400 BB MOPAR questions

[cbodybob]

i just bought this drag car & it has a 400 in it. I have 2 questions. The previous owner said he shifted it at 6000. It has a 6200 chip in the MSD box. Just wanted to know if that's safe in general terms. The bottom end is all stock except pistons. That sounds high to me for a cast crank. Also he said the Pistons where changed out & the stock heads shaved .50 & 2.14 intake valves installed. I believe stock these had 8.1 compression & he said its 10.1 now. Have not taken it to the track yet, but it sure sounds good. So question # 2 is roughly how much horse power was picked up from the compression increase. Stock bore according to him. .430 lift Lunati cam. Sounds like it has a bigger cam. I'm thinking 470ish. It has a 750 Holley on a Eddy Torquer intake. I'm thinking 30 horse increase??? Any ideas.

 

[khryslerkid]

Did he show you any time slips?

 

[cbodybob]

No , he told me he only took it to the track one time. He lost his job & the car sat for a while. Someone else built the car. The guy I got it from didn't seem to know too much about it.

 

[Cranky]

A buddy and I was turning a stock bottom end 318 6200. Mom's cast cranks are not like the old cast cranks like GM and Ford had. They are much better. Granted, the teens internal parts are lighter but so are the rods vs what's in a big block. Does it have to turn 6k to run the number? I would try 4800 for a base then kick it up to 5200 and see if it goes faster then 5500 but we really need more info on it. What's the gearing in the rear, torque converter stall and on and on? The cam we have in the teen is a .480 lift.....

 

[cbodybob]

According to the seller it has a 4:10 with a sure grip. 29X10 tire. He said the converter is the stock one & was sent off to be matched with the cam. It idels at 700 in neutral. Drop it into gear & makes no difference. The guy told me it ran a 7.30 spinning the one time he took it out to an 1/8th mile track. I just don't believe it. I estimate 3700 pounds & about 375-400 horse. I'm thinking 8 flat if it hooks. It's got a header leak, trans pan is leaking & front tires are dry rotted & just generally check it over before I can take it to the track. Hopefully in a couple of weeks I can. I'll probably do as you said. Shift it low & work my way up

 

[multipleBs]

According to the Direct Connection performance book published back in the 80s stock bottom ends are safe to 6000 for an RB engine and 6300 for the B engine. Being a B engine the 400 should be safe to 6300. It's a short stroke engine but the mass of the piston and rod are quite high, but as mentioned earlier these cast cranks weren't junk. Of course this assumes that everything is in good condition, and the oil supply adequate etc. I regularly ran a 360 with stock crank to 6000 and it has a longer stroke than a 400. No issues were encountered. Since the engine internal conditions are unknown to you at this time and let's face it, sellers can exaggerate or omit info, you probably should not push it too hard the first few runs until you can assess it's condition. If it idles smoothly at 700 rpm I would assume the cam is stock or almost stock. If it is truly 10:1 compression it could use a lot more cam than that.

 

[cbodybob]

The idle is lumpy, can certainly tell it's got a cam. It's just that's when I drop it into drive it's seamless & the idle stays the same. Makes me think it's got a real loose converter. In other words I can't feel it go into gear.

 

[Cranky]

Do a foot brake test and see how high the rpm gets before the brakes won't hold. It's not the perfect test for a converter but it'll at least tell you it's stock or not....as for how much horsepower does an increase in compression create....I've seen numbers all over the map. As for the 318 I mentioned, with it's deck height and the CC's of the 360 heads it has, we guesstimated compression to be around 7.8 and it still pulled a 13.51 @ 102 out of hat.

 

[SlinktRR]

I regularly shift a 383 B motor at 6200 RPM. It loves it. Forged crank '71 HP. Bottom end is fine with the short stroke/oversquare design of low decks, the valve train and valve float is what you will want to keep an eye on.

 

[Cranky]

I regularly shift a 383 B motor at 6200 RPM. It loves it. Forged crank '71 HP. Bottom end is fine with the short stroke/oversquare design of low decks, the valve train and valve float is what you will want to keep an eye on.

Do you take it to the track and will it run the same shifting at say 5800? I know (and like) short stroke engines like rpm but sometimes they will do just as well at a lower rpm.

 

[747mopar]

I regularly shift a 383 B motor at 6200 RPM. It loves it. Forged crank '71 HP. Bottom end is fine with the short stroke/oversquare design of low decks, the valve train and valve float is what you will want to keep an eye on.

Same here, mines got a forged 71 440 rotating assembly and I shift it at 6,000 regularly. ARP rod bolts are a good idea when cranking them up too.

 

[SlinktRR]

Do you take it to the track and will it run the same shifting at say 5800? I know (and like) short stroke engines like rpm but sometimes they will do just as well at a lower rpm.

Good question cranky. Car will be at the track later this month so I'll let you know. On the street my car keeps pulling so I keep feeding the gas. The only dyno (engine) its been on showed that horsepower fell flat at around 5500; this was with a 650 cfm AVS on a stock cast iron intake. With the 800 cfm AVS on a mopar M1 on it now there is no RPM ceiling that I have run into other than my own fear of things going boom. Whether shifting at 6200 leads to better ET's, depends on how the car is set up I would guess with cam gears and tires. But on a stock motor I think 6200 is fine as far as whether it can handle it or not.

 

[cbodybob]

My last drag car a smallblock had a 3000 PTC converter. I could foot it to 1800 & then it would start to creep. I'll try this one after I get that header leak fixed

 

[65 3 times]

How about some more pics. Looks like a interesting car.

 

[cbodybob]

How about some more pics. Looks like a interesting car.

You asked for it LoL

 

[65 3 times]

Thank You!! Looks like a real purpose built race car. I'd change the oil.(don't forget the zinc) Add some new tires and check the brakes and wheel bearings change the oil & filter in trans and trust the previous owners. (6200 RPM) Run the wheels off it and have fun. Nice Car. Dave

 

[cbodybob]

Thanks Dave. Yes I need to go through it & look see just what I bought. $2000 so I thought what the heck. If it will run in the 7's I'll put a trans brake in it this winter & go pipe rack huntin' LoL. I'll have the only 77 Sport Fury out there

 

[Shorthorse]

Lots of good posts but first things first, safety, safety, safety. Like you said, check the brakes, stop the leaks especially if they could make their way to the rear tires on a pass. Also, make sure it will pass tech or you might make the tow for nothing. Sure, some tracks don't even look at stuff but that's you in the car. I noticed your seat back is not supported. Plastic seats can break easier than you think. Once you're safe, have fun.

 

[cbodybob]

Yes I need to fab up a seat brace. I'll be busy on stuff like that for a little while.

 

[SlinktRR]

That sport fury looks really good in race trim without a vinyl top and headlights. Changing to 1 7/8 headers and 3" exhaust will net some easy gains.