Bore and stroke for new motor

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wikd69
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Bore and stroke for new motor

#1 Post by wikd69 » Mon Sep 01, 2014 11:21 pm

I'm considering building a bigger displacement motor, starting with a Big M standard block, forged flat tops with moly rings and a Callies 4340 crank.

I'd go with the standard 4.25 bore but I'm not sure what stroke to go with. I'm thinking I don't want anything bigger than a 505 or 525 CI build and would look at going with a Stage 2 871 blower at 10+ pounds of boost,, Fast EFI and a hat.

What do you guys think ? This would be a combo street / track motor like my little 427 but I don't want to have to tweak it as harshly to turn mid to low 9's.

What bore and stroke would you go with if you had the option for a brand new motor ?
1969 ProStreet Camaro RS Best 9.75@139 1.46 60'
Blown 427 BBC, TH400 w/Brake, Back-Half Ladderbar
Narrowed 12-Bolt, 4.10 Gears, Spool, Moser 33 Spline

http://www.marsh-racing.com/harrys_camaro-1.htm

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supernova
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Re: Bore and stroke for new motor

#2 Post by supernova » Tue Sep 02, 2014 9:32 am

Blackhoodmafia!!!! :mrgreen: :mrgreen:

1972 Nova SS
572 C.I. BBC

Best to date: 1/8
et: 5.28
mph: 134
new wt. 3340 lbs

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wikd69
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Re: Bore and stroke for new motor

#3 Post by wikd69 » Tue Sep 02, 2014 10:05 am

supernova wrote:try this.

http://www.wallaceracing.com/cid.php
Yup, been there, dinked with that. I was looking for real world feedback, on piston height, rod length and stroke. I've read that I want to get the longest rod I can to help minimize cylinder wear - but whats the offset disadvantage to a longer rod choice ? And as to forged flat-tops - what are other folks running and what should I avoid ? I've heard a larger bore size helps to unshroud the valves better but presents a broader combustion wavefront with can cause problems and limit RPM range.

I've read that the pro-stock and top fuel guys are running relatively small displacement motors, somewhere in the 500 ci range, with smaller (4.108) bores and longer strokes and they make incredible power albeit in a short-lived engine.

I'm still playing with the idea of going single or twin turbo on the new build, but space constraints in my street car will likely put the kibosh on that. The next option will be to step up to a larger, tighter roots style blower, either 8-71 or 10-71.

With this in mind, whats the best bore and stroke combo ? One of the benefits of keeping my overall displacement down is being able to re-use my current Dart 310's. I can send them out to be ported as needed to increase the runner size - they're already running the big 2.30 intakes and I can convert over to iconel on the exhausts. That will save me a fair bit of money. Staying with a standard deck height for the Big M block will also allow me to re-use all of my current top end hardware - cam, rollers, pushrods, rockers, heads, etc. More money savings.

This leaves just the long block to build. New Big M block, new Callies (or similar) crank, I might be able to re-use my current Eagle 4340 h-beam rods (or not), and a new set of forged flattop pistons.

All this combined makes the possibility of stepping up to a bigger CI motor possible. Given this, I need to figure out the best bore and stroke combo for the new build, and that will let me come up with a rough out of pocket cost to take back to mama :smt003

This new build (if I undertake it) will be a street / strip build just like my current setup, but I want to make larger power with a more reasonable build. This little displacement 427 delivers the performance I wanted but I have to run a large cam, very heavy springs and wind the snot out of it to do it. While delivery the goods, that combination has turned out to be very expensive to run on the street. I want the power, the low ET but with a more reasonable motor combo with a hopefully longer life.

I'm mostly in the mode to learn at this point and I may end up not doing anything, depending on the cost factor. But if I can get a plan put together to minimize my costs to something reasonable, I might be able to do this.

