worship79

This wednesday my car will be on the dyno to tune the new engine components (heads, intake, cam, rockers).

A buddy of mine suggested I should try out 1.6 rockers versus the 1.52 installed now. I did the math to calculate the extra lift this would add given my XE268H cam: 0.025 for both the intake and the exhaust lobe.

Is there any way to calculate power gains for the extra lift?

My setup:
350 SBC
CompCam XE268H, 0.477 int./0.480 exh. lift
64cc performer heads
performer EPS intake
1411 750 cfm carb
1.52 compcam roller tip rockers

Durango_Boy

I don't think there is a good way to actually tell without before and after dyno runs, but I remember reading someone did it and saw a 7 HP increase. Not worth it in my mind.

bojangies46

Yes but 7 HP is the difference between a loser and a winner in racing, but for a steet car you will not notice much difference.

worship79

Well, after my dyno session today I think I'd better first address some other issues. Turns out she's missing under load/running on 7 cilinders under load. Only 205 RWHP is not good for this new setup.

rayluka

ouch

ajrothm

F A I L.....

:d

worship79

Yeah... throttle response not to sharp either, bet it's related. Air-fuel ratio is correct over the whole band though, so at least I don't have to check into that. On the plus side: my 1500 tot 2000 rpm stall problems have been resolved completely.

I'll first do a compression check, then inspect plugs, after that replace plugs (if neccessary), wires (definately neccessary), airfilter, PCV filter and check iginition order. Dyno operator suspected either bad plugwire(s) and/or valve not closing. Latter might explain the coughing when I start the engine.

ajrothm

Yeah something definetly isn't right. So it runs OK until upper RPMS then it drops a cylinder? or its only running on 7 cyl all the time? You still running the points distributor?

Did you bolt on the top end parts on your stock lower end? maybe rings/cylinders worn?

With your combo, I would have expected 250-275rwhp....if not more...

Hell my old turd slung out 200rwhp with only the air cleaner lid removed, headers/exhaust and a tiny L79 cam, thats in stock 71 low comp 350(270hp) with 145k miles on it, going through a TH400.

Let us know what you find....

worship79

It seems to be running on 8 in the lower RPM's, however it doesn't respond to the throttle very well in the lower ranges. As if she doesn't really feel like revving up, if that makes any sense?

For this build we took the engine out stripped down to the short block and inspected pistons, deck and such. Except for a little carbon deposit on the pistons, it all was very clean and tight (I'm no expert though, I took my buddies word for it).

Here's a picture:


The block was bought new in '97 and has perhaps driven 15 to 20k miles since. I'm running ACCEL high performance HEI by the way.

ajrothm

Well all that sounds like a pretty solid foundation to build on. Gotta be something ignition related or carb related. You said your AFR was good across the board so......assuming the secondaries are opening fully, that means your jetting/power valves etc are working well together...

Time to start diagnosing now.... Check plugs, check timing, compression test and/or leak down and go from there.

Usually if it runs ok and is hitting on all 8 cyl down low but developes a miss upstairs, its an ignition problem.......Weak plug, bad wire or something dumb....

V-Twin

Sounds like a wiped cam lobe to me. As the lobe starts to wear down it will choke one cylinder above idle and start to sputter. It'll probably get much worse as you keep running the engine.

The XE series run a pretty aggressive ramp profile, on the ragged edge of what can reliably be done with flat tappets. It's very common to wipe a lobe if the proepr precautions aren't taken like running the proper oil and using the proper (and plenty of) cam lube.

worship79

Could be, although we did follow all the procedures to the letter and plenty of cam lube too. I wouldn't be the first though, so is there a quick(er) way to tell a wiped lobe?

bojangies46

Look inside your distributor cap or plug wire first, a wiped cam lob will back fire through carb at higher rpms.