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3/01/2018 7:48 PM  #1


On the subject of cracks in your block

The machine shop that is doing the work on my 302 roller block called me today to tell me they found a small crack in the exterior of the block on the back where the dowel pin is for the trans, driver’s side.  They think they can remove the dowel pin, repair the crack and then install a longer dowel pin and it will be fine.

It seems like an odd place for a crack to me and I’m not sure about using the block. Has anyone seen a block crack in this location?  Would use it?  I had been thinking about going with a Dart block anyway to support a potential future Paxton upgrade, so this would be a convenient excuse to do that. Since I already have the reciprocating assembly for a 331, a big bore 347 would be interesting.

 

3/01/2018 8:12 PM  #2


Re: On the subject of cracks in your block

I've heard/seen claims they "crack-right-down-the-middle"....not where you described!
If you got the bux for a Dart block....whine-not
Butt.......if no nitrous/big number turbocharging plans....350-375hp would "prolly" be OK.
I vote "331and-let-it-rip"!
6sal6

Last edited by 6sally6 (3/20/2018 9:42 PM)


Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
 

3/01/2018 9:11 PM  #3


Re: On the subject of cracks in your block

Here ya go!


Good work ain't cheap, Cheap work ain't good!   Simple Man
 

3/02/2018 8:21 AM  #4


Re: On the subject of cracks in your block

If you're planning a blown engine, build a blown engine.  Trying to build an NA engine with plans to put a blower on it in the future is not going to work out for a couple reasons.  First, to get power from an NA engine you need compression.  Getting even 1HP/cube from a 331/347 is going to require 9.5:1 or better compression.  A blown engine would be best at 8:1.  An 8:1 NA engine is going to be a dog.  You may say "I'll only run a couple psi and I can push that 9.5:1 engine just a little bit more and it'll be fine."  And that'll last about as long as it takes to realize that spending all that money on a blower to add another 50-75HP is weak and you really want to add more like 100-150. 

Second, blown engines allow more power to be made very easily.  Swap a pulley and add 100HP.  You may say "oh I'll be fine with 450HP and never want more".  The reality is that eventually that 450 won't affect you the same way any more and you'll want more.  Then you get into pushing a marginal design too far, and the crank winds up on the street.  If the blown engine is a serious consideration just buy the Dart block now and be done with it.

IMO you've got two courses of action.  I think the block will be fine with a repaired crack in an NA combination.  That crack is probably from someone drawing the trans up to the engine rather than getting the two mated properly and THEN tightening the bolts.  Its not in a critical area, so if you don't try to exceed the limits of a stock block (500-550HP NA) then I really think it will be just fine.  I welded a broken bolt bung for the bellhousing back together on an SBC years ago and that engine is a 383 stroker making 450HP NA and 600HP on the bottle.  If you want a blown engine in the future play with this NA one for now and build a dedicated blown engine in the future.

Or, just build the blown engine now.  Use the Dart block, etc.  It saves the cost of having to build two engines, and it removes the idea of compromise from the equation. 

 

3/02/2018 9:46 AM  #5


Re: On the subject of cracks in your block

Thanks. You are absolutely correct.  However, my thinking is as follows:  build the NA motor right now to about 10:1 with 58cc heads,and if I want to do a blown motor later, I can swap the heads to a 72cc and not have to touch the short block.  I haven’t run the numbers yet to see if the math works to drop the compression ratio enough to make that a viable plan,  but that’s the thought anyway.

I’m heading down to the machine shop this afternoon, so I’ll get a look at the crack and then make my decision after that.

     Thread Starter
 

3/02/2018 10:55 AM  #6


Re: On the subject of cracks in your block

That math doesn't work.  I see your logic, but to make a change that extreme you'd have to start with an 18cc dish in the piston and a 48cc chamber to get a 10:1 on your NA engine, then swap to a 70cc chamber to get 8:1 for a blown combination. 

More realistic might be to start with an 18cc dished piston, a 58cc head, and 9:1 compression.  Then get to 8:1 with a 70cc head for the blower combo.  This should allow it to work without a lot of head milling and worrying about having to mill the intake and then having it not work on the new unmilled heads you run in the future.  9:1 isn't ideal, but its not that far off.  Matched with the right cam with a wide LSA to bolster low speed compression and torque and it should be just fine.  I would call Crane and ask them what cam they recommend.  I really like their tech line, and you will actually speak to someone quickly unlike a lot of the other companies I've tried.  The last custom roller I bought directly from them cost me $350 I think.  Could have gotten it cheaper through Summit, but I was already on the phone with them and they spent a good 10-15 minutes with me to make sure it was right so I didn't mind paying a little extra for the advice. 

