[Wanton Pontan]

Feel like I must have not searched enough, b/c these seem to be the most abundant iron head choices... but here goes

Starting with a 500xxx block.
Goal is to make something like 360+ HP/ 440 ft lb. at the flywheel (gross)
Rear end is still up in the air…

I was hoping to do it on 3.75” stroke

I thought it was possible to do with the 068 cam (melling spc-7)
And wanted to stick with iron heads. So I was considering 2 paths:

Should I go with 670 heads or 6x-4 heads. IF the latter, thinking about having the shop shave 0.030” off for ~85 cc bowls.


So questions:
Would you shave more if 6x-4? Opinions on my HP goals and shaving the deck?
If 6x-4+ with the stock lift cam are the 1.77” exhaust seats gonna be beneficial?
I was originally thinking of a more mild build, of the 6x-4 route which should net ~9:1 (assuming 0.45 for gasket and quench) but I’m not sure if I should go the other route and aim for closer to 10:1

If I’m building on the 500557 block, would I run into issues at 10:1?

Separately, I’m really up in the air re. bore / pistons -- It looks like going 0.040” over and building a 408 is a good choice… but again I’m worried about the block -- is it more revs or heat or long stroke moment arm that kills them?

Are my power goals out of reach for the milled 6x-4?

[steve25]

I have this build article and just need to dig it out.
The stock 670 heads heads will get you what Dan got with this RA III build.

[Formulajones]

Easily doable with a 400 and 068 cam using either of those heads.

My RAIII 400 with unported 12's that dont flow any better than your choices, 10.13:1 compression using a melling 068, stock intake/carb etc..RA manifolds made 301/355 on a chassis dyno and has pushed my bird to 12.70's at 106 mph at a 3890 race weight. It's easily making 370-ish at the flywheel.

Engine meets the ps rules, nothing super fancy, still using old heavy trw slugs with a standard ring package.

I could change some things in the short block and other minor tweaks and I think I could get close to 400 HP at the flywheel

[JB Eng Wis]

I have never tested the 557 block.... but I would use it for for your build. 360hp goal.
10:1 with the SPC-7, I would think you should be close to your goals... Keep your RPM's in check, so your connecting rods stay connected.
And the weaker block does not split...
Please jump in Anybody.... if you feel the 557 block can not handle say 440 ft Lbs...or 360 HP @ say 5000 rpms

[Stan Weiss]

Take a look at this thread

https://forums.maxperformanceinc.com...d.php?t=834245

Stan

[tooski]

My 408 with #48 heads (chambers measured at 70 cc) was 9:1 cr. Cast 8 valve relief pistons .040 in the hole. Detonated badly. Octane booster was a no go. Pistons changed to Speedpro (TRW) .026 in the hole. Heads changed to 6X4 (chambers at 92 cc) Compression now at 8.2:1. A bit lower than I'd like, but I'm not willing to spend the money and time to do the work required to go 9:1 or higher. Cam is just slightly less than a 068, but on a 110 LSA. I am satisfied with the performance. YMMV.

[Jay S]

What kills 557 blocks is the dowel pins are drilled clear thru, the other older blocks the holes are blind. If the dowel holes on the caps are not quite lined up, or it has enough power the make the caps move and put leverage on the dowel it starts a crack in the block there at the dowel. If the alignment is off even a bone stock 2 bbl engine can fail just from the clamping force of the bolt. -
As long as the block has good cap and dowel pin alignment at 400 HP you really don’t need to do anything special. Some shops increase the dowels to 5/16” and line hone/ream the dowel holes for better alignment. I don’t do that on the 557s, we line hone the mains and to run ARP main studs, it increases the clamping force so the caps have a harder time leveraging the dowels. I think that is good to 500 HP pretty easily with a 4” or 3.75” crank.

[Wanton Pontan]

Wow, thanks for all the great responses. Wealth of info here.

