How do you get around high compression?

[Anonymous]

How do you get a high compression engine (10/1 or higher) to run on regular gas (read that cheap gas) without mixing into the fuel various chemicals and octane boosts.
We all know that higher compression gets you better performance and economy but what good is that economy if you have to buy expensive additives to enjoy it.
I have tried a makeshift EGR system. I placed a 3/8 copper tube in one of my exhaust pipes and rerouted it to the intake manifold, but it didn't seem to help. I noticed no difference in performance or economy.
I have been considering diesel fuel in the gas tank (see other post), but apparently, .. not a good idea.
Is there a way to do it?

Doc

Has anybody actually done it?

 

[Asa]

search for Brocnr's posts on water injection
cheap and easy

EDIT: as a sidenote, i think he's boosted his MPG up 2.5 gallons on average, and i know how crazy you are about the milage
did i mention that the setup is cheap too?

 

[Anonymous]

I run water/alcohol injection on mine. Since your old school, look on ebay for the vintage 1980's Holley water injection kit. They go for around $30.00-$45.00 + shipping being they are obsolete.

Thats what I did and it works fine for me!!

A straight water mix works fine until the temperatures reach around 85 degrees, when it gets hotter than that I mix it 60% water 40% alcohol.

Later,

Doug

 

[rickwrench]

In addition to the above...
A cam with some overlap or a tighter LSA will bleed off pressure at lower rpms, reducing the effective compression ratio.
Also, a correct quench distance will help considerably.
Rick(wrench)

 

[wsa111]

Doug & Rick, are you using 93 octane???

Rick, a wider lobe center will bleed off more compression because of the later intake closing, yes & the increased overlap will also dilude the intake charge with exhaust just like an egr, so both situations work.

With a 10-1 ratio, a later intake closing will help keep cranking compressing under 200 psi.

All working examples welcome. William

 

[80broncoman]

All are good ideas.
Also if possible run propane or alcohol for fuel, .... It likes compression much more than plain ol gasoline.

 

[rickwrench]

Doug & Rick, are you using 93 octane???

In my Squire I use mid-grade 89 with no ping, and run about 10* advanced. Stock 65 engine.

Rick(wrench).

 

[rbohm]

Rick, a wider lobe center will bleed off more compression because of the later intake closing, yes & the increased overlap will also dilude the intake charge with exhaust just like an egr, so both situations work.

With a 10-1 ratio, a later intake closing will help keep cranking compressing under 200 psi.

All working examples welcome. William

actually a wider lobe seperation angle will close the intake valve sooner, as well as reducing the overlap, and will increase dynamic compression. that little trick will help a low compression engine "see" a higher dynamic ccompression ratio and improve power. it is when you narrow up the lsa and increase overlap, that you get a later intake closing, unless you design a cam with the later intake closing.

 

[wsa111]

For example Mike's 274 cam with a 110 lobe center intake opens 27 degrees before top dead center & closes 67 degrees after bottom dead center.
The same cam ground with a 112 lobe center intake opens 25 degrees before tdc & closes 69 degrees after bottom dead center.

Advancing the 274 with the 112 lobe center makes 29 intake opening & 65 intake closing will make more low end power because the intake closes sooner, but will raise the cranking compression.

Putting in a cam with more duration is a good way to let an engine run on lower octane fuel.

 

[rickwrench]

Heads with the step milled out to form a large quench surface, a cam with longer duration and a tighter lsa lets me run 10.6/1 in my Corvair.
The cam is a 280 with an lsa of 108, straight up. The quench distance is 040", but the pistons are forged TRWs so they expand some and tighten the quench. I run 93 octane and advance the initial timing to about 8*. No ping, screaming top end power.
Rick(wrench)

 

[rbohm]

For example Mike's 274 cam with a 110 lobe center intake opens 27 degrees before top dead center & closes 67 degrees after bottom dead center.
The same cam ground with a 112 lobe center intake opens 25 degrees before tdc & closes 69 degrees after bottom dead center.

