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  #16 (permalink)  
Old 11-10-2008, 09:39 PM
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Quote:
Originally Posted by coldknock
Not really, GM stuffed 10.8-1 compression into the LT4 engine, 10.5 in the LT1, with a short cam. They tamed the combustion with reverse cooling and a wide lsa, it was a nice engine. It really woke up with a better cam and ported heads too.

Like I said, nothing's written in stone. Many engine builders prove it on a regular basis. I've done it twice myself. Neither of the engines were what you would call docile though. Not even a daily bruiser kinda engine. In fact, they both ran better with 110 gas and a bit more timing. The point is that they can, and do, run on 93 octane on a regular basis.

I understand your point of view though. Once upon a time I would told me that I was a nutjob, but I learned.


Larry

Yea, so many modern engines are running around 11:1. It used to not be possible, and I wouldn't dare to try it on an old open chamber head with domed pistons, but with modern heads, intakes, cams, ignitions, and open exhaust systems the engines can take alot more than they used to. I think the LT1 is a great example becasue its not all that different from a Vortec engine.

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  #17 (permalink)  
Old 11-10-2008, 10:15 PM
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Ok, I'm learning a few things...

So I still don't know how total compression is measured in order not to screw up the engine, long or short run.
I have a daily driver 305cu.in. Ford engine, stock compression is 8.2-8.5:1.
Question is what is the cheapest way to up the compression and to how much ?
I read many hotrod mags. and I like the roller lifter arms myself.
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  #18 (permalink)  
Old 11-11-2008, 02:18 AM
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In my opinion, if it's your daily driver, leave it alone. Big mistake trying to hotrod your daily driver. If you want to hotrod something, start with the lightest body and biggest motor you can get your hands on.
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Old 11-11-2008, 08:07 AM
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that's not the whole story, oterwise you'd never see a hotrodded Chevelle with a 350, its a heavy car and a smaller displacement sbc. And that setup may be the most common one out there.
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Old 11-11-2008, 12:05 PM
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Quote:
Originally Posted by ap72
that's not the whole story, oterwise you'd never see a hotrodded Chevelle with a 350, its a heavy car and a smaller displacement sbc. And that setup may be the most common one out there.
It may be the most common, but that doesn't mean it makes the most sense. I, also, had a different mindset when I was your age.

Peer pressure and the opinions of friends is a strong motivating factor when you're a young man. If 2 dozen of your friends are urging you to change the cam in your 350 Chevelle daily driver and 1 old guy is urging you to leave the Chevelle alone and stuff a 500 inch BBC into a Vega, it's pretty clear who is going to sway you.

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Old 11-11-2008, 03:31 PM
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Quote:
Originally Posted by techinspector1
It may be the most common, but that doesn't mean it makes the most sense. I, also, had a different mindset when I was your age.

Peer pressure and the opinions of friends is a strong motivating factor when you're a young man. If 2 dozen of your friends are urging you to change the cam in your 350 Chevelle daily driver and 1 old guy is urging you to leave the Chevelle alone and stuff a 500 inch BBC into a Vega, it's pretty clear who is going to sway you.
well the vega would be faster, but the chevelle looks better, and you'd be hard pressed to argue that one. My favorite car is still my Olds Cutlass which was my first car and I still drive regularly. Aftr that its a toss up, I've drove some real fun cars, hell I had a 4cylinder S10 with a manual that was a blast to drive. (it was the iron duke for the 4cyl dirt track guys) Having the best power to weight ratio does not make the best hotrod- otherwise we'd all be driving motorcycles (whihc I also used to hotrod until I wrecked one).
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Old 11-11-2008, 03:32 PM
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There are reasons to my madness



I want higher compression so I can use 87 octane and get the same or better mpgs (without knocking or choking) as I get at 91/93.

I know there's more stress on engine parts, it's why I asked how much compression can stock engine withstand without excessive wear.
I don't have the money or the will to change vehicles to an econo model. This 1991 V8 gets about 15c - 23h mpgs with good oil and high octane.
Wider is Better and so is longer wheel base, far as comfy ride.
BTW if you never tried, the oil usually used for truck engines - Rotella - is both cheap and up and above any oil you can buy.

Is there a compromise or am I stuck ?
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Old 11-11-2008, 03:39 PM
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I'm toying with the idea of going slightly over 11:1 with a Vortec engine. The heads have been completely reworked and the chambers will be polished (they're on my work bench right now). I'm thinking of doing a short fill on the block, running an oversized oil cooler, and a 170 T stat. I think with all of that my cooling will be pretty close to the LT1's system. The cams I'm trying to decide between are the 60122 from lunati or the cc503 from Comp. both of these cams have been run in LT1's with 11.5:1. I may just page through the lobe catalogs and spec one out myself though.

