New Stroker, Need Advice

[Emptypockets]

I fired up my new 4.6 stroker today. It is in the family Grand bought new in 1993. I have been drooling over the Hesco kit for a couple of years just waiting for the wife to retire Old Faithfull so I could turn it into my personal project.

Well, my number one son went off to college and he got the jeep. A couple of months ago the jeep broke a rod bolt and put the rod through the side of the block. Not the way I wanted to start my stroker project but oh well. I sent my truck to the kid and I started gathering parts.

My recipe:

balanced 4.2l, 4cwt crank

4.0 rods, weight matched

LT1 chevy pistons (3.907"), 12.2cc dish, .026" deck (deck not ideal but machine shop screw-up)

Reciprocating assembly weight matched to .25 gram

.051 head gasket

original 7120 head, ported to make peak power at 4900rpm, chambers opened to 64cc & matched

modified 93 intake

2" ss intake and 1.6" ss exhaust valves

Comp 68-232-4 cam, intake centerline set at 108 degrees. Didn't want this cam but Comp tech insisted this would work best with the computer.

beehive springs

Still using stock TB and injectors, trying to find the best combo. 63mm TB will fit the manifold without mods.

OK, here's where I need some help. The engine started right up but had to be babied to 2000rpm. It ran fine at a steady 2000 but began to miss when rev'd to 2500. It eventually began to overheat (the fan clutch never engaged, will replace it.) I got the engine through the cam break-in by cooling the radiator off with the garden hose.

Now the engine is very slow to start. When it does it will idle smoothly and can be coaxed to about 2000rpm but has no power and misses badly above 2000. In gear it won't rev above 1200rpm.

I know the stock injectors are too small but I would think it would start and run ok in the lower revs. Any ideas?

[Emptypockets]

OK, I need some help wrapping my head around this one.

I set the distributor at TDC on the compression stroke when I was doing the final assembly. The rotor was pointing at the #1 terminal but since these engines aren't timed at the distributor I didn't give it too much thought.

This morning I discovered that with the dampener mark set at zero, the leading edge of the rotor was pointing just before the #1 terminal. In this position initial spark advance was 12degrees. I repositioned the distributor on the very next tooth which put the rotor just past the #1 terminal.

The engine started right up and ran perfect. So far everything is making sense, I did advance the cam after all.
The wierd part is that the spark advance is still at 12 degrees.

This is my first experience working with computor controlled engines and I admit I am stumped.

First Impressions:

The stroker motor runs very strong off the bottom and through the mid range. It runs out of fuel at about 2500 rpm and it really needs a bigger TB. So far though it runs like a strong small block V8.
There is just the faintest amount of lifter noise at idle but less than the stock. It will also occasionally knock when loaded at low rpm.

So far I think I will be very happy with this motor.

[Don H Jr]

Do you have your Serp belt on correctly? If you don't, you could have the waterpump working backwards and thus overheating. I'd check/double check timing issues, even look at dist gear. As always, look for big and little vaccum leaks, especially loose intake/exhaust manifold bolts. Check Fuel Pressure as per manual. Make sure coil isn't cracked and look inside your dist cap for gremlins, arching, black dust, metal shavings, bad wires.
TBS is always a possibility and easily voltmetered or changed if not right voltage throughout the close to Wide Open Throttle positions of butterfly on TBody.

Just a few thoughts. If you think you found a problem and fix it, then reset the computer: Pull pos battery cable off batt and ground it for thirty seconds. Put it back on battery. Put key in ignition and turn it on, but don't start engine. Turn headlights off and on twice. Turn off Ignition.
Next time you start it it forgets bad codes from before the fix and runs on basic program in computer till 50 starts of the engine. It has to relearn how your engine's new needs.
Good luck, as I'm fighting stupid problems right now too, but not on a new engine that is a bugger to break in right with ZDDP and all that to keep in mind with new cam breakin so you don't end up like those on the trail of flat cams and lifters.

don jr

[Don H Jr]

I hope your atypical build pistons work out for you. If they are right for a stroker build, I'm surprised I hadn't heard about it by now.

