400 slight warm up

[ToiletDuck]

my 4x4 has a 400 in it that im switching over to propane to run better at high angles. It runs good no noises and doesnt burn any oil and has a 383 4bbl intake.

Now propane has lower btu's than gas so it wont make as much power but it has a higher octane rating, something like 110. So i was thinking of shaving the heads a bit to increase cr. What is the the stock cr for a 76 400 and how much would i have to shave the heads to get to 10.5-11 cr? The intake would also have to be shave too? Also would I have to get shorter pushrods?

Also im thinking about a different cam. What would be a good cheap cam for this situation?


Thanks for the help, Im going to make a 451 out of this someday but thats not in the budget right now.

[dave571]

Factory is 7.5 to 7.8:1 or so.

There is no way you are going to get enough off the heads to do 10 to one.

Those open heads are at least 88 cc. If you replaced them with the older 516 closed head (78 cc) they will still only be around 8.3:1
(try the math at http://kb-silvolite.com/calc.php?action=comp

The piston is just too far down the hole.(.100")

Best bet is live with what you have until you do the 451.

[bbeckwith]

Hey Dave, haven't heard from you in a while. How's it going? Done anything with the van lately?

[TK]

Originally Posted by ToiletDuck

my 4x4 has a 400 in it that im switching over to propane to run better at high angles. It runs good no noises and doesnt burn any oil and has a 383 4bbl intake.

Now propane has lower btu's than gas so it wont make as much power but it has a higher octane rating, something like 110. So i was thinking of shaving the heads a bit to increase cr. What is the the stock cr for a 76 400 and how much would i have to shave the heads to get to 10.5-11 cr? The intake would also have to be shave too? Also would I have to get shorter pushrods?

Also im thinking about a different cam. What would be a good cheap cam for this situation?


Thanks for the help, Im going to make a 451 out of this someday but thats not in the budget right now.

as far as the cam, run a 440 resto cam, they make some heat, another problem you have with propane is engine oil. make sure you get amsoil propane eng oil or equivelent. also, we had a 65 2 ton dodge with a 361 propane/gasoline set up. it worked pretty good, but you had to get it warm on gas, then switch it over to get any power out of it, and boy, could you feel the propane hit. can you say BOG??? you wont be loaded quite as heavy, so you wont notice it as much.

[dave571]

Originally Posted by bbeckwith

Hey Dave, haven't heard from you in a while. How's it going? Done anything with the van lately?

Hi bbeckwith

Just put a 650 speed demon on it. Much improved throttle response and top end power. I'll have to do a newsletter on it, when the track opens again.

The car is taking up a bunch of my time right now. Doing a head upgrade, and some caltracks, Racer brown rocker arms, blah blah blah.

Hopefully I'll see some good gains, and not just a bunch of money spent

[ToiletDuck]

thanks for the replies.


What if i got a 440 crank and had it cut for the mains/block clearance and had it ballanced to exactly the same weight as the stock 400 crank. Then put it in the engine with new main and rod bearings. I know this is not the proper way of doing things but it is not in the budget for a complete 451 rebuild.

would i get into trouble with piston to head clearance?

[rumblefish360]

Yes I believe so. Save for the 451 the right way and be real happy about doing things right instead of a band aid move.

[ToiletDuck]

Originally Posted by rumblefish360

Yes I believe so. Save for the 451 the right way and be real happy about doing things right instead of a band aid move.

For now its either keeping it gas or a band aid, im already blowing my load on the tires/wheels/suspension/steering at upwards of $3000. If i go with a performance 451 rebuild it is not only going to cost more money but also introduce other cost factors.

1. The cost of converting to propane will double. One propane mixer cannot flow enough to feed a built big block, so i would have to run dual mixers.

2. dual quad intake manifold for the 2 mixers. Propane works better with low rise dual plane intakes, and the only low rise dual quad intake i have found is an edelbrock for 440 heads.

3. 440 heads from either edelbrock or aerohead and rocker arms. Also a new cam

4. Quality 727 trans to handle the power, big $$


The only 2 options i have are dealing with the power loss or a bandaid fix. I would love more than anything to be able to do it right the first time but i just cant afford it right now.

[rumblefish360]

I may have read this wrong, but just incase;

You can not put a 440 intake on a low deck 383 - 400 engine unless you use the MoPar Stage VI (6) heads. There alot of money and would eat up your budget in short order.

Build yourself a killer short block. You CAN go fast even with stock heads.

[ToiletDuck]

Originally Posted by rumblefish360

I may have read this wrong, but just incase;

You can not put a 440 intake on a low deck 383 - 400 engine unless you use the MoPar Stage VI (6) heads. There alot of money and would eat up your budget in short order.

Build yourself a killer short block. You CAN go fast even with stock heads.

Ya have been thinking about it and ill probably wait i dunno......I thought you could put rb heads on a b engine then use an rb intake??

[racintracy]

Originally Posted by ToiletDuck

Ya have been thinking about it and ill probably wait i dunno......I thought you could put rb heads on a b engine then use an rb intake??

Sorry man but you can't use a rb intake on a b block. The rb heads are the same physical size so there's no problem there. The problem is the b block is narrower and shorter so that's why you have to use a b intake on a b block and a rb intake on a rb block.

Only exception is the one Rumble mentioned where you use stage 6 heads.

[ToiletDuck]

Originally Posted by racintracy

Sorry man but you can't use a rb intake on a b block. The rb heads are the same physical size so there's no problem there. The problem is the b block is narrower and shorter so that's why you have to use a b intake on a b block and a rb intake on a rb block.

Only exception is the one Rumble mentioned where you use stage 6 heads.

what about rb heads on a b block with a b intake?

[racintracy]

Originally Posted by ToiletDuck

what about rb heads on a b block with a b intake?

Yes. That will work.

[dave571]

There's not really such a thing as a B or RB head.

They are the same.

Example, ALL big blocks (B or RB) came with "906" casting cylinder heads in 1969.



What you were suggesting with the 440 crank is doable, but not cheap either. That is actually where the 451 came from. A cheap racer dude decided to use a rb crank in a stock bore 400 to raise the compression and displacement.

The stroke difference is .370" On each end, that's .185" The piston is at least .100 in the hole already, maybe even .110, so mill off .075 and you have a flat top.

Not worth the cost of milling stock pistons, and balancing an assembly to do it these days.

I guess the same thing can be done by using stocker 400 pistons in a 440 with a 4.15 stroke crank. No milling required. Works out to 492 or something like that, with 9.8:comp.