Boost numbers and opinions needed
 

So I finally think all the kinks are worked out with my build and I have a question on boost numbers...we can over look the obvious that I'm running a fragile drive and getting the motor dialed in would be step one...however I don't want to spend all the time tuning and jetting for what I have just to have to do it all over again so please bear with me and offer what advice you can

Motor...454 bored .030 over, dart iron heads, stock crank, eagle rods, JE pistons(8.2:1 comp ratio) Dyers 8-71 blower, twin holley 850s, comp cam(don't have all the specs off hand but can get them if needed) its a hydraulic roller with roller rockers as well...

On to the question...

The few WOT runs I did on the boat netted 5 lbs. boost at WOT....is it worth uppping the boost a little to say 8 lbs?? My goal here is not an all out race boat but a quick "reliable" pleasure boat....is upping the boost a few lbs going to change anything speedwise?? is this going to be a 1 MPH change that's going to stress the crap out of the motor?? is it going to be worth 100 hp and 5 MPH?? just curious if its worth doing some pulley swapping to up the boost slightly and tune from there to do it once and be done....This will be run exclusively on 93 octane pump gas

Thanks

3lbs of boost is not going to increase HP by 100 maybe 25. 5 MPH unlikely maybe 2, I will let others share!

Yea I was exaggerating my point of course lol but ya know why stop there....is 10 lbs "safe"?? could I run double what I'm running now and still be as "reliable" as a performance boat could be excluding drive issues??

So I guess in reality...a pulley swap being as cheap as it is would be worth it up to the 8ish lb range?? under a hundred bucks to maybe gain a MPH or 2 potentially?? I guess my biggest question is where would the cut off for "reliability" come into play?? the 8 lb range from what you're saying obviously??

To add to that...I kept the motor with low compression to keep some reliability on the table...with my setup would the 8 lbs vs the 5 lbs be any less reliable?? I mean I live in reality and obviously more boost is going to stress engine components and I do NOT want to run it on the ragged edge all the time but am I being too conservative at 5 lbs??

thanks

With 8.2 static, you probably do not want to go more than 7# of boost on 93 octane.
Ref chart http://documents.holley.com/techlibr..._tech_info.pdf

You always have to come in with technical real world bubble bursting data don't you griff hahahaha

Thanks for the info!! looks like 7 is about all I should do to keep it somewhat reliable

Fair enough...thanks guys!! probably just leave her at 5 for now and get it dialed in nicely then maybe play with it next year

3lbs more of boost will likely net you 75-100hp. Been there and done it on the dyno with a similar combo.

theres alot of factors that go into what amount of boost is safe. An 454 with locked timing, 177 blower, 9:1, single carb, warm coolant temps, small cam, will not tolerate the same boost as a 8:1, 8-71 equipped underdriven healthy cammed dual carb setup with a timing curve.

its all about managing cylinder pressures, and what octane is available. Your air intake temps shouldnt be very high, and with the right tune, 7-8psi should not be an issue at all.

i run 9psi on my 468s, 8:1, iron heads, superchillers, etc. Id run more, but im already spinning the engines to 6200-6300rpm with the props i have. With 10psi, id be probably in the 875-900hp range, and 6500rpm wot range. Pretty sure sooner or later im gonna push the crank out of the stock block.

http://www.wallaceracing.com/hp-blower.php

So that being said and knowing my build...do you think I should wait for chillers to try upping the boost or do it now and tune accordingly for the higher boost?? Again I don't want to run it on the ragged edge and hurt it and I repsect everyones opinions...just trying to not have to jet this thing a hundred times hahaha

Well a hypothetical 100 hp gain is worth it enough for me to try...If my baby big block made 750+ I wouldn't know what to do with myself hahaha

I guess detonation would be my biggest thing to watch?? And I'm still researching the best way to recognize and combat detonation since especially in a boat from what I understand you will never hear it...I plan to tune my WOT air fuel to mid 11's and pull my plugs after 1 or 2 WOT passes...I assume detonation will show on the plugs??

