The Only 3300 lb. Buick V6 in the 8s using...

Cubes makes more low end torque but not necessarily more hp. I promise you can make just as much power or more power with a 231ci and a 70mm than you can with a 280ci and a 70mm. The difference is the 280ci will come up much faster and won't need the rpm or boost to get a decent 60'.

People do have monster turbine sides on small engines and run 8's. Supra comes to mind And they also need nitrous to spool them.

The reason you don't see it everywhere is because nitrous isn't allowed on boosted combo's. Take the nitrous off of yours and see how well it works. If you had to race without nitrous you'd be forced to go back to a smaller turbo and you would slow down.

I have seen a car drop backpressure and instantly need an extra 200pph of fuel. 6 second drag car. So yes that is where your gains are at. It's not magic engine design....it's all about that back pressure.

Low backpressure allows you to take advantage of the scavenging affects overlap in the cam provides. Some think overlap is used to get the exhaust to help pull some extra intake charge into the cylinder. The most important thing it does is help remove more waste exhaust products from the cylinder. It's been a long time since I took my IC engines class in school, but I'm thinking it's typical to leave a fairly large percent of your waste exhaust products in the cylinder after the exhaust valve closes. For numbers sake, lets say 10% by mass of exhaust products stay in the combustion chamber for a give cam combination. On an NA engine that see's roughly the same pressure on both the intake and exhaust ports that means 10% of the combustion products stay in the cylinder as waste that is not going to burn on the power stroke. On a blower engine that see's positive pressure on the intake and atmosphere on the exhaust that 10% goes down considerably. But if for some reason you can't get all that 10% out. The cylinder should still be at a lower pressure than the intake port so you compress those waste products down to 5% of the mass when the cylinder is filled at the bottom of the intake stroke. In a turbo engine where you typically have more exhaust pressure than intake pressure you have a hard time getting down to 10% waste out of the cylinder and everything in the cylinder is still at higher pressure than the intake port. So, you end up with around 15% by mass of waste products at the bottom of the intake stroke. In all situations, that X% of waste in the cylinder reduces the power output by X% or more.

In a situation where you get backpresure lower than 1:1 your in a situation more like the blower, but without the power robbing effects of turning the blower. That engine is more effecient for the amount of fuel and air used. You can see it on the dyno with lower bsfc numbers. I've seen lots of turbo gas motors on the dyno and I've only ever seen one of them be close to 1:1, but it was still a few psi higher in the exhaust. I don't' have much experience with alky turbo motors, but I would bet they can get lower than 1:1.

Does that make sense?

For most turbo motors, people don't go after that effeciency. Normally if you loose 5% of your power on a 1000hp engine (50hp lost) you just add 2 lbs of boost and gain it right back. No need to look for max effeciency when you can easily add boost.

You can even do a test if you want. Put a 2 inch nozzle on the end of the downpipe, take a bp reading and let us know how much it slows down.

Don't take this the wrong way because I don't know all the details of your motor. In my opinion it appears you have added nitrous and weird tricks to fix the symptoms of problem with your combination. Instead you could fix the root cause of your problems, whether it be cam, converter, heads whatever. Slow spooling is the symptom of a problem.

Even with only a 224" motor with the right combination of cam, converter and tuning you could spool that 91 just as quick without the nitrous as you do now. For example, my friends PM car: 482" motor spooling twin 91mm turbos (241"/ turbo) on alcohol with a clutch (no converter load). Butler Performance -The Worlds Fastest Pontiac Ever Watch the videos to see how quick it spools the turbos, they have no issue spooling them on a pro tree time after time. But Travis is the wizard with alcohol and turbo's.

Another example would be the Duttweiler/ Galina car. I have no idea what his combination is, but he spools two 74's? with 270"? on alcohol with no need for nitrous.

IMHO, the small heads are not as much of a restriction on a forced induction engine as they would be on a n/a setup. The cold dense 29 psi air doesn't have to be told where to go......combine that with the smaller cubic inch engine..... it is even less of a restriction as compared to the same heads on a 272ci motor. You already have a decently big bore.... so the valves are not shrouded.

I agree that you have done amazing things with a relatively small ci engine...... your cocpit looks like the space shuttle. You really are Turbo Buick's equivalent to "the professor" in NHRA ProStock back in the day.

I applaud your efforts and look forward to seeing how quick you can go with your oddball combo.

I would like to see where you would be with a 272ci motor and 300cfm heads...... or better yet...... LSX motor and 400CFM heads...... and apply the same attention to detail as you have with the little 224ci motor.

If you compare a 500 cid, twin turbo engine running 30 lbs of boost to my engine, it becomes very clear how more cid will increase torque AND horsepower. Cubes will always be king.

Let's not get into comparing a 4 valve, high rpm import engine to our old 2 valve engines. It's not really a fair comparison. Although, the import crowd was not afraid to advance the use of nitrous to spool a large turbo.

What is it about the decrease in exhaust back pressure that caused the need for more fueling?

I think Dusty was talking the same size single turbo on both engines he listed..... not same boost level with twins. It is fair to say that a turbo is "rated" at so many CFM's.... and will support so many HP....... cubic inches is nowhere to be found on a turbo map......