So what do you guys think ? Bore and stroke ? Assume I start with the standard 4.25 bore size and opt to re-use my standard length h-beam rods ? What sort of stroke and piston height ?
1969 ProStreet Camaro RS Best 9.75@139 1.46 60'
Blown 427 BBC, TH400 w/Brake, Back-Half Ladderbar
Narrowed 12-Bolt, 4.10 Gears, Spool, Moser 33 Spline

http://www.marsh-racing.com/harrys_camaro-1.htm

bracketchev1221
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Re: Bore and stroke for new motor

#4 Post by bracketchev1221 » Wed Sep 10, 2014 7:53 am

Build a 540. Building a small bore engine is not worth it anymore. A basic combo is a 4.25" stroke crank, 4.5" bore block, and a 6.385" rod. You can get it all internally balanced with the longer rod and it will live forever. Rod lengths, I have not really seen any issues with them. Engines like these don't really run long enough to develop significant wear. I use a 6.385 rod in my 540. On one carburetor, its made 910 hp at 7100 rpm.

silvanova
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Re: Bore and stroke for new motor

#5 Post by silvanova » Wed Sep 10, 2014 9:09 pm

^^ this. If it were me I'd even go 4.60 bore.
5.004 @142.6

bracketchev1221
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Re: Bore and stroke for new motor

#6 Post by bracketchev1221 » Thu Sep 11, 2014 5:49 am

Oh, I saw your comment about rpm limits. My 540 was run on the dyno to 7500 rpm and has been at 7800 in the car with teh 4.56's in it. So large bore has no effect on rpm. A 540 probably could use a 335 head as being correct. Having the supercharger on it, I think it will overcome a small 310 port by forcing air through it. And it will be really responsive at lower rpms. I ran my 540 first with a 325 Dart Pro 1 head on it, and managed to go 9.30's at 141 with it.

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Re: Bore and stroke for new motor

#7 Post by wikd69 » Fri Sep 12, 2014 10:45 pm

bracketchev1221 wrote:Engines like these don't really run long enough to develop significant wear.
Gee, I was feeling great until I read that line. :nutkick: :smt005 :smt003 :smt003 :smt003

I was looking at just the reverse, 4.25 bore, 4.5 stroke. That's a 510 ci motor, but I dunno if or what rods are available for that mix. That's a long stroke, dunno what that does under a blower...
1969 ProStreet Camaro RS Best 9.75@139 1.46 60'
Blown 427 BBC, TH400 w/Brake, Back-Half Ladderbar
Narrowed 12-Bolt, 4.10 Gears, Spool, Moser 33 Spline

http://www.marsh-racing.com/harrys_camaro-1.htm

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wikd69
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Re: Bore and stroke for new motor

#8 Post by wikd69 » Sun Sep 14, 2014 10:45 pm

Here's a different way to ask my original question. How do you determine rod length ? Are there just so many combinations of rod length with stroke, based on where your wrist pin is located ? What determines rod length ? One of my goals is to reuse as much of my current build as I can - cam, lifters, push rods, rockers, heads, etc. I'm running a set of Dart Pro-1 310 heads. These are relatively small runners for a big displacement motor. I can port them but if limiting my cubes can help me contain that cost, so much the better. I'm in the middle of replacing my old 671 blower (and have come to the conclusion that a turbo solution is probably not in my future) so I'm going to step up to a tighter 871 blower. More boost at lower RPM with lots of room to spin it higher.

I mean geezo, with my current .030 over 427 I'm actually hitting about 434 cubic inches. I'm running about 8.4:1 static and spinning my loose street blower at 12% over, making 10 to 12 lbs of boost. At that displacement, with that much boost, my 3650 lb ride launches with 1.44 60's, hits 9.75 at the stripe and makes just a hair under 140 mph. Not bad for a small displacement street motor - this little big block makes significant power and torque. One place it can really improve is in the bottom end - and the only real way to do that is to add more displacement. If my goal is low 9's with a lot lower 60' I need to add more displacement, pump in more boost and make more bottom end.

I need more horsepower overall and more torque in the bottom end. But, I need to try and live with the flow budget my small runner, big valve Darts deliver. Lots of cubes means lot of air flow which means more cfm all the way through. I can spin the blower higher, but not really that much higher. Realistically speaking, stepping up to 18 lbs of boost means really crazy dynamic compression and the need for really stout valve springs and things start getting more exotic for what is really a hot street motor.

I can port these heads if I have to, but I'd rather wait to see what I can do with a mix of boost and bore and stroke. I don't yet know where I'll hit the wall in air flow through these heads. I can step up to 1.75, 1.8 or 1.85 ratio rockers on the exhaust side, that'll open up flow out of the heads, but I'm only running 2 1/8" primary tubes on my headers, with 3.5 collectors. Again, it's going to be somewhat limiting on that end unless I step up to 2 1/4" (or bigger) header primaries, and that's another $800 to $1000 for headers.

