Im looking at buying an old poncho motor that was hopped up back in the day(leaded gas, that was before my day...). Its got around 12.5:1 compression, and I was wondering what type of fuel Id need to run... Could I get away with avation fuel? Theres a place about 20 minutes up the high way that sells 100 octane(cant rember if is lead or unleaded) on the pump, that might cut it? I used to race motocross, and I still have connections and I can get pretty good prices on 114 leaded race gas, but a good deal on that shits still not cheep.... Any sugestions?
its an old wives tail about avgas... it is for running a lower rpms and will not help you up top...i ran 13-1 in abbc. if you own a station and like too wrench your motor go for it if not 9-1 is nice
It may cost you more to REDO the poncho than its worth. And 12.5 compression is too much for the street unless you're building a KICKASS street bruizer, and not a daily driver. You'll have to buy VERY expensive race gas if you can get it in your neighborhood. Last time I bought it, it was almost $4.00 a gal. Some guys buy it by the drum and it's alittle cheaper. Keith
I like working on my stuff, but theres a pont where it get to be not worth it... Im just not shure where I wanna draw the line... I am goin with an early poncho so Im alredy in for more work than an SBC... And I know there is some level of truth to the AV gas, but Im not shure to what point. When I raced moto I didnt run it, cause of some of the adatives and it just wasnt enough... I ended up running 118 oxygenated leaded race gas(and again, it was puttin out over 40hp out of a 125cc)... What is yalls opinion of what octane I should run on the street with a 12.5:1 CR? And whats the lowest I could get away with?
If the engine is a good deal you could always swap to later model heads with larger combustion here is a link www.wallaceracing.com/cratio0001.htm or back of the timing a touch and add water injection. just a thought.
Ive got a 6x2 cross ram that fits 55-60 so even if I could swap heads I wouldent want to... But... Will later heads fit the 59-60 motors?
[ QUOTE ] What is yalls opinion of what octane I should run on the street with a 12.5:1 CR? And whats the lowest I could get away with? [/ QUOTE ] That really depends on the cam. Something with a lot of overlap will bleed cylinder pressure at low rpm. Do a static compression check and see where you are at. I have run 180psi with 93 octane. You can also take some timing out to be safe. I would run 110 and see how it reacts, then mix some 93 and keep your ears open for detonation. Here in Orlando they sell Cam2 110 race gas at a couple of gas stations for $3.49 a gallon. I would drive my 12:1 race car on the street now and then. Made for an expensive night of cruising!
You don't want to try and run pump gas with 12.5:1. You can eternally mix AvGas or racing gas with pump gas to make it happy (50/50 should be plenty), but... ...if I were you, I would want more flexibility than that, and the ability to get gas anywhere. So, I'd probably get some thicker head gaskets (Cometic or Fatout probably have them in stock- if not, I bet they'd make em' for ya) and lose a point or so of compression that way. Then, I'd fill 'er up with pump premium (91, 92, or 93 in some places) and back the timing off until the pinging went away under full load. It's a band-aid fix, but it'll allow you to run the motor on pump gas without spending a ton of dough on it. If it were mine, I'd spend a ton of dough on it, but I'm goofy like that. I'd coat the heads and get the cam I'd need to make it work. I'd research teh head gasket thing and nail compression at about 11:1, which would be fine with coatings and the right cam. I'd also run a solid roller because I am a glutton for punishment and I actually LIKE lashing my valves. Solid rollers make more power anyway...and they sound just plain evil. You DO have a good ignition system on this thing, right? MSD or something hot like that? A good electronic ignition, I hope? At least HEI? Please? Scotch~!
Scotch is right on the money. 1. Thicker or double head gaskets 2. A multi pulse ignition that fires over the full dwell, Jacobs is an example of a top of the line ignition. 3. Run 93 Octane and make your own octane booster. Get a gallon of Xylene or Toulene to start and experiment with what works best. It only takes a little to make a difference. 4. Is it really 12.5:1? Do the pressure test. 5. Check out the web for home brew octane boosters. Ive run a 12.5:1 396 on a home brew mixture of Toulene and a dab of ATF for a few years now. Found an industrial place that buys it in 50 Gal drums and sells 5 Gal at a time to me for their cost. End result is way less cost than race gas.
Right now its got a big solid lifter cam... Not shure, but if it came out aof an old rod with 12.5:1 and dual quads, I bet the cam isnt anything mild... Can you get away with running 2 head gaskets especially on something with this much compression? Whats avaibel as far as thicker head gaskets go and how much can I get compression to drop by changing to a thicker or two gaskets? And tell me more about the home brew race gas... Where can I find out more about it?