Like I said I'm going to research it more but other than detonation what should I really be concerned with when upping the boost to 8 lbs and how would I detect said problem?? Sorry for the rookie questions like I've said in other threads related to this build I'm new to the blown bbc game and don't have the money to trial and error this thing hahaha

Thanks guys!!

Well if that doesn't convince me nothing will hahaha

I assume that holding this thing pinned for like miles at a time is a quick way to make a lot of scrap metal so with no chiller right now would say 1/4-1/2 mile WOT pulls after tuning be realistic??

Hahahaha

Very true...not the kind of income to allow for rebuilding the motor over and over lol

How would one measure cylinder pressure and IAT?? I'm sure intake air I could get some kind of gauge but how would I measure pressures or is that not something that's measurable??

I gotcha...btw sorry if some of these questions are redundant to other threads of mine I just want to try and be as clear as possible fine tuning this guy as like I said I can't afford to keep rebuilding this guy lol

IMO, If you can't pin the sticks to the dash for a solid 2-3 minutes or longer, then something is not set up correctly.

I agree with that griff...just makes me leary to do it anyway for extended periods especially without a chiller at any boost level...Idk maybe I'm just scared of hurting the ole girl haha

I can tell ya chillers arent exactly a gigantic benefit on a setup like this. Dont get me wrong, they help, and anything you can do to lower charge temps is a bonus.

My intake temps with a chiller, vary with lake temp. On lake michigan, where the water is very cold, they run in the 100-110* range. Slightly hotter at loto late summer, in the 115-120* range.

icdedppl has 10-71s on his 548's, making about 7psi without intercoolers. His wot temps are in the 140-150* range if i recall.

what ive noticed, is the intake charge temp with the larger blowers, doesnt seem to increase a whole lot when you up the boost a couple lbs. I can only assume thats because they arent being spun more than 20% over, and the chemical intercooling from the gasoline is helping.

I have a prosport IAT gauge. Im monitoring both engines intake temps on the dash at all times. Glowshift now makes a nice digital gauge as well. I recommend getting one. Youll need to drill and tap the intake for the sensor though.

Icdedppl has 548's, 8.5:1 , dart iron heads. He runs about 7psi no intercoolers. He has egt , afr, iat, knock sensor monitor, etc. Hes been running that setup for a few seasons now, with quite a bit of wot time in a heavy old 38 cig. He just bought some intercoolers, will be interesting to see what his temps are after the install.

As Mild mentioned, I`ve been running 7.5lbs. Ive seen up to 8.3lbs on my data logs on my port motor @6300rpm.
I`m trying to push the Titanic thru the water so I`m usually already at 3.5 lbs at cruise(62mph) AFrs in the low 12`s, EGTs 1320ish. timing around 29* intake temp is always 140-150*
No powervalves. 82 jets in front, 102 in back .

5lbs is "safe" but kinda low if everything else is dialed in, meaning good timing map and AFR`s.
I have kinda the same set up as you.

My motors are currently having a growth spur , not sure where I`ll end up with boost. Going from 5.2% under to 2.1% over


https://cimg6.ibsrv.net/gimg/www.off...38b696548b.jpg


You could always just enjoy for a bit and add boost later .

Technology has come a long way. Not too long ago, the thought of a 9.5:1 engine, running 12lbs of boost, on pump gas, making 2hp per ci, with a full warranty off the showroom floor, was a crazy concept. Now, every dodge dealer has a couple sitting on their lot. I know its not a "boat " engine, but each hellcat engine gets ran on a dyno for 42 minutes, at 5000rpm, with 90% load. Not 42 seconds, but 42 minutes. Thats a long time. So its not some "oh its a 10 second drag race engine". Show me one aftermarket marine engine builder that validates an engine like that on their dyno. Most do a couple 10 second dyno pulls and thats their claim to endurance testing and tuning. Guys are beating the crap out of those engines off the showroom floor slamming down 9 and 10 sec 1/4 mile times in a 4500lb car all over the place, and then driving them to work monday morning.

My point is, not too long ago, the average marine supercharged engine ran locked timing, read spark plugs for fuel mixture (many dont know how to read a plug), never monitored intake air temperatures, and so on. Thats all you heard about was blower motors burning down. Today, you can do alot more careful tuning with ignition maps, wideband, and so on.

