:

Can someone explain how overlap effects dynamic compression?

.

Like you have already said, a late closing intake valve is the prime controller of your dynamic compession ratio; If your intake valve closes on your 12:1 motor when the piston is half way up the bore you have 6:1 dynamic CR.

My thoughts on overlap;
For overlap to effect the ability for a high cr motor to tolerate pump gas, I would expect a delayed intake valve opening event to reduce the intake charge, and dilution of the intake charge with a delayed exhaust closing event to be the primary controllers

Theres enough cam gurus on this site that should be able to fill in some of the blanks

Yes you're on track with the theory. Compression cannot start until both valves
are closed, and in this case we're referring to the intake valve closing which is the
sole factor in determining the DCR value.

Overlap is tricky to understand and tune. You are correct that a late opening
intake and early opening exhaust will at times cause the exhaust gas to
remain in the chamber and displace the fresh air/fuel mixture.

Residual exhaust gas helps to cool the chamber and therefore acts like additional
quench. This is a variable effect and will happen at only certain RPM.

If setup properly overlap will help create better VE by using the exhaust
system to 'boost' the intake charge. By creating a depression (low pressure)
in the chamber just about the time the intake valve opens and the intake pulse is moving down the intake runner and head port, the engine can achieve
over 100% VE at certain times (Pro Stock tuners are masters at this).

So you can see that overlap can work with you, and it can work against you
but the Intake Valve Closing point (IVC) is what determines the DCR value.

That's great stuff man I appreciate your willingness to share. Ill probably run super thin head gaskets from here on out. LOL. Ive always been one to build my own engines from start to finish out of parts I picked and hardly every run into problems with trying to lose compression.

For the record I knew that the piston dome actually hinders flame travel but it also makes the mixture more volitile and creates a give and take scenerio as far as making power goes. All my dome pistons have flame notch's cut into them. Most pistons do now days. Thing is with a wedge style engine that's really the only way to get 13.5 or better compression without some really custom stuff.

Another thing to remember is the fact that heat also is a pre-detonation factor , so You run an over-sized rad with the same thermostat , even when the gauge says a given temp , You're engine is cooler . Also rod ratio makes a huge difference . An article in a Hot Rod mag from about 12 years ago has an article about 2 guys that made a chevy 350 using a 400sm bl .030 (4.155") bore and a 307/327 crank (3.25") stroke , Ford 300 6cyl. rods (6.209") machined narrower to fit chevy crank , custom JE pistons I'm guessing domed with pin location higher up on piston , "stock" dur and lift roller cam and aluminum heads with 58cc chamb . 11/1 scr . I think 2.02/ 1.6 valves a Quadrajet and headers . HEI . With pump 87oct were able to total advance of 36deg . 412 hp 435tq . So I estimated a gen 1 350 with the same heads ,comp, carb, cam, headers to put out about 245hp 285lb. ft. A diff of 167hp 150 lb. ft.

Why not just put a meth kit on it?

http://www.popularhotrodding.com/tech/0605phr_pump_gas_secrets/index.html

12.5:1 is pushing it, but read...

We have a 355ci 650 hp on pump gas. From 11.7 to 1 to 12.7 to 1 picked up 30hp still on 33 deg timing, It is all in dynamic compression, If it still knocks on low loads it needs a tighter quench, say 30 thou on a steel rod, and a lot of chamber work no sharp edges blended nicely and polished, Remember tighter lsa gives higher dynamic compression, all we normally do is retard the cam timing 2 to 4 degrees OR run a wider LSA so if you are 112+4 go to 114+1 or 0. Run colder ects aswell.

