i have swapped from 305 to 350 to now a 400 sbc. had a custom chip burned for my 350 and it ran great. Now my 400 requires more tuning. i have all the equipment to burn my own chips and i have messed with it quite a bit but i am still new to all this and dont know exactly what i am doing. i am not concerned computer tuning wise with this post. i am more concerned with the physical aspects that i need to change. i am running 350 injectors and i have a high volume TPI fuel pump in the tank. also i have an aftermarket oversize throttle body to flow more cfm. That 400 sbc is acting like a turd. has better low end (obviously because 400 are known for their low end torque) but after 3500 rpms it struggles so terribly bad to keep climbing the rpms. even the lowed still sucks. It can hardly spin the tires in first gear (i even have 3.73 gears). what am i missing? where am i going wrong? i feel its a fuel/air problem. am i not getting enough air? i have messed with the fuel pressure all over the place and i cant get it to react any better. do i need 454 injectors? i dont have a wideband sensor so i know i wont be able to get it perfect with out that but still.... it should be able to smoke the tires through 2nd gear at least.

 

What is your scan tool showing for fuel trim numbers, O2 voltage and cross-counts, coolant temperature, knock sensor activity, etc?

I bet the answer is in the data stream. Then you just have to figure out how to correct it with different parts or different calibration.

 

What is the setup on the 400??? Stock at 8.5:1, tiny 929' cam and 76cc 882 smog junk heads they wheeze out about 180 hp at 3,600 rpm with the stock 4bbl Q-jet. Unless you put better heads and a bigger cam its not going to want to rev.

 

Make sure the timing is advancing.

 

i dont doubt there is a problem with my calibrations. i am still learing how to read all that stuff and interprate, but thank you for your advice. i just wonderd if anyone had any advice on my outward physical parts that i needed to change injectors or intake.... ect stuff like that. i am running 11.5 compression and i have a mild cam that comp cams recomended for a mild street strip engine. i dont know the numbers off hand. i could uses a bigger cam not that i am at 11.5 compression. i used the same cam i had in my 350 build and it was running 9.1 compression. heads are stock TPI heads with port and polishing.

 

Your info is kind of confusing, you have a larger TB, but what injectors? A mild performance cam for a 350 is a dog for a 400. I don't think you could open up TPI heads enough to wake up a 400. Are you saying you have 11.5:1 compression on this engine? That's not a mild street performer number.

 

i have a factory tbi that has been bored out with bigger throttle blades to flow more cfm with 350 injectors. the cam is a mild street strip cam that was recommended for a mild tbi engine build. basically my motor could use a hotter cam. and yes i am running 11.5:1 compression. basically you are saying my heads are the real problem here?

 

First Guess: You need bigger injectors. If bigger injectors are required for a 350 over a 305, then a 400 would need more fuel than a 350.

A mild cam and a high-compression, iron-headed short-block that's probably running shy on fuel is very likely to have MASSIVE detonation problems. I'd love to see the knock-sensor activity on a scan tool.

I'm not familiar with TPI heads. If they're anything like the TBI heads, the ports are terrible for performance use.

 

Well when you think 400 small block Think Big block 396, look at the ports on a big block engine .... pretty big. As an example a 406 (30 over 400) in a 67 Nova I owned had Canfield heads with 185cc ports on it, it ran 10.60 in the 1/4 mile. It was a slug. I got a hold of Canfield , they said the heads were too small for that engine. It was a flatop piston engine with a 40136 Lunati cam 5.40 lift. I switched to the Canfield 230cc head and with just that change it woke up to 9.40 @ 141mph. Yeah heads make a big difference. There is no factory head that will let that engine breath.
For the injectors on your pup, yeah I think they can't keep up, get injectors for a 454 engine, there are all over Ebay or check the local parts salvage yard.
I can't address any ECM tune for that engine but there are real experts on this site google around here. With 11.5 compression and pump gas I bet the ECM is constantly pulling the timing back on your engine.
Good Luck.

 

Thank you for the information, thats what i was thinking as far as my heads being the problem and the injectors not being big enough. Also yes i agree 11.5:1 compression is way too much for pump gas (especially at my elevation of 6000+ feet in colorado), but i have addressed that problem and adjusted my timing table in my ECM and pulled the timing back enough so it doesnt knock (or ping, which ever term you prefer). There again is another issue as to where some of my "loss of power" is going. as far as the intake goes.... do you think a spread bore manifold would work better then a dual plane to allow the motor to draw air/fuel out of both sides of the TBI unit instead of just one side on a dual plane manifold like i have now?

 

Good question, but I don't have an answer. Have you ever had the CFM measured on the TBI? If you go with larger port heads I would first try porting the stock TBI manifold first, port matching, seeing what can be done to increase flow. You have nothing to loose messing with it. Check out you tube for a quick lesson on porting if you've never done it before. Generally you always want to smooth the outside edge of the radius and not the inside radius. Think of parade, where the outside of the turn has to take larger steps and the inside of the turn marches in place. It's the image I keep when I clean a manifold or head up.
With the price of porting stock heads, new guides, valves springs, retainers, some valves, assembly you could have bought a pretty good set of aluminum heads from Jeg's or Summit...... just a thought.

 

thanks for the advice i might just give that a try. i have done quite a bit of head porting but not so much into gasket port matching so i will have to look into that.