Thread: 400ci sbc

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Hi, iam doing a budget rebuild on my 73 400 that i had in my 67 chevyll for 13 years. Over the years i put in a crane cam 272 -216-454 lift, timeing chain, small tub headers,holley street domanater intake, 750 vac holley carb, Hei distributor, 350 trans, 355 gears,2200-2400 stall conv. This is a weekend warior car and take it to the track 1or 2 times a year. This motor has standerd bore,crank,rods, stock 76cc heads.Compression test was 165 all around. Best time was 13.60 98 mph. This motor had lots of torque down low but died at top end. 5500 Max rpm. My plan is to hone cylinders, molly rings, rod and main bearings. New cam that i think would not be to big for street is a 280-230 480 lift, for heads i have a nice pair of 69-70 302- 350 041 heads with 64cc will be close to 10.1 with my dish pistons. What hone stones can i use 400 grit? Hows my combo? THANKS

What You've got is an absolute torque motor in the lightweight chevy 11 . You not doing too much when you get past 4500-48oo rpm. this is going to sound strange to you but if you ran a higher gear ratio in that light car(308--323) you wouldn't light up the tires as bad and it will pull all the way thru the quarter.Just because you're turning 5500 doesn"t mean you are making horse power.If the car still runs good ,put a taller gear in and try it before you rebuild it. You will be pleasantly suprised. If you were running a 283 -302 -or 327 then you would go the other way . You would need to turn it and you would want more gear.No matter what cam you select ,( both of those cams are a good choice) You still will not turn that short rod motor too hard.The 041 heads are a good choice but I dont think they come with hardened seats. You need to check . they are around 67 to 68 cc and your compression should be a little over 10 to 1 . Have Fun!

Just saying hello to someone in Philly. I used to commute on the Shortkill (Schuykill) Expressway when I went to Drexel years ago. It sounds like what you want to do is what we used to call an "overhaul" as compared to a full rebuild of the engine. On the one hand a machine shop will probably recommend a 0.030" overbore with new pistons just because the parts are the cheapest and then you need to worry over the condition of the rods. I got a kit for a 350 rebuild for $215, heads reconditioned for $300 and all new rods for $225 (you could rebuild your rods for less). I say this because you reminded me of a deal I did way back when by going to one of those inner city garages who "rebuilt" my Chevy 235 ('54 Bel Air convert) for just $300! What they did was grind the valves and add rings to make compression better and it ran great until one day just west of the City Line exit a rod poked through the side of the block at 65 mph. I pulled over and it still idled and I could see the rod moving in and out of the block so I drove it home on 5 cyl. The next day it started up fine (on 5 cyl) and I drove it to the Sears in Norristown for a fully rebuilt engine. Interestingly the clutch was not torqued right in that job and about two weeks later the clutch on that new engine disintegrated on the old Black Horse Pike on the way to the shore, although Sears replaced the clutch at no charge. The moral is that if your engine has been run hard occasionally over a 13 year period you are probably taking a short cut in the overhaul that may backfire and fail, probably with a rod failure?? So, just bite the bullet and have the block hot tanked and bored out and make sure the rods are reconditioned or replaced. Just my 2 cents, but it sounds like you have a neat car there and an inexpensive rebuild can still be done cheaper than a crate motor from Goodwrench ($1400), although you may need to put out $35 for an engine stand if you do the assembly yourself. Another tip is that I think the Auto Zone rebuilt engines are assembled in the Phila area and sold exchange for about $1300(?) and they are run-tested and shipping would be negligible for your location. The point is that if you increase compression with other heads and a valve job with new rings, the next weakest link is in the rods, so that is risky. Well anyway you just reminded me of driving on the Expressway with a broken rod. Good luck.

Don Shillady
Retired Scientist/teen rodder

Thanks , riverhorse59

I had a 63 Nova Bracket car with a 400 with a lot of similarities to yours. Mine was not a street car at all, but a budget race car. Mine was .030 over with dish top pistons. I used some old 461 double hump heads with 1.94-1.50 valves. I had a Cam Dynamic hydraulic cam that woud spin to 6500 and pull strong up to about 6200. I was in Nebraska racing at 1200 feet above sea level. With 5.13-1 gears and a 28" tire I would cross the finish line at just about 6300. Best ETs there were low 12.30s. Dropping to 4.88s might have been the better thing to do. The 5.13s were right until I made other changes that improved my performance from 12.70s. I was running a powerglide with a 3000 Stall converter. I moved to CA and ran at about 60ft above sealevel and the car ran consistant 12.08-12.16. One cold dry fall night it ran an 11.98. It became very apparent that I had way too much gear at this point as it would lay down about 150 feet before the finsih, but man would it pull till then. Where all this is going is to say I think you have an excellent combo, and that riverhorse's suggestions definitely are worth trying. Your motor combo with the new cam sounds very similar to mine. I know that I was spinning my motor more than most people like to turn a stock bottom 400, I guess I was pretty lucky as the bottom end had over 350 1/4 mile runs on it when I sold the whole package. And yes I did warn the buyer!