One mans 408 for example may take more lead, some say it is because VE is reduced I know for a fact many engine builders would argue that, it is true to an extent but all motors are different and if it takes low timing generally if you look at the chamber it can be improved upon and also altering quench and wider LSA. I have seen reports of 102 lsas in hemis running 240psi cranking comp with no issue, then a Ford motor running 220 psi and struggling on pump gas in which scenario a 114 lobe sep cam is installed on a later ICL and problem solved. Use cranking compressin as a guide, Get your ballpark figure based upon experience and then alter cam timing slightly is the best way at the end of the day excellent results are achievable.

cheers

Still wondering how LSA effects dynamic compression?

I know someone who is 13.7:1 and drives it like that on 93 pump. Not sure if he has made any passes like that, I will ask him tomorrow.

Still wondering how LSA effects dynamic compression?

Because a wider lsa has a later intake centreline and so the compression starts later. If you look at 2 stroke specs you will see they advertise compression by a dynamic value not static, because it does not start to build until the piston closes the intake port much like when the 4 stroke closes the inlet valve.

I know someone who is 13.7:1 and drives it like that on 93 pump. Not sure if he has made any passes like that, I will ask him tomorrow.

Far out, he must have a big cam in it!

Why not just put a meth kit on it?

I was wondering this as well...

Is Methanol not a good alternative on N/A motors?

LSA or LCA is the degrees between the intake and exhaust centerline. It does
not dictate when the intake valve closes.

Intake centerline is at times used to dial in camshafts, but even that cannot
tell you IVC because the duration my differ.

YOu need to use Intake Valve Closing (IVC) to determine the dynamic compression ratio.

Yes that is true, But if you have a 240 240 112+2 cam and the cc is too high and you need a later ICL with the same cam duration, By say 6 degrees you need to run a wider lobe sep. Wider lsa cams also have less overlap, the overlap effect works like a vacuum cleaner in certain rpm ranges so more cylinder pressure can be created with a tighter lobe sep through peak torque just because the running cyl pressure is so high.

For eg I run 25 deg through pk torque with a 232 234 112 I have a 46 deg IVC, with a 227 239 115 cam. in the same engine it has a 45.5 IVC it makes best tq at 28 degrees but it still wont knock with 32 degrees, the 112 cam will knock at 26.5 degrees, Even though the cranking compression is less with the 112 cam it takes less timing. Why? Because the extra overlap is scavenging and filling the cylinder better. cranking compression is a guide, Even going the same cam even slightly wider in lobe sep and a mere 2 deg later ICL can change things drastically, Overlap drops off running cylinder pressures drop off, all of a sudden the motor is taking more timing. This is normally what we do if the compression is to high, Even the same motor same parts can be different.

You are confusing cylinder pressure with dynamic compression according to
your last post.

Scavenging / overlap that you are tweaking improves cylinder filling which
increases the amount of charge presented to the chamber. This creates
a higher cylinder pressure.

When you degree a cam by shifting ICL by 2 degrees you are effectively
phasing all valve timing events...which directly alters dynamic compression
because the IVC event has moved.

Think of it this way:

A camshaft with the exact same lobe installed at the same intake center
will have the same DCR even if the lobe separation changes (110 to 112 LSA for example).

Overlap changes, but DCR does not in the above scenario.

DCR is just a mechanical ratio of when the intake valve closes based on the
amount of static compression available.

IF (and thats a big if) the combination is right and fills the cylinder adequately, your not going to get much gain out of stretching it another point of compression. The margin for error can become so close (little lamer fuel one time, carbon buildup starts a pinging, a little edge here or there in the chamber)

If you have a small motor with a ton of cam in it it may want the upper end, but i dont think Id build buzzer for pump gas drive around duties.

When we built a LS motor originally at 13:1 dropped down to 11.5:1 saw virtually no loss in power, it was filling the cylinder. Even on high octane fuel the difference was little to none

Get the combo right and you dont have to rely on rolling the dice on compression, and youll have a tuning window with some margin. Just did a 408 LT1, hyd roller, forward facing intake made 466 thru a 5200 stall on our Mustang dyno. Decent CYlinder head and cam timing are close, not abunch of compression just 11.3:1

And your not going to want a dome in a chamber running on the edge of pump gas capabilities. Get the piston right to start

Unless you have some elaborate (& highly dialed-in) water-injection, other after-market anti-detonation device, or your later model engine assembly came with some detonation prevention mechanism(s) - of course you can NOT use 13:1 c/r(!)