I guess this means you're going to the Dart block too then? 

 

3/03/2018 7:40 AM  #7


Re: On the subject of cracks in your block

TKOPerformance wrote:

I guess this means you're going to the Dart block too then? 

That's a definite "maybe".  LOL!  I went down to the machine shop yesterday and the crack is a very small hairline crack that only goes about 1/4 length of the boss where the dowel pin goes and it looks like it can be easily repaired and won't be an issue going forward. It looks like whoever separated the bellhousing from the block used a pry bar on the other side to separate them and instead of doing a little bit at a time on each side, did it all at once from the other side causing the small crack. 

Part of me really wants to go with the Dart, but given my intended use for the car, the Dart block and a Paxton probably aren't necessary, so I'll probably just build this into a 10.1 NA 331 and leave it at that.

But, if someone has a lead on a good Dart block for sale for not a lot of $$, let me know! 
 

     Thread Starter
 

3/03/2018 9:11 AM  #8


Re: On the subject of cracks in your block

If the goal is NA, and a realistic 400HP, then the block you have will be fine.

A Dart block for not a lot of $$?!  If you find one let me know, I'll make sure my unicorn plays the lottery that day

 

3/03/2018 7:20 PM  #9


Re: On the subject of cracks in your block

Grind out the crack........heat the block......weldup crack.....spray hot weld area with CO2 extinguisher... Call it done..
6sal6


Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
 

3/03/2018 7:28 PM  #10


Re: On the subject of cracks in your block

No way I'd go down as low as 8:1 for a blown engine. Not sure what you plan on doing other than a Paxton, but with modern EFI, cams, intercoolers, E85, heck even blow through carbs, etc, etc you do not need anywhere near that low. A 9-9.5:1 motor would be fine.

 

3/04/2018 9:28 AM  #11


Re: On the subject of cracks in your block

Maybe it cracked there when someone was removing the transmission at one time. Maybe it was stuck and they jammed a BMF screwdriver and pried it off on one side. That could explain it.

I have no experience in forced induction but I do know there is that camp that believes in higher compression with SC. With the higher static compression you still have that low end crispness, you’re not giving anything up. Sure you don’t run as much boost but then again you’re not adding a lot of heat from compression of air or mechanical heat. There’s pressure from expansion from heat and press from compression which are two different things. Personally I think it’s an intresting view. I realize this is comparing apples to oranges and many other factors involved but look at the Ecoboost. In the Raptor Ford upped the compression to something like 11:1 and upped the boost pressure on top of that. Again, I know there are many reasons they can do it.

If I could get the same power with higher compression and lower boost I certainly would look into it


I'm not a complete idiot.....pieces are missing. Tom
 

3/04/2018 12:58 PM  #12


Re: On the subject of cracks in your block

Boost pressure is really a pretty meaningless figure.  What its really measuring is resistance to flow, and engine to engine, even combination to combination its a fairly useless number.  The problem is that people don't understand mass flow, which is what actually tells you something useful.  There's no easy way to measure it though.  Just consider that if I take an engine with a blower and it peaks at say 11psi, then I port the heads and intake, and free up the exhaust it now makes 7psi.  It gained power, but lost boost pressure, because mass flow improved. 

Sure, you can use all kinds of electronic and fuel trickery to make it okay to run higher compression on a blown engine.  I submit two thoughts on that though.  First, if you need bottom end that bad don't run a centrifugal.  Instead run a roots style blower.  It'll make power instantly.  On the street though the build to power tends to make the car safer to drive and spare the tires a bit more.  If you need to leave hard at the track all you have to do is stall it up and run the right converter, or dump the clutch at the right RPM.  But on a street setup boost production is not going to limit your launch.  That will be a function of tires and suspension, which are never going to be truly aggressive enough because of the street compromises you have to make.

Second, if you're building a blown engine clean sheet you know that there's little point trying to get power out of the engine in an NA configuration.  Power in a blown engine is made by moving air with the blower; Period.  Running 9.5:1 vs. 8:1 nets you about a 15% increase in power in theory in an NA engine.  In a blown engine what's a simple pulley swap net you?  Blower drive ratios are where all the power is made, and that's how those guys go up or down, along with some help from the tune up. 

Also, cam selection has a profound effect on how the engine responds compression wise.  Again, if building a dedicated blown engine use a dedicated cam designed for a blown engine.  In the end its like anything else.  You can bolt a blower onto an engine that was an NA engine to get a little more power, but just building a blown engine is always a better idea, because there are far fewer compromises and work arounds. 

