Cam's maro

I have a 93 speed density LT1. It has 160,000 miles on the clock, 3.23:1 gears, untouched trans and converter, and a stock motor except long tube headers, cold air intake and a PCM chip. We just ran at MIR this past Sunday. It went 12.968 @106, 13.05 @ 103 and 12.968 @ 106. I'm new to the LT1 format, but learning as we go. Are these times what we should expect? Faster than normal? Slower than normal? Any thoughts as to what the limit will be for ET without doing any more to the motor i.e. gears, converter, stripping weight etc.?

michaelzilinski

I'd say that's around normal. My first z was a 93 all bolt-ons and my best time was 11.9, that was an,m6, but I'm sure there are better all bolt-on times then that.

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Cam's maro

So, maybe there is still a little more speed in it somewhere? I can tell you that open headers on that car will damage the fuel line on the drivers side. I didn't pay attention to the routing very close when the headers went on. It will melt the lines and high pressure push fittings for sure! I am very lucky it didn't rupture, but the heat on the line had to have a huge affect on the fuel being delivered to the injectors. I guess this week will include some fuel line mods...

Injuneer

Open headers can also expose the O2 sensors to an air backwash, and screw up the A/F mixture.

Cam's maro

When I contacted PCM they suggested that I unplug my O2s' and run in open loop. They told me the exact thing you posted. It must have helped, the best time prior to the tune and unplugging the sensors was a 13.50

Cam's maro

Injuneer, reading your car's engine combo I see you have LT4 castings. I have a friend who wants to sell me his complete LT4. I was toying around with the idea of doing that and having a real good port job done on the heads and intake. Are you happy with the flow numbers and performance from them? For my money 200 bucks for a complete LT4 and port work seems a heck of a lot cheaper than paying top coin for aftermarket race heads.

Injuneer

My LT4 heads were ported back in 1999 by CNC Cylinder Heads in Pinellas Park, Florida. No longer in business, but the owner now has VMax Motorsports.

The flow numbers were good on the intake side, and actually improved by 3% when flowed with the LT4 intake manifold they also ported - something my builder had not seen before. Just about 300 CFM. The exhaust side, on the other hand, was not impressive. My engine builder felt that the exhaust runner was hogged out excessively. The guy at CNC, Pete Incaudo (who claimed to have been involved with GM in the development of the LT4 head) had told me up front his exhaust work was better than others, because he measured the exhaust results on the pressure side of the flow bench, to more closely replicate the exhaust flow. When we saw the relatively low results when flowed on the suction side, my builder and I tried to call Pete to discuss, and he never returned our calls.

In the end, the builders spec'd the valve train to produce the desired 0.590" lift with a 1.55X roller rocker, so we could bump it up to a higher lift with a 1.6X rocker if required. But after all the engine dyno testing they didn't feel the need to bump up the exhaust flow.

If you are just looking at stock LT4 heads, there is only about a 15-20% flow increase over the stock LT1 aluminum heads. Unless you are porting the LT4 heads, there is no reason to use them. The stock LT1 heads can be ported to support 500 HP normally aspirated. Advanced Induction cites a 10-20HP improvement with their 215cc ported LT4 heads (300 CFM), compared to their 200cc ported LT1 heads.

Cam's maro

That's good information. Thanks. My thoughts on the 4 vs. 1 head is based on power potential and durability. With the 4s' having a thicker deck, taller roof and I believe a larger rocker studs (?) I figured they would hold up better and handle a bit more compression. Also have a more stable valve train with the 1.6 roller rockers. I'm not going out there to break any ET records, but I want to have a well thought out respectable combination. I'm learning as I go here. So far we have had some rear end issues and some minor cooling issues along with the apparently obligatory opti-spark issues. It's been pretty rewarding to get theses ironed out and I have had fun doing it. Hats off to who ever shoebox is, I think I have read every page on the site. For now I think the fuel lines will need to be addressed then I will leave well enough alone with the motor and concentrate on things such as LCAs', springs and shocks, torque arm, gearing and some converter. Who knows, maybe I can pop off a 11.999 with ole' red.

JakeRobb

I could be way off base here, but 13 flat in an LT1 car that is completely stock other than the headers/CAI and tune sounds very quick to me. 106mph is likewise quite fast for just those mods. 14.0 @ 99 was typical in stock form. A full second and seven MPH is a LOT to gain with the mods you mentioned.

No other mods? Suspension? Weight reduction? What kind of tires? What were your 60' times?

The other factor is the air. I see you're in Maryland, which is low altitude and therefore high density air. What was the weather like that day? You might have had a very good DA, and that could be contributing to the excellent timeslips.

Cam's maro

I'm running Hoosier drag radials. only other mod is a line lock. Full weight full interior. Best sixty foot time to date has been 1.66. It seems that I'm around 1.8 consistently. I posted a pic of some time slips in my garage. I have 3.23 gears I the stock 10 bolt. I went thru the rear and replaced the springs and friction plates after our first pass of 16.77 spinning only one tire well past the 60' mark. It's been quite a learning experience so far, very enjoyable. We are still chopping away at it.

Cam's maro

Here are a couple of the time slips from our last trip to MIR. It was about 65-70 degrees out. Oddly enough the fastest 60' (1.66 w/13.48 et) time was BEFORE I ever ordred the PCM tune. You can see the sixty foots are slower, but over all picked up a ton of et.

JakeRobb

Ah. Drag radials and a line lock (and the resulting 1.6x 60' time) make all the difference in the world.

Cam's maro

I only use the line lock to heat the tires. Using it to leave would improve my 60' times?

Mr99SS

trans brake makes the car leave harder .... line lock just locks the front tires for burnouts ..

Mr99SS

put a small wet shot 150 .. u will be surprised and foot brake it no need for t brake