I was planing on running a solid cam setup, but I just purchased a fully machined unassembled long block last night. Since its a roller block I figured I'll just go with a roller cam for easier upkeep and break in.

For my piston I'll be running a 2VR coated hyper from Speed Pro, and .040" quench. That should put me right around 11:1 depending on where my chambers finish up at.

And I know what F'bird is going to say, "Oh my God! you'll destroy a piston!" To which I'll respond, this has all been done before and proven.
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Old 11-11-2008, 03:41 PM
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Why are you using 91/93 octane fuel in a motor with 8.2-8.5:1 SCR? It should run great on 87.

And by the way, your thinking is skewed. If you raise the SCR, you'll need higher octane fuel, not lower.
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Old 11-11-2008, 03:42 PM
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Quote:
Originally Posted by Cyberats


I want higher compression so I can use 87 octane and get the same or better mpgs (without knocking or choking) as I get at 91/93.

I know there's more stress on engine parts, it's why I asked how much compression can stock engine withstand without excessive wear.
I don't have the money or the will to change vehicles to an econo model. This 1991 V8 gets about 15c - 23h mpgs with good oil and high octane.
Wider is Better and so is longer wheel base, far as comfy ride.
BTW if you never tried, the oil usually used for truck engines - Rotella - is both cheap and up and above any oil you can buy.

Is there a compromise or am I stuck ?
Get a set of AFR 195's, cam with short duration, and compression at about 9.7:1. It should run real well on 87. You can choose other head options too, and some may work better. 195's are pretty much a failsafe head though, they work pretty well in just about every application.
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Old 11-11-2008, 03:51 PM
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Quote:
Originally Posted by ap72
Get a set of AFR 195's, cam with short duration, and compression at about 9.7:1. It should run real well on 87. You can choose other head options too, and some may work better. 195's are pretty much a failsafe head though, they work pretty well in just about every application.
Once again, I am in disagreement with you mon ami. 195 heads won't support a short duration cam. And they are not a good match for a 305 motor on the street. Now, if this was a race only motor buzzed to 7500-8000, then fine. And 9.7:1 won't support a short duration cam either. Too much cylinder pressure for anything this side of E85 or race gas.
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Old 11-11-2008, 03:58 PM
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Someone mentioned to me this before, and I had a carburated engine Ford Crown Vic. before this Mercury. I always got a smoother ride and better mpgs with high octane gas. I am a techie and a gear head, please have the patience to teach me, how is it low octane gives better mpg and less knocking ? It's dirty gasoline basically, requiring higher detonation points, not lower comp..
Make me understand, give me all the details.

15 - 23 mpgs is the best this vehicle ever seen, or at least at 17y.o. and if I could get or wanted to get an econo car, I wouldn't be here asking questions.
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Old 11-11-2008, 04:01 PM
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I run a short duration cam in my Cutlass with 9.8:1 compression... So there's not really an argument there, not to mention what the factory is churning out...

You are right about the 195'2 being over kill for a 305 though. I was thinking of something more like a 350 with a hyd. roller cam and 1.6:1 rockers- which even with 210ish duration the AFR's would work on.

For a super cheap milage miser 305 I'd just use factory 305 Vortec's with cleaned up runners, maybe larger exhaust valves, long tube headers, a single pattern cam, 1.6 rockers, and a 600 cfm or smaller carb. Still shoot for about 9.7:1 compression, unless you have a unusually heavy car or super low gearing.
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  #29 (permalink)  
Old 11-11-2008, 04:07 PM
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Wait, a Ford 305?! well if its a ford you're on your own, I'm not into them really. From what I do know I'd just pull a 5.0 from a late model Explorer and swap the intake to a carb setup. But other's may have more to say.

As far as octane goes, higher octane reduces detonation, higher compression usually leads to higher octane- but there is a LOT more to it besides compression.

LT1's ran on 87 octane with 10.5:1- they were kind of the turning point on V8 design. more compression means more efficent, that's why you want it to go up, but there a lot of limiting factors on how high you can go.
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Old 11-11-2008, 04:10 PM
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Ap72

Thanks again, I know I didn't post my vehicle specs. so it's my fault but it's a 1991 Mercury Grand Marquis LS, heavy four door sedan.
Vortec is 4valve per cyl. heads ? Does Ford make anything similar ?
OK at least I got some idea where my compression should be.

Ah! if only I had my own JunkYard for cars
Given unlimited funds, yeah I'd swap engine and intakes, change transmission and rear gears to positronic. That's just mildly upgrading for not much performance, but I bet it would.

Last edited by Cyberats; 11-11-2008 at 04:19 PM.
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