I am running a carbed 305. When idling no smoke can be seen coming from exhaust but when rpms go to 1500 + thick white smoke comes out that does not dissapate quickly. Originally thought it was a bad head gasket but engine runs strong and does not miss and no bubbles can be seen when readiator cap is removed. Engine coolant levels did drop drastically which caused the engine to overheat a couple times but refilled it and had no everheating problems. I think it might the intake gasket but not sure. Once I revved it to 4000 rpms ( stupid I know ) and the smoke was so thick I couldn't see. I have not driven the car since I bought it a month a go I just rev it for fun sometimes and to show off since my neighbor thinks his mitsubishi 3000gt is so loud and cool. His car sounds like crap if you ask me lol! Thanks for any help! Also how many more mpg does a stock 305 get over a 400hp 350 engine?

 

sounds like you might have a cracked block or head if it has overheated it could also be a warped head or deck only way to tell for sure is a pressure check on the coolant system and or a compression check. As far as fuel mileage is concerned its all a matter of how the engine is built and the tuning Ive seen some that can get up to 20 MPG when driven reasonably.

 

Atilla the Fun, a member on these boards gets 25-26 on his carbed 350, which has a bunch of work done to it. V8s don't get bad gas mileage at all if they're highway miles. It's the in-town driving that drops our average. It's much more complicated than +hp = -mpg. It's about power to weight ratios, gearing, where your torque band sits, etc. My buddy used to constantly brag about how his civic got 30mpg, then I tuned my car up and hit the 26mpg range (with a 350), and he's slowed down on the sh** talking. I'm chasing him down haha, hoping to hit 29-30mpg this summer.

As for the smoke, definitely do a compression check - lots of smoke is never a good sign. If all cylinders have good compression, inspect your top end gaskets and intake manifold.

If you have a cracked block, or really messed up heads, I think it's time for you to drop in a 350

 

I Just wanted to know what you mean by tune up. I'm new to all of this and do you mean tune the carburetor or tune other stuff as well. I know for my 350 engine the torque band is in the 3000 - 6000 rpm. specs are as followed:
3000 - 410 lbs
4000 - 430 lbs
5000 - 430 lbs
6000 - 420 lbs
these are for my 350 engine but Would i get a better torque band if i went with a 3.75 stroker crank istead of stock crank. Would the bigger crank reduce fuel mileage. The cam I use is for very strong mid range torque. would switching to a very strong low end torque help? Also what must be done for the gearing? Well in other words how did you "tune" your car? thanks!

 

Well the 26mpg is fairly tame for a 350. I replaced a bunch of crap parts (injectors, ign system, and air intake tube/filter) then tuned the computer - dialed in the VE, had the torque converter lock up much sooner, etc. High 20s with be accomplished by playing with the "highway mode" in the computer

That's a pretty impressive torque band if I may say so. As for mileage vs. torque - the engine is most efficient when it's making peak torque. That doesn't mean you'll get the best gas mileage right there (especially if peak torque is at 3000-4000rpm), but if you're still in a reasonably flat part of the torque curve, you're doing well.

 

Borrow a coolant system pressure tester from O'Reilly's/AutoZone/etc. Pressureize the system to 20 psi and if the pressure doesn't hold, you'll need to break out the tools.

It could be an intake gasket leak, but most likely it's a bad head gaskets. Let's hope it's the former.

Jake

 

This may sound stupid but is there a computer on a carbed engine

 

the only stupid question is the one you dont ask. Your car does in fact have a computer in it that is linked to the carb if it is still stock. the computer controls the timing advance and converter lockup among other things. The computer is on the back side of the passenger dash you should be able to see it by removing the cover on the underside of the dash and looking up.

 

That explains what the device was under there then. I acidentally found it a couple weeks ago when I was looking for the hatch release harness. Well, I do have another question and it is how do I tune that. thanks HF_monster.

 

I dont think that their is much you can do to tune it but I may be wrong. I tend to get rid of them and go to an aftermarket carb and intake at that point you also have to replace the dist. Someone else might be able to answer your question.

 

If you dont want to get a hold of a pressure tester or take it to get pressure tested, you can always pull the spark plugs. If you're blowing out that much steam, at least one of them should look, VERY different from the rest.

This is from one of my builds that developed a crack in the cylinder bore after the cam break-in.



See how clean #6 looks? There's a clear difference, and it only has about 30 minutes of run time on it. The plug was noticably different looking also. Plugs should tell you a lot about what the inside of the engine looks like.

Note - I didnt see ANY steam out the exhaust when it was running. I discovered a problem only when I went to re-check valve lash and saw milky oil. So that was a pretty small amount that did that.

 

If I send you my exhaust valves, can you steam clean them for me? XD

 

Thanks everyone for helping. I am sure now that it is a head gasket problem