 

3/16/2018 4:53 PM  #13


Re: On the subject of cracks in your block

Well, I decided to have this block repaired but not to use it for this car. I’ve got another project waiting, so I’m going to grease this block up and put it away until I’m ready to start the next project.

So, I decided to get a Dart block for this one and turn it into a big bore 347 (already had the internally balanced 3.25” crank), which then brings me to the next question: cam selection.

When I was planning the 331, I had decided to run the Comp Cams XE266HR cam, which is 216/224, 544/555 with a 112LSA. Stated operating range is 1600-5600.

But now that I’m going to the big bore 347, I’m thinking I should go with a slightly bigger cam. So, I called Comp Cams and Crane to see what they recommended. I gave them the following parameters: 10.5 compression, 3.5 rear, 58cc AFR 185 heads, T-5z, Air Gap intake, carb (at least initially), realistic redline of 6,200 and want to it to have good driveability and make enough vacuum for power brakes. I like a little pope at idle, but don’t want it to beat me up.

After going through the data, Comp Cams recommended the XE274HR, which is 224/232, 555/566, also on a 112 LSA.  They said it will be very streetable, will make great power in the midrange and will provide plenty of vacuum for brakes.  They also said that the recommended operating range in the catalog for the cam (2200-6200) is based on a 302, but in a 347 it would move that range down a few hundred RPM to about 1800-6000 range, which would work well for how I’m planning on using the car.

When I spoke to Crane, they recommended a custom grind which I was a bit surprised was VERY close to the XE274. They recommended a cam with 228/232, 552/563 and a 112 LSA. 

I know a lot of people use the XE274 and give it good reviews. And I know it’s also supposed to be a very good blower cam if I ever did swap heads to lower the compression and install a Paxton. Anyone here use it? 

Anyone have thought on these 2 suggestions or have another recommendation based on the above criteria?  This is going in a 64.5 vert which won’t see a track (well, maybe once) but otherwise will be used for fun blasts down back country roads and the occasional long highway cruise. 

I already know anything 6s6 recommends will be too big!

     Thread Starter
 

3/16/2018 7:16 PM  #14


Re: On the subject of cracks in your block

I use Crane cams.  I've been using then since '98 when I built the first engine for my '87 K5 (a 350 with Edelbrock heads).  I like their products for several reasons, but one of the top ones is that when I call their tech department I speak to a person within 2 minutes.  That person then gives me excellent advice, which I've always found to be accurate.  I have Crane hydraulic rollers in my 383 (2nd engine I built for the K5), the 347 I'm building for my '67, and the 331 I'm building for my '89 GT.  The cam they recommended for your 347 is close to the one in my 347, but mine's a tad more aggressive.  I gave them a HP target of 450, but their tech convinced me to back off that a little in the interest of a more streetable combo that would run power brakes, etc.  He said it should be 415-425HP with the cam he sold me.  The rest of my combo is very close to yours.  I'll also be running 185cc AFRs, about 10.5:1 compression, Air Gap, and I too have a 3.50 rear gear & a T5. 

Either way I don't think you'll be disappointed either way, and I always prefer to let the company that grinds the bumpstick tell me which cam to run.  They know their products far better than I ever will, and when it comes to selecting a camshaft I think I know just about enough to be dangerous most of the time. 

 

3/17/2018 6:47 AM  #15


Re: On the subject of cracks in your block

I've used both Comp and Crane and had good luck with both. In fact, I've got a Crane custom ground hyd roller in my other car right now and it's great. Out of the two above, I think I'd be inclined to go with the Comp since there's a little less duration on the intake and just a touch more lift which will work well with the AFRs.

I think you'd be closer to your goal of 450FWHP than 415 with that cam in your 347. I came across the below article last night which I'm sure you have seem before.  They set up 306 and a 347 with the same parts and same cam (274HR) to show how the displacement affects the cam and power production. Anyway, they got 456hp at 6k and 435 tq at 4500 rpm from the 347. That's pretty good. 

http://www.mustangandfords.com/how-to/engine/mmfp-1009-306-small-block-engine-vs-347-small-block-engine/

     Thread Starter
 

3/17/2018 10:35 AM  #16


Re: On the subject of cracks in your block

Interesting article.  I've got to believe that the AFR heads are a smidge better than the TFS heads too.  I wasn't able to find flow for the TFS heads, whereas AFR comes right out with their numbers.  I think the TFS heads were hot back in the day, but their R&D budget is being spent elsewhere now, and they're just churning out the same SBF heads they've been building for 30 years.  I'm not saying it's a 30HP difference or anything, but I'd bet its 10-15 all things being equal with better low lift flow.  AFRs are just another class of head.  Their sole downside is their initial purchase price. 

