I promised Don in this thread that I would post some numbers once I had the engine running and tuned, so I just took it out in the country and made 3 0-50mph runs to see what it would do compared to a 4.3. Don's truck has slightly larger tires and his engine is somewhat limited by the electronics, but I have nothing else for a comparison.

All three runs were on level ground, tires at 35psi, no power braking, 200 cargo lbs, 1/4 tank of fuel and wing vents closed. <img src="/forums/images/graemlins/wink.gif" alt="" /> Starting at idle, full throttle was applied over the entire run and 7psi boost was online from the beginning. My test isn't as scientific as Don's - didn't use a stopwatch - just waited until the wristwatch second hand was at 12:00 and glanced back at it when I hit 50mph, so I may be a little off, but not much.

1st run = ~7 seconds
2nd run = ~8 seconds
3rd run = ~8 seconds

There was too much wheel spin on the last 2 runs. <img src="/forums/images/graemlins/scared.gif" alt="" /> <img src="/forums/images/graemlins/kewl.gif" alt="" /> <img src="/forums/images/graemlins/smile.gif" alt="" />

I think that might be proof that dynos can give highly suspicious numbers.

If you haven't experienced the rearend of a Gen1 shorty breaking loose on acceleration with 32" M/Ts and counter-steering it on dry pavement, you ain't lived. <img src="/forums/images/graemlins/lol.gif" alt="" />

Where's that dang Escalade V-8 shorty? <img src="/forums/images/graemlins/evil.gif" alt="" />

There was a small amount of surging on full-throttle acceleration continuing above 50mph.... still need a little tuning, or the blower belt might be slipping a bit - so I'm not quite ready for a 1/4 mile attempt. <img src="/forums/images/graemlins/ignore.gif" alt="" />

Frank

Now that sounds right. Get ride of that wind correction factor of that dyno next time.

Well, we ain't racing dynos...... <img src="/forums/images/graemlins/lol.gif" alt="" /> That's what I was trying to explain before - the numbers will vary according to what the operator loads into the dyno software. The idea is to load the same numbers in every time for a closer comparison. I've heard so many outrageous claims, the numbers don't matter to me anymore - only how fast and how quick. <img src="/forums/images/graemlins/kewl.gif" alt="" />

I've heard of too many dyno/tuner shops that jigger the numbers real high so when they finish the tune, the unsuspecting racer/owner/dope dealer says "Wow.... man you really can tune an engine!" Then he sends all his buddies (maybe)... or worse yet, he thinks he has a powerful engine, goes bragging to another (more knowledgeable racer) who asks where he had his car tuned. As soon as the poor fellow answers and spits out the numbers, the wiser guy (who knows the shop's reputation) challenges him to a race - and you know what happens then..... his nice car now belongs to the other dope dealer. <img src="/forums/images/graemlins/lol.gif" alt="" />

Oh - the heads and exhaust are apparently flowing really well.... she spools up fast. <img src="/forums/images/graemlins/kewl.gif" alt="" /> I need to try it a few more times just to watch the shift points.

How'd that last msq from the tuning session look to you?

Frank

They look good, it really wanted more timing. I always find it interesting when fuel mapping has highs and lows in them such as the 2250 row, harmonics most of the time. I have come to expect it on many engines. I used to try to tune them out but they have more to do with the internals of the engine.

Have you done any work to the shift points in the trans as to firmness or rpm changes? I know it sure made a difference when I retuned the auto in my turbo Monti.

No, not yet..... I put the rebuilt lockout TQ transmission in not long ago and haven't yet paid a lot of attention to where it's shifting because I haven't been driving the truck hard (until today). It's shifting pretty fast and firm, but at light throttle pressure it may be shifting too soon - which could be why I think it needs more low end power. I haven't checked the shift points on full throttle runs yet.

For the short term, instead of making a cam trial change, I may put on some smaller tires and see how it does. That would put some pep in the low end without the blower coming on line so soon. I'll have to keep my foot out of the throttle, though - or I'll burn up some tires pretty quickly. <img src="/forums/images/graemlins/lol.gif" alt="" />

Frank

If I put 29, or 30 inch tall tires on my truck it is absolutly stupid how fast it is, and how much tire burn you get. It will straight Get It with street tires.

Dang - I thought my tires were at 35 since I just had the tires rotated and balanced before going on the dyno and I told the shop monkey to set them at 35 psi. I just went to let some air out and found the fronts at 25 and the rears at 20 psi. <img src="/forums/images/graemlins/rolleyes.gif" alt="" /> I wonder how much tire slip I'd get at 35 psi? <img src="/forums/images/graemlins/notooth.gif" alt="" />

Frank

Frank, convert 50hp to heat energy. You ain't losin' that much, or your tranny/tcase/diff would boil the gear oil. I'd run 7 sec thru a elapsed time to hp conversion calculator. My money (ain't run the sums) is north of 240fwhp to get that kind of wheelspin. Lotta WHEEEE in tire smokin', ain't there, big guy...

Yep - plenty o' WHEEE. <img src="/forums/images/graemlins/kewl.gif" alt="" /> I'll be in Atlanta for the next few weeks - maybe you'll have a chance to drive it and see what your butt dyno says.

Charlie, take a look at the cam table I posted and see if this makes any sense to you -

What I find interesting is that the 3000GT TT closes the intake valve 11* earlier than the Diamante SOHC. Valve overlap is also reduced 9-11* on the 24v heads. The Montero heads sit close to the middle ground between the two extremes.

I would think that part of the reason the 24v heads can close the intake sooner is because they have better intake efficiency with the extra valves. The TT obviously has even better intake efficiency with the turbos and because the TT static CR is 8:1, it can use more boost than my 9:1. My engine has the benefit of minor intake port work + forced induction, so it should not need the intake open as long as a N/A SOHC engine and any extra delay is robbing available volume for the piston to compress.

On the exhaust side, the Montero cams open earlier than any of the choices. I don't think the early opening necessarily hurts power since most power is produced early in the downstroke. Since I have the single exhaust valve with only mild porting of the exhaust manifolds, I may actually need the early opening to clear the cylinders.

I guess the valve overlap is less in the 24v heads because of better flow which allows for more time in the power stroke, but again the Montero specs are middle ground.

Does that make any sense? If so, it's pointing me back to the Montero cams.

Frank

Unfortunately one can not compare specs between a 2 valve head and a 4 valve head.
General speaking a 4 valve engine needs 10 to 15 degrees less duration to make a comparable torque curve to a 2 valve engine.
Also there would be little to compare between a hydraulic valve and mechanical, except maybe event timing might compare. Not the case here.
You might want to add the 3.5 DOHC timing to the list.
One thing to note on the DOHC is there is no change between the intakes of a NA engine and a boosted one. The 3.5 did change the timing but not the duration if I recall. The exhaust side of the TT has more duration to drive the turbos, not a comparison the a Supercharged app.

You might want to pull specs from the 2.6 to compare since that engine will be closer to what you are doing. It can provide NA car and truck as well as a turbo application.
We never got the last 2.6 head here that has a similar combustion chamber to the 3.0 but the 2.6 never had straight intake ports to truly get the flow up. A problem that goes back to the late 60s when that engine was developed, the days of swirl rather than the tumble of todays combustion process.

I would consider swapping the cams to answer the what if question since it would only take an hour longer than getting the valve covers off, which might take a day for all I know. But personally all the readings in the books are talking of more optimized power with cams specked 20+ degrees longer than you are working with when they refer to changes between NA and boosted.
Your engine might benefit from an increase in lift with a touch more duration, Kind of like the RV cams of the past. Just to let the air pass through.