Maximum compression ratio for A-series on pump gas

[Westfield_XI]

I am having a hot 1330cc engine built up for me by APT in Riverdide CA. I want to maximise the power, of course, but also want to be able to fill up at any high test pump. APT suggested 10:1 but I have heard that I can go higher with "fresh" fuel. They will make it anyway I want, so I wonder what experiences the members of the Forum have had.

 

[DrEntropy]

Re: Maximum compression ratio for A-series on pump

IMHO: 10:1 is about the limit, if not a bit high for what we can get as fuel on the street. Another member, Hap Waldron, has a great deal more experience tweaking Spridget engines... hopefully he'll pap up and offer his tuppence here.

...or you could buy an airplane to get access to AvGas! /ubbthreads/images/graemlins/devilgrin.gif

 

[Westfield_XI]

Re: Maximum compression ratio for A-series on pump

How effective are octane boosters? This is a playcar and I could always carry a few cans if I had too.

 

[DrEntropy]

Re: Maximum compression ratio for A-series on pump

"Snake Oil", the lot of 'em. Save yer money.

 

[Bugeye58]

Re: Maximum compression ratio for A-series on pump

Mike, I have a 1098 in NoCal that runs 10.4:1 on Chevrom premium, with 104+ booster. I can tell the difference without the octane booster. Of course, it <u>prefers</u> Unocal 108. /ubbthreads/images/graemlins/grin.gif
Jeff

 

[aeronca65t]

Re: Maximum compression ratio for A-series on pump

The octane boosters available at most auto parts stores need to be used in massive amounts to make any real difference.
My 1500 racer has about 10.25:1 comp ratio and I also drive another race car on our little Spridget team that has a 1275 with about 10:1.
Both will run on 93 octane pump gas if we back the timing down to a 'safe" point. But that really negates the benefit of having the high compression in the first place.
For the record, the 1500 runs nicely on 100 octane Sunoco GT unleaded ($6.80/gal) and I can use a max ignition advance of 32 degrees at 5000+ rpm.
If I run the 93 octane (rarely), I back things way down to 26 degrees of max advance to prevent detonation. You can't feel the difference in mid-range too much, but top speed is quite a bit lower.

 

[DrEntropy]

Re: Maximum compression ratio for A-series on pump

/ubbthreads/images/graemlins/lol.gif /ubbthreads/images/graemlins/iagree.gif *this* from a physics major(!)...

The "boost" concoctions only change the burn characteristics: extend the "flash" time (ie, burn time). With that, you can expect attendant problems with valve overlap and some pretty funky combustion events. There's no additive comparable with tetraethyl lead: it was bonded to the benzine ring with temps and pressures NOT found in a poured-in bottle of "boost"... Yeah, there's a "seat of th' pants" difference but it isn't a benefit to the engine. More like a trade off. Adding "Dry Gas" (alcohol) is about as effective.

Not tryin' to "pick nits" here... I'd HUNT for the Unocal instead of "horsepower in a bottle" every time! /ubbthreads/images/graemlins/wink.gif

 

[Westfield_XI]

Re: Maximum compression ratio for A-series on pump

Looks like I will be sticking to the APT suggested 10:1 then......They say it will run just fine with their cam and head mods. And since they worked closely with the guy who wrote the book (Vizard) I'll follow their advice.

 

[DrEntropy]

Re: Maximum compression ratio for A-series on pump

"Vizard the Wizard!" /ubbthreads/images/graemlins/england.gif

 

[GB1]

Re: Maximum compression ratio for A-series on pump

Stick with APT suggestions, they have done great work for me and their suggestions have been very sound.

They are a lil expensive, but worth the end result.

Tell Phil - Patrick says hi /ubbthreads/images/graemlins/wink.gif

 

[Westfield_XI]

Re: Maximum compression ratio for A-series on pump

They are a lot expensive, but then again, I wanted all the bells and whistles and the parts prices are the same as anywhere else. As far as the labor, well, that's what it costs in 2006 for that type of expertise. I just swallowed deep and went for it. Got the full Vizard treatment on the internals and belt drive timing and alternator. Gonna run their modded SU's for the mid-range and driveability.

 

[GB1]

Re: Maximum compression ratio for A-series on pump

What Cammy did you go with?

 

[Westfield_XI]

Re: Maximum compression ratio for A-series on pump

Not sure, I'm just leaving it up to them, I set the paramaters of power and driveability and let them get on with it. Having said that I recall a VP-3 being mentioned. I am in Switzerland for the next 3 weeks but can ask when I return

 

[JerryB]

Re: Maximum compression ratio for A-series on pump

The cam you use will have a large determination on what c.r. will work with pump gas and the iron cyl head.

Aero was right in saying lots of aditive is needed for small results. Problem is you forget to add and sometimes not availiable.

I would go a little lower on the static cr as fresh gas or not this is problematic.

You certaily want to keep the engine temps below 180 with a nice big radiator/airflow.

Follow Daves recommendations....he does a few street motors ...but good drivability/pump gas might not have compatibility of "but I want the big HP numbers".

 

[GB1]

Re: Maximum compression ratio for A-series on pump

/ubbthreads/images/graemlins/iagree.gif
Dave was great when I was assembling my engine, I would call him on Saturdays; he would be there cleaning up the paperwork and actually answer the phone.

Patrick