Originally Posted by tooski

My 408 with #48 heads (chambers measured at 70 cc) was 9:1 cr. Cast 8 valve relief pistons .040 in the hole. Detonated badly. Octane booster was a no go. Pistons changed to Speedpro (TRW) .026 in the hole. Heads changed to 6X4 (chambers at 92 cc) Compression now at 8.2:1. A bit lower than I'd like, but I'm not willing to spend the money and time to do the work required to go 9:1 or higher. Cam is just slightly less than a 068, but on a 110 LSA. I am satisfied with the performance. YMMV.

tooski - your build is almost identical to my thought process. Can you specify which pistons you went with? .026" from TDC piston to deck? Did you shave the 6x4 heads? I was expecting almost 9:1 static CR based on:

1. 0.040 gasket,
2. -6 cc piston,
3. 0.024 deck height
4. 0.030" shaved from the 91 cc bowl -> 85 cc based on Jim Hand's book.

His example of 85 cc with a 0.15" deck height is in this realm too.

I was thinking this way originally and wondering if anyone had any specifics about whether the 1.66" exhaust valve seat was the bottleneck (assuming mild some porting, which is a big variable.... FYSA I am trying to stay low budget and learn so intend to port myself. In this build, the valve job ends up being ~1/4 of the budget: $400 for seats+$200 for valves.)
I have 1976 low compression pistons, so figure those have to go anyway. And it's kinda hard to argue with the price of these for getting me close:
https://www.jegs.com/i/Sealed-Power/...62F40/10002/-1

I'm just thinking being north of 9:1 stands a better chance of the torque/power goal. And the (estimated) 10cc smaller chamber of a worked 670 vs a shaved 6x4 gets me there (at the cost of needing to redo the valve train--I'm taking off a set of 6x8 and planning to reuse).

Is this feasible with 6x4 heads and zero-decking the block, or am I getting carried away with deleting material (0.030" shave, matching the intake, zero decking the block, trusting the -6.7 cc spec on those pistons)?

@formulajones - You're car is probably a little hotter than I want to be, but it's taking CR to 10.1:1--where I live 93 is available at the pump, but I'm a real novice here and worry about detonation...but then again 670's + 068 is a close to a factory RA III

@JayS - This is really great..so what info is there on cap/block alignment? How are you measuring? What constitutes good alignment? 0.005"? less? What info can I give the machine shop/what corrections can be made? (or is this way you might retap the caps at 5/16"? i.e. if alignment is out of alignment)

[tooski]

The Sealed Power forged pistons are the L2262F40 for a 4.160 bore.(I had to wait three months to get them) 4 valve reliefs at 6.7cc. Measured after install at .026 below deck, at TDC. Felpro 8518 at .045 crushed thickness.
The 6X4 head chambers measured at 92 cc. I added 1 cc for the space between the piston top and the first ring. Compcams shaft 211/221 i/e @.050, .445 lift with 1.5 rockers, 110 LSA. Stock rods. This is my backup engine while I build a higher performance engine ($$). I bought the cam when the engine had cast pistons in it, well before I joined PY. If I were to do it again with the massive info available from PY members, I would use the 068, Summit 2801, or crower, lunati comparable. I would also try to up the CR by either decking the block or using pistons with a custom compression height.

[Formulajones]

Originally Posted by Wanton Pontan

Wow, thanks for all the great responses. Wealth of info here.





@formulajones - You're car is probably a little hotter than I want to be, but it's taking CR to 10.1:1--where I live 93 is available at the pump, but I'm a real novice here and worry about detonation...but then again 670's + 068 is a close to a factory RA III

It's not hot at all it's a factory stock build that has run on 91 octane for the last 20 years, raced that way as well
Where people get in trouble with these things on pump fuel is putting pistons down in the hole, that's never a good idea. Mine is zero decked. The other area that always seems to be a problem is cam timing choices and where the icl is installed. Most don't even check it.

[JB Eng Wis]

tooski is there something wrong with your backup engine? Or just was not what you were expecting??
I would think it would be a good everyday driver on pump gas......

