beginning a 4.25 350 Stroker build
 

I've been wanting to do this out for years and years, and now I'm finally getting into the resto/build of my Tempest and I'm starting with the engine. The car will be a factory stock looking street car with some hidden upgrades that may go down the strip on occasion. Here are the details of the plan. It will be going to the machine shop for cleanup, mag, and machine work soon, and I'm planning on doing assy, and porting myself

numbers matching block YU 350, std bore will be bored .030 over, and decked ~.005, and have new cam bearings installed
2 bolt mains will be converted to ARP studs.
Butler balanced stroker kit with cast Eagle Crank, and H beam rods, and Ross forged pistons
stock #11 heads will get a valve job with new seats, new stock size 30 deg, 1.96/1.66 valves, convert to threaded studs and TBD porting and flow (not sure what flow I should really be targeting, but it looks like more is better for power based off some calcs, but I don't want to take too much torque away.)
Only measured one chamber so far at 90cc (I had seen Rock Rotella quoted previously that these were 87cc, so it seems in line)
Cometic 3.95 bore, .027" MLS HG (is ~.032 quench going to be a problem?)
Hayraulic Roller cam (looking at a few options but likely XR264HR-10 with a DCR of 7.85:1 or Lunati 20510710 with DCR of 7.91:1 if I'm doing the ABDC calcs correct for the Keith Black calc.)
Roller rockers, ratio TBD, probably will do 1.6 or 1.65 if I can get the heads to flow with the valves up high
I have a 70 4 barrel manifold I will be putting on and likely track down a qjet from the era
Stock exhaust manifolds will be ported and go into a 2.5 exhaust with quiet-ish mufflers


It's a TH350 car, and the rear gear and converter are undecided, but probably will change to something in the low 3.xx (has a 2.56 open diff in it)

SCR works out to 9:1 (*without bore chamfers calculated*) using Keith Black and wallace calcs (butler's shows 9.5:1 so not sure what's going on there) (stock was only 8:1), and a gain of 53CI to 407. Compression ratio may bump a little as heads are surfaced and valves are done, and if it starts getting too high, I'll go to a thicker or larger bore gasket.

Thoughts? Opinions? Red Flags (aside from being a 350 block :))? I'm a little up in the air about the porting at this point

Definitely interesting, keep us posted. Would be good if you could get it dynoed to know what its actually doing. (Ignore the "go 400 block " folks as we alredy know that's a given.)

I'm not the expert here, but the .032 quench might get you in trouble....035 is generally considered as tight as most will go. Jon Kaase built an Engine Masters engine, 2005, a 507 inch Pontiac with .035 quench. He takes stuff to the max. Not sure if you want to test that situation.

The cast after market crank is another area of question. Some have been fine, Some have had bad luck with them...

A aftermarket converter tailored to your specific combination is an awesome thing. One of the best performance upgrades you can make!!!
Porting? you are at about 408 cubes. Proper port work will help, although not terribly needed, this seems like a street/driver engine.

There's some perferred roller cam lobes. I do not know if yours are lobes that are perferred...or not...

Iron intake, spot on!

Quadrajet. There's better than the early 70's models. 76-79 Q-Jets are awesome carbs

Everything else looks good.

THere's a tech article on SD Performance's website about running a stroked 400, using the HO exhaust manifolds and a roller cam, you need to read that.

Next!!!

I don't understand why you want to do this? I assume for more power, but there are better ways to get there. Stroking a motor increases the stresses on the rotating assembly, and you are going to max stroke with a cast crank. Piston speed is higher, rate of acceleration/deceleration near TDC and BDC is higher, side thrust forces perpendicular to the cylinder bore are higher.

All of these increased stresses mean that either forged parts are needed, or the maximum RPM of the engine has to be decreased so you don't blow the engine.

You would be a lot better off with 72cc chamber aluminum heads and a nice roller cam.

The reason is I would like to have the #s matching block in the car, and get better performance out of it. If I can get it working with the factory heads, that's even better.

Everything but the crank is forged. The 4.25" kits are cheaper than the 4.00" kits, so why not? The switch to a forged crank is about $500 over the cast crank after factoring in the appropriate bearings. It's not out of the question, but I'm only planning on 5500ish rpm max anyways. Better off or not, aluminum heads is not the goal for this car, and doesn't fit in with a factory resto look. The only deviation noticeable under the hood will be the 4bbl which will be a factory setup (single snorkel if I can find one).

Cometic has a .040, 3.95 bore HG that will work as well, so that would bump quench up to ~.045. I'm guessing I'll be close to where I want to be on CR after the heads are trued and valvework is done. I also have a set of corteco 3.93, .045's I could try before going to the big bore gasket.

It's not so much at what power level you need a forged crank it's more like Chinese cast cranks are sketchy even for mild use.

China forged cranks are of a lesser quality than top USA forging but still are usually superior in strength to any cast crank

Could you aim for lower peak rpm and try to select parts for more torque a little lower to avoid any issues from high rpm? Like trying to keep port velocity high

Sure a forged crank would be nice, but you really should not need it. The rotating assembly should be very light with the small bore, if a cast crank would survive in anything it would be this. Lots and lots of those cast aftermarket cranks take more abuse than this.