A lot of these engines really like th extra plenum volume a carb spacer adds.  I've seen magazine articles where a simple 1" spacer added 20HP, and that's where you've got to be careful with those types of tests because you can sometimes do things on a dyno that would never work in an actual car.  Headers can be used like that too.  They always run long tubes on a dyno, because its easier and they tend to make better peak power.  Long tubes on anything but a truck on the street suck.  They're always hitting stuff, and working on them can be a real chore depending on the chassis.  Most guys are going to run a shorty or mid length header.  That will actually bolster the bottom end, but you'll lose some top end HP.  Then there's oil control, which is easiest when the engine is sitting still.  Once you start subjecting the engine to G-loading the oil starts moving around and windage can cut 10-20HP really quick in the real world.  Then there's the complete lack of any accessory drives.  They typically use an electric water pump and run no accessories (unless the engine needs a vacuum pump to seal the rings).  There's not a ton of parasitic loss from that stuff if you're using fairly modern accessories, but figure 5HP to run the WP, 5HP to run a Sanden AC compressor (more like 20-25 for the old style ones), a couple ponies for PS, a fractional loss to drive the alternator, etc. 

I'm not saying your engine's going to be a dud or anything, just that magazine articles are written with the goal of publishing big HP numbers that are typically not very realistic in the real world for the reasons noted above.  I find its best not to get caught up on a number.  Is the car fun to drive and/or race?  That's all that really matters.  I've seen a lot of guys, and been guilty of myself, ruining a perfectly good, balanced combination chasing another 20HP.  Its more important that the parts are well matched than that it wrings every last pony out of the engine. 

Last edited by TKOPerformance (3/17/2018 10:36 AM)

 

3/18/2018 12:15 PM  #17


Re: On the subject of cracks in your block

I agree, you definitely have to take these magazine articles with a grain of salt, but I thought this one was interesting- especially since it wasn't written with the purpose of hawking any particular product. The AFRs probably will flow better than the heads used in the article, but I will probably use JBA mid-lengths (considering FPAs, but not sure if I want long tubes) and running at least an alternator (on the fence about an electric fan too), so even it came out with an honest 400/400 through the mufflers, I'd be very happy.

     Thread Starter
 

3/18/2018 6:18 PM  #18


Re: On the subject of cracks in your block

Its particularly interesting for illustrating the different those extra cubic inches make.  This is why  always advise people to build strokers if they are rebuilding the engine with any kind of performance in mind, especially if the block already needs to be bored.  You're buying pistons, rings, bearings anyway.  By the time you have a set of stock rods Magnafluxed, resized, and new bolts installed you're looking at the cost of an entry level set of aftermarket I beam rods.  If you're smart you are at least getting the crank Magnafluxed, micropolished, and the rotating assembly balanced, which is going to be about $250.  So you're additional cost to build a 347 instead of a 306 is about half the cost of an aftermarket crankshaft; $300.  If you only picked up 30HP & 30 lbs/ft. that's all of $10/HP, which is a bargain.  Plus, more torque off idle, and a better idle with the same cam, or go to a slightly bigger cam and make even more power. 

Its crazy how much things have changed.  I remember a time when strokers were race engines only the big boys could afford.  There were no affordable cast or forged aftermarket cranks, or off the shelf pistons.  You either had to have a factory crank welded and offset ground, or buy a very expensive billet crank.  Pistons were going to be expensive too, unless you could find a set that just happened to have the right compression height, often for another engine than the one you were building meaning at least some custom work.  Nowadays this stuff is easy and affordable. 

I'd go with the mid length headers.  Long tubes can be a bear, hitting everything in their path as you drive.  Plus, the dirty secret of long tubes is that they make great peak power, but always have a soggy spot in the torque curve right in the midrange where you really need it on the street. 

I know a lot of guys here won't run an electric fan.  I personally do.  I enjoy the control and I have no overheating issues, or even times when I start to get alarmed about how hot its getting.  My argument is that almost every new vehicle has an electric fan.  The wiring for them is very simple and pretty bulletproof.  So long as you use an OEM or quality aftermarket unit it will last and perform for a very long time.  If the fan fails it could certainly overheat, but that could also happen if the clutch fan, water pump, or thermostat fails. 

I think you'll see that 400HP, maybe a tad more. 

