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Engine Build Compression Question

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pikeapn View Drop Down
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    Posted: 14-November-2013 at 6:44PM
Ok, I'm throwing around ideas for an engine build.  My block is a 351w out of my 72 montego gt. (I haven't had time to get the casting numbers off of it yet.)  It will need to be bored 30 over and decked slightly.

I will likely be putting together a stroker 408 (forged crank?, H-beams?, and forged pistons), AFR 205 heads, and a roller cam.  I am hoping to stay under $5000 on the build, but know it'll go up quick (I will be building it myself except for the machining).  Again, I'm just throwing around ideas, and would like some advice.  It will be carbureted and naturally aspirated.  I basically want something that I could take to the track on weekends and beat all my friend's mopars.

My question is, what would be the highestish compression ratio I could run without doing much as far as cam bleed off, etc.  If I polished the chambers and smoothed the piston corners, would that help as well to reduce the chance of detonation?  I also know that I wouldn't be revving the thing up to 6 grand all the time, but I would like it to work well at a moderately high rpm while still keeping good lowish end torque.  I'm shooting for 500hp to the wheels.

I just need some ideas...  I won't be starting it tomorrow either.  This probably won't be finished for a couple years, since I have to get through school and don't have any money, lol.

Also, what would be a fair cost estimate for general block work?  I am trying to find a good machinist in my area and would like to have an idea of what it normally costs for a generic block overhaul. (Cleaning, mains, boring, honing, etc.)
- Andrew
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ilyes Quote  Post ReplyReply Direct Link To This Post Posted: 15-November-2013 at 12:55AM
Block work varies from place to another. I was quoted about $750 for a bore 30 over in VA, went to Maryland and got a guy do it for $250, and for that price, he event installed my new pistons (needed a press for it). My advice would be to check around, probably in a 50 miles radius and compare offers.

Concerning the compression ratio, you could go up to 10.5 before seeing any timing issues. Are you gonna go with stock heads or aftermarket? 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GranTorinoSport Quote  Post ReplyReply Direct Link To This Post Posted: 15-November-2013 at 5:00AM
First let me say the 351W is an outstanding engine.

Regarding compression ratio - it is sort of limited by fuel unless you plan on running special fuel. I don't know what the absolute CR is for pump gas Octane = 92. I would estimate it to be at or around 10:1. 

I know in my discussions with my engine builder that use of aluminum heads will allow use of a higher CR. Not sure if that is worth it, but it is something to consider.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pikeapn Quote  Post ReplyReply Direct Link To This Post Posted: 15-November-2013 at 1:21PM
Thanks, yeah I'm planning on using something along the lines of Aluminum AFR205 heads.  I just wish they weren't 2 grand...Dead  91 octane pump gas is what I'd be running.  What causes detonation anyway?  Is it just the residual heat left in the chambers?  I know aluminum has a much higher thermal conductivity than steel/iron.  I also heard that sharp edges will also increase the chance of detonation.  Is this true?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GranTorinoSport Quote  Post ReplyReply Direct Link To This Post Posted: 15-November-2013 at 3:31PM
Good to hear you are going with AL heads - I think you will be able to run a higher CR because of it.

Your thoughts on detonation are just about right on. The sharp edges is more of a general term of "hot spots", which as some engines age and get carbon deposits those can cause detonation as well. You are right that AL heads will extract the heat better, which is why I had to go with a lower CR on my 521 build (iron heads).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 15-November-2013 at 5:20PM
nice heads!
 
 
for a 408 i'd absolutely start with the 72cc chambers. I ran the numbers, with .030" deck clearance & a .040" head gasket a 6cc dish volume makes 10:1, & an 8cc dish volume makes 9.8:1 to give you an idea
 
you may have to leave a plug wire or 2 off if you only want to make 500 hp Beer
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pikeapn Quote  Post ReplyReply Direct Link To This Post Posted: 16-November-2013 at 5:20AM
Originally posted by Rockatansky Rockatansky wrote:

you may have to leave a plug wire or 2 off if you only want to make 500 hp Beer

Lol!!!Big smile

What kind of hp could I expect from a combo like this (and would this kind of combo work well):
 - AFR205 Heads (72cc)
 - Eagle Stroker Kit (Balanced, 6.25" H-beam rods, Forged crank & 5cc pistons) http://www.summitracing.com/parts/esp-b14125030/overview/make/ford
 - Hydraulic Roller Cam (Not neccesarilly this one, I would have one spec'd out for my build) http://www.summitracing.com/parts/hrs-cl220325-10/overview/make/ford
 - Edelbrock RPM Air-Gap Dual Plane intake (I got a used one for really cheap a month ago)
 - 1 5/8" Hooker Headers
 - 750CFM Speed Demon Carb (Vac secondary, Annular)