So my goal here is to target a good bore and stroke to add cubic inches while staying within reason with my current virgin Dart 310's and my 2 1/8" supercomp headers. I'll port the heads if I need to, but unless I shell out for new headers, I'm stuck with what I have for exhaust.

You recommended just building a 540 ci motor. That may be too big for my virgin heads and/or current headers. Something in the 505 / 510 range may be better suited to allow re-use of my top end, etc. If I target that motor size, how do I come up with the best bore and stroke combo, and with that, rod length and piston offset ? If I do this, I'll go with a good set of forged blower pistons and moly rings, and would buy a good 4340 rotating assembly. The Dart Big M block has the extra head bolts coming up from the valley which adds extra clamping pressure - this is what I need to hit those high boost numbers without worry - for instance - 8.4:1 static compression at 16 lbs of boost generates 15:1 dynamic compression ratio. At 18 lbs of boost, it'll be 16:1. Things get really wild with blower builds. This is why the aftermarket block, 4340 bottom end and forged parts. Geez, my stock 454 block right now at 12 lbs of boost is living with 13:1 dynamic compression. This is why the starter puts his fingers in his ears when I light it up in the water box - that is just too damn cool - dunno why, but watching that track veteran plug his ears while standing next to me makes me grin :thumb: :smt003 :smt003

So is there a published chart for BBC's which provide stroke, rod length and wrist pin offsets ? I'm clueless on this.

Any pointers you guys could provide would be helpful 8-)
1969 ProStreet Camaro RS Best 9.75@139 1.46 60'
Blown 427 BBC, TH400 w/Brake, Back-Half Ladderbar
Narrowed 12-Bolt, 4.10 Gears, Spool, Moser 33 Spline

http://www.marsh-racing.com/harrys_camaro-1.htm

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wikd69
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Re: Bore and stroke for new motor

#9 Post by wikd69 » Sun Sep 14, 2014 11:06 pm

1969 ProStreet Camaro RS Best 9.75@139 1.46 60'
Blown 427 BBC, TH400 w/Brake, Back-Half Ladderbar
Narrowed 12-Bolt, 4.10 Gears, Spool, Moser 33 Spline

http://www.marsh-racing.com/harrys_camaro-1.htm

bracketchev1221
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Re: Bore and stroke for new motor

#10 Post by bracketchev1221 » Mon Sep 15, 2014 7:37 am

Here is my take on big block chevy combinations based on my bracket racing expereince. Rod length means nothing. It is a component of the engine to connect the piston to the crank. The biggest gain to long rod length is being able to make the counterweights big enough to avoid externally balancing and making the piston skirt shorter to make the pistons lighter. For a general purpose engine, the internally balancing is the biggest gain. I am not a big fan of small skirt pistons for anything other than a max effort engine. It cuts down on side thrust area to eliminate weight and drag, but concentrates the forces to a smaller area increasing wear on the parts. It also puts the wrist pin up higher in to the ring package and can involve getting into the oil ring and having to use ring supports.

If you are looking to utilize your stuff, and you have a 310 head, then get a big bore block. Use a 4.5 bore to unshroud the intake valve, because a 2.30 valve is more effective in a 4.5 bore than a 4.35 bore +.100 over 454 block. If you are worried about cubic inches based on your head flow, you can use a 454 crank and build a 509. A 310 head is a good size for that naturally aspirated, but you may be just choking any engine above 454 with the super charger on it. The 4" stroke crank will give up some of the low end torque that the 4.25" crank will make. My 509 ran a Merlin II 4.5 bore block and a stock 454 crank with 325 heads. I made just under 800 hp with it at 7300 rpm.

Stay away from playing with rocker ratios. Buy a cam based on what you want to do. Rocker ratios just mess with pushrod and valve angles trying to get geometry right and increase wear. And when you are done, you really don't know how the rockers have affected the duration of the cam. Put the lift in the lobe. Not the components.

As far as headers, we ran 2 1/8 headers on my 540 on the dyno when it made over 900 hp N/A.

I would look at getting your car to leave better right now where it is. You are losing a LOT in 60'. The car should be high 1.30's in 60' at least right now. The motor is making hp based on the 140 mph.

