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Old 07-04-2008, 09:49 AM
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junkyard 13:1 compression SBC

Without going into too many details (E85) I'm thinking of building a junkyard 13:1-14:1 compression small block 350 mill for as cheap as possible.
basically I would like to pick up a decent hydraulic roller 1piece main 350 short block from a yard or local classifieds and use heads I already have.
Is it possible to somehow get this engine up to 13:1 compression just sourcing available used/junk yard parts? Are there any particular factory combinations or parts out there I can pick up to get this together? Or do I have to go the route of new pistons and/or milling the heads?
I have a stock L69 305 at my disposal, so I could use those heads (58cc I think). I assume the only way to do this would be to get some affordable cast high compression (domed?) pistons, and run a thin head gasket. Or maybe mill the 305 (or similar 58-60cc) heads for even less volume, increasing the compression. I would like to keep the amount of parts and machine work needed to purchase and at a minimum. If I go the milling route I *assume* I would need new push rods for the change as well as possibly needing to mill the intake to compensate.

thoughts? I'm open to ideas but really want to keep the cash out lay to a bare minimum. No expensive parts, extensive machine work etc.
Just a good useable short block w/ minimal work, maybe squaring it up, decent pistons, new bearings & rings, and throwing on those heads. the more I can throw together in my own garage, the better.

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Old 07-04-2008, 10:14 AM
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Why do you want 13:1 compression? Do you realize that you would need a very special fuel source for something like that?

I doubt if 305 heads and junkyard parts could get you into 13:1, and even if it did you would never get their flow rate to match that kind of potential.

I suggest getting a copy of "how to build maximim horsepower on a budget" by David Vizzard. Then you will know how to select junkyard parts to compliment each other with a specific goal in mind.
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Old 07-04-2008, 10:23 AM
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E85
I'm not trying to make max HP or even a high RPM screamer for that matter, nor am I trying to spend a bunch of coin on go fast parts. I would like a cheap, high compression engine I can cobble together so I can take advantage of the of this specific fuel.

Instead of buying a book I 'd like to see what feedback I can get within the forum.
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Old 07-04-2008, 10:53 AM
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Ethanol ay!! Well according to my source 57 cc heads on a stock 350 with flat tops will yeild about 11.2:1 compression. Your 305 heads might even have smaller chambers than that. Angle mill the heads and use thin gaskets and you should be getting pretty close.
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Old 07-04-2008, 01:12 PM
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thanks for the info.
Are there any production 350s (trucks, b-bodies, etc) that came w/ flat tops allowing me to resuse the full short block instead of popping for new pistons?
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Old 07-04-2008, 02:25 PM
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305 HO heads are 54cc chambers IIRC.

Shane
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Old 07-04-2008, 03:29 PM
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416 casting 305 heads are the best flowing of the 305 small chamber heads.Not that that is saying much for them they will onlyt rev to about 5000rpm.
Anyways a set of those milled down a few might get you close.
But you will have a torquey stump puller that will give great short bursts but no top end and cost you a fortune in fuel to get what you could get out of a basic hi-po pump gas street 350 with steep rear gears IMO.
My uncle had a iron headed 12:1 327 in his old vette and on 93 octane pump gas it was a useless pig,did nothing but ping and rattle.
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Old 07-04-2008, 10:22 PM
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You can build a low buck high compression 350 around these pistons

+.030 350 0 decked block 5.7 rod 58cc cylinder heads will give you a 14.74:1 compression ratio.
These pistons have a 14cc dome volume. piston dome to chamber wall edge must be checked. Minor edge clearance grinding may be required.
A fully ported #416 305 head with 1.94x 1.60 valves, (230-240cfm) port matched vic Jr
750-850 cfm holley
Isky # 201549 cam 1.5:1 roller rockers with 1- 5/8" headers should make 450-460hp on 110 octane race gas or methanol.

Just one of many ways to build cheap hp on a budget.

There are lots of ways to skin a cat.
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Old 07-05-2008, 04:04 PM
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Quote:
Originally Posted by y5e06
thanks for the info.
Are there any production 350s (trucks, b-bodies, etc) that came w/ flat tops allowing me to resuse the full short block instead of popping for new pistons?
Unless Im misunerstanding your question, the main things that will determine if your short block is worthy of a simple re-ring job will be the wear on the cylinders, pistons, crankshaft etc. Ive done many re-ring jobs before and the best candidates are from low output "grandma's" cars, truck with 2 barrel carbs and such. In a nutshell, motors that havent been thrashed and/or are low mileage. You can check to see if the bores are good to go without being bored out with a new piston ring and a feeler gage. 9 times out of 10 if it doesnt need to be bored out then you can re-use the old pistons as well.

Again, there is another book that is excellent for walking you through this entire process, if your intrested.
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Old 07-05-2008, 04:48 PM
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Stock parts won't live very long at that high of a CR. Most advise no more than 9.5-1.
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Old 07-05-2008, 05:04 PM
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E-85 is 106 octane.. can 13:1 even run on that?
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Old 07-05-2008, 06:22 PM
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Static CR is fairly irrelevant. The CR that the engine actually 'sees' is the DYNAMIC CR, which is determined by the cam. It is feasible that an engine could be built with a static CR of 13:1, but it has such a radical cam in it, that valve overlap bleeds-off so much compression that regular gas could be used. So, static CR doesn't mean too much without reference being made to the cam specs, from which dynamic CR can be calculated.