This was all I could think of off hand.  For the above items, I am already at $5000.

I was also wondering what the capabilities of a 351W block are? (assuming it is free of cracks and bored 30 over.)  I don't want to put a bunch of expensive parts into it just to have them ruined.


Edited by pikeapn - 16-November-2013 at 5:22AM
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Post Options Post Options   Thanks (0) Thanks(0)   Quote robot9000 Quote  Post ReplyReply Direct Link To This Post Posted: 16-November-2013 at 8:37AM
I think the real question is: what are you building this for?

If you are doing this to go racing, then talk to a builder to get the engine/cam/trans/diff/wheel combo correct. 

If you just want to impress the locals with a weekend hot rod, then you don't have to push tolerance's or go for ultimate performance and can same some time and $$$ (how much HP do you really need to sound badass and make black marks?  Way less than than you think, lol).

So I think your build starts with your goal.




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Post Options Post Options   Thanks (0) Thanks(0)   Quote pikeapn Quote  Post ReplyReply Direct Link To This Post Posted: 16-November-2013 at 8:58AM
Originally posted by robot9000 robot9000 wrote:

I think the real question is: what are you building this for?

If you are doing this to go racing, then talk to a builder to get the engine/cam/trans/diff/wheel combo correct. 

If you just want to impress the locals with a weekend hot rod, then you don't have to push tolerance's or go for ultimate performance and can same some time and $$$ (how much HP do you really need to sound badass and make black marks?  Way less than than you think, lol).

So I think your build starts with your goal.

I honestly don't care about impressing people, and I'd rather have my tires stick than burn.  My goal is to make it something I can drive to and from the track and do damage.  I want to build the most engine I can for $5000, while still keeping it dependable.  I am not planning on pushing tolerances to the absolute limit either.  I am just getting ideas right now.

The above plan is what I really want to do to it.  I may just go with a reasonably cheap rebuild if I get too impatient to save money, but in the long run I want to build it up.


Edited by pikeapn - 16-November-2013 at 9:00AM
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 16-November-2013 at 9:01AM
agree with robot on chasing a hp #, bottom line is that it's hard to not make 500+ hp with a good 408
I don't have or use any programs to figger TQ / HP output, but it's gona make good power unless the cam ain't right. i'd say you're right in the ballpark of you 500 @ the wheels goal give or take like I said depending upon the cam
the block should have a long life at this power level unless the tune is off(carb lean, too much timing) so bad it destroys itself, or it has an internal component failure that can't be helped short of X-raying everything before it goes together. FWIW an old bud of mine had about 10 sbc con rods to choose a set from, his dad was an X-ray tech & took pics of them all... at least 2 showed internal flaws
 
here's a link that gives more info on your kit than the Summit page shows
 
the stack height comes up to 9.495", which would give .005 deck clearance if the block is blueprinted to 9.5" deck... but your block if untouched will 999% probably be in the 9.510" -9.515" range. they aren't machined to published blueprint spec from the factory. so if your deck surfaces check out flat & good to go as they are w/o needing to be cut i'd estimate your deck clearance will be .015" - .020", which isn't too bad as far as quench with a .040"~ish head gasket. some builders IMO place too much emphasis on tight quench, as if there won't be any effect if the quench distance exceeds .055". Horsehockey! a 4" bore / 4" stroke smacking the A/F mixture into a chamber with a .080" quench gap is gonna cause some turbulence!
 