you might increase your detonation problems by raising the heads with gaskets because you are increasing your quench dimension. I am not sure though
Ive got a du-coil distrubutor that I want to run... That is of course unless I find a magneto.... Ait this is a 59-60 ponch in case I didnt mention up there(not that it makes a big diffrance...) Thanks, Cory
The previous posts were on the money . Someone told you that it had 12 1/2 compression. If the deck is cut right ,if the head gasket is the right thickness ,if the head cc'c are right. But chances are it is not 12 1/2 . The only way to do it is to get it running and do a cyl.pressure check or a compression test. If the cam is large with a lot of overlap it will bleed compression off and it may only have a true ratio of 10 to 1. You can never the less change the valve lash and bleed off more or less. same thing on the timing ,it may not damage the engine with pump gas and 24 degrees of advance but may detonate at 32 degrees. Performance will proably suffer considerably as you detune it for pump gas. Unless it's free it's probably not going to work for you and if it's free just stick it in and run as long as you can. In my opinion the worse thing you can do is get a bunch of cans of fuels and mix them or store them in your garage.
the Du Coil is a good distributor, I ran one on my 394 Olds they are a little sensetive to initial setup and they give a good solid spark by doubling the saturation time but the caps and rotors are getting tough to find, for on the street running around I might try to find a slightly less exotic setup. or at least carry the stock distributor in the trunk, just in case. Paul
Lotsa good ideas here. I haven't tried mixing pump gas with anything but race fuel, but find the thought interesting (BTW JoeCool, I know 2 guys from Glenwood - small world - pm me if you care). The magazine I work for did a story last year (I think) where they stacked head gaskets 5 deep! That was on the dyno (it worked), and nobody wanted to try it on the street. Hmmm...Anyone here tried it??? If it were me, I'd go through that engine and make it what I want, rather than change my life to suit the engine - use modern (better) stuff inside, and leave it the same on the outside...Okay, first, I'd fill it with 110 octane and drive it as is, just for the adventure................
i would pull the heads then measure the deck height see what pistons are actually in the thing, popup/flatop? cc the combustion chambers of the heads measure the thickness of the head gasket in there now then do the math and see what actual compression the thing has, if you do need to adjust it at least you would know what measurements you would be changing i.e. piston to head, quench etc.when you went to a different head gasket. if thicker head gasket would get you into the ball park of where you want to be ,i would go with Scotch's suggestion of using the cometic brand, and have them build it the thickness you need, rather than stacking gaskets. Fred
Well, I dont think Im gonna get to try any of these great ideas... Ive hot a HAMBr whos going to sell me 2 60' 389's that need rebuilding, one with all the 4 speed stuff, and the other one is a really solid low miles motor, and some extra speed parts all for a fair price, so Im gonna go that route and build what I really want insted of what I can try to deal with.... Cause picture this... 389 that 60 over, a nice big cam, some head work, forged pistons(around 10:1), 6 94's set up with progressive linkage on a crossram, du-coil distributor(unless I fina a mag), and un corked lakes headers.... Mmmm I like the sound of that... not bad for someone whos almost 20 eh?
IF you do try to make your own octane booster, just make sure you know what chemicals you are dealing with, and how badly they can mess you up. Toluene is some pretty dangerous stuff.
There are a number of guys I know who run Av Gas in their stroked high compression Harleys and it works well. The small airport they get it from has a couple of grades of Av Gas, and the guys say it's cheaper than the $4.00 (and up) a gallon "race" gas a few stations sell. When they idle, it smells just like the exhaust at a drag strip when cars are running race gas. I have known guys who ran 12 or 12.5 to 1 compression in street engines, and got by by modifying the combustion chamber so that the squish band was "right", picked a good cam, had a reliable hot ignition, ran water injection and always ran top of the line major brand hi test gas, often with a can of octane booster. Unfortunately I have been on rod runs where they were nearly running out of gas in some back woods area and they were forced to buy some off-brand "hi-test" gas, that wasn't that good, and as they drove up hills the knocking in their engines made it sound like an umwarmed up diesel engine.
Yea, no joke. But Id still be intrested in hearing about the how to go about making your own octane boost.... Could be pretty intresting. Oh, and I just finished reading an article in the 1960 Hot Rod Annual that was given to me a while back by a hamber on hopping up the 59' pontiac motor. Their 389 ran with 12.2:1 CR ran well on 100 octane(leaded).. Puttin out 410 HP. Thanks, Cory
I'm not saying that you shouldn't, because I'd sure as hell like to hear all about it. I'm just saying that I've heard that you toluene will do bad things to your body...even if you look at it wrong!
Id be more intrested in looking into just to have that knowledge... Im probably going to going through some chemistry and haz-mat classes pretty soon... Might actuly try it one I have a fuckin clue what Im doin. Also, I was reading in the 1960 Hot Rod Annual, and the head mods to the combustion chamber actuky drop the CR by one full point(12.5:1 to 11.5:1), and that combined with a thicher head gasket and I shouldent have any problem runnin on 93 octane with a little some octane boost.. Something kind of intresting, while lowering the compression ratio on a somewhat stock motor from 10.5:1 to 9.5:1 the combustion chamber head mod still showed a slight increse in power... So if any of yall have any heads I can pratice on... Oh, if anny of yall have any 55 poncho rocker arm studs(and thoes pivot ball things , cant rember what there called) let me know. Where are some of the best places to get parts for me to go in and build a motor like this... Forged pistons, high strength bearings, high flow oil pump, gaskets, cam, ect...
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