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I had about 0.005-007" wear on all of the lobes on my original L71 Cam and the Lifters were near flat, I'm assuming it was due to years of declining ZD.., my Car didn't get driven much by two of the PO's.
I went with a Hyd. roller and I don't think I'll go back to flat tappets again. Like you I intended to just R&R the Cam (I wanted to add AFR heads from the begining), once I thought about the labor/pain of doing it in the Car and as other posters are pointing out the Bearings etc. I decided to pull the Motor as the better option,
Doing the Oil Pan and Timing Cover while it's in the Car is doable (I installed a new Pan and Gasket the year before I pulled the Motor), but I'd think a full rebuild will put you ahead in the long run.
After doing more research, I've decided to go hydraulic roller. I just don t want to worry about ZDDP anymore, and modern rollers have more area under the curve. I'd like to get a 6000+rpm hydraulic roller that can idle at 750 rpm. Is that possible?
So, motor will be coming out. I'd like to reuse stock pistons and be able to run on 93 octane. I'm debating rebuilding stock heads, pocket porting them etc, or going aftermarket aluminum. Can these old iron heads be made to work with a modern roller? Do I have to worry about CR with the stock heads running a roller? Thanks as always.
A HR is a great choice. I have seen several 100% stock fresh L71/L72 engines dyno around 460-480HP. A HR could easily gain you 20 on the top end and 20-30 TQ on the lower end. Choose wisely. Keep .050 duration near the stock 242, or slightly less. not more. The newer, tighter lobe center (110) and faster ramps will gain you the TQ. More area under the curve will get you the HP. HRs have a little more lift and that helps HP. With any cam like that I would always check the piston to valve clearance just to be sure. (clay) IIRC the stock pistons don't like a lot of lift before issues happen. Bowl work, pocket porting and back-cut valves will gain you another 20-30. AFR heads and you could bolt on 40-50. Watch the CR, your 11:1 advertised is likely 10.5-10.7:1 if measured, but you sure don't need any more. A little less would be better with iron heads.
It sounds like you don't won't to touch the short-block. Can you run a leak-down test on it while it is still together? That would tell you if the ring seal is still good. If the cam hits the pistons it'll need to come apart anyway. I do not know how much lift you can get away with. Maybe someone else here does. A good experienced engine builder should be able to give you a ballpark.
FYI: My 230/240 S.R. idles at 17" vac at 850, and dyno'd just a week or two ago at 485 in my LS6. And 550 ft lbs. And we really weren't done tuning.
Last edited by leigh1322; Feb 13, 2020 at 08:54 PM.
Ok, update. I cut open the oil filter and unfortunately found "gold"....bearing material. Motor pulled and disassembly / inspection now in progress. Here are some photos and I'd really appreciate your expert comments regarding condition, wear, and way-forward recommendations. Thank you advance.
Cylinder honing marks look terrific! Low wear here.
Deposits on valves look normal. Like you said, loose guides, using oil, smoking. etc. Use bronze liners on the guides, not whole new guides.
Pocket porting the heads is a great idea. So is a good cleanout and new bearings.
Thumbs up on the HR!
Some how guessing budget$ not a significant constraint.
Getting adequate fuel for an Iron street 11:1 L71 tripower can become a chore, if not a gamble.
Rebuild w/ aluminum heads and piston combo to drop compression a bit.
Hydraulic Roller cam & retrofit lifters
Have distributor professionally rebuilt AND recurved-optimized for your combo
Replace or Rebuild harmonic damper
Have shop dynamically balance rotating assembly
Headers & 3" exhaust system
Bowl blend and do the short turn radius on the heads. Then buy a set of Manley Street Flow or Ferrera 5000 valves with the back cut. Find someone like Mark @ Vortec Pro to perform a 5 angle cut on the seats using your valves as a guide. A knowledgeable person will be able to sort the valve seat pockets and spec the spring/lock/retainer as well as and cup or locator you made need. Iron heads do not absolutely have to have spring cups or locators but this is key to keeping the springs stable at high RPM.
I would do the heads first......lay back the chambers a bit and unshroud the intake valve. Then measure the CC's. Get the number off of your piston and get the dome size, do the math and see if you need to lower compression. You can take a lot of meat out of the chamber on a semi-open chamber........new bearings, .010/.010 the crank, touch hone the block, new rings/bearings/oil pump/etc......and you are back in business.Use moly file fit rings......upgrade the pushrods to Trend one piece .080 and a set of nice roller rockers to compliment the HR cam. Use a Cloyes Hex-a-Just to get your intake centerline spot on. Use a STANDARD volume oil pump.
A correctly curved distributor and jetted trips will round this out.......
An engine like this will easily make over 500 horsepower and a flat torque curve.
Use a cam with at least 230 degrees at .050....I would go in the 240's and about .600 lift.....the rec ports want a cam......my stock 427/400 didn't idle at 750 so not sure what you are looking for there.
Jebby
Last edited by Jebbysan; Mar 31, 2020 at 07:24 AM.
Thanks everyone. Jebby I like all your ideas regarding the combustion chambers and port work. Hopefully my local race engine builder can do all that. I haven't talked to him yet as I want to complete the disassembly and inspection first.
I did talk to Chris Straub about his GTA cam packages. He sent me a quote for his 288/300 HR cam and a 2nd quote for a custom SR grind. I mention the SR for no other reason than I like the sound (valve lash through headers sound awesome) and I like adjusting valves.
