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Detune 388 Stroker

14K views 54 replies 12 participants last post by  bygddy 
#1 ·
Hello All,

Was looking for some advice on a cam selection.

Here is my current setup:
388 stroker
bored over .060
Speedpro powerforged flat top pistons with 6 cc 2 valve
Eagle 5.7" rods and forged crank
deck clearance .010
Felpro head gaskets 1003
Edelbrock Perf RPM heads 64cc
Comp 268XE cam and springs
Edelbrock Perf RPM intake with Holley 4160
Edelbrock double roller chain
Milodon high vol oil pump, windage tray, 7qt deep sump pan
MSD 6AL and Procomp billet dist
Hooker Header 1 5/8" with 2 1/2" Flowmaster 40's



79 Caprice 4 dr. TH350 built with shift kit, 2,000 B&M converter and 3.42 gears. The car weighs 3600lbs empty.

I am going to pull the engine and swap out the pistons to these:
Sealed Power #844-8-KH859CP60
383ci w/5.700'' Rod, Hypereutectic Pistons, .060'' Overbore
Piston Dia.: 4.060''
Piston Top: -12cc Dish, 2-Valve Reliefs
Pressed or Floating Pin
Comp Ratio: 10.28:1 w/58cc Heads, 8.65:1 w/76cc Heads
5/64'', 5/64'', 3/16'' Chrome-Moly Rings
These should net me right around 10.1 CR

I also want to change the came to the Comp cams XE252H. Will this cam work ok. I really want to de tune this combo as it is to radical and I want to just make a strong daily driver. I built this engine when I was a teenager and Hot rodded alot.

Thanks for your help.
 
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#36 ·
Well made some headway today. Started the engine up to operating temps. Shut it down and starting pulling spark plugs and valve covers so I could adjust the valves.

I FOUND MY PROBLEM!
#2 cylinder has some issues.


Broken pushrod and 2 rocker arms off. No wonder it ran like crap. It also split the pushrod guide in 3 places. It marred the edge of the valve tip but I think it is ok. A couple of the other rocker arms on this side were very loose. SO I guess when I adjusted the valves I obviously did it incorrect. So I am going to pull the intake to get the rest of the pushrod.

I hit the intake valve using a block of wood and hammer and it went down and back up fine so I am hoping it is not damaged.

When I pull the intake I am going to pull each lifter out individually and see if any are damaged. Hopefully this will only need a pushrod and new guide.

Thanks to all those who have been giving advice.

Bret
 
#44 ·
This makes more sense, there wasn't anything about your build that otherwise would lead to unusual problems, by today’s standards this is really a pretty moderate build and the XE268 isn't all that hot of a cam. This combo should be a good sturdy street engine. I get the feeling you ride it pretty hard which will take the life out of the motor pretty quickly. I don't think your rocker selection was up to the task and perhaps other parts as well. I consider roller tip rockers with ball fulcrum to be a complete waste of money. The problem with rockers is the fulcrum more so than the tip. The ball and socket gets really hot with high spring pressures, valve float, and high RPMs. There isn't any way of really dealing with these temps and friction in the fulcrum other than a fully rollerized rocker. Grooved balls will let you push the edge a little but the XE286 does need a pretty good spring. You did match the Comp recommended (should be required) spring kit with this cam, didn't you? This is big time important and often overlooked when people buy aftermarket heads with an included "racer springs" by someone's definition who are selling the heads not the cam. My best recommendation when buying aftermarket heads it to purchase them bare, use a known good quality valve and use the springs and retainers sold by the cam manufacturer unless you’re sufficiently knowledgeable in the rocket science of valve train dynamics to go off on your own. I find there are damn few people building engines that are that good. This takes expertise and pieces of really expensive development equipment the average guy and many if not most equipment purveyors just don't have. This is a place where you need to pay like Goldylocks, not too soft and not too stiff, just right. Too soft will float the valve train which pounds the parts to pieces when they snap closed. Too stiff and the pressures just wear everything out too quickly. The XE268 does not need a fast leak down lifter, keeping these things tracking the lobe quietly is a problem. You're walking a really fine line between pumping the lifter holding the valve open or pounding the tappet into the lobe.

When you start getting up around .5 inch lift you also need to consider a stepped push rod guide to give more support closer to the rocker as that end with high lift is going to move a considerable distance from the point of support so any deflection of the push-rod will become increasingly magnified where it interfaces on the rocker as this distance increases. That will cause the rocker to want to wander off the side of the valve stem.