Good luck with your project, that combo has definite high 12 potential.

Pat

thanks DON,what a storyHAHAHA, i cant beleave it i live 2 miles fron that sears store.

Thanks STU COOL, sounds like a nice nova, 6500 with stock bottom end wow.

DeRo, One thing we did not mention.When and if You pull your motor down make sure you have the block checked for wear in the cylinder walls,to see if you can go back with the standard bore. Also,mike the pistons to see if the skirts have colapsed.I have an article here somewhere on a short rod 406 verses the long rod 406. I've read it many times and think I remember most of what it said. Looked for it tonight for an hour ,can't put my hand on it ,but did find many articles on camshafts.that relates to our discussion.ANYWAY, the motors were identical except for the rods.The short rod motor held a slight advantage at 4800rpm and the long rod motor had a 12 horse power advantageat 5500. Neither motor is a high rpm motor , BUt------At 5500 The short rod motor was done. Found several cam comparison articles and all cams close to the comp. 280--480 started droping off in horsepower substancially after 5500rpm.So ,You may have a short rod 400 that will turn 6500,it may have a good seat of the pants feel,But if you were to put it on the dyno ,you'd be awfully dissapointed.If You want a 400 that will turn 6500,still making horsepower,open your wallet.W-I-D-E.Crank,Rods and a real good set of heads For starters.A 400 is like no other chevy small block and you have to approach it differently. You can build yours for not a whole lot of money if you keep in mind that you want to make all the power at 5500 or below. Stu Cool turned some impressive numbers with his 63. If he had kept his motor in its power band he would have loved the results. Just One Mans Opinion, Not Worth Much!

Thanks Riverhorse59, your right i need to have it checked. I have it all apart, no scraches in cylinder walls and i see some hone markes in there, no scharches on pistons skirts.

I would like nail down my comp ratio as close possable, 73 400 has a 4.125 bore 3.75 stroke, 76cc head, 0.041 head gasket, piston dish cc ?? should be 24cc dish piston to be 8.5 comp ratio.So with the 041 heads i plan to use i need to find out what cc they are,mortec site calls them 64cc is that right, i dont wount to be over 10.1. Thanks DeRo

I was thinking the 041 had 67 0r 68 cc's . I stand corrected. According to my book the 3947041 head came on a 68-70 , 350 with 300 h.p. and 64 cc's 1.94 and 1.5 valves. Some of these guys are very good at computing compression ratio. maybe someone will help us be more precise.

Thanks techinspector1 but i dont understand it, are the 9cc gasket the same as the 0.041 gaskets, and if i get the block zero decked i will have 9.46:1

Techinspector1, Wasn't the advertised compression at least 8.5 to 1 from the factory on the 400 with 76cc heads? We are dropping to 64 cc heads. What am I missing here? I dont know the formula . Will You give it to us? Also, please help me compute the compression on my motor. I have a 355,manley flat top with 2 valve reliefs, .005 in the hole. Be right back. Its 6:30 in the morning and Im going to the garage to mike a head gasket. Must be nuts. I should be in bed. O.K. .023 uncrushed. The heads are Brodix track 1 alluminum 76cc. Proberly not a good choice for a street head but I have them, they are new, so I may use them.What do you think?Thanks for your help in both cases. Anyone else feel free to respond. thanks

Lets change that head gasket. It didn't sound right. I checked again and the gasket looked like it had been chrushed but not run. So lets just figure on a Felpro 1003

Thanks techinspector1, i appreciate you trying to help me understand all this but i'am still lost. I will take everyones advise have it checked out. If i do get it bored would i need a deeper dish piston with it decked. Do you think the 64cc heads are to small a cc? I will sell them and get the right cc head. What comp ratio sould i shoot for so it dont dentanate. THANKS EVERYONE