Thread: 350 to 383 coversion how to.

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I asked this question a while back but it was buried in a post, so let me try once more...

I have a 88 350 non roller engine block, rods, and heads. I will be replacing the crank,pistons,pins, all block components aside from block and rods, heads will be stock with new valves, hand porting at least to gasket match, new hyd TQ cam with new lifters and springs.

Assuming I wanted to get a 400 crank, what other tribal knowledge do I need to know to get this together as painlessly as possable? Are the rods good, are the heads ok, do I need special pistons or other work/parts? What is the whole story on making a 383? My target is $1300 for parts and machine work.

Thanks for any help you all give me!

Larry, I am running a 383 and love it. Mine is an older block(70's) so i think you may have a different rear main seal setup though. In my set up the block had to be notched slightly for the crank clearance but it was no big deal.(bottom of the cylinder walls and oil pan rail) I used the 5.7 inch rod and standard .030 over forged pistons. One issue that you may have is the cam/crank interferance. I have heard of this in some blocks. I beleive that if you run a smaller base circle cam it will not be an issue. Hope this helps a little.

Larry. Do not buy a 400 crank. Get a one piece 383 crank.

The 400 crank will need to have the mains turned down to 350 size. The 400 is available only in two piece seal.

In this area, it would cost you more to have the crank modified than a new Scat or CAT crank would cost. Plus you need seal adapter.

You can use SBC 5.7 rods, some will need rod bolt mods to clear cam. You will need 383 specific pistons for an aftermkt crank and 5.7 rods.

You will need to grind the cylinders for clearance on most blocks. The last block I did only needed grinding on two cylinders at the rear left side. Every block is different.

OK, I have decided to get the Speed-o-motive 383 kit and add the ballance and the flexplate/spacer. Total is just at $950. This engine is a factory 88 TBI truck engine code "K". I will be re-using the intake, heads, and TBI as well as the factory computer programing. This has been pushed beyound the original planned $1300-$1400 max, but I think we will end up with a much better and reliable engine.
My cam choice is a SBC Crane Compucam/powermax 2030 with Harland Sharp S1002 roller rockers. I am buying the new springs from Crane to match the cam.

Will the factory TBI handle these changes witout noticing?
Will the factory "High Swirl" heads be able to breath well enough to feed this engine to the low max RPM of 4500?
I was told that these are a low flow, high velocity head.

I have to get the parts ordered in the next 7-14 days, this is the time to stop me from buying a mistake. Cam, heads, kit, TBI...is this all going to work or be a huge mistake?

Larry ,
We built these and many other stroke combinations in our shop years before these kits became available. Some combo's are better than others for specific performance goals. With the KITs available it is a plug and play build except the needed clearance issues.
If you are comfortable with areas that MUST be checked then right on- build away. Forgetting to check or grind enough clearance on pan rails - bottom of bore on block and , makes for broken parts.
You can build it and be very happy with performance. If not sure about all needed clearances and if 0.060 will work on bore to rod instead of 0.080 then get help. BTW a big paperclip is about 80 thou and is a must for rod to bore clearance. You can also spot weld paperclip to end of 1/8 welding rod to make easy ,quick tool to verify clearance you have to grind to get to 0.080 in that area.

Larry0071 - I have a very simular situation. I want to do the same set-up as you mentioned. The only dif is my motor is an 89. I was wondering about using the stock intake and TBI. Have you started your project yet? How did it go? I would like to hear any input you may have on this build.

I have 900.00 so far collected, I should be ordering the parts this week I hope. I also will be using the stock "hi swirl" TBI heads/intake and TB. I hope the computer does not go nuts with the extra air flow, if it does I will most likely change to a set of older style heads with a perforomer intake and a Holley 4150. The big problem I have is that the 2 4150 carbs I have are non choke and modified for race use and there is no budget to buy a new carb. I wonder how bad a non chock carb would be in the winter mornings trying to start this thing. Techinspector, I will look into the cam your talking about. I'll reply once I take a look and consider its effects.

