Cracked a piston some years ago running to much boost on my stock shortblock L98. I have finally put together my new forged shortblock and made my first attempts on the track.



Best trap speed was 91mph (1/8) which I find somewhat dissapointing since this is what I basically managed with less boost, smaller displacement and "stock" L98 heads. Only made four runs before breaking left half shaft and twisting the right one....

Outside the shortblock, the major differences are:
-changed the 3" dual exhaust to a stock LT1 system
-went from 3.5 to 3" pulley
-changed "mild" blower cam to a somewhat hotter one ( approx 224/236, 114 LSA, 0.590/0.590 lift)
-AFR 210 Eliminators (giving slightly lower compression (9:1))

Boost peaked at 12.5 PSI at 6200 (overspinnning the blower...) with AFR =12.1, water injection (pure water) coming on at approx 5 psi. Spark advance 24-25 at max boost/RPM, no knocksensor hooked up so no knock retard.

When looking at numbers from others running similar combinations, this seems on the lower side (??).

Maybe the Edelbrock Hi-Flo base (basically stock) intake is choking the engine? The exhaust ( I´m running dual RT 3" metal matrix cats, should be ok flowwise)?

Any ideas where to start looking ?

 

My friend and I both used to have 5.0 Z-28's with that same tpi vortech kit (non-intercooled) and the cars both could not get over 114mph in the 1/4.

The heavier car had a cam with the 5.7 sized valves in stock heads and the other had a stock cam with rocker arms with headers and port matching etc. Edelbrock lower manifold- couple of bolt on's etc. I don't think it's the manifold base- the super ram runners are shorter- can it spin to 6000? If not, change to the mini ram or LT1 or whatever will fit the head. Is your 330 ft time slower? less boost on a bigger port volume sounds like a slower car- maybe higher on a dyno, but area under the curve might be suffering. Also, I feel that blower might be great for a 5.0 car, but you need more (and better less overdriven) air from a larger head unit.

On our cars, I feel the cylinder heads capped the hp as well as the TPI of course keeping the range to 5200 rpm's.

 

First question: Is traction, tire size and gearing optimized for the 1/8 mile? Are you anywhere near your hp peak/rpm peak at 91 mph? If not, or if you're still spinning through most of the 1/8, this will hurt your trap speed.

Regarding power: The low compression ratio hurts. Water-only injection also hurts since it carries combustion heat out the exhaust. Spark advance may be too low as well, due to the water's effect on slowing the speed of combustion.

A water methanol/mix is likely to be a better compromise for power and detonation control, however with your relatively low compression, relatively low boost and spark advance along with forged components, use of internal coolants may not even be necessary, depending upon the quality of your fuel.

Since you already have the hardware, I'd consider adding some methanol to the mix and also adding some spark advance. Determining how much advance to compensate for the water/methanol injection will take some experimentation.

Also overspinning the blower requires more crankshaft power and results in greater charge temperatures. I'd also consider spraying a portion of the water/methanol mix directly into the blower inducer to help improve the compressor's efficiency. This is where water/methanol injection really shines.

 

When looking at the log from the runs, rpm at the end of the run was about 5200. According to a simulation (Engine Analyzer), peak hp is reached around 5500-6000 so its pretty close. I did notice that I was not at 100% throttle during take-off so some spinn was probably the case. Traction was however excellent (ET Streets) and I dont recall any wheel spinn later during the runs.

Mike; its funny you could not go beyond 114mph-this is actually exactly where I reached the limit as well (with the old shortblock). I have a friend that is willing to sell me his Miniram for a good price (actually its from a Lingenfelter 434 and heavily ported, quite tempting...) but I have also understood that there might be air distribution problem with ram style intakes combned with FI (I am considering a single plane intake but funds and time are limited...). I will have to dig up my old time slips to see if there are any major differences on the 330 feet.

I have had some discussions with Greg (Blowerworks) and it seems like I need to reduce water injection rate considerable. His advice was to replace the 16GPH nozzle to a 8-10 and also run 50/50 mix instead of 100% water (I have some concerns though if the reservoir will be hurt by the methanol). I also suspect that present setting with turning on the water at 3 psi (half speed) and 5 psi (full speed) is also to low.

I don´t have any reliable tools to detect high speed knock so until I get this I feel a little reluctant going higher than about 25 degrees.

I did experience high charge temperatures but the overspinning were an "accident". The tune is not optimal and the compensation tables for charge temp is not really tweaked outside the default values (this will scew the AFR). BTW Im running a stand alone ECU so almost any parameter is possible to tweek easily.

Injection before the impeller sounds interesting. I googled it and found a thread at the Aquamist site (43 pages long!): http://www.aquamist.co.uk/vbulletin/...read.php?t=251
Went through it briefly yesterday night and it is quite easy for me to put in an extra nozzle before the blower. I will probably test this but need to do some more factfinding first-Thanks for the tip!

 

That nozzle is probably a bit big. The intake isn't the greatest but I'd expect more than 91 mph with afr 210's on there

 

The flow of the Edelbrock + SR seems to be somewhere around 24x cfm vs the heads that flow around 300 cfm so this looks like one of the bottlenecks. I have also measured the exhaust tubing diameters; The tubes are 2.75 " but only 2.25 in the resonator (and muffler entry) so an easy way of freeing up the system might be to replace the resonator with an X-pipe and hopefully keep some of the good properties of the system (low noise, no resonance)?

First thing (after replacing the broken half shafts) will however be the water injection (this will probably give most hp/$); 1. smaller injection nozzle (will start with 10 GPH), 2. raise the threshold for injection to 1/3 of max boost (from 1 to 4 psi) 3. add 50% ethanol to the water

 

I ran into something similar when I first started running water alcohol injection. My trap speed really fell off. I think I was using about a 15 gallon nozzle. I played with the start up point and ramp rate and went back to about an 11 gph and the car picked up trap speed. You'll just have to play with it a bit and see what works. Also, since you were going straight water, it might have been an even worse effect.

You'll pick up some boost by spraying before the blower. That's the conclusion that I came to after reading a bunch of similar threads.

Too bad you can't get a better intake on there. The last car I raced at the drags had afr 210's on there and he ran 100 in the 1/8 with no blower or nitrous.

 

it looks like alot of hp´s are missing for me!

 

Well, I managed to reach the water injection control box buried deep inside the dashboard and found a sticker stating halfspeed triggering at 1.5 psi and full speed at 3.5 psi. Considering what I found on the Snow forum (suggested trigger point at 1/3 of max boost) plus the recommendation to use a 8-10 gph nozzle instead of my 16 gph, I probably quench the engine with my present set-up.