I think what your doing is neat and sounds like you have a good plan.
32 quench is fine and your RPM's are fine also. Probably won't be seeing
The 5500 limit with that stroke and factory heads. Anyway have fun
with it, I'll have my wife vetura with a 350 out here pretty soon.

GT.

Sorry that I'm late to the game here as I just spotted this forum with a random search on another subject,

I've got a 1970 350 stroker using the Butler Performance 4.25 kit with the cast Eagle crank, forged H-Beam rods and forged Ross pistons. Block was bored .60 over for a displacement of 413 cu in. With the 6X-4 heads (2.11/1.66 valves) and Fel-Pro gasket, compression ration calculated out to 9.13:1.

Intake is an Edelbrock Torker I for spreadbore carb with the stepped plenum floor. Carb is a quadrajet for a 1971 Buick GS455 Stage-I modified for Pontiac throttle linkage.

Running Comp X276HYR with Comp 1.5:1 roller rockers, Comp springs and Johnson hydraulic roller lifters.

Dyno runs produced 442 ft lb at 4200 rpm and 453 hp at 5600 rpm. Engine easily pulled to 6200 rpm. Thanks to the smaller bore, rotating mass isn't as much a concern for rpm range.

Pretty sure Ross pistons are 2618. I have 2618 pistons and the noise isn’t that bad, but for longevity and startup noise reasons I will go 4032 next time and would recommend as much for almost any pump gas N/A car with reasonable compression, assuming you can get them.

Tempest-T37 here is a easy way to figure out the total number of CCs you need to achieve a given compression ratio.

To do this you need two things, one being the total CCs of your .030” over 350 with the new 4.250” stroke.

When you run the numbers you get 51 cid per cylinder, for a total of 408 cid.

We need to convert this CCs so we Xs that by 16.387.
Now you have your cylinder volume in CCs which is 836.2 .

Now let’s say you want to end up with a 9 to 1 compression, to get this answer we subtract 1 from 9 for the result of 8.

Now simply divide 836.2 by 8, the result is that when the piston is at TDC you will need a total CC volume of 104.5 to get your 9 to 1 compression.


If you where looking for a 9.5 to 1 compression you would need a total CC volume of 101.5 .

Some things to take into account when figuring out your compression is adding 1 CC of ring land volume for your size bore and also that some head gaskets like the common Fel Pro 8518 and 6014 is the fact that these do not have round bores, that are oval, so they contain more CCs then if you figure out there CC volume with just the bore size.

From what I show here you can safely assume that every 4 CC change up or down will change your final compression ratio by 1/2 a point,

I'm surprised you like that torker 1,,I never had any luck with that intake on a medium build street motor.

As far as the 350 build...I'd say go for it,,sounds like a cool build.

I was trying to wait to post an update until it is finished and has been run. But I'm making headway on my build.

My setup is pretty similar to srmmmm's, except I'm using my stock #11 small valve heads that were refreshed. I'm also using a very similar cam, but with a wider LSA because I'm using log manifolds.

-Block align honed and converted to ARP main studs
-Eagle forged crank
-Eagle H-beam rods
-Ross +.030 pistons
-Comp/Butler std grind hyd roller 276/282, 224/230, .503/.510, 112LSA installed @107 ICL
-Johnson roller lifters
-Heads refreshed with stock sized valves, converted to threaded stud, new seals and Lunati springs that came with the Butler cam kit.
-1.5 Harland Sharpe roller rockers
-Corteco headgaskets (I would have preferred to run Cometics, but wasn't able to get a set in time)
-stock 1970 4 barrel manifold
-qjet
Final CR 8.98:1
The first pic is a spreadsheet I made to calculate compression ratio for all the different headgasket options. The Corteco were my backup plan.

https://i.imgur.com/tKKZavJ.jpg
https://i.imgur.com/fTSjDVi.jpg
https://i.imgur.com/vLjG2G8.jpg

do those johnson roller lifters have grooves in them? whats the purpose, better oiling? never saw that before.

I did make sure to port match the intake to the gasket and heads, but no other mods were done. The heads were from a 1978 W72 option 400 providing screw-in rocker studs and eliminating worry about unleaded gas. The only issue encountered was ordering custom length push rods for correct rocker geometry and having to add the RamAir valve cover spacers for clearance.

Of course though, that meant the factory A/C compressor brackets didn't work any more so I had to throw another $1700 in for a serpentine conversion......

Navy Horn 16, Iots of generalities here; most are grossly inaccurate. One, engines with long strokes use longer rods as a rule. Longer rods decrease piston speed. Two, if done correctly (lighter pistons, pins, and connecting rods) a stroked engine is under no more stress than the base engine was. There are literally tens of thousands of stroked SBCs, BBC., SBFs, FE Fords, 385 series Fords, LA series Chrysler’s, R/RB Chrysler’s, Hemis of all series, LS, and Pontiacs that have been successful stroked without destroying the base engine. You MIGHT want to read a book or two on engine theory BEFORE opining.

No, I think you're seeing a reflection from my overhead lights. They have a normal oil band around them.

LOL. that is weird.. on my screen it looks like every lifter has machined grooves in it.

Calculate Piston Speeds / Strokes

http://www.wallaceracing.com/calc-pistonspeed.php


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