LSXSeven

iTrader: (1)

Car is an 93 mazda rx7 with an 02 F-body pullout from an auto. The ECU has been reflashed with a manual program. wiring has been converted for manual as well.

Ok, here is what's happening. Dropped the car off this morning to get tuned. Get a call that the car wont rev out past 6k. I had it happen to me a couple of times while I was driving it around but figured it was something with the tune. I didn't want to rev it out to much with the raw tune anyway so I stayed below 4500 for the most part.

He said the car drives fine and pulls strong all the way to right at 6000rpm where it falls on its face. Even free reving it it starts to break up a little over 6k. He has loaded 6 different tunes from 6 different cars and the problem stays consistant. The tunes alter the way the car performs a little but do nothing for the 6k issue. He thinks it is something mechanical that is causing it. It makes good vacuum and works fine at anything under 6k. Fuel pressure is rock solid and the TPS and MAf readings are right on. He has turned off everything in the ECU with regards to knock and chassis feedback stuff. He is an LS1 performance shop and said he has never seen anything quite like this. He ran out of time today so he is going to start checking other things tomorrow.

we want to recheck pushrod length and maybe swap the coils. Any suggestions would be great. I trust him but if there is something that is particular for the swap, he will not be on top of that. He works on a lot of corvettes and GTO's. Pretty much lS1 stuff.

My particulars are as follows:

Stock bottom end with ARP rod bolts
CNC'd 243 casting heads with 2.05int and 1.6exh valves milled 20thou
crane double springs with titanium retainers
comp cams 232/236 .595/.600 114lsa cam
flycut pistons
LS4 oil pump
ls2 timing chain
GM high rev lifters
comp cams 7.450 pushrods
Jesel shaft mount 1.7 rockers
LS6 intake
cometic .40 gaskets
fuel system holding 58psi
38# injectors
slp 85mm maf
jtr long tubes

hope to figure this out asap and hope its not going to be internal.

Mike

Keenov

iTrader: (5)

Valve float? What does the graph look like after 6k?

LSXSeven

iTrader: (1)

I have not seen the graph. I will tomrrow. What would cause valve float. I have dual springs and new lifters. Could pushrod length cause the problem?

chuckyt1

iTrader: (33)

Did you use a pushrod checker to verify the length? 7.450 seems like it might be 'kinda long with .040's and a .020 mill. That could be a problem if your valves aren't closing but I think that would show up before 6000 rpm.

LSXSeven

iTrader: (1)

here is my post from when I was doing all this. It seemed odd to me as the #'s pointed toward shorter as well. checking with the PRLC is what made us choose the size. We are going to recheck again now that the car has been run and the lifters have been filled with oil.



just got the valve train assembled and started checking my pushrod lengths. I am running a comp 232/236 cam with int. base circle of 1.457 and exh. base circle of 1.445. My heads have been milled .020 and I am running a .040 cometic. I have Jesel shaft mount rockers and after market valves. I am also using the new LS7 race lifters.

After assembling everything, I quickly found out that it was a good thing that I got an adjustable pushrod checker. The after market valves and Jesel's through a curve ball at me. according to the base circle figures I should have lost .0495 on the intake and .0555 on the exhaust. with the milling and thinner gasket, I should have made .035 of it back up therefore keeping some preload(assuming .050 preload to start) This wasn't the case. With the stock pushrods I don't even touch the bottom of the rockers. There is .012 play on intake and .006 on exh. I guess the valve train is skewing the numbers.

Anyway, after checking. I come up with 7.397 on the int to get to 0 lash and 7.391 on the exh. Adding .060 for preload I get 7.457 int and 7.451 exh. These are overall length measurements. Whose pushrods are measured in OAL instead of Guage length. I want to find the best match for length to get the recomended preload.

Mike

LSXSeven

iTrader: (1)

Ok, here is the theory I am working on. This theory assumes that it is mechanical and not electrical. Both possibilities are still open but my tuner thinks its mechanical so I am working on that at the present.

Since it seems that I did eveything correct when measuring the pushrod length, the only possibilities for valve float would be either lifters over pumping up or bad valve springs. He says the car idles fine and drives fine all the way up to 6k. After 6k it runs like **** for a bit till it recovers. The heads were just gone through so I am putting my attention to the lifters.

I am running the high volume LS4 oil pump. I am seeing over 100psi on my Defi gauge. Is it possible that too much oil pressure is taking all the preload out of the lifter and driving the plunger all the way to the top at high Rpm. This might be floating the valves as they can no longer shut. After letting off, the lifters remain pumped up for a bit and the car now runs like **** until they bleed back down and everything returns to normal. Has anyone else here run this pump and/or experienced this type of problem.

On the dyno we are getting 401hp at 6050 rpm and then it plummits to 250 something by 6150. Fuel pressure is rock solid at 58 psi. As stated after the pull it runs like crap for a bit till it recovers. Then runs fine unless we rev it past 6k again.


Mike

Imfamous Images

Sounds to me like you have too much oil pressure like you were saying. If not then it might be something in the ignition causing it to fall off.

LSXSeven

iTrader: (1)

turned out to be the pump. I bought a stock z06 pump and pressures are 35-40 idle and no more than 75 at WOT. I still have valve float though. I think the springs need to be replaced. They are crane duals(144832's I believe) and were used with the heads. I am not sure they are up to the task. I am going to have them replaced.

My cam is a comp xer grind 232/236 .595/.601 114lsa. The springs are crane duals according to the previous owner. He had a much more aggresive cam than this so I figured they would be fine. Maybe they are just worn down or not shimed enough. Do you guys think that these springs are under rated for this cam. I am also running Jesel sportsman series shaft mount rockers. They are stock 1.7 ratio. I also have hardened pushrods which give me .060 preload on the caddy lifters. I am considering the new patriot extremes or the crane 144833's. Since I already have the locks and such, I can just buy the srings.


Also, of interest is that the part # on the LS4 pump I was sold does not match either of the part #'s listed in the SDPC thread. As a matter of fact, we can't find the part # on any GM website. I plan on calling Fred Beans on Monday. This pump might not even be for my this engine.

Mike

71CamaroLS1

It sounds to me like you're getting a resonance in the valvetrain around 6K - probably in the valve springs themselves - which is probably creating some valve bounce. This would allow your lifters to pump up, particularly with 100 PSI of oil pressure (way too much, good thing you replaced that pump in any case).

I'd replace those springs - Patriot Golds seem to be an almost universal standard these days. I'm running AFRs upgraded springs with XER lobes, revving to a 6800 RPM limiter no problem, and I think the upgraded AFRs are the same spring as Patriot Gold. Note: the interaction between cam and spring doesn't really have much to do with how big the cam is, it has to do with the cam lobe design, and XER lobes are extremely aggressive right off the seat (even more aggressive in that area than LSK lobes).