65 Fuelie - 11:1 compression - Octane Booster?

[Michael H.]

Re: 65 Fuelie - 11:1 compression - Octane Booster?

That is all well and good until you realize that much factory "engineering" is done for financial expediency and not for performance optimization. The "bean counters" rarely let engineering have their way with things. Most if not all designs can be improved upon if a systems view is taken with optimization being paramount.[ATTACH=CONFIG]37104[/ATTACH]

Joe,Your chart seems to show exactly what the cyl volume is at a given piston position/crankshaft degree. Can you show the math/formula that you used to make this calculation?

[Joe C.]

Re: 65 Fuelie - 11:1 compression - Octane Booster?

Hi Duke,

Again I want to thank you and everyone else for all the guidance and wisdom. There is nothing like experience and you folks certainly have a bunch.

I think I have settled on the 30-30 cam for nostalgia's sake (I just remember how much I liked the sound). I will have the heads only pocket ported, port matched, and the valves/seats ground as you described. It looks like I will settle for 10:1 compression, realizing that this may cost me a little on the power side of things but I plan to drive at least 3k miles a year and don't want to worry about boosting the octane.

Looks like H beam rods and light weight forged racing pistons are going inside.

The engine will of course be balanced and I have asked that the flywheel and harmonica balancer be done separately, in case one need replacement I won't have to worry about the system being out of balance.

The folks performing the engine work have geat reputations and Jim Lockwood will be handling my fuel injection.

I also realize that timing is critical and will discuss this with the builders.

Brooks,

We spoke offline a few weeks ago, and settled the issue of how to configure your engine block. The correspondence then ended before a camshaft choice was made. I'm disappointed to see that you have settled on a vintage camshaft as opposed to an aftermarket roller. In light of your decision to go with a 346 cam, then I can tell you that in a former configuration, my engine was once built/"blueprinted" with the 346 cam installed 4 degrees advanced (as original), and 10.75:1 SCR while running on 93 PON gasoline with 14 degrees initial advance plus 24 degrees centrifugal, all in by 2200 RPM, as well as the standard 17 degrees vacuum advance. There were no detonation issues. I was able to temporarily advance the timing another 15 degrees (purely as a test for detonation) without detonation, which leads me to believe that the engine would have tolerated significantly more SCR than the 10.75:1 that I had built in. The above chart bears this out. I say TEMPORARILY because many people believe that more spark advance is always better. Contrary to mistaken belief, more spark advance is beneficial, but there is a point past which more advance will sap power away from an engine. It is generally accepted that maximum cylinder pressure must occur 14-15 degrees ATDC to develop maximum torque. WOT timing of 36-38 degrees (using a slow burn, vintage SBC cylinder head) will result in max pressure at this point. More spark advance causes max pressure to occur too early, which will significantly reduce torque!

You are making a mistake in building in only 10.0:1 SCR. If you are decking the block, then you should be using a modern composite gasket of .038" compressed thickness. The Mr Gasket 5800 in an excellent choice. You should be at 65cc chambers (if your heads have not been surfaced), a .038" thick gasket, 5.3cc domed pistons, and your decks should be shaved so that the pistons are .004" "out of the hole" when at TDC. This will give you a nominal SCR of 11.25:1 and a detonation-suppressing but safe quench of .034". You can further un-shroud the intake valve by safely enlarging the chamber to 66-67 cc which will increase high end flow even further and drop your SCR to a nominal 11.0:1, which is well within the non-detonation range when running 91 octane. You will be able to use a very aggressive advance curve such as the one I use, if you stay within these parameters.

Currently, my engine runs 11.30:1 SCR with a solid roller whose intake valve closing event is a few degrees EARLIER than the 346 (consequently higher DCR), .030" quench, 20 degrees initial spark advance with 16 degrees centrifugal all in by 2200 and 14 degrees (rather than 17) vacuum advance. I use 93 PON pump high test without a trace of detonation. A correctly engineered engine will deliver ALL of the power/torque and detonation should not be an issue.

[Joe C.]

Re: 65 Fuelie - 11:1 compression - Octane Booster?

Joe,Your chart seems to show exactly what the cyl volume is at a given piston position/crankshaft degree. Can you show the math/formula that you used to make this calculation? Or did you actually measure the location of the piston at these positions?

