521 or 545 and why?

I'm starting my hunt for a stroker kit to match nicely ported SCJ's.Street car.I see a 521 and 545 are the same price or very close.Now I'm leaning toward 545.Opinions,pros/cons?The surrounding car is built tough and should handle either one,tires not so much.

Since they both have the same 4.39 bore and the stroke is a 4.3 for the 521 and 4.5 for the 545 I would go with the 545 if it's just a little more money?

Personally I'd be more concerned about the quality of the components in the kit more so than the 24 additional cubic inches. If the kits are otherwise identical and you're keeping the max RPM's below 7K or so might as well go with the 545. The 521 can make the same power but it will take more RPM's to do it.

I have purchased good quality products from CNC Motorsports in the past (close enough for me to drive down) but the pistons in their stroker kits have a 38cc dish which is too much.I do have a budget for this venture so I want to stick with a shelf kit,no custom pistons and it will also be a SFT cam.The chambers in my SCJ heads have been cleaned up which added about 7cc and I don't want compression below 10:1.I'm looking at the Probe Villian kit which uses a 32cc dish and puts me a smidge over 10:1.Standard stuff but looks good,Scat cast crank,Scat 6.8 4340 rods with ARP bolts,Probe SRS forged pistons and I will get it internally balanced by them.Again,it's a street car that sees thousands of miles a summer,not hundreds,so I'd prefer a big torquer with max rpm below 6500 if possible.Opinions?

I’ve always heard rumors of balancing issues when internally balancing cast cranks over a 4.150 stroke, expensive mallory is often needed which can make a forged crank much more logical $$ wise.

Interesting point.I spoke to Mark live on the phone (who appears to be the guy at reigns of the outfit) to fill in some details and a balance is a couple hundred bucks.About the same as having it done in my town.He did not indicate it may be problematic with the big crank or possibly more costly but I will definitely follow up on that.Thanks.

Just what I have always read/heard, I’m sure the machinists on here will chime in at some point.

the tree man wrote:I'm starting my hunt for a stroker kit to match nicely ported SCJ's.Street car.I see a 521 and 545 are the same price or very close.Now I'm leaning toward 545.Opinions,pros/cons?The surrounding car is built tough and should handle either one,tires not so much.

It all depends upon what you intend to do with it.
They will both make about the same horsepower but, the smaller engine will be at a slightly higher RPM and the larger engine will exhibit more torque under the torque RPM peak ... that is, if everything else is the same.

At what point does a short compression height piston become an issue with engine longevity? If you put a couple thousand miles a year it's a none issue but if you actually drive 10,000 miles a year a 545 may not be your best choice.

I put on a few thousand miles per summer so I should,hopefully,be good for lots of years with either kit.I would prefer the torque over outright horsepower and less rpm should help with longevity/reliability.I'll verify the Probe balancing procedure on Monday and scale back the cubes if that's what it takes to stay on budget,which sucks.I'm starting this project way later than planned so time is also a bit of a factor and turnaround on both kits is a month.Can't drag my feet.Thanks for the input.

rmk57 wrote:  At what point does a short compression height piston become an issue with engine longevity? If you put a couple thousand miles a year it's a none issue but if you actually drive 10,000 miles a year a 545 may not be your best choice.

It doesn't.

wickettoby1 wrote:I’ve always heard rumors of balancing issues when internally balancing cast cranks over a 4.150 stroke, expensive mallory is often needed which can make a forged crank much more logical $$ wise.

Sometimes it takes 1 piece. Not a big deal.

the tree man wrote:I'm starting my hunt for a stroker kit to match nicely ported SCJ's.Street car.I see a 521 and 545 are the same price or very close.Now I'm leaning toward 545.Opinions,pros/cons?The surrounding car is built tough and should handle either one,tires not so much.

I'm assuming from the narrative, you are building a street motor. I've read Jon Kasse loves the 4.3 stroke. That would be good enough for me. #2. If you don't buy from a vendor here, Summit will beat everybody else's price. You can get a Scat 521 stroker, forged pistons -3cc eyebrow. They have a kit that is externally balanced that comes with a SFI balancer and flexplate (SFI sticker). No tax, free shipping. If they haven't changed, that kit comes with 6.8 rods, Mahle pistons. You have to add an X or XE to the end of the part number to get the $5 SFI sticker for the flexplate. Which you don't need if you don't have plans for the dragstrip.

Even if paying a dew extra dollars, it is a good thing to buy from members here as some personal service you get is worth it; if you ever need any further help it will be there.

rmcomprandy wrote:Even if paying a dew extra dollars, it is a good thing to buy from members here as some personal service you get is worth it; if you ever need any further help it will be there.

