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Discussion Starter · #1 · (Edited)
OK, the original thread was "QSB 4.5 without the electronics"
I have a 4.5L front gear train, 8 valve head, mechanical injection.
Block is back, bored and honed .020. Pistons installed. I just degreed the stock camshaft.
At .050 int. dur 100.5 degrees, lift 254 Exh 245 degrees and 264 lift.
I have been searching for weeks to find a cam that will give better performance. I believe a 3.9 cam will fit, they appear identical. Does anyone know where I can get a better cam? Not a wild build, just something to give better road drivability.
I found a place in Canada that will regrind my current one, but do not know what specs to give them. Any help would be appreciated. Char, any ideas?

Oh, BTW, the cam lock pin engaged just shy of 2 degrees before TDC. I set it to actual TDC and loosened the two bolts. It moves around a little. Locked it in at exactly TDC and retightened the bolts. Also piston protrusion is .019" above the deck.
 

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OK. The engine you have is a QSB 4.5-30. It is an industrial design with a longer stroke but the same bore as a 4bt 3.9. The cam for the two engines should be interchangeable. Other parts like push rods etc. are not the same. You have to be careful as to how much power you plan to increase that engine. Stock limit was around 100 HP. Part of the reason is piston rod angle which mean that engine has thinner rods than a standard 4bt. Are you using the stock injection pump or changing it. It came with a VP30 which is electronically controlled. Here is a link to Colt Cams who specialize in diesel cams. They only show 3 grinds now but used to have 5. Cummins 4BT - Colt Cams They are in Canada. Another possible is Hamilton Cams. They have grinds for the 6bt which could be done on a 4bt. 12 Valve efficiency 178/208 Camshaft Combo
 

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Discussion Starter · #3 ·
Yes, I know what I have, 4 of them in fact. I am also aware of the rod situation. Two of the engines came with the thinner fractured rods, two with the heavier machined rods. Guess which ones I used. :) I saw both Colt cams and Hamilton, but am not in the mood to spend nearly $500 on a camshaft. I found a place that has a Marine cam for $180. I am waiting for the salesman to get me the specs on it. If it is close to the specs for the Colt or Hamilton cams, I will go for it. If not, I will see what it will cost to regrind the ones I have to the Colt specs. The engines did not come with injection pumps, so I am wide open when I get to that point. Thanks for your input, I will post the outcome. Here is a picture of the different rods and pistons:
 

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Man, there is some serious difference in those 2 rod/piston sets. The 4.5 has roughly about a 1/2" longer stroke so that piston in the left side appears to have a taller deck. Heck, that rod on the left might weigh near double what that tiny thing on the right weighs. I've seen gas engines with bigger rods than that. That one on the right appears to be about the same length and the piston having a shorter deck. Are you sure both those engines were built by Cummins. Even the piston pins in that right rod are light weight. Almost looks like a gas engine setup and Cummins did make gas engines too on the same frame as the diesel. Curious, is there a part number on that heavy rod? I see some numbers on the one side in the photo but those don't look like a Cummins number. I have one of those engines on Quick Serve and would be curious if the rod numbers match. The engine I have into on uses rod 3939407 which appears to be that skinny one. They are super expensive as well. Have you checked both engines to be sure they have the same crank? I swear that piston on the left appear to be a 3.9 with a taller deck so it could use a standard 3.9 rod in a 4.5 block. Just weird looking.

As far as injection pumps go, you can mount a VE pump or any other types you wish so long as you have the correct front gear housing. We have several members who are currently working on that same type engine. Not surprising that the injection pump might be missing. That 4 cylinder VP30 costs in the $5000-7000 range. Probably need different injectors too as the ones on that 4.5 were a special part.
 

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Discussion Starter · #5 · (Edited)
Ok, so after much research and confusion, here is what I came up with: of the 4 engines I have, 2 of them had data plates. These were the 4.5L engines. The other two were 3.9L. I assumed they were all 4.5L, you know the old saying about what you get when you assume. :) The sintered rods and pistons were from the 4.5l engines (the smaller looking rods on the right). The other rods and pistons are from the 3.9L engines. Sintered rods are supposed to be stronger than machined rods, that's why they look smaller. Nearly all manufacturers are now using sintered rods in their engines. These were the only rods I saw in the years that I worked in the engine development labs at General Motors. (Retired BTW). I measured the stroke on the engines to confirm displacement. Bores are the same. Crankshafts are different on the 4.5L to accommodate the sintered rods. Here is the part that amazed me: the blocks are the same. The 4.5L is not a taller block. All four measure 16 1/4 inches from oil pan rail to block deck. Push rods are all the same length as well. That explains the different pistons in the 4.5, stroke is longer, so pistons are changed to work in the same block. Makes sense, Cummins would not have to retool and cast a new block for the 4.5. We have two 5.9l and two 6.7l engines in the back as well. on Monday I will measure block height on them to see if deck height is the same for the six cylinder versions as well.
At any rate, the engine I chose to build is the 3.9L I found a camshaft company that will regrind one of the cams I have to specs that I want, for 185 dollars. Onward and Upward!
 