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supernova
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Re: Bore and stroke for new motor

#11 Post by supernova » Mon Sep 15, 2014 4:59 pm

IMO,
Harry, if you build a big BB the blower will have less affect on it. Unless you are planning to run your blower faster or putting a bigger blower on it.
with that said, IMO you would be better staying around or close to a 496-522 c.i. motor. Remember a blower motor is a torque motor and does not need to turned to 7800 rpm's. A short stroke big bore motor likes to be turned higher rpm's and doesn't make as much tq. than a longer stroke one does.
Case and point, My 572 is a 4.5 X 4.5 bore and stroke motor, my buddies is a 572 is a 4.600 X 4.250 bore and stroke motor. They're both 572 c.i. motors but here is the differences. Mine made 952 hp at 7400 rpm's and 812 ftq at 6100 rpm's. my buddies made 960 hp at 7900 rpm's and 750 ftq. at 6300 rpm's... neither motor has been dynoed on nitrous, we run the same size kit so it equals out on n2o. I out run him by 2 tenths and 8 mph in the 1/8 mile. and my car has been 250 lbs heavier. we predict that mine on the juice makes around 1200 ftq and his closer to 1000 ftq. HP is to close to matter but look at the tq. BIG difference. Big difference in rpm too........ :mrgreen:

Big bore short stroke motor combos came from Pro Stock mentality. I built mine like I did because I don't have a Pro Stock car and the last time I looked you don't either! LOL!!!!! :smt003 :smt003 :smt003 Now I'm not knocking those kind of combos at all "they work well"!!!!! But are they the best combo for every drag car out there? I don't so. I have raced against lots of big bore short stroke combos and most of the racer are shocked at how my car runs against theirs.

In your case you will be a step ahead staying on the smaller side of C.I.'s.... :thumb:

The bigger the motor the more blower you need to feed it!!!!!!!!!!!!!! :smt005 :smt005 :smt005
Blackhoodmafia!!!! :mrgreen: :mrgreen:

1972 Nova SS
572 C.I. BBC

Best to date: 1/8
et: 5.28
mph: 134
new wt. 3340 lbs

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Hitchcock
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Re: Bore and stroke for new motor

#12 Post by Hitchcock » Wed Oct 01, 2014 10:33 pm

You could always do a inch stroke and a 4.5 bore. Not to discredit what super Nova said, but in that combo there is lots of room for rod, and a durable piston. But super is right, heavy car likes torque.
73 Vette, moly back half
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bracketchev1221
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Re: Bore and stroke for new motor

#13 Post by bracketchev1221 » Wed Oct 08, 2014 7:21 am

Here is David Reher and Dick Maskin talking about rod length.

http://www.youtube.com/watch?v=CCd4jF-WqVY#t=277

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Mike Peters
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Re: Bore and stroke for new motor

#14 Post by Mike Peters » Wed Oct 08, 2014 12:18 pm

If you're looking for longevity in a durable street engine and not hung up on making the absolute most power, I'd opt for a shorter stroke to lessen the side thrust of the more severe rod angularity. Should be less wear and tear on pistons and rings. The Big M will accept lots of bore and we all know big bores helps the engine breathe easier. The blower will make all the torque you will need for the track.
"If winning was easy, losers would be doing it"

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wikd69
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Re: Bore and stroke for new motor

#15 Post by wikd69 » Thu Oct 09, 2014 5:41 pm

Mike Peters wrote:If you're looking for longevity in a durable street engine and not hung up on making the absolute most power, I'd opt for a shorter stroke to lessen the side thrust of the more severe rod angularity. Should be less wear and tear on pistons and rings. The Big M will accept lots of bore and we all know big bores helps the engine breathe easier. The blower will make all the torque you will need for the track.
Thanks for the comment Mike :)

I think I've pretty well settled on a 4.5" bore and 4" stroke with a 6.385 rod length. That ratio is close to that of my little 427 today and should provide a similar hp/tq profile, albeit a fair bit higher on the graph.

4.5" bore x 4" stroke yeilds a 509 cu in short block which is within reason for my Dart 310's and I'm scoping out a new 1071 blower to feed it, the combination of which can live with my current 2 x 750 CFM 4150 HP carbs after significant jet increases. This displacement also can use my current 2 1/8" supercomp headers. All combined this will be the most economical path forward for a much lower ET, higher MPH and lower 60's.

I'm looking at moving over to EFI with a hat on top of the blower later on and the above combo should be a perform platform for that.
1969 ProStreet Camaro RS Best 9.75@139 1.46 60'
Blown 427 BBC, TH400 w/Brake, Back-Half Ladderbar
Narrowed 12-Bolt, 4.10 Gears, Spool, Moser 33 Spline

http://www.marsh-racing.com/harrys_camaro-1.htm

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