383 engine build questions

[ogre]

I am restoring a 1970 Challenger 383 RT. It was missing the engine/transmission/rear so I don't have much to go on for measuring. I picked up a 383 block august/70 stamping so its a G block HP. I had it bored 30 over and decked to straight at a machine shop.
I also picked up a 383 forged crank, I was hoping for only a polish but it needed cutting 10 mains and 10 rods.
I bought a new set of connecting rods from 440 source, since I didn't have any new or old. Now down to the pistons and heads. After a lot of reading on sites, I ordered the E series heads from Edelbrock, 75 CC.
My piston choice was either KB162's or 400's or Speedpro l2315NF-30's.
Camshaft was considering comp cams 474/474  or 470/470 cams. I looked at Lunati.

My objective, to build a new 383 that has instead of the original 335HP, something in the 375 range. Pump gas not a racer just a little more snap with automatic transmission that it has to have. I am guessing based on my numbers a 10:1 CR or less. i dont want to blow the valves out with the pistons.

Anyway the rear will have 3:23 or 3:55 suregrip if I can get it. I have 3:23 open now in a 489 case.

Just looking for opinions, personal history with the components, is it over built or underbuilt. i dont want to Stroke it, or use 440 rods, but it will have headers and 2400 stall in the transmission with manual shift.
No Nitrous I dont want to see a real RT wind up in the fence.

Thanks in advance!   

[Cuda Cody]

I prefer something in the 9.1 to 9.5 for pump gas.  Unless you're using aluminum heads. 

[DeathProofCuda]

It's been awhile since I built my 383, so I don't remember many of the details off the top of my head anymore.  Piston choice is super critical for 383s because of their short stroke.  Make sure that you do all the math to ensure that you get the compression ratio you want.  Lots of pretty anemic 383s have been built by dropping KB162s into an otherwise mostly stock 383, because of their low compression height.  KB162s might work for a closed chamber head, but I had to go with Diamond pistons to get 9.5:1 compression in my 383 build with original 906 open chamber heads.  My block was zero decked and I used the thin steel head gasket.

[EV2RTSE]

I had my 383 rebuilt with the goal of keeping it original appearing- carb, heads, intake & exhaust manifolds, RV2 a/c compressor, and factory cruise control so I wasn't looking to add a gigantic cam and so on. It went .030 over and the builder picked those same SpeedPro pistons and a Comp Cam that was a touch over stock to give it a little more lope. I think he said he would shave the heads a 10th to give it a bit more compression as well, I haven't run it yet but I'm hoping I don't regret going with a higher compression piston.

Not sure which intake you're going with but I believe switching to something like a good dual plane Edelbrock along with the headers are probably going to be the two things that will give you the most bang for the buck. I seem to recall an article where they tested a bunch of different 383 combos and just a better intake and headers resulted in a gain of something like 35 hp.

I also went with the helical gear sure grip from Dr. Diff, it runs a couple hundred bucks more than a regular sure grip replacement but looks to be the way to go. Supposedly goes around corners really smoothly and also locks up instantly when you want to hit the gas.

https://www.doctordiff.com/8-3-4-helical-gear-sure-grip-sure-trac.html









 

[broughj]

I built the 383 for my Challenger R/T in the late 2019 early 2020-time frame. I wanted a basically stock 383 that ran good.  Mine needed a 0.030 overbore.  I bought custom pistons from Racetek.  They adjusted the compression height so that the top of the piston would be above the deck by about 0.045".  With the open chamber 906 heads and an 0.039 head gasket I got a measured 9.8 CR.  I used the Mr Six Pack hydraulic flat tappet cam.  Using stock holley carb and points distributor.  This combo makes good power using the seat of the pants dyno. I never drove the car with the 383 as it was before the rebuild, so no way to compare. Starts easily, runs cool with stock 22" radiator, no pinging on premium pump gas and works well with the auto trans and power brakes.  My only downside is that I have been chasing a vibration ever since I got the engine in the car.  I've gone down a lot of rabbit holes trying to figure that out and it is very much better than it was, but not completely gone.  The only thing left is something not exactly right with the internal balance, but I'm not ready to pull the engine at this point and go through another rebuild.

[HP2]

The heads you chose  are a smaller, heart shaped chamber. These would be about half the cc volume of the stock heads, so right off the bat, you are dealing with less volume in each cylinder which ill result in easier access to higher comp ratios. This is certainly good thing, to a point.

The KB400s have a pop-up pad. Good thing, this means your engine builder can "blueprint" each cylinder to be exactly the same by shaving down the pop up to achieve exactly identical ratios in each cylinder. Downside to pop-ups, they impede flame travel and may not get as complete a burn. This is where the KB162 or Speedpros would really work better because they do not have any surface features to interfere with flame travel. However, these may require decking the block to get the piston tops to zero deck height. If this can be done, then the small chamber heads and a .030 compressed gasket would provide the right amount of squish to really burn the mix well and make plenty of power. However, you don't want that ratio to put you  outside of pump gas territory, unless you are planning on adding octane boost or methanol injection

I have built my last few engines with a cylinder pressure target, rather than a static ratio target. This is because the cam selection can have a big impact on how much of that compression ratio actually gets used.  Doing this, I've actually backed off cam specs on one of my engines and it ended up making more power.

In any case, first calculate the combo of hard parts and where that puts you comp ratio wise.  I've often had good results with this calculator:
http://www.wallaceracing.com/cr_test2.php

Once you have that dialed in, then you can address the dynamic ratio based on engine and cam specs. This will determine your cylinder pressure which, in turn, will tell you what grade of gas you need to run. The limit for pump gas tend to be around 190 psi. I use this calculator for that. Nice thing about this is you can figure in boost if using forced induction and/or you can figure for altitude, which makes a HUGE difference where I live:
http://www.wallaceracing.com/dynamic-cr.php

[torredcuda]

I built mine to look stock but have more grunt - 906 heads have been ported and polished, around 9.5-1 if IIRC, KB162 pistons, Comp Cams 265DEH-10. I ma using the factory intake and Holley carb, I have the stock exhaust manifold but may go headers - haven`t decided on that yet, 727 with shift kit and 2500-2800 stall converter (again haven`t decide on one yet) and 3,23 rear gear. I wanted a nice cruiser with a little more power than stock, I have not run it yet so not sure on the HP but I may have it run it on a dyno before I install it.

https://www.summitracing.com/parts/cca-21-404-4

[7212Mopar]

I thought people are not doing octane booster anymore. Instead they mix gasoline with ethanol or just ethanol to run high compression engines or run crazy high boost with big turbos. The sound of high compression engine is music to the ears.

[HP2]

Running pure ethanol is as big a pain in the rear as running race gas as far as accessibility goes. But yes, I'm sure some people do that. E85 is also another approach some are using to deal with high compression. An issue with that though is that E85 can run as low as 40% and as high as 90%. Unless you have a distributor in your area that is reputable with how much they mix it, you can get highly varied results. You also have to build your fuel system to be compatible with the alcohol. Regular fuel pumps and rubber hoses don't work well with high alcohol content.

You can go with a h2o/methanol injection system that will meter how much alcohol is consumed and when. These are fairly trick but do require special controllers, additional plumbing, wiring, and sensors to be installed, even if using a carb. Upside is that depending on alcohol content, wiper fluid can be used for this.