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Old 04-02-2009, 01:58 AM   #1
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gas mileage hit for aftermarket camshaft?

Hey guys. My buddies are all avid 4 banger fans (I'm sure most of you can see where this is going). I'm not one to knock other cars, but they however are being quite relentless in their V8 bashing - we've heard them all at some point. I challenged them to a competition that states by the end of the summer, I can build my GTA to get better gas mileage during typical cruising, yet still take them in a race.

Now for the question; I was wondering what kind of hit I'll see in gas mileage with a moderate cam. Something that can theoretically break the 11s on my 350, which will have the HSR, AFR 195CC heads, longtube headers (with cutoffs), and a few other less notable mods. I will be doing all computer tuning and will fab up an EGR system so I can engage highway mode in the stock computer. It will also be transfered through a T-56, with the nice 0.5 final gear to help. I'm shooting for 35mpg before the camshaft switch, just as a personal goal. I'm just curious if I should brace for a 10mpg hit, or a 15mpg hit, or what.

On a side note, the biggest V8 basher will be piloting a honda. I'm not one to take these turbo cars lightly, which is why I'm shooting for 11s on the motor. If they can break into 11s by then, a 150 shot might be in order. Thanks for all the help guys.
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Old 04-02-2009, 11:58 AM   #2
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Re: gas mileage hit for aftermarket camshaft?

You'll never get 35mpg on a V8 like that. No chance. 25mpg would be AMAZING. You also won't hit 11's unless you have mondo camshaft. Or an LS style engine or something.
You can't win that argument. They win in mileage, let that one go. You win in style, torque, fun, on tap HP, etc. You'll beat the pants off of them in a race every time. There are VERY FEW 11 second turbo hondas out there. Honestly fast one, lots of braggers, but very few really fast ones. If you already have the HSR, AFR heads, etc, you're already a few seconds faster then them, let that be.
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Old 04-02-2009, 12:35 PM   #3
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Re: gas mileage hit for aftermarket camshaft?

with the HSR and T56, you better be able to do 15+mpg on the highway.. its all about cam and tuning from there.. high flow induction and smaller duration, high lift cam..
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Old 04-02-2009, 12:51 PM   #4
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Re: gas mileage hit for aftermarket camshaft?

Well heres my take on it. Now my understanding of what you want is a good MPG car that still gets great performance. Now although i think your goals of 35 MPGs and 11 secs are out of the question unless you have tons of money to throw ar this project i dont think its out of the question to pull off maby high 12s low13s and get high 20s MPGs. The thing you have to realize are a few concepts about how motors work. Now without getting into the real fundamentles of it (you can send me a pm if you want more in depth info) the 3 big factors that effect performance and MPGs are weight aero dynamics and engin displcement and efficency. Now because your primaily focased on the engin lets talk alittle more about that. As you probably know already engins have different levels of effeciency at different RPMs (interms of converting gas to mechanical energy). So for fuel economy perposes you want to hit your RPM of peek efficency at a very low RPM say like 2000-2500 where ever you spend most of your time just cruseing. This minimises the amount of fuel you use to generate x amount of torque. Now the parts youve selected shift the peek efficency RPM way up in the rev range to yeild better performance but the flip side is where you spend most of your time cruseing will be in a much less effeciant RPM. So long story short you have to make a balance between economy and performance. Now if your primary concern is to just beat them then i think we can tone it down a bit and improve on other aspects of the car to further improve it. I think here your best friend though is NOS. Because with that you can use very tame parts and still throw down great track times when you need to. Forced induction also has some very interesting benifits but since you wont be running it i wont waist your time with it other than to say in the MPG vs performance your at a significant dissadvantage to your friends.
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Old 04-02-2009, 01:29 PM   #5
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Re: gas mileage hit for aftermarket camshaft?

I believe it's Grim reaper who gets 30+ MPG with his L98 (350/700R4). I said 35mpg before the camshaft swap. With increased breathing (heads/HSR) and a T-56 with the 0.5 final, and a hell of a tune, I'm pretty sure I can get above 30mpg also. I'll obviously be making subtle changes to the aerodynamics. BTW, this will be a highway mileage challenge, not city. If I can still get above 20mpg with the camshaft, I'm pretty sure I can beat them at that also. The honda guy keeps talking about removing O2 sensors because they're useless, and none of them know anything about tuning.
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Old 04-02-2009, 02:39 PM   #6
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Re: gas mileage hit for aftermarket camshaft?

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The honda guy keeps talking about removing O2 sensors because they're useless, and none of them know anything about tuning.
Doing so will make your mileage worse more than likely, plus the ECM will wonder where the hell it went.
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Old 04-02-2009, 02:48 PM   #7
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Re: gas mileage hit for aftermarket camshaft?

You will 90% of the time never beat a honda in gas mileage... specially a turbo'd honda. Turbos make motors more efficent at every rpm. even if you get 35mpg before the switch they are going to be getting 35mpg-40mpg before they do anything

Now if they put a turbo on their car it will push their mileage up 5-10mpg... but if they just romp on it and drive it like they stole it, they will lose mpg.. but if your just going to cruise at 60mph your going to lose this bet.

I'd just try to make it faster and say screw the bet you have a better faster car. and be done with it.
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Old 04-02-2009, 03:12 PM   #8
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Re: gas mileage hit for aftermarket camshaft?

