Making HP with todays pump gas

[spikebot 81]

Today I just got back from a well known local engine builder. This is a full machine shop builder with high HP experiance in buisness for 30 to 40 years. I went there to pick his brain about building a sbc engine that would not exceed 400hp for my 81 Vette. We talked quite a while about todays pump gas fuels in old engines with carbs. In a nut shell his opinon, was "Your not going to build a engine with a carb that will make 300hp with the junk gas coming out of the pump. Go fuel injection and modern electronics and I can make you any haul butt motor you want." He also told me that if it where him he would not exceed 8.5 to 1 compression on any engine with a carberator because you'll have to take out so much timing to keep the motor from detination. We all know what retarding the ignition does for HP. So ponder this info from a guy that built engines for some well known NASCAR drivers here in the NW and still building some really fast motors for folks from Seattle to LA .

 

[Hib Halverson]

What's the name of this engine builder or what's the name of his business?

 

[tracksnblades1]

I agree and disagree.
For his customers of unknown technical abilities and warranty concerns, I agree.
For your owner built and driven engines, I disagree.
Having said this though he has been in business a long time. I'm sure he can sort it ALL out by now.
For the unknown owner and driver I believe the control parameters within the computer would make better decisions than the uniformed and unknown.
Once that non electronic carb engine leaves the shop, he can only make reccommendations to the owner on fuel, timing etc. At the very least, the computer allows him some control. AGE QUOD AGIS Do what you do, Well. To all, Only the Best

 

[spikebot 81]

What's the name of this engine builder or what's the name of his business?

I didnt go there for the purpose of this shop to build a engine for me. I was really looking for cylinder heads that might be a good deal, but one thing lead to another and this conversation came up about todays gasoline and high hp. I really thought his comments where very entertaining. The shop caters to racing folks so fuel from the pump may not get much merit with them.

I would rather not list the Co. name. First time I've met the guy and was refered by a co worker some yrs ago.

 

[JohnZ]

In a nut shell his opinon, was "Your not going to build a engine with a carb that will make 300hp with the junk gas coming out of the pump. He also told me that if it where him he would not exceed 8.5 to 1 compression on any engine with a carberator because you'll have to take out so much timing to keep the motor from detination.

I'll disagree with that. "Today's gas" isn't any different than "yesterday's gas" - only the numbering system on the pump has changed; today's 93 octane is the same as yesterday's 96-97 octane. I've built (and still own) plenty of carbureted small-blocks with factory 11:1 compression ('67 Corvette L-79 and '69 Z/28), and they run just fine with plenty of ignition timing and no detonation at all; most folks don't understand that the factory L-79 and solid-lifter cams had late-closing intake valve timing, which reduced peak cylinder pressure (dynamic compression) at low and mid-rpm's, which made them much less detonation-sensitive than either standard "base car" or aftermarket cams in spite of their high static compression ratios. Aftermarket cams (which work fine in "race" engines) don't have that feature, in the never-ending quest for more power, and are very sensitive to detonation at higher compression ratios due to the rate of rise in cylinder pressure from early-closing intake valve timing.


Tuning criteria for street engines and race engines are very different, and it depends on lots more than just static compression ratio. Engines are a "system", and they need to be designed as such, with components carefully matched to each other for the intended application. L-79's and Z/28's with 11:1 compression will run all day long on pump premium without a hint of detonation if they're tuned properly and run the factory cams; install an aftermarket cam, and the whole ball game changes.

 

[spikebot 81]

Well thanks for that John. Might you take a look at the post I just sent about engine combo advise. Somehow I have it posted in the C5 section but asked the mods. to move it to C3. It should come soon and I really value your input. So many smart guys here, could'nt imagine owning a Corvette without CAC

 

[Hib Halverson]

"John-Z" is spot on and this unnamed engine building shop is either blowing a bit of smoke up your you-know-what or simply has far less knowledge than you think.

I have a 460-in BBC with 9.75:1 compression, a Holley 850 which runs in 91-oct and has no detonation problems.

There's plenty of evidence published in many automotive magazines and books which refutes this unnamed engine builders claims.

I'd find another engine shop.

