https://www.theturboforums.com/thre...rger-blow-through-355-quot-grenade-quot-style

Boost + junk =

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Hell yeah nice buildup! Your engine combo is surprisingly similar to my old chevelle with a Holley 420 megablower. Almost duplicate cam specs except mine was on a 114 centerline. Same casting heads too! With 1.5 rockers mine liked 29-30 degrees total timing and 1.6 rockers improved the efficiency so much it was pissed off at 30 degrees and 26-27 was the new hot number. That should be a great guess for your combo with so many similarities.

Another thing to give you a heads up on is whether that hat has a divider wing in it. I had some problems once with a setup with the same pipe layout as you in the compressor outlet was still spinning the air quite a bit when it hit the hat and the 45 degree orientation of the hat and wing was really messing with the booster signal since the wing was right over 2 of them.

The best solution ended up being ditching the winged hat for a cheap spectre hat and pointing the pipe out ot the procharger straight across the motor and using a 180 degree bend directly into the carb on the other side. The pipe radius BARELY allowed it to work and clear everything and it looked pretty cool. Way easier to get the piping off for servicing too since it was a big U.

 

Thanks for the compliment and the advise on the discharge pipe plumbing. I have the new-style Procharger hat which appears very similar to the 1st gen EV hat, but does not have a divider, and appears to have an improved short-turn radius as compared to the EV design.

I thought about the 180-degree tube idea when I was putting this together. I haven't ruled that out yet... I guess it depends on how the plugs read once I start leaning on it.

I actually would have preferred a cam on a 114, but this was a brown-box special from EPW for the paltry sum of $59.00, so in it went.

The 993's are completely original less the valve springs. They're "Hecho En Mexico" castings that came off an old 290 HP 350 crate engine. Once I've seen what this combo is capable of I'd like to upgrade to some "race" heads... you know, like a ported set of 441's or something along those lines.

 

Ha ha i like how you think. My crappy 1.74 intake commercial small port 991's made around 525 whp and 616 whp with a 90 shot at 22 lbs boost to give you an idea where you might land for power numbers. If you have an O2 bung in the passenger header use it because the cylinders usually lean out the worst on the far side of the hat. If you leave the piping alone, it might not hurt to jet the pass rear barrel a few sizes up since you might not be able to read much differences in plugs when your close to right. Id hate to see you poof a cylinder over something so dumb and ruin the fun!

Your ring gap is perfect to beat the hell out of it too! What did you torque the heads to? They have to be at least 80 and preferably 85 ft lbs of the gaskets wont live. I torqued the grenade to 85 last night and forgot how terrifying things feel to go that high but those studs had been there before so i forged onward with no problems. I swear you can feel things settle in and finally gain some serious clamping in the last 5 lbs torque. It really is that picky on stock type composite gaskets.

 

trbo355, I have been following your grenade build since you started posting about it. It is amazing to see what can be done with the old reliable GM iron and a little new school tech thrown in. I have always MADE horsepower from my old junk. My dad is an old school drag racer and auto tech, so naturally I have got the speed bug. He used to race a 66 nova with a l79 327. (He bought it new) He swapped the cam to a 30/30 solid lift corvette cam, did some trick carb work, a little head work, added a clutch out of a truck, and put in 488 gears. He raced back when they ran heads up classes. He ran A super stock and had to run against 427 Vette's, 426 Hemi's, 428 Cobra Jets, etc. He has got plenty of trophy's to prove that he put down the big engine beasts. The little nova running 9' Goodyear slicks would pull the front tires off the line and hold it through 2nd gear. He was dropping the clutch on the starting line at 8,500 rpm! Talk about a little screamer. He normally ran 1/8 mile, but he ran 1/4 one time and ran low 10's at 128. Pete, keep up the good work buddy! The more you run these little Nova's, the more they like it!

 

Trbo355, I read where you torqued about everything on your motor to 85ft. What was the bearing clearance on your motor? Did you ever plastigauge it?
Pete, when are we going to get some videos of this beast on a rampage?

 

Already posted in the build but wanted to say it again - congrats on getting some miles on it. I'm sure it brought a smile to your face ;-)

 

Yep 85 on heads and main bolts. The 2 bolt block was cap walking a bit at the stock 75 lbs and stock fasteners will do 85 no problem. Its all about bringing a fastener to the yield point without ACTUALLY stretching the bolt permanently. Thats when the fastener is truly clamping and what it takes to make head gaskets live. Never really checked bearing clearances accurately but plastigage said it had .003 main clearance and it needed it.