It doesnt end there though. You need the whole package. The right engine tolerances, parts, spark plugs, head gaskets, valves, valve seats, valvetrain, temperature control, and so on if you are building for reliablity. Theres so much more to it, than 2psi of boost, whether or not the engine will succeed. 5lbs with a crappy tune, is worse than 7lbs with a good tune imo. :bigbird:

All very good points...I'm still trying to wrap my head around the timing "maps" I understand what is being said with it but I'm still trying to figure out real world in the boat not on a dyno how do I judge if the timing is coming in too early too late not enough timing too much timing etc...that's my biggest concern at this point....I think the boost will stay where its at for now and like you guys have said I will up it later once I get all the other bugs worked out...I think changing too many variables at one time trying to get max performance out of it while tuning is just asking for trouble...I'm sure that I'm over thinking all of this from the fear of hurting the engine...gonna try to settle down and try some things slowly and see what happens...or all else fails I'll buy a keg and trailer it to Chicago and look for MT hahahaha

I will be researching and buying an IAT gauge soon as the intake is off now so I plan to at least drill and tap it before it goes back on...should the sensor be located directly under the blower I'm assuming...like where a boost gauge would be mounted??

Thanks guys!!

Here is one of many posts on line of how to read a spark plug. https://www.dragstuff.com/techarticl...ark-plugs.html

I wouldn't hold the engine at WOT for 1/4-1/2 mile to check the plugs. If your tune is pretty far off you could cause substantial damage.

very good read!! thanks for sharing def helps me a lot!!

IMO and I am no expert but boost numbers dont mean alot as an overall. boost only exists due to restriction between the blower and cylinder. you are at 5 pounds making 'X' amount of power but if you are at the limit of what can be pushed through the ports, valves, and cam allows then you could raise the boost to 40 pounds and maybe only make another 20-30 horsepower. if you are at 5 pounds and all the other factors are capable of more then 8 pounds could net 100 hp. I have seen plenty of motors that made 600 hp at 5 pounds and with a cam change made 700 hp at 3 pounds. why? the cam was holding it back and the new cam let the air and fuel fully fill the cylinder. egt would tell a lot about how well the cylinder is really filling plus o2 sensors to let you know what is going on under load.

the problem with detonation, is the temperature and pressures spike hugely when it occurs.

take spark advance for example. You can increase spark advance, and increase cylinder pressure/tempeature However, that doesnt necessarily equate to more output at the flywheel. A simple adjustment of the timing curve, can have a detrimental effect to the combustion process.

this is a reason I dont get worked up over egt's. You can advance the timing, and see egts cool down. However, that doesn't mean the cylinders peak temperature is cooler. All you did was light the fire sooner, and the spent gasses the probe sees have cooled down sooner. If you had a temp probe on the intake valve, youd see the intake valve get hotter, while the egts get cooler with more spark advance. The spark plug will tell a better story imo. Of course, this is where tuning ignition curves on a dyno is enlightening. Egts are great to see if somethings going wrong, but im not sure id want to tune my engine around them.

then theres the fuel mixture. Pure Gasoline makes its best power at 12.5:1, or with an ethanol blend, maybe 12.2:1. Youll see guys saying their engines made best power at 13.5:1, or 11.5:1. Imo, its not that air fuel ratio that made the best power, its that their timing setting caused it to make best power there.

meaning, if you made best power at 11.5:1, you prob had too much spark advance in it. If you made best power at 13.5:1, you probably didnt have enough spark advance in it. Simply put, rich mixtures need lots of advance, lean mixtures dont. A guaranteed way to burn a supercharged engine down, is a lean mixture with lots of timing. Prob why many years ago, guys were scared to run more than 28 or 30* total timing. It prob wasnt the timing that hurt the engine, it was the mixture.

at any rate, today we can get away with alot more, if youre willing to invest in the tools to learn whats going on in the engine. Id love to get a dyno in my barn, with some tfx pressure transducers to monitor cyl pressures, along with an 8 pack o2 setup.

this looks like it could be very enlightening
http://www.tfxengine.com/faqs5.html#TFX1