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At what point should you stop using 87 octane, when looking to make decent HP by kawana
Started on: 08-21-2013 12:17 AM
Replies: 16 (538 views)
Last post by: IFLYR22 on 08-22-2013 12:55 PM
kawana
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Report this Post08-21-2013 12:17 AM Click Here to See the Profile for kawanaClick Here to visit kawana's HomePageClick Here to Email kawanaSend a Private Message to kawanaEdit/Delete MessageReply w/QuoteDirect Link to This Post
Im going to be starting a project car pretty soon, and im trying to plan out what sort of engine setup I want. This car is going to be a daily driver at some point down the line, and with 91 octane creeping up on $1.50/L, Im trying to keep the cost of fuel in mind. There is the very popular 3.8sc, but from my understanding, forced induction always needs higher octane fuel. If I were to build an N/A 3.8, could I get away with using 87-89 octane, while still making some decent HP?
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trotterlg
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Report this Post08-21-2013 12:27 AM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post
The way to get more horsepower is to get more fuel and air into each cylinder. When you compress it you get to a point that it detonates, and that is bad. I am afraid there is no free lunch here, lots of boost means lots of fuel and air which means you need higher priced fuel. Larry
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NoMoreRicers
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Report this Post08-21-2013 12:59 AM Click Here to See the Profile for NoMoreRicersClick Here to Email NoMoreRicersSend a Private Message to NoMoreRicersEdit/Delete MessageReply w/QuoteDirect Link to This Post
If it's knocking, you need more octane.
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olejoedad
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Report this Post08-21-2013 07:08 AM Click Here to See the Profile for olejoedadClick Here to Email olejoedadSend a Private Message to olejoedadEdit/Delete MessageReply w/QuoteDirect Link to This Post
The octane rating requirement of an engine is dictated by compression ratio. More compression or boost = higher octane.
E85 is one way around it, but fuel mileage suffers due to lower fuel BTU value.
Lower compression and more displacement would be another option.
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Slow6
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Report this Post08-21-2013 07:41 AM Click Here to See the Profile for Slow6Click Here to Email Slow6Send a Private Message to Slow6Edit/Delete MessageReply w/QuoteDirect Link to This Post
Yes you could use 87-89 in for a NA build, but what do you consider decent HP? If you want anything over 250whp then don't even bother with staying NA. I can tell you from personal experience it gets boring real fast.
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MulletproofMonk
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Report this Post08-21-2013 08:36 AM Click Here to See the Profile for MulletproofMonkClick Here to visit MulletproofMonk's HomePageSend a Private Message to MulletproofMonkEdit/Delete MessageReply w/QuoteDirect Link to This Post
Perhaps you are looking for a comparison like this...

The 3800na Series 2 makes 205hp. It runs 87 octane and is a 58% hp gain over the stock Fiero 2.8L V6.
If you start doing any HP upgrades other than porting the cast iron front manifold, you are going to start pushing more HP and should just do the 3800sc.
Pros: 87 octane and better power than the stock 2.8L V6
Cons: Same time and cost as doing the 3800sc (mounts and wiring are virtually identical)

The 3800sc Series 2 makes 240hp. It runs 91+ octane and is a 84% hp gain over the stock Fiero 2.8L V6.
It is very easy to start making more HP on the supercharged motor (3.4 pulley for example) and you are already into 91+ octane...
Pros: Plenty of HP upgrades and better power than the stock 2.8L V6. Mounts and wiring are virtually identical to the 3800na swap.
Cons: More expensive fuel, cost of motor is typically a little higher.

3800sc Series 3 is 260hp.

I have a 3800na that I just got running that I want to use as my daily driver. I'm also doing a 3800sc for pounding...

------------------
-Brian

My 87 GT Poly Suspension Upgrade (all pics) thread
Removing the roof panel
My HUD install thread
Modified stock air canister and base to 3.5 inch for 3800na

Isn't it strange that after a bombing, everyone blames the bomber, his upbringing, his environment, his culture, his mental state but … after a shooting, the problem is the gun?

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2.5
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Report this Post08-21-2013 10:20 AM Click Here to See the Profile for 2.5Send a Private Message to 2.5Edit/Delete MessageReply w/QuoteDirect Link to This Post
Your compression ratio in the cylinder dictates the need for higher octane, higher compression needs higher octane.

A boosted engine may require higher octane even with low compression.

I suppose you need to pick a hp number you want, or 1/4 mile time, and then decide how to get there.