 

[spikebot 81]

Your right on the money Hib. He might be all smoke but at least now I know the recomendation was invalid for this local shop

 

[lars]

As Hib and John have indicated, there is no problem whatsoever making power on pump gas with a carb - even using the ethanol-enhanced stuff that's mandated in most parts of the country now. We run 91-octane 10% ethanol pump gas in all of our dyno runs, and my engines are all in the 10:1 - 10.5:1 comp ratio range putting out 450 to 550 horsepower with less than 420 cubic inches. These engines run great on the street, but some tuning precautions are in order:

If the engine is to be street driven, I always recommend running a return fuel line system. A return line will eliminate the pesky vapor lock problems on hot summer nights with the high vapor pressure of current pump gas.

The ethanol-enhanced gas needs to be run richer than "pure" gasoline. Rather than running 14.7:1 at idle and cruise, you have to richen it up to 14.2:1. WOT mixtures with 10% ethanol likes to be in the 12.5:1 range for best power.

The modern fuels will not take as much vacuum advance as the "original" fuels, and you can get some "trailer hitching" effect (jerking) at light throttle cruise if you don't limit the vacuum advance to about 12 degrees-or-so ("normal" vacuum advance will run 16 to 18).

Henry Olsen with Ole's Carbs has written a good paper on the effects of modern fuels on timing advance - you can e-mail me for a copy. My current "Vacuum Advance Specs and Facts" paper also has a section dealing with setting up the vacuum curve for the modern fuels - drop me a note for a copy. Once your timing curve has been properly set up, running high-power carbureted engines on pump gas is no issue at all.

Lars
V8FastCars@msn.com

 

[Gohot]

I have a 86 Dodge Van, a cool windowless old Surfer van from Gardina California, the local group there at the time 'Competition Vans'. Now I'm not entirely sure they were hotrodders, but it would seem that the group were into the usual small builds. I have a complete Mallory system 4 bbl, headers and I believe a purpleshaft with the 302 swirlport heads and for all other respects what looks to be a stock motor. I moved out here to North Carolina in 06 and was pleasantly surprised to find that there are several Sunoco gas stations out here, and that 'pure gas' in the 93 octane was their usual venue. I know this is a Corvette forum, so pardon me but the point being the Sunoco gas. I burn regular quite often since I just putz to town and back and run errands and with the regular, non-Sunoco at about 55-65 mph. I can discern the slightest amount of ping. Very slight, but 'I' know its there. When on the other hand, I know I'll be traveling around and expect to put on several hundred miles, I'll buy the Sunoco 93. My mileage goes from 450miles a tank to around 525 miles a tank, 'no lie' and there is a complete absence of any ping or detonation. The gist of it is that it's my belief that the Mallory system and the Sunoco 93 make all the difference in the world. The difference in price is usually only around 5-7 cents a gallon. So bottom line is, the Sunoco or Shell 93 is worth the wear and tear on the motor and the cure for detonation. Around here, you do have to 'look' for pure gas, and it's likely only to be found at the premium service stations, the major name brand stations, and not the mom and pops gas and cafe.

PS. that would be about 8.5 to 11 compression on this motor

 

[Vettehead Mikey]

PS. that would be about 8.5 to 11 compression on this motor

I presume you meant 8.5 to 1 compression. If there's even a hint of detonation with this compression ratio while using 87 octane, something's very wrong. Might want to go back and check the ignition advance curve.

 

[Gohot]

ooooop's, your so right...! 8.5 to 'one'

And in reply to the ignition curve, I believe it's at the most advance possible before it goes to pinging.. It will smolder the tires from a non brake stop, just flooring it. I didn't make it obvious but I havn't timed it, but ran it as it came. So honestly I don't know the exact number BTC or ATC.

But really the point was the PURE Gas thing, and my belief in the usefulness of it compared to ethanol blends.

 

[Vettehead Mikey]

But really the point was the PURE Gas thing, and my belief in the usefulness of it compared to ethanol blends.

If by 'pure' you mean gas with/without ethanol, 93 octane is 93 octane or 87 is 87 irrespective. No difference from a detonation point of view. If your engine runs without detonation on 87, it won't make any additional power or get better mileage on higher octane. Complete waste of money.

Some drivers using extremely fuel efficient cars have noticed a decrease of 3-4% in mileage when switching to E10. That much variation in consumption on an 'fuel hog' like your van would be lost in measurement scatter.

 

[Gohot]

My measurement came from nearly 2400 miles of freeway driving out here from Ca. at a constant 65 mph. Tanks of regular yielded 450 miles to a tank and premium yielded 510-525 miles per tank. You can't have too much of a better condition, it was mostly level ground on I 40 east, and only once hit rain in Arkansas for a couple hours. That was simply the difference in octane and not the exclusion of ethanol which I really had no choice of picking along the way.