Sales@Tick

iTrader: (3)

10% is generally accepted as what most normal pump gas contains today.

No it does not have that ability.

I would say 9:1 in a N/A motor or any motor is 93 pump friendly, but that is right on the verge of being too much. 8.8:1 is about as high as I like to see it and still be ok, leaving room for variance between gas stations.

I will talk to some of my colleagues about your question as I think I know the answer, but want to confirm.

Sales2@Texas-speed

iTrader: (5)

So is anybody in this thread going to roll out any of the other variables that go into whether or not you can run pump gas? IE: Climate, cylinder head efficiency/design, the rest of the cam specs which affect cylinder pressure, quench, etc.

Sales@Tick

iTrader: (3)

The only cam specs that affect cylinder pressure are total duration and ICL of the camshaft.

Cylinder head efficiency is pretty much a given as he is running 243's as stated in the first post.

He's got a stock short block which have the piston out of the hole .006 and if his heads have not had the quench pad modified then his quench is the same as any other 243 head out there.

Sales2@Texas-speed

iTrader: (5)

Pardon me, of course the exhaust valve is open while the piston is coming up from BDC to TDC on the exhaust stroke so it's not cylinder pressure building, but rather scavenging we're concerned with. None the less, the ability and efficiency of getting rid of burnt A/F mixture in the cylinder is absolutely a factor in what octane can and should be run (not to mention being huge in terms of where the powerband lies and average numbers on the dyno graph!)

OutrunNAScaR14

iTrader: (4)

No man keep the questions coming I'm learning here

SS10Tech

Higher static compression ratios help with scavenging as the pressure allows the cylinder to be fully scavenged of expended fumes. Dynamic is understood as when the intake is closed and compression is building based on all of the variables of valvetrain events and cam phase. The octane on the exhaust stroke does not really matter as any un-burnt fuel is being exhausted at this point - the higher the CR the more efficient the burn process and the improved efficiency on all 4 phases of a 4 stroke engine. Also the tighter the quench and better squish/swirl design the more complete the burn just after TDC and also decreased detonation possibilities BTDC.

Timing allows for the latency of the spark to actually ignite the fuel - higher compression ratios speed up this process. I would say it puts more emphasis on quench, squish, ICL, LSA, chamber design, exhaust valves that hold heat causing sources for detonation on the compression stroke, etc. but not the exhaust stroke itself - at least not independently.

You can also get away with more compression and timing at night. Or in high humidity where the water content of the air is greater.

Sales@Tick

iTrader: (3)

You just went off on a tangent that was not highly relevant in this thread.

LS heads being on a 15* valve angle stock are naturally efficient. They have faster burning chambers than a SBC or SBF head of relevant valve angle. One of the main reasons why they require so little ignition timing compared to one of those motors to make peak power. You can really get away with more in one of these than you can using an older school train of thought.

The exhaust valve being open when the piston is coming up from BDC to TDC has no effect on dynamic which will determine what octane fuel may be used. Getting it out is the EVO events job.

As SS10tech pointed out, when you take care of the static by raising it and coincidentally also raising the amount of DCR per degrees of crank rotation, you end up raising the volumetric efficiency of the motor by itself. This in turn raises the efficiency of each valve event either building more torque on the same events you'd run with lower compression or building more torque and more horsepower on larger events than you'd normally use with a lower compression engine because you can get away with making it larger in terms of duration and it's effect on valve events when you raise compression.

A proper EVO event will exhaust the cylinder properly and complete piston blow down by doing so if specified correctly for the application. I understand your thought on making the most use out of the energy given from the power stroke, but that still didn't apply in this case to "how much can I mill my 243's and still run pump gas".

vmapper

iTrader: (8)

Hmm, ok Ill just through out some specs.

Advertised Intake Duration 281
Advertised Exhaust Duration 289
Lobe Seperation 115
Intake Lobe Centerline 114
ABDC = 74.5°
BTDC 26.5°
BBDC 80.5°
ATDC 28.5°
overlap 55 Total Cam Advance 1°

LS6 heads (243 casting)
66cc chamber
Bore 3.905 / 3.622 stroke
Head gasket thickness 0.041
Head gasket bore 3.910
Piston to deck -0.006 (out of the hole)
-8.6 cc dished pistons
Quench distance 0.035

Static 9.723


Now can you add 14psi of boost (so double ambient) on pump fuel 93 ? how about 17?
Centrifgual type blower (procharger)

Typical ambient conditions
Ave 70°F,
26.31 in-hg
89.8kPa - 92kPa measured with baro
Humidity 27 - 40%
Typcial SAE correction factor 1.11-1.13

OutrunNAScaR14

iTrader: (4)

Hell yeah

mark21742

When I was doing my setup on my 408 everything I read for n/a said max of 8.5:1 dcr.....I ended up going 12.5 scr which gave me an 8.22:1 dcr do I could safely run full timing and get 0 knock....are you guys saying a could go higher on compression and still be very safe, or am I at the safe ceiling?

