I have a mpfi 355 in a 89 chevy 4x4 which was rebuilt a few years ago and have found the machine shop build quality sadly lacking. Last winter replaced the heads due to severe valve guide failure due to the use of s/alligning rockers and guide plates these were iron rhs vortecs, they were replaced with afr vortecs due to downtime and location issues. The pistons are Mahle 9:1 which were fine with iron but I would prefer to go with 9.5-10:1. I am also having valve train (I think) issues with noise and have replaced the crane rollers with ls7 units, when engine is hot getting a subtle clacking sound (engine has crower ss roller rockers) on the drivers side and have seen that 2 rockers have come off the valve stem at some point. Had the oil pressure checked to back the gauges and pressure is good. I'm thinking that the guide material may have caused other issues, an oil passage is partially blocked or they installed restrictors, oil takes a long time to show at the rockers but does come and has even distribution on both banks- I'm used to healthy flow (Melling standard pressure pump). When replacing the heads, had a look at what cam lobes I could see and the old lifters showed no sign of abnormal wear. The engine doesn't like to rev either.
Any way the engine will likely be pulled barring some easily solved problem, so I'm looking for an excuse to 383ize it.
1/ I've used KB hypers in the past- was disappointed in how loud they were- perhaps this is a function of more sloppy machining- using the Mahles now they are OK when hot but at the time seemed to have limited selection of what I wanted- what would a good piston choice for the application and what material would give longest service life. Not decided on 5.7/6in rod, seems like its a fad these days for the 6in but am prepared to let the machinist make that choice. 2/ tossing it around that I will change cams to a 'softer' ramp style roller for less noise and am wondering if the 4/7 swap would encourage better engine temps/detonation for towing. Noise is an issue for me and use 15-40 in summer and 0-40 winter synthetics any else sounds like a diesel. (it's actually been commented on how loud it is on cold starts).
For cooling, using a big block rad with twin electric fans, about twice the size of the original. Changed the heater bypass from rear pass side of block to front of intake to heater core- and from cool side of rad to the water pump fitting, I always thought that the engine ran coolish with 195 stat and now seems to run warmer and heats up faster- haven't tried towing with this as the engine isn't healthy but I wonder if I'm heading for an issue here- I'm in northern Canada so the faster warm up is appreciated at -35C.

Dave

 

yea, self-aligning rockers AND guidplates is a no-no.

does your oil pressure drop when the motor gets warm?

i doubt the 4/7 swap will do anything for towing/detonation.

 

Yes when I saw him bolting that up I questioned him about it- I should have been more aggressive as guides were completely hooped.
Hot oil pressure is just under 200kpa=29psi

It seems quality machinists are harder to find than I thought- I researched them before hand and they were ok, but now I'm hearing bad things- $7k into this, if I change to 383 I'll reuse the block as it's studded top and bottom and line honed.

So 4/7 is marginal for power as well- so who actually does that swap?

 

4/7 swaps the firing order. You want to work with cam timing if you have preignition issues. Do you know if your vac advance is set up and working well? That would be a biggie in your case.

Piston slap (cold noise) is likely due to excess piston to bore clearances if in the bottom end. oil not showing at all rockers is normal when priming. Try rotating the engine 360 degrees and priming more. If you have 2 forms of pushrod control it can cause a ton of valvetrain issues.

 

The firing order swaps the 7 for 4 and moves the hotter cylinder around. It adds about $80 to the grind there is another swap as well the ford/LS as well but that gets $$. Cooling 7 was more my question and if I'm going to change cams might as well enquire.

As far as priming- the engine has 10k on it and is in service- I swapped back from 1:6 to 1:5 rockers as I had a set on hand to see if it cuts back on noise (it doesn't) and noticed at start up that the oil takes it's time getting to the top end- and is more a heavy seep rather than the squirt I'm used to- I don't think the rocker push rod pockets would be metered.

When changing the heads I measured rock at .020 top to bottom. Another issue was bank to bank piston to deck was not the same. Just small things that a good machinist would not tolerate.

Another question regarding hp/tq balance. Building a 383 2 ways (probably more cam than anything else) if I told you I wanted 400hp to keep up with the factory hemi's with a bit of a camy idle vs a prperly spec'd engine built for 4x4/towing- what ould the balance of hp vs tq look like. both would use FIRST tpi, afr vortec heads, compression could vary 9-10:1, cam would vary.

Dave

 

Can anyone help? I have a 1986 I rock z, I have built a 87 350 block, everything from crank heads pistons everything is new and aftermarket. I am not going to use any of the cars harness I am going carb and running a electronic high flow fuel pump ( on a toggle switch) and a after market push to start. So basically other than lights nothing will b ran off the stock harness. The problem I have is I am running a hei Mallory with the internal coil, does anyone have a wiring diagram? Like I said I am not ushering any stock harness, do I just plug + to a switch directly to the battery? And the ground directly to chassis ground or block? Will I need to put a inline fuse or use the fuse box in the car I'm worried about either burning up the distributer by having it without a fuse or killing the bat without a switch.

 

You should be asking Mallory direct.

 

I'm running the same setup, fuel pump, fan, ignition and accessories are all on switches and push button starter.
That's how I ran my ignition. 12v with a 10a fuse straight to dizzy, dizzy ground to..well..ground.. plus your tach.

I'm no longer running hei, but I'm still wired the same way. Both worked

 

Thanks