Michael,

Variables used:

• RD = Rod horizontal Displacement in inches
• ICA = advertised Intake Closing timing (Angle) in degrees ABDC
• RR = Rod Distance in inches below crank CL
• RL = Rod Length
• PR1 = Piston Rise from RR in inches on crank CL.
• PR2 = Piston Rise from crank CL
• ST = STroke
• 1/2ST = one half the STroke
• DST = Dynamic STroke length to use for DCR calcs

Plug these number into a formula to find the Dynamic Stroke (DST).

Calcs:

• RD = 1/2ST * (sine ICA))
• RR = 1/2ST * (cosine ICA)
• PR1 = sqrt of ((RL*RL) - (RD*RD))
• PR2 = PR1 - RR
• DST = ST - ((PR2 + 1/2ST) - RL)

Apply the formula to arrive at the dynamic stroke and substitute the result in the formula that you use to calculate displaced volume. Substitute the dynamic displaced volume for displaced volume in the formula you use to calculate static compression ratio.

Where:

SCR = (ring land volume + chamber volume + compressed head gasket volume +/- piston dish vol/dome vol +/- quench vol)/ displaced volume + (ring land volume + chamber volume + compressed head gasket volume +/- piston dish vol/dome vol +/- quench vol)

You may also use Google to find online calculators.

Joe

[Michael H.]

Re: 65 Fuelie - 11:1 compression - Octane Booster?

Michael,

Variables used:

• RD = Rod horizontal Displacement in inches
• ICA = advertised Intake Closing timing (Angle) in degrees ABDC
• RR = Rod Distance in inches below crank CL
• RL = Rod Length
• PR1 = Piston Rise from RR in inches on crank CL.
• PR2 = Piston Rise from crank CL
• ST = STroke
• 1/2ST = one half the STroke
• DST = Dynamic STroke length to use for DCR calcs

Plug these number into a formula to find the Dynamic Stroke (DST).

Calcs:

• RD = 1/2ST * (sine ICA))
• RR = 1/2ST * (cosine ICA)
• PR1 = sqrt of ((RL*RL) - (RD*RD))
• PR2 = PR1 - RR
• DST = ST - ((PR2 + 1/2ST) - RL)

Apply the formula to arrive at the dynamic stroke and substitute the result in the formula that you use to calculate displaced volume. Substitute the dynamic displaced volume for displaced volume in the formula you use to calculate static compression ratio.

Where:

SCR = (ring land volume + chamber volume + compressed head gasket volume +/- piston dish vol/dome vol +/- quench vol)/ displaced volume + (ring land volume + chamber volume + compressed head gasket volume +/- piston dish vol/dome vol +/- quench vol)

You may also use Google to find online calculators.

Joe

Joe,

Nice program. I'll take it for a spin. In the old days, we had to figure this out with calculators. Very confusing formula.

[Clem Z.]

Re: 65 Fuelie - 11:1 compression - Octane Booster?

i would not run a after market roller cam on the street without using a REV kit. this will keep the roller under pressure on the cam lobe so there is no "skipping" of the roller on the cam lobe. if this happens the roller and or the lobe and be damaged. stock hyd rollers on new cars have a constant pressure of the rollers on the cam lobe.

[Joe C.]

Re: 65 Fuelie - 11:1 compression - Octane Booster?

i would not run a after market roller cam on the street without using a REV kit. this will keep the roller under pressure on the cam lobe so there is no "skipping" of the roller on the cam lobe. if this happens the roller and or the lobe and be damaged. stock hyd rollers on new cars have a constant pressure of the rollers on the cam lobe.

Absolutely right! If the tappet loses contact with the lobe (due to "lofting"), then there is a risk of shattering the tappet when it impacts the cam, and releasing needle bearings into the nice engine
Rev kit is ESSENTIAL with solid rollers, although not nearly as important with hydraulics.

[Joe L.]

Re: 65 Fuelie - 11:1 compression - Octane Booster?

i would not run a after market roller cam on the street without using a REV kit. this will keep the roller under pressure on the cam lobe so there is no "skipping" of the roller on the cam lobe. if this happens the roller and or the lobe and be damaged. stock hyd rollers on new cars have a constant pressure of the rollers on the cam lobe.

clem------


Hydraulic rollers have been used on small blocks since 1987 and on big blocks since the introduction of the Gen VI big block. The valve train on these engines is essentially the same as previous flat tappet engines. There might be some difference in the configuration for LS-series engines, though.

[Domenic T.]

