Blow through problems

[Supervette]

This is my first blow through system. I have a procharger D1sc with a 12 rib setup running 12 lbs of boost. When your crusing around town it feels like its surging. Or like a bad miss that never goes away, but when i get on the throttle it smooths out??? I have 15 degrees initial, and about 33 total. I know the timing is right on par. My compression is about 8.25 to 1. my jets could possibly be to big 80s and 90s. It ran find on the dyno but they had an MSD digital 7 and i only have the 6 could that be another reason they could go in and program the curve and i can't. Can they also lean the system out with that digital 7. Cuz i think im running way to rich right now. Any feedback would be awesome.

[camcojb]

This is my first blow through system. I have a procharger D1sc with a 12 rib setup running 12 lbs of boost. When your crusing around town it feels like its surging. Or like a bad miss that never goes away, but when i get on the throttle it smooths out??? I have 15 degrees initial, and about 33 total. I know the timing is right on par. My compression is about 8.25 to 1. my jets could possibly be to big 80s and 90s. It ran find on the dyno but they had an MSD digital 7 and i only have the 6 could that be another reason they could go in and program the curve and i can't. Can they also lean the system out with that digital 7. Cuz i think im running way to rich right now. Any feedback would be awesome.

who did the carb prep?

Jody

[Supervette]

a buddy of mine did. I just went in and knocked the primaires down to 77s

[camcojb]

a buddy of mine did. I just went in and knocked the primaires down to 77s

any idea what mods he did? No regular (even talented) car guy that I know can do all the mods needed to get the carb to run right with that amount of boost. In addition to jetting, milling the choke housing, and solid floats you need the metering blocks completely re-worked, probable booster mods or swap, bleeds need work, etc. You really need a good shop who does the blowthrough carbs to do it.

What you're describing sounds just like what mine was like when I did the mods myself as per Procharger. I could cruise great but no wot, or great power but the cruise was all goofed up.

Jody

[Supervette]

the mods are as follows. Ported power valve restriction orifice. solid nitrophyl floats, it has epoxy in certain areas to stop boost leakage, Nothing has been done to the air bleeds though.

I just went out and gave her hell and the low end to mid range feels great but then it starts to feel like its hesitating and falling flat up top. Like it wants to go but something is stopping it

[Supervette]

choke tower was sawed off as well. But im starting to wonder if efi is really the way to go or not. ive also been hearing these holley 750 double pumpers can't handle that much boost. I wish fuel injection wasn't so expensive.

No one really knows blow through carbs around here in Mn that I know of except for the guy that put mine together. I really dont have anywhere else to go

[Supervette]

Cool website by the way!

[camcojb]

choke tower was sawed off as well. But im starting to wonder if efi is really the way to go or not. ive also been hearing these holley 750 double pumpers can't handle that much boost. I wish fuel injection wasn't so expensive.

No one really knows blow through carbs around here in Mn that I know of except for the guy that put mine together. I really dont have anywhere else to go

we had a 750 prepped by http://www.sd-concepts.com/ on my friends 406 at 14-15 psi and he made over 700 rwhp on pump gas, no intercooler. He went to EFI for mileage only, the carb ran flawless everywhere.

Jody

[69Bbird]

CSU is a good place to mod your carb. I had the same problems when I was running a carb with my procharger. I did all the mods myself and could never get it to run right. I ended up going to efi best thing I could have done. My car would lean out bad at wot with the carb. It would be wise to get a wideband afr gauge or you might pay the price.

[shmoov69]

any idea what mods he did? No regular (even talented) car guy that I know can do all the mods needed to get the carb to run right with that amount of boost. Jody
Meaning?

I do agree however, it would be best to send it off to CSU or somebody that does carb mods for blowthru.

[Turbo Hen]

You need to get yourself a wideband 02 system........that takes the GUESSwork out.

Surging while a VERY light cruise is probably you idle circuit....you'll need to play with your adjustment screws.