I tried for many years to get away with 10.9/1 c/r, and after trying many after-market inventions I simply bit the bullet and mixed LL-100 AV fuel with pump 92 octane, and only then was I okay and actually got to enjoy my high(er) compression. If your local municipal airstrip won't sell you the (100) AV gas, then you'll have to pay the price via your local speed/off-road shop.

If you try to run high compression with pump gas your expensive motor will suffer (and not last long). Years ago someone built a 12.5/1 350 sb, it could pull the front of his Vega off the ground with good traction - but his motor was always noisy only lasted 8-10,000 miles (that was with 92-93 octane & so-called 'octane boost' - which only boosts your octane about .5 -.7 {½ to 3/4 octane, or "five to seven octane points"}

If you don't have access to better fuel don't use more than 9.3-9.5/1 c/r (!)

Unless you have some elaborate (& highly dialed-in) water-injection, other after-market anti-detonation device, or your later model engine assembly came with some detonation prevention mechanism(s) - of course you can NOT use 13:1 c/r(!)

I tried for many years to get away with 10.9/1 c/r, and after trying many after-market inventions I simply bit the bullet and mixed LL-100 AV fuel with pump 92 octane, and only then was I okay and actually got to enjoy my high(er) compression. If your local municipal airstrip won't sell you the (100) AV gas, then you'll have to pay the price via your local speed/off-road shop.

If you try to run high compression with pump gas your expensive motor will suffer (and not last long). Years ago someone built a 12.5/1 350 sb, it could pull the front of his Vega off the ground with good traction - but his motor was always noisy only lasted 8-10,000 miles (that was with 92-93 octane & so-called 'octane boost' - which only boosts your octane about .5 -.7 {½ to 3/4 octane, or "five to seven octane points"}

If you don't have access to better fuel don't use more than 9.3-9.5/1 c/r (!)


Wow disregard everything this guy just said, most of them are 10.9:1 from the factory now bud

I want to no more about meth injection on n/a motors.

Wow disregard everything this guy just said, most of them are 10.9:1 from the factory now bud

No doubt, been running 11.8:1 all day long on 93 octane for 3 years with no issues..:D

I ran 12:1 on pump gas, 422 cid LS setup, back in 2001-2002.

SBC's are different.

I'm thinking that maybe 12.5:1 on pump gas is doable, but I wonder what sort of compromises there would be with respect to timing advance...

If I build a new NA motor next year to run on 93, no meth etc., I'd probably go about 11.75:1.

I ran 12:1 on pump gas, 422 cid LS setup, back in 2001-2002.

SBC's are different.

How so?

I want to no more about meth injection on n/a motors.

Dont. If cyl head is good, there will be nothign to had except for complicatedness.

A very well thought out engine that moves air isnt going to car much about a hair more compression. Waste of time.

I have dropped a point made the combo happier and picked up bunch of power. Compression is what you use when you cant fill the cyl well, squeeze the shit out of it! :D

Free bump for you, i'm interested in this as well as i am wantin to do a high compression build but dont have e85 real close by.

Same thing I posted few month ago. Interesting> I read the other E85 forum that those cars runs with 12.1-15.1 c/r on E85 and no problems...:D
Build 14.1 CR LS on E85 DD (http://www.ls1tech.com/forums/generation-iii-internal-engine/1289007-build-14-1-cr-ls1-e85-daily-drive.html)

No doubt, been running 11.8:1 all day long on 93 octane for 3 years with no issues..:D

I ran 12:1 on pump gas, 422 cid LS setup, back in 2001-2002.

SBC's are different.