[This message has been edited by 2.5 (edited 08-21-2013).]

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rogergarrison
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Report this Post08-21-2013 10:57 AM Click Here to See the Profile for rogergarrisonClick Here to Email rogergarrisonSend a Private Message to rogergarrisonEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by NoMoreRicers:

If it's knocking, you need more octane.


This is what I believe is right...depending on how much timing you want to run.

I had a professionally built turboed engine built for one car. They said with the lower compression in the turbo motor I had, plus the timing they recommended...that 87 octane was their recommendation that higher octane was just throwing money away for no benefit.

The way Ive always understood it is streetable boosted engines almost always have lower compression and only require 87. Octanes only benefit is that it deters detonation. If it dont knock/ ping under accelleration and high load, you dont need any higher. You might need higher IF you run a lot higher timing than normal, to prevent knocking you would have. If all things remain the same and you just fill up with 93 octane, you wont find any more magical performance. It will just drain your wallet faster. None of my recent cars ever ran any better with higher octane than they did with 87. I would run some thru occasionally because I believe there are more cleaning additives in it. My mom insisted on running 93 (premium) gas in her 4 cyl Pinto because better, more expensive had to be better for it. My 2000 Northstar Caddy said use only premium right on the dash. I never used more than 87 and it ran just fine without a single problem. I never understood it, but my 6 cyl Astro van also said to use premium ? It only got 87 for the 7 years I owned it and still runs like a new one.

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Marvin McInnis
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Report this Post08-21-2013 11:01 AM Click Here to See the Profile for Marvin McInnisClick Here to visit Marvin McInnis's HomePageSend a Private Message to Marvin McInnisEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by NoMoreRicers:

If it's knocking, you need more octane.


 
quote
Originally posted by 2.5:

Your compression ratio in the cylinder dictates the need for higher octane, higher compression needs higher octane.

A boosted engine may require higher octane even with low compression.


 
quote
Originally posted by rogergarrison:

Octanes only benefit is that it deters detonation. If it dont knock/ ping under accelleration and high load, you dont need any higher.



These are the correct answers. The antiknock ("octane") rating of gasoline is unrelated to its energy content. Using "high octane" fuel is unlikely to produce any more power in an engine designed for "87 octane" fuel ... in fact, it may produce slightly less due to its marginally slower burn rate.

That said, the key item dictating a particular engine's fuel antiknock requirement is peak cylinder pressure (and, indirectly, peak air/fuel charge temperature). Increasing the compression ratio and/or supercharging will increase peak cylinder pressure and temperature, and intake, valvetrain, or exhaust modifications may have a small additional effect. In fact, anything you do that affects engine torque (not necessarily power) output will affect peak cylinder pressure and temperature, and thus the detonation margin.

[This message has been edited by Marvin McInnis (edited 08-21-2013).]

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darkhorizon
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Report this Post08-21-2013 03:06 PM Click Here to See the Profile for darkhorizonSend a Private Message to darkhorizonEdit/Delete MessageReply w/QuoteDirect Link to This Post
Displacement is really going to be your biggest part of any equation involving octane vs horsepower.... dynamic compression ratio dictates what octane you are required to run, and dynamic compresion is directly related to displacement and horsepower....

Long story short, you can make 1 horsepower per 1 octane per 1 displacement... add more octane, get more power, add more displacement get more power, add both, get alot more power.

A 3800 SC runs fine on 87 octane.. my stock GTP will show ~10-15whp reduction in power, but the torque is still almost all there, and there is an element of danger in extended wide open throttle sessions.

Luckily its easy to switch up and down from 87 to 93 octane here... and its also EXTREMELY cheap to buy 93 octane over 87... its hardly even $1.50 extra per tank of gas.
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ricksmastermix
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Report this Post08-21-2013 08:55 PM Click Here to See the Profile for ricksmastermixClick Here to visit ricksmastermix's HomePageClick Here to Email ricksmastermixSend a Private Message to ricksmastermixEdit/Delete MessageReply w/QuoteDirect Link to This Post
You could raise the octane level with water/methanol injection. Windshield washer fluid is much cheaper than 91 octane fuel.
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Report this Post08-21-2013 09:40 PM Click Here to See the Profile for dobeySend a Private Message to dobeyEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by ricksmastermix:

You could raise the octane level with water/methanol injection. Windshield washer fluid is much cheaper than 91 octane fuel.


"If you can't afford race gas, don't go racing."