Valid point Randy. The OP was referring to an outside vender that will cost him more than the same purchase from Summit. But I agree with you  "Buy here/get knowledgeable help here".

I'm new here and still getting my sea legs;however,I agree with supporting site vendors and I do that on other forums where I'm a member and glean information.I also like to spend my money locally as much as possible but unfortunately some things,like this kit,are best dealt with hands on by me from an outside source.I could not find a vendor list here and did go to Randy's RM Competition site.I didn't see any rotating assemblies listed and it appeared to be more of a machine shop/engine builder type of business,not a parts retailer.Some suggestions as to who here may be able to help me out would be appreciated and I will contact Randy regardless.Thanks.

the tree man wrote:I'm new here and still getting my sea legs;however,I agree with supporting site vendors and I do that on other forums where I'm a member and glean information.I also like to spend my money locally as much as possible but unfortunately some things,like this kit,are best dealt with hands on by me from an outside source.I could not find a vendor list here and did go to Randy's RM Competition site.I didn't see any rotating assemblies listed and it appeared to be more of a machine shop/engine builder type of business,not a parts retailer.Some suggestions as to who here may be able to help me out would be appreciated and I will contact Randy regardless.Thanks.

For a rotating assembly ... Adney Brown; Performance Crankshaft ... Lem Evans; B.F. Evans Ford ... Mark O'Neal; Probe ... and there are a few who only sell an assembly to that customer who has an engine built; like myself and other engine builders.

Hope this helps.

That definitely helps.I'll assume it was Mark at Probe that I spoke to.Now that I've torn things apart and have some time to invest in a bit of research I can tidy up a few loose ends to put my mind at ease before pulling the trigger on anything.Doing my due diligence.This whole stroker upgrade hinges on me being able to swap/reuse some parts from the current powertrain to the new.

The 4.3 stroke crank and piston/rod combos for the 385 Series blocks like a glove.

Finally got the engine back in the car. Did a bit of carb tuning to help idle,light cruise and tip in but was very close. The cam liked 30 degrees initial and I locked it out there. Runs fargin' awesome! From 1500 RPM up the grunt is amazing. Not sure what kind of shift point I should be looking for. 6000?

Ordered my kit from Mark at Probe and I'm very pleased. We had a couple little hiccups along the way but his communication (phone calls to Canada no less) was excellent keeping me in the loop and he stepped right up. Nice. The product is great and speced out bang on. Thanks,Mark.

Shift point/redline? Any thoughts?

545
10:1
Ported SCJ's
SFT,6.55/6.55 258/262@.050 (lost a bit of lift with a full spring compared to the checker springs in my other post.)
Home ported Blue Thunder 2X4 w/2X600 Holleys

Thanks again for all the help.

the tree man wrote:Finally got the engine back in the car. Did a bit of carb tuning to help idle,light cruise and tip in but was very close. The cam liked 30 degrees initial and I locked it out there. Runs fargin' awesome! From 1500 RPM up the grunt is amazing. Not sure what kind of shift point I should be looking for. 6000?

Ordered my kit from Mark at Probe and I'm very pleased. We had a couple little hiccups along the way but his communication (phone calls to Canada no less) was excellent keeping me in the loop and he stepped right up. Nice. The product is great and speced out bang on. Thanks,Mark.

Shift point/redline? Any thoughts?

545
10:1
Ported SCJ's
SFT,6.55/6.55 258/262@.050 (lost a bit of lift with a full spring compared to the checker springs in my other post.)
Home ported Blue Thunder 2X4 w/2X600 Holleys

Thanks again for all the help.

Thanks for the update sounds like it runs strong!!

I bracket race a similar 545 and have put 750 laps at the drag strip before I opened it up. ( Only because I broke a Lifter). I shift at 6000 rpm and red line at 6800. Just went thru it and it could of went a lot more.

[quote="airford1"]I bracket race a similar 545 and have put 750 laps at the drag strip before I opened it up. ( Only because I broke a Lifter). I shift at 6000 rpm and red line at 6800.  Just went thru it and it could of went a lot more.[/

What does it run?

It has gone 9.80 @ 136mph on 91 pump gas. Shifting at 6000 it goes thru the traps at 6200 4.30 gear with a tall tire.

airford1 wrote:It has gone 9.80 @ 136mph on 91 pump gas. Shifting at 6000 it goes thru the traps at 6200 4.30 gear with a tall tire.

Nice times for 91 octane Pump Gas!!