pump gas engine vs. high compression

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wirenut

wirenut

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Hi All,
I'm new to racing and trying to figure a few things out this being one. i'm trying to buy a car, done or mostly done and one thing I have come up against is some cars I look at are pump gas motors, and some are high compression 11, 12, 13 to 1. What do I want and why? is the cost of racing fuel the consideration of going pump gas motor or is there more to it? I was told High Compression motors are more likley to fail? THe cars I am considering would be a BB 11-10 sec bracket. My thought is that the BB turns lower rpm so maybe reducing the incedence of breakage?
I appreciate any advice.
 
In the interst of affordibility, durability, conveinience, go with the pump gas motor. You COULD run high compression on E-85 but thatmay be an issue of availibilty in your area. High Compression engines will require usually somewhere around 108+ octane & at $8.00/gal at least filling up the tank, even for a week-end cruise gets pricey. Plus you have the issue of even findint THAT kind of fuel.
Today's technology let's you run as high as 11:1 on premium unleaded so I seriously doubt you'll miss having an extra point or two in compression.
 
You can run 10:1 with Iron Heads (9.5:1 is better) and 11:1 with Aluminum Heads on Premium Pump Gas.
 
well see all we have is 91... so you need to give an idea what pump you are using...

but your question for a race only motor go with 12.5:1... then you dont need to o ring the block but still gives you a big boost in power over 10:1... bummer you will need to run 108 or so leaded,

BUT, with EFI and having the pistons,valves, and chambers coated you can still run pump gas by backing off the timing and staying out of the throttle...

for a street motor 10:1 is a good number... something also to remember is DCR, or dynamic compression ratio, which is what the comp is with the engine running... thats a better number to use...
 
Throwing out "you can run 10:1 with iron heads" is a really vague statement. Without building a very specialized engine (exspensive) you cannot. 9.2:1 is about the limit for an untouched combustion chamber without quench. But all that's a whole nuther arguement. If you're worried about the price of gas at ALL, maybe you shouldn't even buy a race car.
 
StrokerScamp said:
Throwing out "you can run 10:1 with iron heads" is a really vague statement. Without building a very specialized engine (exspensive) you cannot. 9.2:1 is about the limit for an untouched combustion chamber without quench. But all that's a whole nuther arguement. If you're worried about the price of gas at ALL, maybe you shouldn't even buy a race car.
Click to expand...

I posted this as an effort to educate myself on a subject I dont know enough about, before I spend my money. In the past I have found this to be a sensible way to do business. My question was not wether or not it was more economical to run a pump gas engine. My question or more acurately part of my question was if the fuel cost was the only reason to consider running a pump gas engine.
 
wirenut said:
Hi All,
I'm new to racing and trying to figure a few things out this being one. i'm trying to buy a car, done or mostly done and one thing I have come up against is some cars I look at are pump gas motors, and some are high compression 11, 12, 13 to 1. What do I want and why? is the cost of racing fuel the consideration of going pump gas motor or is there more to it? I was told High Compression motors are more likley to fail? THe cars I am considering would be a BB 11-10 sec bracket. My thought is that the BB turns lower rpm so maybe reducing the incedence of breakage?
I appreciate any advice.
Click to expand...

Problem with Pump gas engines is most guys push the compression limits of this type of build and the engine ends up being on the edge of detonation. Now remember, Pump gas is VERY inconsistent and can vary drastically even from the same source.
Most times I recommend mixing pump and race gas on pump gas only builds if it's for racing or has more compression than it really should.
Any engine is likely to fail if not build right or taken care of...I've seen many high compression engines last years with regular maintanance.
Brian
 
ou812 said:
Problem with Pump gas engines is most guys push the compression limits of this type of build and the engine ends up being on the edge of detonation. Now remember, Pump gas is VERY inconsistent and can vary drastically even from the same source.
Most times I recommend mixing pump and race gas on pump gas only builds if it's for racing or has more compression than it really should.
Any engine is likely to fail if not build right or taken care of...I've seen many high compression engines last years with regular maintanance.
Brian
Click to expand...

Brian, What would taken care of and regular maintanance be out side of oil changes?
G
 
higher compression = you get more power out of the same amount of fuel. will detonate if the octane is too low or if the build is not a smart build ... quench, cam overlap, aluminum heads, good cooling system, etc. help prevent detonation

lower compression = you can run pump gas with no worries, iron heads, not have to worry about quench, etc. but you will get less power from the fuel (the fuel burns less efficiently).
 
wirenut said:
Brian, What would taken care of and regular maintanance be out side of oil changes?
G
Click to expand...

