slagburn
After a couple of years of .010 piston clearance and .024 ring gap it's time to punch the 401 to .040. I had the machine shop send off my one remaining .030 flattop to Arias to recreate a new set, compression will be 12:1. The heads are 993's that flow 285 intake, 203 exhaust. Cam is a Comp Magnum 292H. Torker, roller rocks, 900cfm throttle body. I'm thinking 3500 stall on the TH400.
I'd like to see if that's a decent cam for this combination. Last year I ran 10:1, unported 291's and the same cam and only made 260rwhp to my endless frustration since the ET's matched the dyno.
I guess the last time this 401 had flattops and these ported heads on it was a real rip snorter but last year's combo felt like a stock LT-1. Just looking for any advice while it's apart.
Holeshot
Advice? .045" piston to head clearance.
260 RWHP? That is low. Something is corking it. Unless you have 250~300HP of parasitic drag. Or crappy valve springs, you can ruin a set with just a few times over revving the cam.
The new combo (with the 292H) should be around 530HP at the crank, without doing anything else.
The 292H is a decent cam, probably one of the better hydraulic cams. You could use a more radical mechanical roller cam, since you may want to bleed off a little compression at low revs, anyway. There's another 30HP hiding there with the Comp A316AR8, 108 cl, 108 sep and .672 lift roller cam. Maybe not worth all the extra money.
I would suggest that you use 1/16" compression rings. Total Seal gapless are worth the extra bucks and will add at leats 5% over non gapless.
Wouldn't be a bad idea to get the block O-ringed while you are at it.
Going from 9~1 to 12~1 is worth around 70HP.
The ported heads should be good for 35 ~75HP, depending on the quality of the port job. Putting oversized, undercut valves in (2.08/1.74) should add between 35~50 more HP peak.
Also, a good distributer (MSD Pro-Billet) & MSD spark box will eliminate the ignition as a weak point. I have found that 18 initial and 20 advance is good for a nice boost. Platinum plugs are available from most mfgrs.
A two-inch open spacer under the throttle body is good for more HP, too.
Are you using old headers? Old headers sometimes hide quite a coating of rust inside, lowering flow. The Hooker "SuperCompetition" 1-7/8" primary, 3.5" collecter lose just a few ponies down low but make up for it as revs increase.
Use an H-pipe the same diameter of the collectors as the first pipe after the headers & as large of pipes that you can get someone to bend. Try to use the same size as the collector for the straight pipe to the mufflers. I always tell people to use quiet mufflers, your neighbors will thank you and your vehicle will be more pleasant to drive. It will make plenty of noise when you nail it!!!
A deeper pan will minimize the oil that the crank has to dip into, and if you hold your brg clearances to the tight side, lighter synthetic oil can be used. You can also get synthetic lube for your trans & diffs, too.
SwampRat
May I ask where you got the numbers that increasing compression from 9:1 to 12:1 is worth 70 Hp? I figured around 35-45 myself :-|
slagburn
Thanks for the helpful post!
The headers may be a bit of a problem, the engine is in a vehicle that really cramps the exhaust outlet, a 1990 Jeep Comanche pickup. The bottom 2/3 is Summit Chevy block hugger and the top is AMC flanges and spuds. I doubt the tubes are bigger than 1 5/8. I can't really improve the situation without a lot of body modification. Beyond that is mandrel 2.5 duals through Magnaflow 7" mufflers.
The heads do have the larger valves installed..
Think those headers are that bad? Can my engine shop bolt them up on the flowbench and see what happens? Only one cylinder flowing through the headers probably wouldn't tell you much, though..
edit: just measured the collectors they're 2.25"
KJMac
Those headers are really going to hurt the performance of your engine! I would use 1 3/4 with a 3" collector type header at the smallest.