I'm not a fan of the simplified method of adjusting valves where you are skipping cylinder to cylinder and side to side doing multiple adjustments at certain crankshaft stations, this especially gets to be risky as the cam durations become longer simply because it is difficult to hit TDC accurately unless you go though the degree wheel and positive stop drill for every adjusting station which is a huge amount of work these simplified adjusting methods were developed to avoid for the flat rate mechanic. I highly recommend that one start at number one cylinder with both valves closed on the top of the power stroke and make you initial adjustments here then rotate the crank through the firing order in order and adjust each as they come up on the firing position. That insures the tappets are not on any part of a lobe. Where one uses older design performance cams with really long ramps leading to and from the action this is a big time problem to get accurate with simplified method. Cams like the XE, the Voodoo, and other similar modern cams where the ramps are short and the action quick are less likely to cause alignment problems on set up but if you're off TDC too much you will have big trouble as these cams come on the lobe really fast.

Bogie
 
#39 ·
Well I was adjusted the valves per the link CDminter59 posted. I put it on TDC and adjusted both valves on #1. Went to turn the over till the #8 intake valve was at full lift so I could adjust #5 and noticed that the #8 intake was bearly going down. Skipped thought maybe it was really lose and the same problem with #7 intake. It went down a little then up a little then down.

So I pulle the intake and found 6 bad lifters. One is not concave yet but it had a really bad burr and I had a hell of a time getting it out. Had to pull all of them out with pliers.

So with this much material gone from the lifters I am assuming that all the bearings are probably bad and I am looking at a total rebuild again.

I'm not sure what happened. Did I adjust the lifters to tight and cause this failure. If anything I thought I had them to loose. But this explains why the valvetrain was so noisy and the rattling I heard.

I will definately say this is the last hot rod cam I will ever run. If I rebuild I am putting everything back to stock!
 

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#43 ·
I realize I can't run a true stock cam. But if I keep the Edelbrock heads what is the smallest cam I can run? The Summit 1103 that Fbird suggested.

I'm not mad at it. I just have started to steer more towards stock style engines from the hot rod engines I use to love. I still love them just don't want to mess with it all the time. I don't even drive this car anymore because the tires are dry rotted from sitting outside for 8 years, the th350 has no second gear and the engine wouldn't even putt down the street. If I could have it all back like it was when I got it that would be awesome. But the cost of that would be too much right now.

I got excited when I found the broken pushrod as I thought I could get it running again for about $25 but that isn't the case anymore.

I have thought several times about parting out the entire car. I have a Camaro SS and now a 64 Chevy stepside. The Caprice is on the back burner. Its my first car and I just know that if I get rid of it someday I am going to regret it. I've had it since 95' and it was my moms car she bought it in 86'. So its been around since I was 8 years old. My wife even likes the car its what I was driving when were first dating. It died at a stop light on our first date and she had to help my push it over to the curb. LOL
 
#48 ·
Well got a new cam and lifters for the Caprice. Went with the Summit k1103. It was on sale and it cost about the same as it would for me to have the Caprice towed to my new garage so I figured what the hell. I know the bearings and what not may all need to be replace but at this point I would rather have the engine run then to have the car as yard art! Will get it installed in the next week or so hopefully when the weather we are having breaks. Will post the results up.





Bret
 
#50 ·
Do you realize all that metal has run through that motor? Your oil pump and bearings are going to be chewed up and you are going to be back in this motor again shortly. Once you have a cam go out (in your case a pretty bad situation), the engine will need to be cooked clean again. Someone should have steered you in this direction - there is still a lot of metal floating around in there - all those oil passages. How did the cam bearings look?
 
#53 ·
Thanks guys for the concern. I realize all the bearings are toast. Had to get this car running so I could move it. The C/R is too high was going to change pistons anyway. I needed to move the car out to my new garage to pull the motor. We might be possibly selling our house soon and this car hasn't left the drive way in 3 years. I realize the cam will be ruined as well but it was going to cost me close to a hundred to tow it and now I will be able to move it around until I have time to tear it down.

The cam bearings actually looked good I was very surprised. I don't even no how it ran with 3 complete dead cylinders and several others only getting the valves open half way!

Bret
 
#55 ·
Hey, I did say "mechanical noise" on page one lol.
As for a rebuild, right in march of last summer a buddy's 383 ate a big lunati cam like a week after it was broken in (yes incorrectly). He thru an old cam and lifters of unknown specs that I had kicking around from 100 years ago that had been hanging on my garage wall as art lol. Lifters miss matched and dusty and shtty in a Kleenex box. Did another "break in" just cause, and ran like 40 litres of bulk oil from our shop through it. Drove it all summer, put a ton of mileage on it and went 12.20's in a fully loaded G-body 84 Monte. Once in awhile you just get lucky..... ;)
 
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