 

3/18/2018 7:46 PM  #19


Re: On the subject of cracks in your block

My 306 makes 430 HP on the dyno, my 331 made 502 on the dyno. The 306 is in my racecar and twists over 8000 rpm. The 331 is in my 65 and never sees more than 6500 mostly below 5000. I run tracks in the racecar that make me want to run shorty's, but still run a place or two that needs the top end to compete. The change over sucks so I just leave the long tubes in and twist it up. My 65 runs on the street and has more cam than most people would tolerate on the street. I live in a small town and never sit in traffic so it works for me. I am buying a set of shorty's for the 65 so I can get in my driveway without the help of blocks to get through the gutter. I remember back in 65 when I took my drivers test in my brothers shiny new 65 Mustang that all the "Hot" guys were all the rage with the long tubes hanging under their Hi-po Mustangs. I know now that it was more perception than reality, but all of us that wanted one then didn't know that. It was just Cool at the Dairy Queen and Big Boy! So having lived through all of that I would say if you want solid performance and ease of use go Shorty's. If you are after perception, Long Tubes are King!

 

3/19/2018 5:07 AM  #20


Re: On the subject of cracks in your block

I gotta believe there's a BUT in there somewhere DC.  A 331 making over 500HP naturally aspirated would seem to need more RPM than 6500.  So did it make that power at 7,500 on the dyno, but just doesn't get reved that high on the street, or...

 

3/19/2018 6:49 AM  #21


Re: On the subject of cracks in your block

TKOPerformance wrote:

I gotta believe there's a BUT in there somewhere DC.  A 331 making over 500HP naturally aspirated would seem to need more RPM than 6500.  So did it make that power at 7,500 on the dyno, but just doesn't get reved that high on the street, or...

 
My thoughts as well, I can’t imagine what my 331 would need to make that much jam.


Good work ain't cheap, Cheap work ain't good!   Simple Man
 

3/19/2018 9:10 AM  #22


Re: On the subject of cracks in your block

Rudi wrote:

TKOPerformance wrote:

I gotta believe there's a BUT in there somewhere DC.  A 331 making over 500HP naturally aspirated would seem to need more RPM than 6500.  So did it make that power at 7,500 on the dyno, but just doesn't get reved that high on the street, or...

 
My thoughts as well, I can’t imagine what my 331 would need to make that much jam.

​I am glad you guys are awake, peak was near 7700 on dyno with a bigger carb than I am now running. We just ran it up there since the curve still had a pretty good slope to it. I feel it is near 450 with the set-up in the car now, but I never run it over 6500 since I hate sweeping up pieces and cleaning up oil. It is a stock block with a girdle. I am happy with the torque it has and the great old school lumpy idle.
 

 

3/19/2018 10:41 PM  #23


Re: On the subject of cracks in your block

DC wrote:

Rudi wrote:

TKOPerformance wrote:

I gotta believe there's a BUT in there somewhere DC.  A 331 making over 500HP naturally aspirated would seem to need more RPM than 6500.  So did it make that power at 7,500 on the dyno, but just doesn't get reved that high on the street, or...

 
My thoughts as well, I can’t imagine what my 331 would need to make that much jam.

​ I am happy with the great old school lumpy idle.

My MAN!!!
 

 


Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
 

3/20/2018 10:18 PM  #24


Re: On the subject of cracks in your block

Why not get the Crane Cam BUTT........have them grind it on a 110* (or tighter) LSA?!  I can guarantee it won't be too rad for your application...(3.50:1 gear AND a T-5)   
My 306 has a 230-236*@050 on a 108* LSA and will  "slow-cruise" in town in 5th gear and 45 mph. And accelerate higher if done gently!
Your 3.50 gear will have you "up-on-the-cam" (1500-1800rpm) almost immediately!.

Its just a shame to have the great flowing AFR heads and the  short stroke 3.25 crank and NOT take advantage of them.
I WOULD suggest a good rev limiter if you went with a tighter LSA because........if your NOT paying attention to the tach when your "pin it".......you WILL over shoot your  red line mark.
The tighter LSA  moves the power curve DOWN (where we spend most of our driving time)  a lot.
Makes'um very peppy(if you get my drift)!!
JMHO
6s6 


Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
 

3/20/2018 11:13 PM  #25


Re: On the subject of cracks in your block

This is also where induction plays a part.  The cam I got for my 347 is on a tighter LSA than the 331, because the 347 is going to be carbureted while the 331 with be EFI.  EFI, especially the factory systems do not like a lot of overlap, and won't run right with too tight an LSA.  The cam for my 331 has 114 degree LSA for this reason. 

 

Board footera


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