It's also much cheaper to take the bus, or ride a bicycle. No fuel costs, property taxes, car insurance, yearly safety inspections, or overly expensive repairs.

It's a compromise. You don't have carry capacity of a car or truck, nor the speed. But a bicycle will save you thousands of dollars, and you'll end up a healthier person (assuming you're a good cyclist and don't get ran over by an idiot in a car or truck). Likewise, building a project car is a compromise. If you want lots of power, and to go fast, you're going to have to pony up the cash for it, and that includes fuel and insurance. If you want moderately acceptable power in a Fiero, and great fuel economy, swap in an Ecotec 4 cylinder. If you want more power, and less fuel economy, go 3800. If you want a whole lot more power, and you're worried about the price of gas, then just go buy a lottery ticket.
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Report this Post08-22-2013 09:10 AM Click Here to See the Profile for 2.5Send a Private Message to 2.5Edit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by ricksmastermix:

You could raise the octane level with water/methanol injection. Windshield washer fluid is much cheaper than 91 octane fuel.


I have heard of this before, I thought people only injected it like one would nitrous for short bursts?
Wouldnt that be more corrosive, and not technically the same as higher octane?
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Justinbart
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Report this Post08-22-2013 09:59 AM Click Here to See the Profile for JustinbartSend a Private Message to JustinbartEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by ricksmastermix:

You could raise the octane level with water/methanol injection. Windshield washer fluid is much cheaper than 91 octane fuel.


------------------
Turbo 3800 E85 F23 5spd spec5
11.17@132.6

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fieroguru
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Report this Post08-22-2013 10:19 AM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
As you plan out your build, designing it around higher octane will allow more peak hp as well as more timing for better fuel efficiency which can help offset the premium for higher octane fuel. I filled up this morning and at the current price, there is an 11% increase from 87 to 93 octane. I was getting 20 mpg on my daily commute and 29 mpg on the interstate. Since I am running 93 octane all the time, I tweaked the A/F mixture and bumped the timing and now see 21.5-22 mpg on my daily commute that nearly offsets the higher fuel cost. Not bad for a thirsty V8 with 382 whp.

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crashyoung
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Report this Post08-22-2013 12:23 PM Click Here to See the Profile for crashyoungClick Here to Email crashyoungSend a Private Message to crashyoungEdit/Delete MessageReply w/QuoteDirect Link to This Post
I had 460 HP from my SBC 355 ci with 10.5 compression.
I ran high octane gas, 5% alcohol, and 5% nitromethane.
As long as you stayed off the loud pedal, it got very nice mileage.
But when you stomped the loud pedal, it got 13.07 seconds
in the quarter mile in street trim.
But that was back when gas was gasoline with tetraethyl lead.

What you can do with fuel made today? Depends on the mods you make!
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IFLYR22
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Report this Post08-22-2013 12:55 PM Click Here to See the Profile for IFLYR22Click Here to Email IFLYR22Send a Private Message to IFLYR22Edit/Delete MessageReply w/QuoteDirect Link to This Post
Understanding fuel ratings...
Octane is used when the rating is below 100 since octane is a ratio. Over 100, the performance rating is used. Example: A rating of 104 is a performance number when the mixture is lean, not an octane rating.

Most often, companies compare their products to a scale people are familiar with, Octane. 91 octane pump gas is 91 octane at lean mixtures, and 96 at rich mixtures. They still call it an Octane rating, but you are actually seeing the performance number at lean mixture.

Iso-octanes are good for knock retard, but only go so far (93 is about the limit at lean mixture without serious chemistry). So, most gas companies modify their formulas by adding knock inhibitors that simulate higher octanes. Prior to the introduction of catalytic converters, lead was (and is) the best knock inhibitor.

Fuel additives that increase the "octane" rating are actually knock inhibitors. You will be able to modify your timing with a better knock resistive fuel, but you will not necessarily get more power from the fuel itself. 87 octane ignites as easily as 93 octane.

The power gain is more from the timing, and not necessarily the fuel. Your optimal timing may be within the limits of pump gas rating for your compression ratio. The only way (I know) to see if your timing, compression ratio, fuel rating is optimal for your engine is to put it on a dyno, or use a data logger over varied driving conditions. Performance and Octane numbers only designate the fuel's ability to to resist antiknock and resist compression related pre-ignition, thus allowing beyond normal timing.

-Dave

edited for spelling.

[This message has been edited by IFLYR22 (edited 08-22-2013).]

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