 

I actually took it out late Sunday night with a camera in the car for some footage of irresponsible tire thrashing on some quiet back streets, but I can't get the video to load to my computer without being all choppy. Once I get it figured out I'll post it up.

 

I appreciate the tuning advice... the staggered jetting is a great idea! No wide-band yet, another item on the "to-do" list. I don't plan on really torturing it until I get a wide-band in the car. I'm pretty confident in plug reading alone at low boost levels, but I consider a wide-band a "must have" for safety once the boost gets turned up.

85/85 on the heads & mains. It does get a little spooky torquing GM fasteners that high, but, like you've said before, once you get a feel for it you can tell if the fastener is pre-loading or yielding.

 

I canrt wait to see how your car runs. You have the perfect recipe of junk to make it a success story! Just dont waste the motor before its tuned. LOL

 

I have a theory on carb hat design. Your first thought would be a smooth radiused hat to turn the air the smoothest but think about how the air wants to follow the outside radius and freak out the carb due to uneven air. Now look at a shitty Spectre carb hat that wasnt even designed for boost. Square as hell on the back wall and if i can picture the theoretical airflow, wouldnt the air more or less bounce off the back wall and tumble more evenly thru the airhorn?

I could be way off base but those spectre hats sure do run good and jet easy. Made over 1000 hp so far using one on several different cars so it cant be too wrong! What do you guys think of my theory? One other thing i recently tried in the quest for nice cruise mixtures and perfect WOT tuning is make some bowl vent extensions out of 1/4 tubing that i bent in a 90 to feed right down the gullet of the spectre hat. Read about it and decided to give it a go and boy does it work!

My turbo Cadillac project has a junky mighty demon blowthru carb that even with NO rear jets would hit 14 to 1 A/F and two extensions immediately dropped it to 10 to 1 A/F and got all my secondary jetting back in a usable range. That slight help to pressurize the bowls works wonders.

 

It sounds like you have a pretty good theory on the Spectre hats. Air will always follow the circumference of whatever it is being forced through. I have not had the opportunity to look at a lot of carb hats so I really don't know what all is out there. But it looks to me like one that had something in it to spiral the air would give a more even boost signal. I imagine it working like the intake ports on a set of Vortec 350 heads.

 

It would be extremely interesting if somebody made some clear composite copies of the commonly available bonnets and then flow tested them using smoke or vapor so you could see what the air was doing.

I plan on trying some vent tube extensions just for the sake of experimentation. I wanted to start with the Hangar 18 modifications just to see how the carb worked in a very basic configuration and then work my way up from there.

 

Pete, I have read somewhere very reliable , (can't SAY where), that vent tube extensions can make a significant different in tubing ability. A friend, making over 1000 hp, with a blowthough setup, was tuning for days and days, running too rich, added vent tube extensions going up through the hat, into the intake tube, and it made a huge difference, got his AFRs right in line, pretty much across the board. I would say it's definitely worth experimenting with.
I know it's definitely on the list of mods I plan for mine....

 

Its crazy how well the vent extensions work. All it can possibly be doing is introducing a VERY small extra amount of boost pressure into the bowls. Since they are in the highest flowing velocity of the charge pipe it must bias the bowls that extra little bit needed to get the boosters flowing again. Most carbs simply quit fueling at high boost and the extensions fire the boosters right back up!

 

any pics on these carb mods fellas?nice combo am planning on doing a turbo setup to on my monaro.doing alot of research from you wise bunch.love this nova project too im subscribbed

 

Not sure where to find pics. The true blowthru carbs like CSU use an annular booster for improved signal strength but the down fall is the primary jetting at cruise is damn near a moving target and they get richer as the rpm goes up. Its impossible to jet them since the sensitive boosters do too good a job at light throttle. If you can avoid the annular units and make it work, you win from every aspect. Its a tricky game thats for sure.

Another rule of thumb, a 650 cfm DP non blowthru carb will convert over easier than a 750 DP due to venturi size being the key. The 650 fuels and responds a lot better so if your building a mild combo, stick with a 650.

 

http://www.hangar18fabrication.com/blowthru.html