Motor shuts off at 6000 rpm

Interesting dilema I have. The old stock LT1 with a Hot Cam, HC springs and 1.6 rockers would rev easy to 6500-6800 rpm with boost.
Now, with a stock cam, better Crane springs, ported LT4 intake and heads, it shuts off just like a rev limiter at 6000. It is pulling hard up to that point.

At first I thought maybe my DFI was acting up, so I swapped to another box, and it does the same thing.

Then I bypassed my MSD and just ran it off the DFI, same same.

Is there anything else in the LT1 ignition that would act like a limiter? It doesn't feel like valve float, it just goes flat and won't rev any higher.

Which really sucks because it feels like it is just getting good when it shuts down! :cool:

What about the ignition coil Jim? A while ago I was reading in GM High Tech's LT1 buyers guide that if the coil goes out on an LT1, a sysmptom can be it wont rev past a certain point.

What about the ignition coil Jim? A while ago I was reading in GM High Tech's LT1 buyers guide that if the coil goes out on an LT1, a sysmptom can be it wont rev past a certain point.

Dammit Neil, don't tell him that. Now he's going to want to borrow parts off my car again ;)

I would just start checking ignition parts against others that you know work.

If you want to try anything Jim, let me know. My car is apart and you've been more than kind enough letting me borrow the hoist. You are welcomed to any of my parts for trial and error purposes!

Btw...is it ok if I borrow the hoist again in a couple weeks? My motor is almost ready for good now :D :D.

Ryan

Dammit Neil, don't tell him that. Now he's going to want to borrow parts off my car again ;)


Thats ok, think of it as weight reduction. We need to get your car sub 3K with driver for going 8s any way, how do you feel about sawzalls?

Neil, Ryan.. thanks for the ideas/offers..

I found that I wasn't getting full throttle, due to a hose clamp being in the way :mad: duH!! Fixed that and it is a whole different animal now, but when it hits the 6000 point it REALLY shuts off now!!

Just for a trial and error thing, I lowered the rev limit on the DFI to 5500.. whow! Definately not that.. it KILLS the motor and you have to back off to get it going again, so I am pretty sure it isn't a DFI issue.

So I guess next thing to try is the coil.. I'll have to steal Speedmisers since the DFI uses the pre-94 coil (Thanks anyhow Ryan!)

And you're welcome to use the hoist, just let me know!

Tim get the motor out of his car yet for his "powerdyne and 210/224" glad hes switching over from his Stock motor with a Hot cam and a 75 wet shot.

Welp, isn't the coil; swapped to a known good MSD and have the same 6000 limit.

I am now wondering if I have a stock lifter problem, collapsing due to the stiffer Crane 99893 springs... they are around 402# open.
Anyone know what the Hot Cam springs open pressure is? I didn't have the problem before, with the Hot Cam and springs... maybe?

Welp, isn't the coil; swapped to a known good MSD and have the same 6000 limit.

I am now wondering if I have a stock lifter problem, collapsing due to the stiffer Crane 99893 springs... they are around 402# open.
Anyone know what the Hot Cam springs open pressure is? I didn't have the problem before, with the Hot Cam and springs... maybe?


You will have a loost rocker arm when your lifter collapses. Did you check to see if you rocker arms are adjusted properly?

You will have a loost rocker arm when your lifter collapses. Did you check to see if you rocker arms are adjusted properly?

Yep. Just reset them a couple days ago, after getting the motor broken in a bit. I am running them about 1/4-3/8 in from zero, just like I did on the old setup. I do hear one making some noise now though....

I also wondered about the fuel filter, still plan to take it apart and clean it, but I have plenty of fuel pressure and the A/F gauge is showing on the rich side when it shuts down.

Very strange.

You know, everyone always preaches the optispark is bad everytime someone comes on here with a sypmtom..

But in your case, I think its a definate possiblity. One of the many optisparks I've had go bad felt just like a revlimitor that slowly made its way down the RPM as time went on.

You know, everyone always preaches the optispark is bad everytime someone comes on here with a sypmtom..

But in your case, I think its a definate possiblity. One of the many optisparks I've had go bad felt just like a revlimitor that slowly made its way down the RPM as time went on.

Well, the car WAS apart for a year, so maybe some crap got into the opti.. ?

Guess my next step just for kicks will be blow some compressed air thru the vents on the opti and clean it out a bit...

And it WAS just a matter of time before someone brought up the dreaded "OPTI" fault!! :D j/k!!

This may sound crazy but my car was doing the same thing on the dyno. I realized that at 6000rpm my rubber elbow on the inlet side of my D1-SC was sucking itself shut. I took it off and the car pulled up to 6800rpm and made another 160 hp!

I couldn't tell from what you wrote if you were super charger or not.....

Good Luck

Mine is twin turbo, with dual 3" steel piping into hard rubber cobra elbows at the turbo inlet. K&N cone filters on the other end of the 3" steel pipe. No collapse here! :cool:

http://memimage.cardomain.com/member_images/10/web/190000-190999/190723_118_full.jpg

Anyone else? Suggestions, shot in the dark?

I'm stumped, I hope you get it figed out. Car lookes sweet, I admire people that go big on the low buck. One ? though, when do the turbos come into boost? I was thinking of running a 6.5 turbo on my 95 S-10, the truck has the 195HP 4.3CPI. Right now it runs a high 15. Well any hoo, good luck. :cool:

What kind of injectors & what is your fuel pressure when it cuts out?

Had the same problem at 6100 rpm with a 1/4 of a turn preload from zero on my lifters. Reajusted them at 1/16 of a turn preload and gained 400 rpm ????

PAT

What kind of injectors & what is your fuel pressure when it cuts out?

SVO 47#, pressure on the mechanical gauge is between 52-55 psi (starts at 43 and is on a 1 to 1 Aeromotive AFPR), A/F ratio is around 11, I have a digital A/F gauge and it is hard to get a quick glance sometimes..

I thought about trying a slightly looser lash, but it is the same stock lifters I ran before, adjusted the same way.

I'm stumped, I hope you get it figed out. Car lookes sweet, I admire people that go big on the low buck. One ? though, when do the turbos come into boost? I was thinking of running a 6.5 turbo on my 95 S-10, the truck has the 195HP 4.3CPI. Right now it runs a high 15. Well any hoo, good luck. :cool:

Thanks! Will be better if I can get to that higher RPM I want!! :mad:

Mine starts making boost pretty much right off idle, I see 7-8 psi at 1/4 throttle.

Last years dyno showed like 170 ft/lbs at 1800 rpm, 513 ft/lbs at 3400 rpm, so they work ok... :D