Beautiful explanation.
If one can get exhaust back pressure equal to or less than intake pressure, one can take advantage of a term known as crossover.
Crossover is the holy grail of turbocharging.
But still, there is another question. Why would one bother to use long tube headers on a turbo application?

First of all, let me make it clear that my engine was set up for top end efficiency only, and getting the most out of these small heads as possible. There was no compromise introduced into the combination with regards to spooling up a large turbo. Zero compromise. Nitrous was always in the plan to cover up any deficiencies in the spooling department. And, the nitrous does a very good job doing just that.
One thousand one one. That is how long it takes for me to be launch ready. One thousand one one.
If you look at todays drag ALSs (no nitrous), they are very hard on the machinery. I wanted an ALS that could be used without worrying about when the next turbo failure was going to occur. I remember walking through the pits during a heavy turbo event and seeing turbos being changed out due to failure, mainly due to the aggressive use of ALS. My type of ALS will never damage a turbocharger, or anything else, for that matter. The nitrous system has so far been the most trouble free system of my combination. Having the experience I now have with using nitrous to spool, I would never consider going to the standard pop and bang deal. Why would I trade? For me to spool this 91mm with my 224, I would have to get crazy aggressive with a standard ALS. No thanks. My machine is holding up very nicely as it is.

I don't know how cold and dense the air is being that it is compressed, but I do agree that the air can be pushed through a small port easier on a turbo engine. Still, when you reach that mach number, it's all over.

Valve shrouding. Good point.
Matching engine size to the flow capabilities of the heads. Another good point. Let's carry this point further.

Think about this. What affect does crankshaft stroke have on piston speed at a given engine rpm?

Engine size and rpm, along with VE, will set the airflow requirement. Compressor maps do consider airflow. That is the basis of matching a turbocharger to a particular engine and operating envelope. So in a round about way, compressor maps do consider engine displacement.

I have to say this again.

Achieving crossover is the holy grail of turbocharging.

Once you achieve crossover, what do you do with it?

That is so true. Let's face it. To do any good with a M&A head, you have to do extensive modifications. It's not worth the effort now with better heads available. Back when I bought the heads, and they are the first generation so that gives you an idea of how far back it was when I bought these heads, I really didn't have the budget to do what others were doing with these heads. Heck, my original goal with these heads was 600 bhp. Look where I am today. I never would have imagined. And besides, there wasn't any other choice available back then, except Stage II. I was putting together my first Buick V6 engine on a budget. I certainly wasn't ready to fork out the bucks for a Stage II setup.
Back when the M&A heads first came out and people were resorting to wild mods to the M&A heads to do 8 and 7s, how many people simply stayed with the original valve sizes and performed 8s in a heavy car? So far, possibly only one other person. We really don't know for sure because no one remembers for sure what kind of mods were done on that car. I find it amazing that I may be the only person to manage to pull 8s out of these small heads when my original goal was to simply hit 600 bhp. Who would have imagined? Certainly not me.

Your comparing your engine to a 245ci or a 274ci and acting like they have a huge advantage but they don't. Your leaving at a higher rpm to get the same 60' as the larger motor but the peak power will be determined by how well the turbo matches the engine. You will find in TSM if the rules are changed that a 231ci will mph just as well as a 274ci when your using the 71mm turbo.

Look at NHRA pro-mod. The top turbo teams are using 531ci combo's and they make as much power or more power than the 632's and the class is limited to twin 88's. Cubic inches are not an advantage on peak power. My big block will not make more than a 449ci small block when using a single 114mm turbo but mine will spool much easier.

The supra comparison was not about engine efficiency, it's about the principle of using a turbine side much larger than required for a given ci. It makes more power but won't spool without nitrous assist. It's exactly the same principle your using.

The engine needed more fuel to burn when the back pressure was dropped. It doesn't matter why the engine needed more fuel but when fuel consumption jumps from 1200pph to 1400pph and sets the NMCA top speed record at that time. It lost a couple # of boost but the hp increase was more important than the boost #

How would you know? Have you ever driven a 1000+ bhp, nitrous assisted, turbocharged car on the street?
Sounds like it would be a bunch load of fun to me.

I don't know why you're wanting to compare my engine to others. I started this thread to figure out why I may be the only person to do 8s in a heavy car with 1.835" intake valves. But, let's go ahead and talk about more cubes.
Number one. I would not restrict myself with rules. Others are into following rules that restrict you in one way or another. I'm not like that. I choose to set my own rules and set my own goals and build for efficiency. If I chose to build a larger cubed V6, I would make sure I used a head that would support the new displacement. I would also choose a turbo that would support the new displacement. I would also configure the engine to be as efficient as possible on the top end. I would also use nitrous to spool the turbo. Dusty, I guarantee you, if I built more cubes, it would result in more power.

Donnie, you are not the only person in the quest for 8's on a set of small valve M&A head. Granted I have a 274ci stage 2 and an pt88 turbo, I also have small valve M&A heads that have mild clean up and gasket matched to 1200's. My first pass off the trailer(5th pass on motor) in BG was a 9.33 @148mph w/ 22lbs of boost and 21* of timing on E85 weighing 3510. A small mishap caused a bent rod and torched piston and block, but hopfully I will be back out some to try again. My goal is to hit 8.50's next year if I still have my car.

Good luck with your engineering challenge. I wish you all the luck. Keep me posted.