Advancing the 274 with the 112 lobe center makes 29 intake opening & 65 intake closing will make more low end power because the intake closes sooner, but will raise the cranking compression.

Putting in a cam with more duration is a good way to let an engine run on lower octane fuel.

ok the difference between what i am saying and what you are saying is that you are using lobe centerline, and i am using lobe seperation. two different deals. wider lobe seperation angles means higher dynamic compression, narrower lobe seperation angles means lower dynamic compression.

 

[wsa111]

Guys,if you are closing the intake sooner, such as with a 108, your cranking compression will be higher, if you have a cam with a 114 lobe separation the intake will be closed later, thus a lower cranking compression.

If in doubt get a third opinion. William

 

[Anonymous]

Bill,

I run 89 octane
in mine untill the temp gets over 85-90 degrees, then I have to run 93 octane in mine.

My cam is on a 110 lobe center.

Later,

Doug

 

[rickwrench]

Lobe separation angle is the angle between the intake and exhaust lobe peaks. It does not describe where the intake lobe is clocked on the cam.
Moving (grinding) the peaks apart (wider lsa) reduces overlap. A tighter lsa increases overlap.
Two single pattern cams with the same lsa, one with a 260 duration and one with 280 duration, the 280 will have more overlap and less cranking pressure (bmep). Regardless of whether the cam is installed straight up, 4* advanced, retarded, whatever. 300+ duration and the same lsa, you would need a high compression motor to get the motor to even run at low rpm.

The overlap is the same on any single cam no matter where the intake event takes place as it is physical property of the grind.

Installing a cam 4* advanced definitely increases cylinder pressure, but that's a whole other can-o-worms.
Rick

 

[Anonymous]

heard of (and seen) decent results in both octane tolerance (knocking) and mileage with a little acetone in the fuel (about 3oz/10 gallon). Water injection, as mentioned, is a real good way to go, as well.

also:

xylene is around 114 octane,
toluene is around 112, both available at paint stores.

good luck
Ern

 

[6bangerbill]

There are several changes you can try without tearing into your engine, all of which can improve detenation, several of which are simple and easy. The first job is to replace your thermostat with a 160 or 180 degree unit. The 160 degree works best in the summer, the 180 allows the heater to work in the winter.( Iam assuming that your radiator is in tip top shape!)
The next change to make is to come up with a cool air ducting system( if you dont already have one) for your carburator or air inlet. You'll be amazed at the difference 10 or 20 degrees will make, plus the added horsepower.The last change requires the front cam cover removal to retard your cam 5 degrees or so. Before you do this, measure your cranking compression and intake closing point with a degree wheel for comparison later. If you replace your cam later you will want to know the intake closing point and dulpicate this point on your new cam. The last item to modify is the distributor timing through experimentation. Usually when the timing is reduced enough to prevent detenation, there is not enought timing for higher RPMs. Some times reducing vacuum advance travel will take care of part throttle pinging, sometimes using ported vacuum or switching to manifold vacuum will do the trick. It all depends on cam timing, temperature and octane. Ive used 10.5 cr with 93 octane and 24 mpg with no knocking or pinging after a month of tuning. Some times richening up the secondary carburator circuits on the carb will help.
Good luck!

 

[ASMART]

Someone mentioned 200PSI cranking compression as a figure to avoid as far as detonation is concerned. If I understand it correctly, this is basically 200PSI for BMEP(Brake Mean Effective Pressure?) Is there any info that would give us max BMEP to for each Octane raing?

 

[rbohm]

Someone mentioned 200PSI cranking compression as a figure to avoid as far as detonation is concerned. If I understand it correctly, this is basically 200PSI for BMEP(Brake Mean Effective Pressure?) Is there any info that would give us max BMEP to for each Octane raing?

8) not really, because so many things factor in, like piston dome design, combustion chamber design, rod length/stroke ratio, valve design, cam design, etc, etc. each may have a large or small part to play, but the parts are vital none the less. you can take two engines that are identical in every way, and make one seemingly small change on one, and its detonation resistance may change dramatically one way or the other.