Broken 4.1 NA Block

[bison]

With wet nitrous systems like yours it's nice to run a cell in the front of the car with a dedicated efi pump. It's very easy to do and you can just keep 118 octane in it. A properly built 200c trans saves weight and get you down the strip faster.

 

[ek02]

My .030 over pistons finally arrived from JE. They put Tuffcoat on them just like my previous order, even though I asked them not to. The coating wore off in no time on my last engine. I have the RJC girdle also, and the block and all rotating parts will go to the machine shop next week. The new pistons weigh a little more than the ones my crank was balanced with. Now comes the long wait to get the block back. It has already been decked by another machine shop to make sure some dings on the head surface would clean up at .020. I countersunk the head bolt threads after it was decked. Hopefully, that will stop the deck from cracking like my old block. The cracks did not cause any problems, but they do not give me a warm feeling. The cracks in the main webs sure caused a problem. I have read that it is a good idea to grind the casting lines smooth that run from the center mains to the cam bearings to prevent cracks. I'm not sure that would stop any cracks. Does anyone think this is worthwile doing? Also, is there any clearance problems with a girdle and a stroker crank? My rods are modified to clear the cam, and the block is clearanced at the oil passage for the H-beam 7/16" rod bolts on # 1 rod. I don't think the rods come anywhere near the girdle, but I would rather ask than mock it up again just to check clearance on the girdle.

 

[dr_frankenstein]

any updates?

 

[ek02]

My parts have been at the machine shop for a month. They are supposed to start on it this week. The pan rail and front cover will be milled flat along with the main caps in a vertical mill, then the girdle will be fitted and the block line honed. The block will be bored and the rotating assembly rebalanced due to the weight difference in the pistons. I have all the parts ready, just waiting for the machine work to be done.

 

[ek02]

My machine shop called today to go over the details of what I needed done. They are finally starting on it. I can't wait to get this engine back together. My 3.8 just does not run as good. It has ported irons with big intakes and the heat passages filled with aluminum, T&D 1.65 rockers, 10-1 hypers, and the same grind as my 4.1 roller cam, but a flat tappet. Same KB intake with a 500CFM Edelbrock. The 600 CFM I have on the 274 does not run good on the 3.8. The stroker 4.1 pulls twice as hard as the 3.8. The extra cubes, roller cam, and GN1 heads really make a difference. I'll post some photos as I build it.

 

[charlief1]

Just as an FYI here, the Q-jet on the 4.1 engine was a 730 CFM carb. Go with a spread bore carb and it will work much better overall.

 

[ek02]

I have used a Q-Jet before, and it worked very well on a Holley manifold on a 3.8. The mileage was better than a Holley for sure. The KB manifolds I have now use the Holley bolt pattern, which is needed for the NOS plate system. The Edelbrock carbs seem to be large enough and are very tuneable. I have zero vacuum at wide open throttle on both engines, so the carbs are not restricting airflow. I have used Q-Jets on a lot of GM engines over the years. They will only flow as much air as the engine needs due to the secodary air blade, and the primaries are small for good mileage. They do work very well for the street.

 

[dr_frankenstein]

that 3.8 is flat with the 10-1 compression eh?

doesnt supprise me.... they are just not right when there built like that.

When I was running my 4.1 NA i was using a holley 950HP on the weiand single plane. Ive found that the difference in pressure drop across the carb affects the tune and drivability. even fires are split 120* this causes shallower and longer breathing pulses. I never had success with the edelbrocks, they just never tuned right for me.

 

[ek02]

I won't say it's flat, it just will not pull like the 274. I thought the 3.8 ran good when I first built it, but the first time I nailed the stroker to the floor, I was surprised at the difference. It was like I found the perfect combo of parts. Do you think more compression would wake up the 3.8? How much compression is streetable on 93 octane with iron heads?

 

[dr_frankenstein]

Id say your already on the hairy edge street wise with the 10-1 compression, maybe another half a point to a point and careful timing you might get away with it on the street. I went the same route early on, ended up using a 700R4 (with its gear spread) and the juice to make up for the motors shortcomings. but the 4.1, non stroked was even a night and day difference, when it comes to the NA im convinced that the bore size has more of an effect then the stroke.

your other option is to crank that compression up and cam it big.... im talking huge for a NA motor.... the way the buick makes power in its curve has me to believe that you cant over cam an NA motor as long as you have the compression. But ive never tried to run it on the street either, so im not sure what to say on its manners in terms of octane and heat.