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You will 90% of the time never beat a honda in gas mileage... specially a turbo'd honda. Turbos make motors more efficent at every rpm. even if you get 35mpg before the switch they are going to be getting 35mpg-40mpg before they do anything

Actually turbos are less efficient at converting fuel to mechanical energy. This should be immediatly obvious when just looking at advertised kits that boast a 30-40% increase in power when there increaseing the effective displacement by 50%. There great for getting more hp per cubic inch than an NA motor and they have the potential to get better gas mileage if not driven hard but a NA motor vs an forced induction motor of the same effective displacement and mod level the NA motor will be a better performance motor. I know im going to catch alot of heck for that statement but if anyone wants to discuss the reason why this is true further anyones more than welcome to PM me so we dont clog up the thread.
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Old 04-02-2009, 05:08 PM   #9
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Re: gas mileage hit for aftermarket camshaft?

while i believe your answer has correct statements in it,

The only turbo's i have experience with would be my dad's srt-4 stage 3 4750hp and 501tq

Stock they get 32-38mpg

With the bigger turbo he went from 225hp to 475hp

and was running at 40mpg.

So in my eyes i think it would help.

and our 2.2L Dodge Neon Magnum gets 31-32mpg.

i'm sure injectors and a proper tune we could get the 2.2 running great and getting the same mpg.

But it would seem to me that the turbo helped out with mpg.

Also to just throw this in there, Turbo's are free power made off of the engines exhuast, and Superchargers run off the serpentine belt thus taking power to make power.

=]
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Old 04-02-2009, 05:28 PM   #10
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Re: gas mileage hit for aftermarket camshaft?

Yea there is absolutly no question that it will more than likely help MPGs.The reason is most of the time your not running the motor at max boost which effectivly makes it act close to its actual displacement. At max boost then it will act more like a larger motor produceing much more power. Although 2 motors of equivalent effective displacement NA vs FI have the same potential to consume fuel further more because the turbo set up is not quite as efficient as a NA set up for a given power output the NA motor would actually more MPGs at its peek performance level. However that dosnt really matter unless you run a circle track race or something of that nature because you dont normally drive at max throttle 90% of the time so the turbo car will likely do better overall. I also have to comment on the turbos are "free hp." They are driven by the exhauset yes which although dosnt really directly put a load on the motor persay it acts as a restriction eating up hp in a different sence. Which takes more hp to run, i can only speculate although i would suspect the turbo because where a supercharger is belt driven transfering nearly 100% of the motors mechanical energy to the supercharger the turbo ,although possably pretty efficient at converting exhaust flow to mechanical movement, i dont think could match the efficiency of a belt driven set up. Seeing that they both have to accomplish the same amount of work compressing air, which ever one is more efficiently doing so use less hp which in this example would be the supercharger. That being said i still think the turbo is better because you will hit max boost much sooner than an equivalent supercharger.
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Old 04-02-2009, 05:41 PM   #11
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Re: gas mileage hit for aftermarket camshaft?

Yes and no.

But not to take away from the topic.

The engine creates exhaust then exhaust gases, expand before the turbo and the expanding gas turns the turbines which force the turbo on the other side to spin and "force" air in.

so since the motor is already making exhaust gases with or without the turbo. it is "FREE" power.

Where as a Supercharger is driven off a belt system. and say a company tells you the supercharger adds 100hp. well a supercharger is about 40% loss 60% gain. So your really only gaining 60hp instead off 100.

=] look it up, you'll see what i'm talking about.
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Old 04-02-2009, 05:44 PM   #12
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Re: gas mileage hit for aftermarket camshaft?

i hit 8psi on my SC honda at 1500 rpm. by 2000 rpm its already at max boost of 10 psi. turbos take time to build, the large the turbo the more time it takes to produce boost.

before i put the SC on i averaged 28mpg/city. after SC is on i averaged 30mpg/city, this is with using very little boost due to not having proper fuel management to handle the boost. after i tuned it i am currently averaging 34mpg/city with moderate boost usage. This is in a car that weighs 2200lbs with me in it.
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Old 04-02-2009, 05:50 PM   #13
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Re: gas mileage hit for aftermarket camshaft?

well my dad would hit 10psi around 2k rpm and 35psi around 2800 rpm
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Old 04-02-2009, 06:07 PM   #14
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Re: gas mileage hit for aftermarket camshaft?

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Yes and no.

But not to take away from the topic.

The engine creates exhaust then exhaust gases, expand before the turbo and the expanding gas turns the turbines which force the turbo on the other side to spin and "force" air in.

so since the motor is already making exhaust gases with or without the turbo. it is "FREE" power.

Where as a Supercharger is driven off a belt system. and say a company tells you the supercharger adds 100hp. well a supercharger is about 40% loss 60% gain. So your really only gaining 60hp instead off 100.

=] look it up, you'll see what i'm talking about.
Well the thing is although i get what your saying it dosnt change the fact that it takes X amount of energy to do a certant amount of work. Now weather its compressing air with a supercharger or a turbo that amount of work does not change. Now the energy has to come from somewhere weather its belt driven like the supercharger or its takeing energy from the exhaust gases it still needs energy to work. Now it takes a certant amount of energy to expel exhaust gases and it takes even more energy to expel exhaust gases against a turbo as it dosnt spin freely. This is where it gets its energy from. So again its comes down to whats more efficient. Now as to the 100 hp gain comment im alittle confused here. Any FI set up will produce a certant percentage increase not so much a fixed number. I assume your talking about a specific application? Even at that if a company says it will add 100 hp it should add 100 hp. If you exclude the load the supercharger adds somehow by driveing it externally it may have added 160 HP rather than just 100 but if a company says 100 hp it should add 100 hp?
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Old 04-02-2009, 06:07 PM
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