[tooski]

JB, Absolutely nothing wrong with the 'backup'. I termed that wrong. It will be my daily driver while I build another higher power engine (weekend warrior) for another car. (Long story about the 'backup')

[Wanton Pontan]

Originally Posted by tooski

The Sealed Power forged pistons are the L2262F40 for a 4.160 bore.(I had to wait three months to get them) 4 valve reliefs at 6.7cc. Measured after install at .026 below deck, at TDC. Felpro 8518 at .045 crushed thickness.
The 6X4 head chambers measured at 92 cc. I added 1 cc for the space between the piston top and the first ring. Compcams shaft 211/221 i/e @.050, .445 lift with 1.5 rockers, 110 LSA. Stock rods. This is my backup engine while I build a higher performance engine ($$). I bought the cam when the engine had cast pistons in it, well before I joined PY. If I were to do it again with the massive info available from PY members, I would use the 068, Summit 2801, or crower, lunati comparable. I would also try to up the CR by either decking the block or using pistons with a custom compression height.

Thanks for the specifics tooski--I really am thinking of a similar build to be very streetable, but did want to squeeze out more pep where possible. Any reason why you don't use a thinner head gasket to reduce total quench? You could go from 0.045 to 0.28 and gain a ~0.3:1 CR increase. You'd still have ~0.055" of quench height.

I should have read ahead more, as it seems like Jim Hand reports shaving 0.060" off the heads is ok--I was worried about valve/piston interference. Any tips on there?

[tom s]

557s are IMO a crap shoot.I built one to just under 600 and it’s still living in a 70 GTOafter more than 10 years.No main studs but solid dowels.Tom

[J.C.you]

I would prefer another block myself and like the 6x4s.

[tooski]

I think a good idea would be to go back to 'Street' page and do a search for mild, or street builds. Cams for a street build. Compression ratios for a street build. Head decking/cutting. Zero decking. Quench.

[Jay S]

The machinist will know that the block will need line honed when you tell them you want to run ARP studs. The extra clamping force of the main studs distorts the caps quite a bit.

A good machinist will usually will look at that dowel alignment and make adjustments if they think it is necessary.

I think after 40 years though most the 557 blocks that had really bad dowel to cap alignment have already broke. I have 3 557 stroker builds that are close to 600 or more HP.

[PunchT37]

I`m in the 670 camp. With a good piston head design. Keep it 3.75 stroke with that block. Get it all balanced. Then, pick a cam for what you wind up with.

[geeteeohguy]

Originally Posted by Formulajones

Easily doable with a 400 and 068 cam using either of those heads.

My RAIII 400 with unported 12's that dont flow any better than your choices, 10.13:1 compression using a melling 068, stock intake/carb etc..RA manifolds made 301/355 on a chassis dyno and has pushed my bird to 12.70's at 106 mph at a 3890 race weight. It's easily making 370-ish at the flywheel.

Engine meets the ps rules, nothing super fancy, still using old heavy trw slugs with a standard ring package.

I could change some things in the short block and other minor tweaks and I think I could get close to 400 HP at the flywheel

What fuel are you running? I haven't been able to run #12 or #670 heads with an 068 cam and flat top TRW's for over 35 years here in CA with 91 octane gasahol being the best available pump gas. I was detonating all the time.

[Wanton Pontan]

Interesting that there's still so much conflicting data on whether ~9.75:1 is too high or not....and these seem to be about the 2 most common heads I see cropping up. I'm working on resurrecting the 670 heads--which are in rough shape...and now thinking of cycling through the permutations.

Build plan is not for 0.040" over, spc-7 (4.10 lift) cam.
Now I'm thinking about going thru the paces with porting heads, trying 0.040 and 0.028" gaskets on the 6x4's. I was planning on keeping the 1.66" ext port on the 6x4....I'm starting to get a nice set of parameters.

Is there anything folks would want to see in the process?