Sales@Tick

iTrader: (3)

Why are you using dished pistons to factor the compression? LS1's from the factory use a flat top piston and LS6 chamber size is 64.45cc not 66cc like the 241 LS1 heads have.

Also the stock head gasket is .052" compressed for pre 2001 graphite gaskets. 2001 and up use MLS gaskets .060" compressed.

You could run a thinner head gasket if you'd like. 8.5:1 is a standard recognized DCR value. 9.0:1 is as far as I'd push it and even then you'll have to be spot on with the fueling and timing.

Way2Fast

iTrader: (1)

So if I wanted to run as high a compression as I could, using either your ported 5.3s or 243s on a stock bottom end, what cc chamber, head gasket thickness and camshaft would you recommend? Goals being obviously most power achieved, ability to be driven on the street, and power peaking somewhere between 6500-6800 to allow shifts by 7000. Looking to run in the 10s at a race weight around 3500.

Other mods for this will include lifters, trays, pushrods, ls6 intake, ported tb and maf, oil pump, your 1-7/8" headers and off road y, 3.73s and yank ss4000.

Sales@Tick

iTrader: (3)

I know this was directed at Matt, but I would go for a 59cc chamber, .052 gasket and a 235/238 .621"/.615" 112+2 camshaft.

This would put you at 11.42:1 SCR and 8.49:1 DCR.

This set-up would be very nice. Throttle response would be great, torque for days even at 3000-3500rpm because of the added compression and peak would come in right at 6700-6800 and have a nice flat curve from 6600-7000rpm with the valve events chosen with that camshaft.

I'd go with the highest stage PRC offers for their 243 heads with this package. I'd even consider their aftermarket casting 227cc heads for something like this. Fly cutting would be required.

vmapper

iTrader: (8)

Just testing you on the stock specs. (not intentional) - should have also noted the bore 3.898 stock

Sorry should have included,
yes. Want to switch out using Diamond 11503.
Stock is 0.052 but want to switch to cometic to improve quench
66cc due to A.I. 243 reworked.
6.125 rods



regardless, the numbers are correct, the Dynamic comes in at? (its really low - low 7s)
so add boost on pump?

Do you guys carry 11503 w steel rings?

Grr

iTrader: (2)

switch to E85 and run the setup in my sig, with a little smaller cam. My DCR is 9.7:1 and it has torque like you average 408

Sales@Tick

iTrader: (3)

You kurmudgeon!

I think you'd be fine with that set-up. Quench on a boosted application should be more than in a N/A application, but that can be disputed depending on the builder you choose.

We do not stock that part. I'd try Texas Speed they stock just about anything and everything.

Camaro99SS

iTrader: (4)

I'm running AI's high compression 241's with a 58.5cc chamber and a 0.040" gasket and am sitting at ~11.5:1 running on 93 octane. Cam specs are in my sig. My tuner said the engine was well outside of any detonation issues and I don't have a nitrous tune. A lot of this is due to the welded chambers in the heads which are very efficient from being re-shaped. It's all about the combo as to what you can get away with.

Jason

Way2Fast

iTrader: (1)

Thanks for the reply. Now the question is, how much more power is the higher compression worth compared to normal comp ratio and are there any draw-backs or negatives to the higher compression setup?

Sales@Tick

iTrader: (3)

I'll just say a good bit of power is there to be gained, along with throttle response and the ability to run a larger cam without any loss in the low or mid range power department.

If kept to a smaller cam torque would be gained, along with some horsepower.

Mainly running a higher static compression allows you to get a little wilder with the cam timing which then creates more horsepower across the board while still retaining the low end power of the smaller cam that would be used with a lower compression engine.

No drawbacks when tuned correctly, and cam timing is correct!

Way2Fast

iTrader: (1)

That's good information to know. Not sure why everyone doesn't run higher compression, but I will be! Look forward to talking to you soon about getting my setup right.