so anyway the exact CR will depend upon all the slight mis-guesses I've made & all the slight variations in the actual parts, your block, head gasket choice etc... but with a .020" deck clearance it comes up 10.3:1 & personally I wouldn't want to get it any higher than that. from that point there you can start to figure what the Dynamic Compression Ratio will be with some specific cam specs for the calculator inputs. some DCR calc's use an intake valve close point that you may need to call the grinder to get because they don't always give the info at the same degree point
 
it's the DCR that really tells you where you stand in the detonation world, the cam can play a role to either raise or lower cylinder pressure to make a low CR engine perform better or a high CR engine to run on pump premium rather than 116
 
the Airgap is reportedly a very good intake on 351 cube engines in the Cleveland family, there are definitely other intakes that'll make more power but in 'going along with the build' it's a good intake to give a shot. the big ol' Monty will appreciate the dual plane in daily driving
 
as far as beating the Mopars on the weekends, whatchya gonna do for a gear, stall & traction?


Edited by Rockatansky - 16-November-2013 at 10:03AM
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pikeapn Quote  Post ReplyReply Direct Link To This Post Posted: 16-November-2013 at 10:20AM
Thanks Rockatansky!  That's exactly what I wanted to know.  I am also just getting opinions on a good max Static CR number to work around.  From what I've heard, 10.5:1 is the max for pump gas.  And if that is the case, I will be going plenty down from that unless I cam it to allow some bleed off.  I just wanted to get some confirmation that I was right.  I know the Dynamic CR is by far the most important factor.  But I'd like to stay clear of a ton of cam bleed off.  From what I've read, that is best in a race engine in the high rpm range, and not for low end torque.  In my build, I am going to be looking for a compromise between highish end hp, and low end torque.

That eagle stroker kit was the closest thing I could find to what I wanted.  I know the compression is a little high with the 5cc pistons but the only others were like 19cc, and that was too far off.  Will Summit change pistons in a kit if they aren't the exact ones you want?

I picked up the air gap before I really knew what i wanted to do to the engine.  I know it won't make the highest hp numbers in a stroker.  But I got it for pretty cheap so I can't complain.  It can be slightly ported too

Lol, I haven't set anything in stone as far as gearing yet.  I will probably change converter, rear end gearing, and diff.  However, I'd like to do a manual swap.  Again, I am not sure.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 17-November-2013 at 11:58AM
sounds like you have a good grasp on reality. i'd rather build a 9.5-9.75 motor & not have issues than a 10.5 motor that I have to figure out how to get it to run on pump gas after it's together & running
 
you could always put your own kit together from individual parts, or make a call to someone that knows their stuff. Tim Meyer can't be too for from you www.tmeyerinc.com and can supply Exactly whatever you decide on
 
& don't be afraid to spec out the kit yourself, you wouldn't believe how many guys have major Cry malfunctions from 'experts'. just don't do anything to make the parts non-returnable like having them balanced until you mock them up in the block & know that the pistons don't come up out the top 1/4" or don't make it to the top
 
i'd run the Airgap as-is before doing anything to it also. it's not that big a deal to swap the intake & carb with a track set-up. most tracks don't like antifreeze so you'd be draining it anyways
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pikeapn Quote  Post ReplyReply Direct Link To This Post Posted: 17-November-2013 at 4:57PM
Thanks for all the advice!  I will definitely give him a call.  Yeah, I would like to spec and put the engine together myself.  I would prefer to get a kit though since things start to get a lot more complicated when you make your own, and I am not at that comfort level quite yet.  But it will be at least a year or so before I actually start with the build, so I might be by then.

I recently spent over $60 in books on the topic of engine blueprinting and rebuilding, so I can study up on all the little yet important things that I might be missing.  I have been picking it up pretty quick and the math is pretty simple (at least compared to what I'm doing in school right now, lol).  I am hoping to get into the engineering and design of engines when I get out of school.


Edited by pikeapn - 17-November-2013 at 4:58PM
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 17-November-2013 at 5:07PM
it seems the most frequent area even the experts get caught up on is for the pistons to clear the counterweights of the crank on the Bottom Dead Center sweep, if that makes sense?
 
it's hard to tell from a catalog if the connecting rod will be long enough to avoid piston skirt to counterweight interference, but the crank makers have gotten a lot better at supplying minimum con rod length info
 
1/2 of the stroke, or the 'throw' + the con rod length + the piston Compression Height(CH) = deck stack
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