 

[ek02]

I got all my parts back today. The block has been bored .030, honed with a deck plate, decked, the girdle installed, and the mains line honed. The crank was rebalanced due to the difference in the .030 piston weight. The pan rails and front cover were machined flat and the oil pickup surface remachined. The caps had the bolt faces countersunk, and flat 1/2" allen head bolts held the caps to the block to machine them to the correct height. I've never seen one done this way, but the machine shop has done some other Buick V6's this way. It eliminates shimming the caps with shim stock. It will be a week or more before I get to work on it again, but I will mock it up and check all the clearances, and file fit the rings. Lots of cleaning to do also.

 

[ek02]

I got to check out the girdle install last night to see how it was done. The pan rail and front cover were machined .060. The caps were machined while attached to the block .055. This gave the required .005 clearance between the block and the girdle without the use of shim stock, or the .060 shims supplied with the girdle that are supposed to go in between the caps and the girdle. With it all machined precisely in a Bridgeport mill, all that needs to be done is to bolt the girdle on with silicone between the block and the girdle. No shims to mess with of any kind. The only draw back is, if the front cover ever needs to be replaced, the new cover will need to be milled .060 on the pan (girdle) face.

 

[750H.P.V6]

Rather than silicone I'd recommend trying "The right stuff". I never had any luck with girdles, they all leaked until I tried "The right stuff" and that seems to fix the problem. Another thing you might want to consider is going with some good quality studs for the pan rail attachment. The ones that come with the girdles are prone to breakage.

Neal

 

[ek02]

Thanks. I planned to use the "Right Stuff", I just said silicone. Everyone on here seems to like it. I will also use it on the rear main side seals instead of the rubber seals. Good info on the pan studs. I can probably find some good studs in the ARP catalog. Even some from Ace Hardware may work. There has to be some stress on them. I broke a Champion rocker stud and replaced them all with ARP studs, end of problem.

 

[750H.P.V6]

We've broke the Champion rocker studs that come with the Scorpion rockers too. I got to the point that we just trash them and go with ARP stuff to eliminate that weak link.

Neal

 

[ek02]

I got to work on the new engine this week. I checked all the clearances. The machine work was perfect. .018-.002 on the mains using .001 over bearings (crank was polished on the mains), .002 on the rods, .0046 coated piston clearance as recommended by JE. I file fit the rings to .020 top, .022 second, and .015 on the oil ring rails. This is what JE rocommended for street/strip nitrous. Crank end play .005. The girdle was time consuming. I had to grind for clearance for the dipstick tube and the oil pickup tube extension. It did fit perfectly though with all the pan rail and main studs in place. The crank scraper needed a lot of work to make it fit the around the studs. It will need more work when the pistons and rods go in due to the longer stroke.. I torqued it all down in stages with the "Right Stuff" between the girdle and the rails, and I used the Right Stuff instead of the main cap side seals. The crank spins by hand. The front cover has just enough clearance at the girdle for some sealer. I used TA rear groove cam bearings and tapped the oil passages at front of the block for narrow plugs. I put my old Rollmaster timing chain on, and it has 1/4" of play with the chain tight on the pull side. I am not sure if I should get a .004 oversize to try and tighten it up a bit. I remember it being pretty loose on the old engine. This block was only line honed with the girdle install. Any opinions on the chain slop?

 

[charlief1]

Most of the timing chains are loose on the Buick V type engines. What I've been looking at is the tensioner on the 88-89 Series I tensioners. They've got a longer bolt so you'd need to cut them off some but it's a 1 piece unit with a bakelite type rub block so it should hold up better. It also has a new spring so you don't have to worry about it getting weak.

 

[ek02]

Some progress at last. The bottom end is together, just waiting for a .004 Rollmaster chain set to tighten things up a little. I CC'd the piston dish, and with a near zero deck height, Felpro .040 gasket, and GN1 heads, it has 10.55-1 compression, .5 more than I planned on, but with aluminum heads and 93 octane, it should be ok. Piston to valve is .140 intake and .190 exhaust with .526 lift. With iron heads cut .030, it was way too close on the old engine, but then I decided to go with the GN1 heads. The GN1's move the valves closer to the center of the cylinder, and opens up the clearance at the valve pockets with these pistons. Everything else is checked for fit and ready for assembly, I just need the chain set.

 

[fuzzyGN]

Looks good. I wouldn't worry at all about the compression. The aluminum heads suck up about a point compared to iron heads. So really you are looking to an equivalent of 9.5:1. Wouldn't scare me in the least. Should run great.

 

[ek02]

On hold again. No one seems to have an oversize timing chain set. They are all on backorder. It may be a few weeks before I can get one. Onward to other projects.