I'm thinking that maybe 12.5:1 on pump gas is doable, but I wonder what sort of compromises there would be with respect to timing advance...

If I build a new NA motor next year to run on 93, no meth etc., I'd probably go about 11.75:1.

So for the most part 11.8:1 is the highest you really want to go for 93 pump and still be safe with a little cushion? 12:1 is MAX safe, but tuning MUST BE spot on... I like a little leeway so I guess it's 11.8:1 ;)

DM

Wrong. As in exactly backwards wrong. Less overlap = more dynamic compression = more detonation.

Still wondering how LSA effects dynamic compression?

I am too :confused:

Because a wider lsa has a later intake centreline


LSA has nothing to do with intake centerline. LSA however has everything to do with exhaust centerline.


If your intake valve closes on your 12:1 motor when the piston is half way up the bore you have 6:1 dynamic CR.

Until you start to achieve more than 100% VE


Overlap is tricky to understand and tune. You are correct that a late opening
intake and early opening exhaust will at times cause the exhaust gas to
remain in the chamber and displace the fresh air/fuel mixture.

You a smart guy, I know this from previous discussions with you and reading other things you write. Would you agree than an overly early EVO point is less likely to leave poluted air in the chamber? Generally speaking, one reason most cams ground for N20 have a good amount split with wider LSA's. Retains overlap to tune rpm band but opens the exhaust sooner to help evacuate the spent mixture. Early EVO's IMO are less likely to leave the cyl filled with spent gasses compared to a late EVO.




So for the most part 11.8:1 is the highest you really want to go for 93 pump and still be safe with a little cushion? 12:1 is MAX safe, but tuning MUST BE spot on... I like a little leeway so I guess it's 11.8:1 ;)

DM


I don't think there is any specific static compression ratio that is "safe" I think as others are saying too, it is about the full combo. Everything must work together to achieve a harmonous motor that will make great power.

So for the most part 11.8:1 is the highest you really want to go for 93 pump and still be safe with a little cushion? 12:1 is MAX safe, but tuning MUST BE spot on... I like a little leeway so I guess it's 11.8:1 ;)

DM


No, i can build a motor that runs 13.5:1 on 93 octane pump gas no problem. And itll probably be a f'ing pig. but you could do it.

Fill the damn cylinder, dont get carried away with compression, and have at it. There are certain circumstances you turn to compression when you dont have other things in place, but in a perfect world, no

Would you agree than an overly early EVO point is less likely to leave poluted air in the chamber? Generally speaking, one reason most cams ground for N20 have a good amount split with wider LSA's. Retains overlap to tune rpm band but opens the exhaust sooner to help evacuate the spent mixture. Early EVO's IMO are less likely to leave the cyl filled with spent gasses compared to a late EVO.

Generally speaking I will agree with this statement. Of course it will all depend
on RPM and what sort of pressures are occuring in the exhaust system; the
chamber; and intake system at that specific point in time the valve is open.

Sometimes reflections and odd pulse phasing in the motor will prevent gasses
from clearing out.

Also to clear things up:

LSA, or LCA is the value given between the exhaust centerline and intake centerline.

Volumetric efficiency is a cousin to cylinder pressure (IE: BMEP, IMEP, etc.)
DCR is just a mechanical ratio of when the intake valve closes in relation to
the total amount of Static compression.


IMEP = ((792000 x HP) / (Meff x CUIN x RPM)

Meff = mechanical efficiency = (-0.000009 x RPM) + 0.9188 (typical values)
Peak Pressure = (((IMEP / FIT) x (((CR - 1) x (y -1)) / ((CR^y) - CR))) + INT) x CR^y x 0.75

FIT = Correction Factor found in complex engine sim calculators.
CR = Compression ratio
y = Ratio of specific heats.
INT = Intake manifold pressure PSI (absolute)


BMEP = 150.8 x TORQUE (lb-ft) / DISPLACEMENT (ci)