With E85 (which is 85% ethanol + gas), the octane rating is higher, but the energy per litre is lower than gas. This results in a fuel that is much more resistant to detonation/pinging, but releases less energy at ignition. I'm not sure how this trade-off puts E85 running at an optimal CR compared to gasoline running at an optimal CR in terms of power. However, an engine with a DYNAMIC CR tailored specifically for E85, will never be able to run on gas.

Cheers,
Ian.
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Old 07-05-2008, 08:26 PM
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Quote:
Originally Posted by v8hed
Static CR is fairly irrelevant. The CR that the engine actually 'sees' is the DYNAMIC CR, which is determined by the cam. It is feasible that an engine could be built with a static CR of 13:1, but it has such a radical cam in it, that valve overlap bleeds-off so much compression that regular gas could be used. So, static CR doesn't mean too much without reference being made to the cam specs, from which dynamic CR can be calculated.

With E85 (which is 85% ethanol + gas), the octane rating is higher, but the energy per litre is lower than gas. This results in a fuel that is much more resistant to detonation/pinging, but releases less energy at ignition. I'm not sure how this trade-off puts E85 running at an optimal CR compared to gasoline running at an optimal CR in terms of power. However, an engine with a DYNAMIC CR tailored specifically for E85, will never be able to run on gas.

Cheers,
Ian.
Every thing you've said here about octane compression and cam timing is untrue.
Cam overlap does not bleed off cylinder pressure. late(er) intake valve closing timing, does.
This later intake valve closing reduces cranking compression. But the actual cylinder pressure whem the motor is running at speed and near peak torque ( highest cylinder pressure, does not directly relate to cranking compression.
Charge wave tuning and volumetric efficientcy must be accounted for.
You cannot predict the fuel octane required based on "dynamic compression ratio" There are many many other factors involved.
The cam overlap does cause a EGR effect (exhaust reversion and charge delution) at idle and low rpm which like the egr valve on a emissions car
reduces the peak combustion temps reducing the tendancy to ping at low speed.
The thing is once the enigine is at or near the peak torque point, the egr effect is gone and the cylinder pressure is high. This higher cylinder pressure
BMEP requires a high octane fuel to resist detonation at WOT.
You can get away with pump gas (to a limited extend) at low rpm at part throttle (cruising) cause of the EGR effect and low cylinder pressure (late intake valve closing) at low rpm.
Once the motor is "on the cam" at WOT you will need high octane.

For E85 fuel the cr should be 12:1 or so up to 12.5:1 . (14.5:1 is a little too much)
You can do that with flat top pistons and max flat milled 305 heads (52cc) with some block decking and thin head gaskets.

With a very high compression ratio you need to open up the piston ring end gap a good bit as the ring runs hotter. Most ring end gaps specs for stock cast pistons are quite tight. Open them up to avoid ring end butting and piston top ring land failure.
Bigger ring gaps are better.

as long as detonation and priignition is avoided the cast pistons will work.
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Old 07-05-2008, 09:31 PM
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thanks for all the responses. there ar good nuggets of info to look into. I'm really not that well versed in engine combos/details.
oh, and I do now have Visards book.
some of the brief readings I came across indicated 13:1 or up to 14:1 for e85.
12:1 or so will be much easier to obtain w/ stock type parts as indicated above.
as far as the plans,
it would be the dirt cheap budget E85 motor as covered above,
as well as T56 trans (picked up this week), and 3.73's, in a driver '87 Monte SS (source of the 305 heads). I'm looking into the e85 carb conversions and off the shelf units. I figure an mild cam such as 460/480 lift and 220/230 0.050 duration, approximately (looking into this more as well), will be on the list.

Last edited by y5e06; 07-05-2008 at 09:38 PM.
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Old 07-06-2008, 12:00 AM
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Sounds like your trying to build a bomb! E85 won't do it, even 100% alchohol would be close for that kind of compression...and you want to run junkyard parts too?

Running a lot of compression to make use of a alchohol/gasoline mixture is a nightmare in the making and most certainly will teach you something about the dynamic climate inside a typical engines combustion chamber.

One of the things an octane rating won't tell you is how it is derived, this rating is done on a test stand at a specific load in a single cylinder engine about the size of lawnmower engine. This engineering model has nothing to with real world engine operating conditions and the ratings it is used to publish are for comparision purposes only.

Saying the E85 you get at the pump is the same as delivered to test stand engine is just not true, the reality is E85 collects moisture from the atmosphere faster than an open can of brake fluid. It is more likely the octane rating of the fuel you get from the gas station E85 pump will be closer to 92 octane from all the water you will have in it.

I'm all for building engines on paper for theoretical purposes but at some point you have to realistic about your expectations and realize that all the paper projections just don't work out in the real world.

If I were you I would work from a 100% alchohol engine and slowly add gasoline to the mixture to see just how much you can add before it detonates under load, of course you would have to rejet for every mixture change and retest on a dyno to figure it all out. At least you will have a certified mixture ratio to work from with pure fuels to verify the effect, I would start with a known fuel quantity like a race fuel delivered to your house in a 55 gallon drum with which to start from. Good luck getting a drum of pure pharmaceutical grade (99.9%) alchohol without a license from the distributor, they get real irate when you are not a doctor or own and operate a pharmaceutical manufacturing plant and try to order this stuff.

Of course if all you want to do is blow up an engine, go for it...sounds like she will run well until she melts those crappy factory pistons from the detonation you won't hear at 4500rpm under load...or the next load of E85 you get from the local station was delivered in a rainstorm and the actual octane is closer to 82 octane.

As is always the case, designing and building an engine to operate on the ragged edge of detonation for the street is a exercise in frustration. Reality will get you in the end and all you will end up with is a engine that "ran really well until it went boom!".

We have all heard the stories, even built a few myself.
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