I have searched a dozen times for what I plan on building.

I cannot find any one is doing for what I am going for: IE:

A low rpm 383. My plan is for this motor to spend most of its life running at 1700 RPMs and operate from 500 to 4000. Everyone builds a Hot Rod version.

I am trying to build as much torque as possible using a mild RV TPI Cam, and plan on advancing it 4 degrees. I am much more interested in LOW RPM Torque than house power, Torque is better at low RPMs than HP which is made at higher gas using RPMs.

The combo I want is: Aftermarket 400 crank for a 350. Stock 400 rods so I can keep my KB “D” shaped pistons. I am aware of the side loading on the bore, one as I do not plan on running over 5000 max, is this major problem?? Is there any piston skirt coating or treatment that can help with this that can be applied to my KB pistons?

Cam will be grounded for RV TPI Operation. Lifters are stock 350 roller lifter set up.

Heads are 1970 early swirl port 192s, and other that major cleanup and 3 angled seats, springs tested and Perfect Circle Street Running (Oiling) valve seals, all rest left stock. I only plan of light grinding to ports to match.

I will also run stock ratio roller tip rocker arms to lower the scuffing of the valves in the guilds.

I plan on feeding this with a 80s Camaro/Corvette TPI running MAF controls. I plan on having the stock Highway Mode turned on until I can get a special add on board to the PCM which allow greater tuning.

Everything is built counter wise to common Hot Rodding standards. Stock heads, no opening the ports, no polishing them, (Everything I have read says the textured surfaces of stock ports HELP low RPM power, polished and opened (larger) ports are for HIGH RPM air flow and HARM lower RPM power) same for the heads. Low RPM cam that will not shift to higher RPM power curves, (the way most cams make more power, move the power curve up the RPM range)

Now we come to the big questions.

One will the improvement in torque add MPG in my appreciation?

Will this torque off set the extra fueling needed to keep this engine running correctly??

Any idea what amount of extra torque this will make over my stock 350?? (Say a stock 350 VS a stock 350 with the 400 crank making a 383??)

So bottom line will this help my car make MPG??

Is it worth the extra cost to convert my 350 to this 383??

Rich

 

Torque and HP are linked, no matter how hard you try to separate them. More torque means more HP. HP is just a mathematical expression of torque and time/RPM. So you can't really build high torque without high HP. Really all you (we) are all doing is building "x" amount of torque, and WHERE in the RPM range it happens. HP then just is mathematically figured out. When you say torque is better at low RPMs, what you should say is that you ONLY have torque at lowrpms. The math is time and torque, so at low RPMs, the math says low HP. At hjgh RPMs you get high HP. HOW high, is just dependant on how much torque you have, so again, you can't have one without the other.

What do you want to DO with this engine? Why are you building it? Don't get too wrapped up in the idea of low RPM torque monster. It's misleading. Compared to a $20k dollar race engine that revs to 7500 RPMs? - yes.....I get that this isn't what you want. But don't think that an engine that revs 1000 RPMs more than yours, makes the same torque, but it comes on 250 RPMs later and makes 100 more HP is somehow an exotic "hot rod" engine that you won't enjoy. The stock TPI was great for torque compared to many other stock performance offerings from the day. The torque really made it feel like more car than it was. -but I have NEVER driven a properly built performance small block for the street, where I felt like I missed the torque. Just because it's not BUILT for torque, doesn't mean it doesn't HAVE torque. ....and they all can smoke the tires, so they're all pretty much over torqued as it is.

 

a 3.75” crank with a 400 rod of 5.565” length would mean the piston needs to be 1.56” for 9.00 deck. Which is .025 in the hole on a virgin block. I get wanting this if you already have pistons. Some kb are 1.54” so watch that. Def want to deck block anyway for good head sealing. It can work and shouldnt hurt much. Yes there can be more sideliading and wear in skirts over time but if built well and good oiling, it should last a long time. Balancing the crank may be abit more difficult tho, it depends.
yes you can get pistons coated but at that price might as well buy the right rods and pistons anyway

make sure you watch your compression ratio. Longer stroke will give higher compression with same piston. I would not want more than 9-9.5:1 for some thing like this

torque is airflow. More torque is more air and that means more fuel. I wouldnt expect better mileage necessarily. It likely will be bit worse but depends how you drive and the environment you drive in. Torque and gearing can help a car move easier in hilly places so you may not load car down as much or require as much throttle input, so may save some mileage

highway cruise is tuning and rolling resistance lol. But a big motor may still consume more fuel. Think of gm 5.3 truck vs 6.2. Now theres a big power difference but the mileage is slightly worse on the 6.2 even on highway with same gears and tires vs 5.3 trucks.

With stock tpi and 70’s heads you dont have alot of airflow so im not sure if added stroke gives big torque benefits. But the concept does work in more racey hot rod street setups so I imagine even with a weak induction system theres off idle torque to be gained.

 

I don't think mixing a TPI intake and 1970s heads with a 383 is going to be worth it. I think you'd be better off with an L31 vortec motor from GM. Inexpensive for what it is considering a machine shop might charge $800-1000 to fully machine everything.

 

This guy keeps regurgitating the same build on sites and has for years now.

He wants to push around a G20 van with a TPI 383 and plans on tall gearing and a double OD.

I have also tried to explain to him why the OBD1 MAF TPI is horrible but he won't listen to that either.

 

I'm looking at going the L31 route myself, using the Scoggin-Dickey Vortec TPI manifold to retain the TPI system. It's all but impossible to find real-world power figures for this combo, but the best we've been able to figure is roughly 300 HP, and 400 foot-pounds of torque. The torque curve is a little broader, and flatter than the original L98. I've already purchased the manifold, but am waiting until I complete the T56 swap, because I'm very certain my T5 wouldn't live very long behind the new engine.

 

whats wrong with it? Lol $6E is my favorite

if a van is his situation, hard to beat a tbi vortec deal with a 7427 or similar

 

I would personally build a 350 with dished pistons, use the swirl ports, add a lower rpm blower cam and put a Weiand 142 on it. Then use a 454 TBI unit and the EBL with a 2-bar MAP sensor. You can have your cake and eat it too. The Weiand draws very little power when you are not under boost and will still provide boost down at 1,500 rpm. The weiand will only provide boost when you are accelerating or climbing a hill. You could even build a 305 to make 450 ft/lbs of torque with the Weaind. My old G20 van with a built up TBI 305 would get 20-22 mpg highway with a 700r4 and 3.07 gears.

 

The problem is hardware not as much software. Those MAFs are junk.

For the best efficiency the 0411 with 24x and CNP LS ignition is where it is at.

Its hard to beat a roots style or screw style mini blower for a Van. I had one on my G20 at one point. 2x700r4s and 2x4L60Es all well built blown up, later I pulled it off.

 

One other bit of advice. The GM 395' marine cam that GM also puts in the HT383 and the Ramjet is a great cam to build off idle torque with its short duration and tight 109 LSA. You can get it new from GM for less than $200. Its also a steel billet cam not a cast core.