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I believe if you check you will find the 4.5 block is not the same as the 3.9. According to Quick Server the 4.5 block has only had 2 numbers and both are obsolete. 3938366 and 5405080 are the numbers. The 3.9 has had 4 part numbers and only the newest is current. 3802269, 3933223, 4089546, and 5406191 are it's numbers.
 

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Discussion Starter · #7 ·
OK, performance cam installed. Head bolted on. I am a bit shell-shocked at the price for a GM trans adapter! WOW! 4L85E is my intended trans. If only I could find the CNC specs for the trans adaptor, I would have the machine shop make me one! Maybe a couple of them and help out some guys here on the forum. :)

Here are the cam specs:

C:\Cam Pro Plus\CDF\SSDD.CPP
LIFT DUR. OPEN CLOSE AREA
Lobe I1 ----- ------ ----------- ----------- ------
Centerline 111.01 BTDC 0.006 234.48 49.10 BBDC 5.39 ATDC 16.24
.050 Lift C/L 111.22 BTDC 0.020 201.18 31.94 BBDC 10.76 BTDC 16.05
Runout 0.00020 0.050 174.24 18.34 BBDC 24.10 BTDC 15.60
Peak Open Acc. 0.000410 0.100 144.62 3.41 BBDC 38.79 BTDC 14.50
Peak Nose Acc. -0.000278 0.150 116.54 10.66 ABDC 52.81 BTDC 12.74
Peak Close Acc. 0.000436 0.200 83.24 27.30 ABDC 69.46 BTDC 9.61
Lift @ TDC 0.0085 0.250 21.38 58.29 ABDC 100.33 BTDC 2.70
Minimum Flat 0.25354 --- PEAK CAM LIFT ---
Follower Dia. 0.8395 0.38031 --- PEAK VALVE LIFT ---

C:\Cam Pro Plus\CDF\SSDD.CPP
LIFT DUR. OPEN CLOSE AREA
Lobe E1 ----- ------ ----------- ----------- ------
Centerline 103.01 ATDC 0.006 301.14 47.11 BTDC 74.04 ABDC 19.70
.050 Lift C/L 102.95 ATDC 0.020 238.63 16.59 BTDC 42.04 ABDC 19.33
Runout 0.00020 0.050 203.01 1.44 ATDC 24.45 ABDC 18.71
Peak Open Acc. 0.000365 0.100 168.79 18.67 ATDC 7.46 ABDC 17.50
Peak Nose Acc. -0.000271 0.150 137.73 34.23 ATDC 8.04 BBDC 15.56
Peak Close Acc. 0.000359 0.200 102.13 52.04 ATDC 25.83 BBDC 12.22
Lift @ TDC 0.0466 0.250 48.93 78.54 ATDC 52.53 BBDC 6.37
Minimum Flat 0.26586 --- PEAK CAM LIFT ---
Follower Dia. 0.7542 0.39879 --- PEAK VALVE LIFT ---
 

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The cheapest GM transmission adapter is G Force which is $995.99 which includes the flex plate. Destroked charges $1420 for theirs. The OEM Cummins GM adapter only is over $2000. The flex plate and wave ring assembly will kick that up about another $1000. So that's about $1000 vs $3000+. Nothing about diesels is cheap. Just the nature of the beast. Have to remember the GM parts from Cummins probably haven't been used on a engine since the late 1980's or early 1990's. In the list of engine serial numbers I keep for reference the newest with GM parts is 1987.
 

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Discussion Starter · #9 · (Edited)
Wave ring assembly. So the only one Cummins has is the one that puts the engine and trans at an angle. Yech. Oh well, I've got a lot of time before I'm ready to put it in a vehicle. I'll continue to see if I can find the specs and have the machine shop make one for me. That would be ideal.
 

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Yes, the Cummins one was designed for the Chevy P30 van that had a clearance issue with the 4bt. So the engine was mounted in a tilted position and the transmission stayed in the normal position. All these aftermarket version do not have the tilt.
 

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Discussion Starter · #15 ·
Yeah, I‘ve seen that site. One thing bothers me, though, he says that since the 4BT crankshaft is such a robust piece that he is sticking with that. No matter how much you change the pistons and rods, if you don’t increase the throw of the crank, the stroke will remain the same. It’s not a stroker if the crank throw remains the same. 🤷🏻‍♂️
 
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