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this is a friends motor and im posting this in hopes that you guys can help diagnose what happened. obviously detonation but im not exactly sure why. this was cylinder #4. the others look ok and the bearings are all still perfect. Here is the combo. 374 cubic inches (4.125" bore - 3.500" stroke), JE flattops, AFR 210 eliminator heads (75cc chamber for 9.3 compression ratio), mechanical flat tappet (252* in at 0.050" - 260* ex. at 0.050, 1.6 intake rockers, 1.5 exhaust rockers), Super Victor intake with some plenum work, CSU 830 carb, e-bay turbos with the following specs - 57mm x 75mm x 0.070 A/R cold side - 58mm x 74mm - 0.068 A/R hot side T4 compressor and turbine. Homemade log style manifolds. Air to air intercooler. TH400 with custom 9 1/2" converter, GearVendors and 3.73 gears. 28 x 10.5 slicks, car weight approx. 3800 lbs. Hadn't gone over 15 lbs with this setup on turbo's yet, had run over 20 with previous Procharger setup. Timing on this pass was 28* using 93 octane.








 

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turbos are very restrictive on the turbine side....cam all wrong...terrible reversion....just a couple things to begin with.
 

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inlet temps are hotter on a turbo then a procharger!! intercooled?? back some timing out of that thing!! 28 degrees on pumpgas?? prochargers loose boost on the shift, and turbos make boost on the shift!! i have seen boost go waaay up on the shift!! but the procharger falls off because the crank slows down on the shift. but the turbo wont fall!! a bad boost spike.... and 28 degrees timing, on pumpgas.=:confused:
 

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way too much timing for pump gas
 

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Maybe pistons are a bit weak for this application. But for sure your exhaust A/R and big cam don't match.
I run almost the same engine (with bigger turbos and more boost) with 93 octane and water injection at a rate of 20 - 30 Gph no detonation.
Just curious, what is your speed with 3800lbs ?
 

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waaaay too much spark for 93, and yes the ring lands appear to be thin.

If the exhaust housings are small and the cam has a bit of overlap you may be able to run that much spark because of an unintended EGR...

I rarely run more than 20* of spark on a pumpgas, boosted pushrod motor...
 

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Discussion Starter #11
thanks for the help guys :cool:. i havent heard from him today so i will answer some of the other questions when i do. ill try to get him to join so theres no third party issues.
 

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Hey everybody, thanks for the advice so far, some of the stuff you pointed out I knew wasn't quite right, but some of it I don't know - that's why I'm here - trying to learn.
cam all wrong...terrible reversion....
Yep, I agree. This was still the cam I used for the Procharger setup. I left it in there to do some debugging. I knew it wasn't going to make the most power possible, just didn't think it completely through about possibly killing the motor.
but the procharger falls off because the crank slows down on the shift. but the turbo wont fall!! a bad boost spike...
Yep, when I ran the Procharger with the Powerstroke intercooler it would make 15 lbs. at the shift and drop to 12 when rpm's dropped. I never saw any spikes from the turbo setup when I datalogged it.
Piston is too thin near the intake valve relief.
Ring package to high,
Yep, these are pistons for a N/A application (JE's), but I figured if I could keep a sorta safe tune in it, they would be o.k. They're in there because I got a good deal on them.
way too much timing for pump gas
I'm basing my timing on my Procharger experience. I had a 383 in the car before this one. It had almost 10 - 1 compression with iron heads and I ran 15 lbs. boost on it also. I ran it on a chassis dyno and it made 20 more h.p. when I bumped timing from 28* - 30* for a total of 609 r.w.h.p. Since this setup had less compression and aluminum heads I figured 28* was a safe setting since I increased the water injection nozzle at the same time. However turbo's are obviously different and I think camshaft really killed it - but that's why I'm here and I will start with lower timing next time. I'm also done with pump gas at the track - the not knowing what you have factor doesn't make it worth it anymore.
Just curious, what is your speed with 3800lbs ?
My best time with the Procharger has been a 9.54 at almost 142 m.p.h. I had 28 x 9 slicks at the time and had to roll into it to launch. 60' was a 1.429 on that pass.
Was he running any kind of wideband? What did the a/f look like?
I do have a wideband (Innovate). I have it tuned to run in the 11.8 range. Here is where carma comes in - the sensor quit working when I unloaded it off the trailer. I haven't seen really any variation in the a.f.r. in the past but what sucks is I can't say for sure on this pass.

As far as exhaust housing size - this is where I flat out don't know. These are e-bay turbo's (figured I would start cheap to learn) so I had to take what I could get. Are they in the ball park to support around 500 h.p. each? I have looked around for months at camshaft specs people are running in various combo's and they are all over everywhere. I realize I definately need to drop some duration and widen the seperation. The question is how far. It will be a mechanical flat tappet setup since I drive it far more on the street than race it. I'm guessing something in the high 240's on in. and ex. at 0.050" with maybe 116* seperation????? Thanks for the input, keep it coming. Clay
 
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