Re: 65 Fuelie - 11:1 compression - Octane Booster?

clem------


Hydraulic rollers have been used on small blocks since 1987 and on big blocks since the introduction of the Gen VI big block. The valve train on these engines is essentially the same as previous flat tappet engines. There might be some difference in the configuration for LS-series engines, though.

I think what Clem may be talking about is the cam ramp which the lifter/ roller lands on.

If there is not eneough preasure the lifter/roller will leave the cam at high RPM and land hard on the lobe penetrating thru the case harening of the lobe.

There was a difference on the landing ramp of a solid lifter cam vs a hydraulic cam that folleowed the cam with hydraulic preasure supplied by the engine oil preasure.

DOM

[Brooks R.]

Re: 65 Fuelie - 11:1 compression - Octane Booster?

Thanks Joe, I appreciate all the detailed information. I may reconsider the CR and go up to 10.5. The car goes in the shop on Monday so I can discuss the timing, gasket, etc with the folks at that time. The pump octane readily available in my area is 91 so I want to be sure the engine will do well with this number.

[Monte M.]

Re: 65 Fuelie - 11:1 compression - Octane Booster?

Brooks,
I am in thew same situation you were in a few months ago. My car is a few years earlier than yours, but basically the same thing. Did you end up going with 11:1, or did you go a little lower to make sure you had no problems?

I had settled on 10.5:1 until I started reading more and hearing what others had done. I also live in an area where 93 octane is a lot harder to find than 91. I too want to enjoy the 3000 to 4000 miles a year I hope to put on my 63.


If you are willing; What did you decide, and have you had the chance to fire it up yet. Any input from you would be appreciated.


Any input form any of you in the same situation would be appreciated.

Thanks,

Best of luck with the car.

M

[Brooks R.]

Re: 65 Fuelie - 11:1 compression - Octane Booster?

Hi Monte,

Sorry for the delayed response.

I just got the car back and I am very pleased with the results.

I went with 10:1 on the compression and the initial timing configuration is 10 degrees with no vacuum at idle.

All in with weights and vacuum is 32. I realize that is somewhat conservative but it runs strong and I can always step this up once things are broken in.

I was fortunate in that the engine builder performed the initial break-in of the cam on his dyne (2000 rpm for 30 minutes).

I asked him to run power pulls so he required me to get some 110 octane race fuel to ensure there would be no problems with detonation with WOT under load.

The tests were performed with a carburetor, not my fuel injection unit, but the results were great.

Four consecutive runs produced 353hp and 330 ft/lbs @ 6200 rpm. I am sure it would have done better with 11:1 and my fuel unit but I will take a little less performance for my peace of mind.

The 30-30 cam really came alive at 4000 rpm. Both curves jumped up and continued climbing steeply all the way to 6200.

The pulls started at around 3000 rpm so I don't have any data for the low end.

I am running 3:36 differential so I can live with the highway noise and fuel mileage.

We also set the idle at 1000 rpm which seems to keep things happy at the stop lights.

One last note, they balanced the engine so it spins up very quickly and very smoothly (I will have to watch my lead foot).

They balanced the rods and pistons to plus/minus 0.5 grams which may be a little tighter than is typical.

I learned something new. They balanced the total rod weight while matching the reciprocating end (crank), never heard this before but I am very pleased with the results.

I also found a 65 fuel unit that will be rebuilt by Jim Lockwood and if all goes well I will be driving the car to the show in San Diego.

Best of luck on your project.

[Timothy B.]

Re: 65 Fuelie - 11:1 compression - Octane Booster?

Brooks,

You installed a 30 30 cam with flat top pistons?

[Brooks R.]

Re: 65 Fuelie - 11:1 compression - Octane Booster?

Tim,

Yes they are KB flat tops and the cam is a Federal Mogul 30-30.

[Monte M.]

Re: 65 Fuelie - 11:1 compression - Octane Booster?

Tim,
I know of at least five or six people running the 30/30 with flat tops and they are all very happy.\
In fact, that may be the way I go with the engine I am building right now.
Monte

[Timothy B.]

Re: 65 Fuelie - 11:1 compression - Octane Booster?

I am not saying the engine will not run OK but I think you both are leaving lots of power on the table by not running the correct engineered compression ratio. Compression pressure (heat) is what vaporizes the fuel load, the gassed mixture is what makes combustion and proper combustion is what makes torque.

Low compression with a camshaft like that will make the low end manners even worse and sacrifice power at the top end. I am not aware of problems with detonation with these engines and the .125 pop up pistons.