Lash, springs tested often and replaced when necessary, oil changes, filter inspection every so often, change plugs often, clean carb air bleed passages often, check compression on all 8 every so often, and it wouldn't hurt to check leak down every 4 months or so (depends on how much you run).
Like yearly checkups for us, engines that are raced and pushed hard should have checkups every so often. You would be amazed at how this can prolong the life of an average bracket engine from 3-5 years to over 10!
Also, on engines that run well over 7000rpm or make exceptional power and are run hard and frequently...teardowns yearly or bi-yearly are a must.
This is where most racers sigh...and they usually skip that procedure. But aside from gaskets and anything that might be going wrong, it's not very expensive and lets you see just what's going on inside and allows you to correct something before it goes bad.
 
This reply is only to the Original Poster, Wirenut.:

The answer to your question, truely boils down to the answer to a question only YOU can answer.....What are your goals? Is the future capability to run 9's IN the Goals? 12s,11s,10s are relatively easy.
The laws of physics apply heavily here.
http://en.wikipedia.org/wiki/Physics

Weight, and power at the tire....the rest is a driving game.

10:1 will only yield so much before 11:1 is the next bump,...then 12.5,......if big power is honestly the only goal you have Go Straight for 14:1 and 114 octane Race Gas.....and never a single drop of piss they call gasoline that comes out of pumps.

I know this 14:1 451 stroker....no power adder,....1000cfm carb....makes 650hp/550tq.....and its a relatively sane build.

To get power to the groundd is to maximize every square inch of a given Chassis for strength and rigidity, and builld a engine, trans and driveline and brake system that has 30% more in it than you need at any time.

From the start....you want to look for a body that is light...A-body good choice,....but 67-69 Darts and plymouth valiants are the lightest starting point.

Your doing well to look at Built or mostly built cars....your money will go ALOT futher.

Personally.....I recommend a 451 stroker in any Abody for a ton of fun.
Here is my fathers 2012 Racing Entry:
[ame="http://youtu.be/oAPM82lll9A"]302 Found[/ame]

I vote to go High Compression right off the bat if you dont intend to add any power adders on down the road.
There is nothing to the maintanence, but charging the battery(s)....removing the valve covers, rotating the engine and checking the cold valve lash.....and changing the oil and spark plugs every so often.


Good Luck!! :cheers:
 
The funnest car I have is a 74 Duster 440 with a 727 trans runs 11.80 off the juice.
The car is jump in and go.
Change the oil every 3000 miles.
Most likely I could run regular un leaded gas 87 octane.
Maybe 8.2 comp

Trainer car
IMGP2002.jpg


Trainee Jon
IMGP1283.jpg


0819001652.jpg


10 sec street car off the juice
440 727
11-1 comp

0102111543.jpg


Pinks
P7040810.jpg


9 sec 120 octane $14 a gallon
It takes about 3/4 gallon per pass
14.5-1 comp

P7030800.jpg


Unknown-4.jpg


This car every 50 pass's the trans comes out and torn down.
Trans brakes are hard on parts
Oil change every 20 pass's
Nuts and bolts checked after every race.
The car is harder to drive.
I get about 50 pass's out of the back tire's because of John Force burn outs

Like I already said the duster is the funnest car I have.
 
Thank you all for the constructive advice
 
My stroker has alum heads and 10-1. I think it is about the limit for 93 pump gas. I run the piss outta it and think the valve giudes may be getting loose. The 2 gallons of oil gets dirty very quickly too. Revving the engine is probably the hardest thing done to it.
 
wirenut said:
Thank you all for the constructive advice
Click to expand...

Without getting into technical stuff - I think Brian's dead on. IMO, you need to decide a few things - Class to be run and budget (overall and engine) need to be worked out. THEN you can decide on what will work for you, and what concessions if any are needed. A lot of bracket guys are going pump gas due to cost. But just like Brian said, the consistency of pump fuel is terrible. So you have to realize that fuel can cost you the round when otherwise everything is perfect. IMO, if this is a race effort, start with the budget, then work out the class you can be competitive in. An 11.60 car will be put together much different (and be much cheaper) than a 10.90 car and a 9.90 car is that much more than 10.90.
 
Well, what a can of worms!!! Theres alot I havent given much thought to. I think I'm more confused now LOL. Thanks again everyone.
 
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