Jr

[SilverXJ]

I don't know if Comp Cams will ever get it right.. the 68-231-4 works fine with the factory PCM.. ugh.. that urks me. I wouldn't have advanced that cam though. See here for distributor indexing: http://www.angelfire.com/my/fan/dist_index.html

[Emptypockets]

Thanks for the help guys. The engine is running fine after moving the distributor forward. Does anybody know what the initial and total spark advance should be? I won't be totally at ease until I figure out why it works retarded but not advanced since it measures at 12 degrees initial in both positions.

Another interesting point, at one point I rotated the dist 180 degrees just to check if it was on the wrong TDC. It wasn't but the back side of the rotor was pointing exactly to my index mark for #1 TDC. Is it possible that the dist gear was installed wrong at the factory? It is a new distributor.

No vacuum leaks and the belt is on right. It stopped overheating as soon as I reset the distributor.

I am using an OEM 12 degree retarded timing set because the cam is pretty mild. I made a handfull of shims to experiment with cam timing and just used the 2 degree shim first. I have 6,4,2 degree retarded and 0,2,4 degree advanced shims. As I mentioned, this was not really the cam I wanted so I advanced it to get a little back on the top end to match my head and intake mods. It will occasionally ping when lugged so I won't advance it any more than it is. I will also probably put colder plugs in IF my son ever gets it back.

I used the LT1 Gen II pistons because they are lighter and have better ring height than the jeep set. The piston and pin are 425 grams/set when finished. There is maching involved to make them work but they are still much cheaper than the KB's. I have also been hearing some not so nice things about the KB's. There is a SBF piston that would have fit without mods but they have been discontinued.

[Emptypockets]

Hey Silver, just saw your link to distributor indexing. I will have to double check tomorrow but it looks like there will be some ear clipping in my future.

Thanks again.

[SilverXJ]

Thanks for the help guys. The engine is running fine after moving the distributor forward. Does anybody know what the initial and total spark advance should be? I won't be totally at ease until I figure out why it works retarded but not advanced since it measures at 12 degrees initial in both positions.

12 degrees where? spark timing or cam timing?

Another interesting point, at one point I rotated the dist 180 degrees just to check if it was on the wrong TDC. It wasn't but the back side of the rotor was pointing exactly to my index mark for #1 TDC. Is it possible that the dist gear was installed wrong at the factory? It is a new distributor.

I doubt that.. at most it could be out one tooth. When you index the distributor what you are doing is indexing the fuel injectors basically, the PCM controls timing. Just ignore what ever timing you are reading and set the distributor correctly according the link I posted above. There is ONLY one way to correctly set the distributor. Messing it will just get you a poor running engine.

so I advanced it to get a little back on the top end to match my head and intake mods. It will occasionally ping when lugged so I won't advance it any more than it is. I will also probably put colder plugs in IF my son ever gets it back.

You have it backwards. Advancing it moves the power band down in RPM, retarding moves the power band up in RPM.

I used the LT1 Gen II pistons because they are lighter and have better ring height than the jeep set. The piston and pin are 425 grams/set when finished. There is maching involved to make them work but they are still much cheaper than the KB's.

Details? what machining was needed? Specs ont the pistons?

[Don H Jr]

I too am interested in, "Whats the skinny on the LT1 Gen 2 PISTON adaptation"? Thanks,

Don Jr

[Emptypockets]

It is at 12 degrees spark timing.

I rechecked the distributor using the instructions in your post and it's set correctly.

You're right, advancing the cam does theoretically move the power down in the rpm range but every time I have ever done it I have seen improvement in the mid range and occasionally in the top end as well. This motor isn't a revver so the top end I was referring to was in the 4000-4800 range.

Another interesting note. Today I had a 2.25" connector and tailpipe installed (cat and muffler were allready 2.25"). The first thing I noticed after driving it was most of the monster torque it had initially is gone. I'm hoping I'll get it back when I upgrade the fuel and intake.
BTW, I paid for 2.5" muffler and cat so I will be having a frank discussion with that shop tomorrow.

