Geo450racer:
give me rough estimate with the previously metioned mods on the 400 how much mpgs would you expect? since its highter compression shoudln't it give me better mpg than now, but  what do you think about big block power?  how much of a mpg hit would a big block do?

It is hard to say because vehicle drag and weight plays a big roll here too. I would suggest a cam with no more than about 215 degrees or so at .050 lift and you want one that is "squared" in that intake and exhaust has same duration if you want best possible MPG. Some cams add a extra 10 to 15 degrees to exhaust but this reduces efficiency at lower RPM's and also lets a little extra mixture out tail pipe unburned too. Higher compression does increase efficiency a bit too. In a heavy 4x4 SUV I like a LOT of torque right off idle and up thru 3000 RPM or so. Myself I could care less is it starts falling flat above 4000 RPM as I rarely ever get there. Example, I have a 350 TBI and a 350 Vortec here and the 350TBI will run circles around VorTec below 3000 RPM and is VERY crisp off idle and pulls really well at 1200 RPM in OD. The VorTec has a lot more top end and pulls good from just under 3000 to about 5000 RPM but I would give a little of that top end up for more on bottom with it.  

yep 215 for a daily driver ya expect ot get mileage out of, I generally keep em below 210 @.o5o unless its gonna race.  

okay cool but if i cant get big power numbers down low in a small block what about a big block, shouldn't a 454 with around 9:1 commpression, good heads, hot cam, intake, carb, ignition, and headers make at least 400 hp and even more tourque at low rpms? how much more of a gas guzzler would it be? i have no expericen with big blocks  

I think you are running in circles here. I suggest you first regear truck then figure out what you want to do with engine. I have this feeling that since you are fixating on torque that you really need to regear first. Also, if you really want max low RPM torque, you do not want headers as they do their best  in upper midrange to top end. (you actually want a  bit of back pressure for best low RPM torque).  

ha guess what, the reason for my lack of power and non smooth running motor?  LOW COMMPRESSION!!!!! my drivers side bank cylinders only have 75 psi and my passenger side cyclinders range from 60-75 psi. i took my 35 inc tires off temperalory and put some stock sized tires on factory rims to see what the truck should be pulling like and i noticed no power increase from the
30 inc tires or the 35s!! so i knew the 400 should be pulling harder than it is now with stock sized tires in it since gears are 4:10s, so i check comppression and to my dissapointment i get those sad numbers mentioned above .  heres some hints on what ails the motor, i have an oil leack comming from the rear of my passenger side bank, there is no oil in the water though, all my spark plugs are fouled black and the truck smokes black and idles roughly  what could be the problem?  my friend said its probabley bad piston rings but im thinking other wise?  Any ideas??   im going to take apart the top end of motor thursday night so some ideas of what i should look for would be nice.  

uhhh, a wore out engine in need of some gaskets and a carb adjustment! LOL.  

You might do a wet/dry (with oil) compression check before you remove heads to see if it is ring or valves. I suspect valves here.  

what do you mean by wet/dry comppression test?  and if its the vavles then you mean it needs a vavle job right?  what does a vavle job include?  

Geo450racer:
what do you mean by wet/dry comppression test?  and if its the vavles then you mean it needs a vavle job right?  what does a vavle job include?

Dry mean you do a "normal" compression check. Wet means after normal "dry" check you squirt a bit of oil in cylinder to "wet" it and is pressure comes up a lot then you have ring issues. If it does not change much then you have some burn valves/seats.  

cracked or burnt valves, Particularly the exhaust, which is very, very, very common on the light cast 882 and other heads whether they have gotten hot or not on a 400.  

here are some good heads to look for, keep in mind the small cc heads are gonna run high compresion with flat top pistons, to the tune of 10:1cr's

441-74cc flat is close to 10:1
041-68cc
186-68cc
292-64cc flat is just shy of 11:1
034-68cc

probably the most popular 9.5 cr with flat top # are the 76cc heads here...

487
493
993
997 all 76cc's

no junk there as the 882, 624,... the list is long.  

mudb8-.:
cracked or burnt valves, Particularly the exhaust, which is very, very, very common on the light cast 882 and other heads whether they have gotten hot or not on a 400.

It is not just heat per say but mostly for detonation even at a low level. Engines of that era had no knock control and detonation causes valve to vibrate in seats and leak and burn over time and sometimes crack from heat stress that burnt valves can cause over time. When you have a load exhaust you do not hear the fuel knock until it is very loud so you may not be aware of the trouble that is brewing. 400SB are a bit prone to knock because the larger bore and quench area has lower surface area to volume ratio. Higher ratios retard knocking because they tend to cool flamer front a bit and slow potential for detonation on low octane fuel.  

Here is what you need, check out link below

http://harrisonoto.com/gm-high-performance-v.html  

LOL, now that takes the cake!

 

ha lol i need a gm v10??  anyways how can you tell what heads you have? where do i look for those numbers, i am probabley going to pull the heads off of my dads 78 corvette 350 since the car isn't being used at all, whats heads came on the corvette, are they better than my 400 heads and yes i know i will have to drill steam holes in 350 heads so how do i do that?  other than that the heads should bolt on just fine right??