BrandenZ Posted March 26, 2012 Share Posted March 26, 2012 Short of the long -- kicked off a rocker arm at the first event of the season, decided to put a rev-limiter in place before the 2nd. Added a HI-6 ignition (thanks, aplyedmind!), have it currently set to 6800. Banged off of the rev-limiter a ton on straights at the second event of the season, so I'm wondering exactly how much I can push it. E88 head F54 with flattops, est 10.1:1 compression HI-6 ignition + PS92 coil Dual weber DGV carbs 8 degrees base timing dialed in at the moment (concerned about ping on 93 octane) 3.9 WRX STi R180 rear differential with johnc's side axles (hence why I'm running out of gear so fast -- 6800 redline == 57 mph in 2nd) Very confident with the spark and timing advance curve, but very concerned that if I over-rev it, I'll kick retainers and rockers like I did after the first event (probably held it at 7200+ for a bit in the long slaloms). The power does _not_ die off at 6800, the car seems to beg to be pushed harder, I'm just not convinced I can safely do so for extended periods of autox and track. Any advice on the subject, particularly regarding the type of combo I'm running, would be greatly appreciated! Quote Link to comment Share on other sites More sharing options...
Xnke Posted March 26, 2012 Share Posted March 26, 2012 You are running cast pistons. You'll end up ripping the wrist pins out of the pistons before you start hitting valvetrain limits, given that you run a stronger spring...factory springs on factory cams start to get weak about 7500RPM, each time you get up to that speed they get a little worse, tend to start to float a little and won't rev as high the next time. Go with the Rebello "A" type springs and new stock inners, and you are good to 8000RPM with the right pistons. Cast pistons on the L28 crank are hitting firm-limit piston speeds at about 7100-7200RPM. Rev one to 7500+ for a pass down the back stretch and you might be driving into the pits sounding like ice cubes in a blender... Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 26, 2012 Share Posted March 26, 2012 ""ou might be driving into the pits sounding like ice cubes in a blender... " My ex wife said that aboutBbrian Blake's engine at the MSA Auto-X his first year out there with the home-made ITB's. When we fired the engine in Arizona, and I was revving it in the yard I asked Brian "Did you build this with Forged Pistons?" He said no, and I said..."Oh, you better watch your rpm's, this is gonna pull hard but your pistons won't last long..." Quote Link to comment Share on other sites More sharing options...
BluDestiny Posted March 26, 2012 Share Posted March 26, 2012 Why dont you have a cam with that combo? On cast pistons I had my hi6 set at 7200rpm. And I wish I had forged pistons because I might have been able to pull more, if my dizzy was up to it. Quote Link to comment Share on other sites More sharing options...
johnc Posted March 26, 2012 Share Posted March 26, 2012 You're going to have to use 3rd gear. Leave the rev limiter at 6,800 and plan on shifting at 6,500 rpm. FYI... the power may not die off at 6,800 rpm but your rate of acceleration will be quicker if you up shift to 3rd. You will lose about two 10ths with each shift but until you optimize you're gearing, you'll have to live with it. Quote Link to comment Share on other sites More sharing options...
BrandenZ Posted March 26, 2012 Author Share Posted March 26, 2012 John -- I thought about shifting to third, but the section I was topping out second on didn't have an appreciable straight-away, it was more slalom cones and gates that were just wide enough for the small Z to be able to blast through wide-open with smooth steering inputs. I fear if I would've up-shifted, I would've upset the balance of the car and lost it. Also I traded my tach for a rev-limiter... need to figure out how to get it working again with the hi6 before I have any hope of shifting at 6500. Blu -- Cam is next on the list. I've got one from a P90 that I think I'm going to have sent off to Delta, figure it should help me dial in a bit more base timing as well. Forgot to mention that the E88 head is a fresh rebuild, but was not done by me, so it's a bit of a mystery. It was clearly hot-tanked and milled (shims in the cam towers), but not entirely sure how much... with a rough test it CC'd at 44, valves appear to have been unshrouded as well. Also the intake valves measured out to 280z spec, but exhaust are just the 240s. Cam has an A stamp on it, appears to be "stock", as do the valve springs and rockers. Quote Link to comment Share on other sites More sharing options...
Xnke Posted March 27, 2012 Share Posted March 27, 2012 (edited) If your head measures out at about 44cc, then you should be able to run a little more base timing than 8*. If you are looking for a cam for that combo, think twice before taking Delta's 280/.480" (really .455") grind...I think I'm overcammed for my 9.75:1 compression at current, although from 3500RPM to the top of the tach it pulls great. When I get another core to send in, I am considering having them grind that lobe profile, but tighten the lobe centers up for a little less overlap. Also hoping that tighter lobe centers would help with the 950RPM idle, and that I have not much torque under 3000RPM. The step in the torque curve is most noticable in 2nd gear, pulls away smoothly, if a little sluggish, but at about 3000 the exhaust sound gets much fuller, resonates, then the car starts pulling pretty hard all the way to 7000RPM. Edited March 27, 2012 by Xnke Quote Link to comment Share on other sites More sharing options...
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