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Camming my stroker.

CRASH

CRASH

NAXJA Forum User
NAXJA Member
Location
Foresthill, CA
Here's the recipe:

258 crank, 258 rods, 26 cc dish pistons, 9.0 to 1 compression, headers, 2.5 exhaust. All based on a Renix motor with a bored TB.

I need to pick a cam from the vast variety of cams available. I've attached a spreadsheet that has a partial listing, though it's pretty complete. What have you stroker guys done for a cam in a mild compression engine like the one I'm building?

CRASH

Spreadsheet
 
Crash,

One thing to think of most people won't know about this is from experience with my stroker and NV.

The cam has a weird affect on the NV. The loap made the gears in the NV knock each other. It was weird, it sounded like there were parts loose in there. I even rebuilt it once before figuring out what it was. Everyone would ask what was wrong with my Jeep while it was idling. So a very melow cam is what I would recomend.

mark
orgs mfg
 
Mine does that already with the worn out crank bearings and the piston slap. It sounds like loose change in the bellhousing.

Do you have the trademark 5th gear NV4500 whine as well? I bought my trans rebuilt, and it's made noise in 5th since day 1.

I want a mild cam anyway, no need for anything extreme, just want to feed the beast and get good mileage and midrange power. When I want to go fast, I'll arm the secret "spray".

That should help me beat Richard back to camp at JV :D

CRASH
 
You need to talk to Dino Savva over at the Speed freaks section of Jeeps Unlimited. Its a zoo over at JU but he really knows his stuff. I think he might be lurking on the speed section of NAXJA too. http://www.jeep4.0performance.4mg.com/ Thats his website and has all sorts of cam listings under the stroker page.

AARON
 
Dino has a firm grasp of the theory in getting more hp out of the 4.0....
 
Crash, I used the Comp Cams 250-H in my stroker, ( I think the # is 68-231-4). It's the smallest in the Comp line, I was looking for all low end torque as I rarely ever see 4 grand in real world driving. This cam produces from idle to 4700 rpm where it lays down, still pulls but definately drops off. Each of the Comp cams has a similar powerband but they move the range up about 200 rpm per cam as you go bigger. The 250 has a smooth idle, sounds stock in fact, so if yer looking to impress the mall cruisers with a noticeable lope this ain't your cam. If the XJ/4.0 weren't such a PIA to change cams I'd try swapping a few out for comparisons, but it's not worth the trouble. TC
 
What is the target RPM range? What gears, tires, speed do you plan to run (to target the peak torque rpm)?

What do you plan for injectors, and what is the target for fuel (87 or 91 octane)?
 
CRASH said:
Here's the recipe:

258 crank, 258 rods, 26 cc dish pistons, 9.0 to 1 compression, headers, 2.5 exhaust. All based on a Renix motor with a bored TB.

I need to pick a cam from the vast variety of cams available. I've attached a spreadsheet that has a partial listing, though it's pretty complete. What have you stroker guys done for a cam in a mild compression engine like the one I'm building?

CRASH

Spreadsheet
Click to expand...

I see you found my spreadsheet. ;)
I think you'd better make sure your CR calculation is correct before you choose a cam. What pistons are you using? Silvolites? 0.030" or 0.060" overbore? Are you having either the block deck or the head surface milled?
I'll calculate the CR for you and suggest a cam that'll suit your needs. You'll also need a set of Ford 24lb injectors to replace your 19lb stockers.
 
MrShoeBoy said:
You need to talk to Dino Savva over at the Speed freaks section of Jeeps Unlimited. Its a zoo over at JU but he really knows his stuff. I think he might be lurking on the speed section of NAXJA too. http://www.jeep4.0performance.4mg.com/ Thats his website and has all sorts of cam listings under the stroker page.

AARON
Click to expand...

I'm right here Aaron. :D
I normally do post in the Street Performance section but CRASH moved this thread over there so it got my attention.
 
Comp Cams 235-4 in daily driver

I have a similar Renix stroker (with a ported head) and the Comp 235-4. This gets 16 MPG around town and I've seen 20+ on a highway trip - cruise at 2400 RPM at 70 - 75 MPH. Power peak is 4700 RPM and it pulls to 5300 without a problem. If I build another stroker I'd use even more cam - the 239 -4 probably. With an automatic trans this has all the bottom and midrange you want - I'd think the 231would handicap the stroker and doubt it would give you any more useable bottom end.
 
OK, sorry for the delayed response time....I was out all weekend stripping the new rig down to the bone.

Pulled the engine, and the bores still have original cross-hatching. I'll be taking it to the machine shop next Friday for a hot tank, magnaflux, and a bore check. I believe it will clean up with a .010 bore, which will be great for cooling the beast.

Further details for Dr. Dyno and Ed.

I run 4.88's, 35's and an NV4500. This puts me at 2700 RPM on long runs to JV, or other exotic destinations. So the cam needs to have decent midrange.

I had calculated my CR at 9.06 to compression with a .010 head shave and a .028 block deck (maybe vice-versa, don't have the sheet in fornt of me), and a .052 head gasket. Pistons are forged Venolia units and the rods are Eagle forged pieces. Both are available from XJ junkie, of this board, for around 500 for the set with ARP studs on the rods.

CRASH
 
BTT.
 
I've also got your CR slightly higher at 9.22:1. Here's how I calculated it:

Combustion chamber volume 55.2cc (with 0.010" head shave)
Head gasket volume 10.5cc
Piston dish volume 26.0cc
Deck clearance volume 0.3cc

TOTAL COMBUSTION VOLUME 92.0cc

Engine displacement with 0.010" overbore and 3.895" stroker crank 4540cc
Cylinder volume 756.7cc

CR = (Cylinder volume/Total combustion volume) + 1.0
CR = 8.22 + 1.0
CR = 9.22:1

Assuming your pistons are the same 1.601" pin height as the stock 4.0 pistons and that the rod length is 5.875", with 0.028" removed from the block deck, the deck clearance will be 0.0015" and the quench height will be 0.053". This is within the ideal range and should make the engine more detonation resistant and improve emissions.
The ideal camshaft for your needs should have an intake duration of about 200* @ 0.050 or about 256* advertised intake duration. The Isky 133125/26 (256/262 advertised, 202/208 @ 0.050) fits the bill exactly though the Crane 753905 cam from Summit Racing (260/272 advertised, 204/216 @ 0.050) is also a good choice. The Isky should give a slightly stronger low rev response while the Crane will do better at higher rpm.
 
I'm calling Venolia today to determine the pin height, though I think it is less than stock, in the 1.58 range. That would lower me back down to 9.06 or so.

I'll confirm today, but thanks for the cam choices, I appreciate your analysis.

Now I need to find a good engine rebuild kit supplier, and wait for the machine shops verdict on the cylinder bore. Any suggestion on a kit that includes main bearings, cam bearings, freeze plugs and all the gaskets?

CRASH
 
Cool, I'll check them out first, since they are doing my machine work (Riebes in Auburn is a NApa dealer).

CRASH
 
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