Don, I'll look up the piston specs tomorrow at work. The pistons were finished back in February and it's not fresh in my mind.
The dish will have to be machined into the crown of course and the pin bosses will have to be trimmed a bit to allow the rod to fit. I chose to narrow the rod small end first to cut weight then took the rest off the bosses. I can't remember the pin height or diameter.

Break-in went OK'ish. My daughter took over at the throttle while I was cooling the engine down and she killed it 5min in. So far though everything looks good.

[Don H Jr]

Thanks for remembering my interest in your piston set up. I did a bit of research since posting and see how close everything is to working. Paying all that money to KB for pistons I don't want that slap and all that is not what I'm going to do for my engine build. But long rods are in my future for sure.

Don Jr

[Emptypockets]

Don, I haven't forgotten your interest, I've ben very busy putting out other fires.

The pistons are Sealed Power hypereutectics, part # H868cp-25. They are for the 350sbc, gen3/4 LS motors. They are the same basic design as the H802cp-30 pistons for the jeep except they have a shorter deck height. You will have to deck the block about .025 for a 0 deck. Personally I think the zero deck is overrated when you have almost no squish.

The pistons are flat so you will have to cut a dish. I cut it to 12.2 but would like to cut it closer to 20 if I do another with these pistons. There is a Ford piston that is a better fit but I can't find them anymore.

The small end of the rod will have to be bored to accommodate a .945 pin. It will also have to be narrowed to fit between the pin bosses in the piston.

I modified my combustion chamber to allow better filling, flame control and to keep the cr around 9.3. I lost some more squish but I think the trade off was worth it. In my next motor I would remove less material from the cc , keep the cr up around 9.5 and either coat the exhaust with ceramic or use an aluminum cylinder head.

The engine has about 2k miles on it now and is running very strong. So far it's list of victims are: Hemi Ram, tuned up powerstroke, merc mountaineer w/v8 (no contest) and a couple imports.

[SilverXJ]

The pistons are Sealed Power hypereutectics, part # H868cp-25. They are for the 350sbc, gen3/4 LS motors. They are the same basic design as the H802cp-30 pistons for the jeep except they have a shorter deck height. You will have to deck the block about .025 for a 0 deck. Personally I think the zero deck is overrated when you have almost no squish.

The standard 4.0L replacement piston will be down in the bore about .035". Are you saying your pistons will be further down in the bore, like .06"?

[Emptypockets]

The compression distance is 1.328" with the H868cp pistons. Mine finished up around .019-.041 initially. I resized the rods and decked the block for a final deck of .026". I am using the long rods.

A key lesson with these engines is to CHECK EVERYTHING. I found the rod lengths to be about .022" off between the shortest and longest. All the others were in between with no two being the same. I found this after balancing and matching

[Don H Jr]

[quote="Emptypockets"]Don, I haven't forgotten your interest, I've ben very busy putting out other fires.

The pistons are Sealed Power hypereutectics, part # H868cp-25. They are for the 350sbc, gen3/4 LS motors. They are the same basic design as the H802cp-30 pistons for the jeep except they have a shorter deck height. You will have to deck the block about .025 for a 0 deck. Personally I think the zero deck is overrated when you have almost no squish.

Empty Pockets: thanks again for remembering my interest as I follow your ideas to modify them and make them mind, lol. Just for my build, of course. My THOUGHTS are that the hyper pistons for an LS engine that is more in the 383 to 427 cu in roughly, would be better for a 4L stroker engine.
That is because of what I wrote you before, that pistons built for a 4 in stroke, which some of the LS engines from the factory have these days, would be a better rod stroke ratio than one for the 350 cu in LS, agreed? Anyone want to chime in. I know Chev LS type engines often have less than a 4 inch bore, just like our Jeeps, and with a 4 inch stroke crank the LS pistons, mathematically in this one respect should be good, in the placement of the rod pin high up in a quality piston.
Long rods need pin placement high. Are yours long, or short Empty?
Any input from anyone here more knowledgeable in this area than us is also encouraged and will be appreciated. LS factory forged pistons I'm sure also exist, and if they do it would be nice to know the cyl wall to piston clearances, to decide if they would work for a guy like me who doesn't go for the slappin and clappin when cold.

Don H. Jr.
Pre-Stroked Forum Member