Here's a photo of the worst cylinder bore. I was hoping a hone will clean it up versus a bore job so I can reuse the original pistons. Thoughts? Thanks, Chris
as long as you are doing liners in the guides why not go with 11/32 valve stems? i see your bores have the valve cut above the top ring. boat guys say that is 30 hp right there. doing porting yourself? see that big square hunk with the spark plug in it? clean that up and make it a little smaller. open chambers flow better than closed for a reason. and taper out the whole perimeter around the intake a bit and take off the sharp edges. a very slight rounding improves flow and reduces small pointy edges that can become glow plugs and cause preignition. you won't be making the chamber 1 cc bigger.
Thanks everyone. Jebby I like all your ideas regarding the combustion chambers and port work. Hopefully my local race engine builder can do all that. I haven't talked to him yet as I want to complete the disassembly and inspection first.
I did talk to Chris Straub about his GTA cam packages. He sent me a quote for his 288/300 HR cam and a 2nd quote for a custom SR grind. I mention the SR for no other reason than I like the sound (valve lash through headers sound awesome) and I like adjusting valves.
Here's a photo of the worst cylinder bore. I was hoping a hone will clean it up versus a bore job so I can reuse the original pistons. Thoughts? Thanks, Chris
That is not going to clean up completely with a "ten pass" hone. It really depends on where the top ring end up at TDC.......measure the ring land from the piston deck.......see how far the piston is down the bore at TDC......do the math to see where you are at.
I just recently did a quick model comparison based on head flow rates of my LS6 aluminum rectangular ports and some AFRs.
Instant 80-90 HP no other changes.
Jumps from 480 to 560 that quick!
At the time I was building mine we knew it would be a lot, but didn't realize it would be that much.
Last edited by leigh1322; Apr 14, 2020 at 12:28 PM.
Well the rough surface is just below the compression ring at TDC, so I presume that's a bad thing and will need a bore job. What do you guts think of the these HR cams specs using stock compression ratio (stock pistons & heads).
You are probably not going to want to run 11:1 if you want to run pump gas. 10 or 10.5:1 is more likely. I like the specs on the HR. Really similar to my SR 230/240 (wink).
But you really want to find out the intake valve closing point, and use a calculator (like Wallace Racing) to figure out the Dynamic Compression Ratio (DCR). It varies a lot by cam. You want to keep it below 8.2 or even 8.0 with iron heads so you don't have pinging problems. Pick the pistons to match the cam & DCR, or machine the pistons.
You'll enjoy that cam. More low end than the L71/L72 cam, but gives away nothing on the top end HP. Newer cams are just better all around.
BTW I'm running 10.5:1 and I wound up with 8.4 DCR, but I have aluminum heads. Even advancing/retarding the cam changes the DCR because it changes the intake closing point.
So I just ran the numbers. Your IVC pt should be 73 degrees. That cam has milder ramps than my SR so you could go up to a 10.7 CR and just have a 8.0 DCR. With the cam straight up. If you advance it the DCR will climb.
My SR only has 270/280 even tho our .050 numbers match.
Last edited by leigh1322; Apr 18, 2020 at 09:34 PM.
Update: Finally finished disassembly and inspection and the news is mostly good. Bad news is that #4 main bearing / journal is wiped along with the journal. #7 journal / rod bearing wiped too. #7 actually spun. Bores look good so the plan is just go with a hone a re-use original pistons. Because #7 rod bearing spun / overheated he wants to go with new rods versus reconditioning old rods. The challenge he said is finding modern rods that will work with pressed in pins (needed for original pistons) versus floating style.
Any assistance / recommendations greatly appreciated. Thanks, Chris
Update: Finally finished disassembly and inspection and the news is mostly good. Bad news is that #4 main bearing / journal is wiped along with the journal. #7 journal / rod bearing wiped too. #7 actually spun. Bores look good so the plan is just go with a hone a re-use original pistons. Because #7 rod bearing spun / overheated he wants to go with new rods versus reconditioning old rods. The challenge he said is finding modern rods that will work with pressed in pins (needed for original pistons) versus floating style.
Any assistance / recommendations greatly appreciated. Thanks, Chris
Eagle makes the SIR rod which is about 5 times stronger than the stock rods and will accept a press pin. They are inexpensive too. It concerns me a bit that your builder doesn’t know this.....
One thing to remember about the modern heads, especially AFR and Trick Flow, is they use modern combustion chambers. Some of the LSx guys run as high as 12.5:1 compression depending on the cam. The other thing about those heads are the decks are something like 3/4 inch thick, so you can mill them down a little to fine tune the compression, once you figure out what cam you want to run. Look up a dynamic compression ratio calculator online, use it to calculate the static compression to run with whatever cam you decide on.
On my LS1, so YMMV, the previous owner had installed a 234/246 duration cam but left the heads stock. I had the heads ported and milled to bump the compression to 11.5:1. I experienced OVER 100 FT/LBS increase in midrange torque.
A good safe dynamic compression value to use for modern combustion chambers is about 8:1. Use the dynamic compression calculator to work back to what your static compression needs to be.
If you change the type of rod, you'll have to re-balance it.
You’re right....I re-read it and he is keeping the pistons so he needs some stock rods.....
I would buy one rod, and have the other seven re-conned with ARP bolts....the rod the OP would buy would of course have to be checked on the big and little end and shaved as needed.....if too light, the other seven would have be shaved.....
Still....one could buy aftermarket rods and have the assembly balanced, but extra $$$$.....although you would end up with a much stronger assembly....with a forged crank and pistons would be damn near bulletproof....
Tough call....