I ran the cam 2032 with the engine sim I made on DD2K and with the 2032 it lost TQ and HP all over the curve. Do you fell that this is an error in the software, or is the 2030 really going to put the most power at the low RPM area that I am looking for. I am going for a stump ripping, earth rotation changing torque monter.

My attachment did not stick, I'll try again:

I know that when I spoke with the guys that sell the 383 kit, they told me to leave the stock cam in if I want to maximize the low end grunt and I am not worried about higher RPM power. I figuire this truck will mostly see use on the highway at about 3K RPM and when its pulling thru the gears at half throttle it should be shifting at about 3500-4000 with a load on it. There is nothing to gain by me camming it to make power as if it were in a car that was going to be hot-rodded, its just a matter of what the intended use is. One thing I did notice, the cams we are talking about are listed as Hyd-Roller grinds and this is a Hyd-Flat Tappet engine. I need to call Crane and talk to them boys to see what they recomend. I'll let you know.

Crane actually recomends going to the cam # 114132 (Powermax 2040). ($154.95 from Summit) along with Spring/retainer kit 11308-1 ($97.88 from Summit)

Cam & Lifters, CompuCam Hyd. Flat Tap., 210/216 .440/.454, SBC 305/350 1981-87

Crane CompuCam cam kits feature cams with special profiles designed to improve engine performance. And they do so without sending the computer into fits, or causing the stalling, surging, or drivability problems some "computer-compatible" cams are known for. They're 50-state legal for the applications listed.

Cam Style Hydraulic flat tappet
Basic Operating RPM Range 2,000-5,000 RPM
Intake Duration 050 inch Lift 210
Exhaust Duration 050 inch Lift 216
Advertised Intake Duration 270
Advertised Exhaust Duration 276
Intake Valve Lift with Factory Rocker Arm Ratio 0.440
Exhaust Valve Lift with Factory Rocker Arm Ratio 0.454
Lobe Separation (degrees) 114

I ran this on DD2K and once more I saw the numbers dip lower yet. Maybe the software is flawed when trying to pick a cam with a non standard engine size? I dont know...I DD2K'ed my Ford 521and it was amazingly similar to the actual Dyno when I went to pick my engine up. Well, what do I do....trust Crane...or go with the softwares pick. Crane has been making cams since long before I was born, maybe I should just stop thinking and follow Crane's advice. Also they recomended I get the spring/retainer kit number 11308-1. Its a direct swap with the factory stuff, no machining the seats needed.

OK, here is what I ordered today:
The Crane Cams 114132 (Powermax 2040) cam/lifter Kit $145.40
Crane Cams 11308-1 Spring/Retainer kit $87.45
Crane Cams Crane Cams Gold Race Extruded Billet Rockers 10750-16 for $259.04 $491.89
P.E.P. (1-800-423-2202) Stelite Ex valves $9.59 each or $76.72
New P.E.P. Super Hard iron valve guides for ex $1.25 each or $10
P.E.P. Stainless Performance intake valves (Swirl polished) $5.00 each or $40.
Total so far is $618.61

Next order will be for the rotating assembly, gaskets, 1-peice rear main seal, rings/bearings, Ballancer, and Flexplate. I expect this to be about $1200.

I assume machining will be another $500, so the total will end up being $2318.61

This will be a totally new engine when its finished, and I hope my choices will get us a reliable engine that is more able to withstand the loads being applied to it.

Desktop Dyno puts this engine at:

RPM HP TQ
2000 129 338
2500 165 346
3000 203 355
3500 227 340
4000 232 304
4500 218 254
5000 183 192

These numbers are using a OEM stock SBC flow chart, I will be cleaning up the ex ports and I will also check the intake to head port alignment to see if they need port matched. This is also with stock manifolds and full exhaust. Basicly its a 16% increase in HP over stock, the K code engine is rated at 200 HP peak at 4000 RPM. Based on 200HP at 4K RPM and do the math the TQ was 262 @ 4000, this is making 304 so its a gain of 16% in TQ as well.