-Carm

[Supervette]

Let me pick your guys brain one more time. What if the carb was fine since it did run good on the dyno and did pull 700hp. Could i have blown head gaskets. Blown but not leaking coolant into the cylinder. These heads were suppose to be oringed out for 30lbs, but what if?

[camcojb]

Let me pick your guys brain one more time. What if the carb was fine since it did run good on the dyno and did pull 700hp. Could i have blown head gaskets. Blown but not leaking coolant into the cylinder. These heads were suppose to be oringed out for 30lbs, but what if?

doubtful. An engine dyno runs it at idle and then under load through the rpm range. It would not see a light cruise condition on a dyno. I'm still guessing it's lean, and highly recommend a pro doing the carb mods.

Jody

[Adam's 55 Chevy]

CSU are building a carb for me which will run up to 24lbs boost but most likely stay at around 16lbs. I would say that even dealing via email their attention to detail and customer needs is second to none. A properly built carb is cheap insurance over a home built one leaning out and damaging your engine.

[Supervette]

So I leaned it out quite a bit and it seems a lot more responsive i brought the primaires down from 80s to 77s and the secondaries from 90s to 85s. Im guessing though since i was so rich that i might of fouled out a plug. I think im going to replace them all and get a wide band and putz around a little bit before i make any decisions. While im playing around with that Im gonna get a custom hood down so the blower will clear. I found a sweet 5 inch cowl for it!


wide band http://www.fuelairspark.com/WhatsNew/

anyone have experience with one of these. Im almost wanna go with a whole fast setup next year if i cant tune the carb. I could start with this.

[Supervette]

http://www.fuelairspark.com/WhatsNew/Files/FASTMotorcycleAir-FuelMeter.jpg
i meant this link.

[Turbo Hen]

With a wideband, you'll be able to get the carb dialed in just like the other THOUSANDS of people out there! Dont give up, it aint that hard trust me.

The FAST system is nice....how about looking into something that will datalog....Innovative or AEM.

-Carm

[shmoov69]

PM me if you are going to go with the FAST stuff. I have a good friend there that may help you out some.

[camcojb]

With a wideband, you'll be able to get the carb dialed in just like the other THOUSANDS of people out there! Dont give up, it aint that hard trust me.



-Carm

trust me, he ain't gonna get there with just jet changes. And I know few people who can (or should) do their own metering block mods, bleed changes, and booster swaps.

Jody

[Turbo Hen]

Well you're right. I think mods to a carb should be done by a professional....but what about when that "professional" doesnt come through...then its in your own hands, and thats where i am.

AFTER i took it upon myself to modify the metering blocks CORRECTLY, did mostly jet changes to get where i am...and i drive my car 4/5 nights a week.

-Carm

[camcojb]

Well you're right. I think mods to a carb should be done by a professional....but what about when that "professional" doesnt come through...then its in your own hands, and thats where i am.

AFTER i took it upon myself to modify the metering blocks CORRECTLY, did mostly jet changes to get where i am...and i drive my car 4/5 nights a week.

-Carm

the reason I mentioned it was because Procharger tells everyone that a switch to solid floats, milling the choke housing, and jet changes will be all that's needed. I've been there, done that and it simply wasn't true for me or anyone I've done or participated in, which is several.

A guy is better off spending $375 for someone like SDCE to fully mod your carb. I've had him do two for me in non-efi builds and both were spot-on right out of the box. Had perfect manners everywhere, actually ran as smooth as efi in my opinion. Just didn't get the mileage of a good efi system.

This was no slam on you, you obviously have a handle on it. But most simply get frustrated trying to make their setup run right following ATI's advice, and there's almost always a lot more modding required. Making the decision in advance to get the carb correctly modded up front saves a lot of frustration and is well-worth the money.

Jody

[Adam's 55 Chevy]

CSU would not finish my carb until I had furnished them with all the cam specs of the engine. They could have given me anything but this shows the level of preperation a carb needs to have for a blow thru application.

[Supervette]

I went to a car show this weekend and met up some other guys doing similair procharger set ups. They told me to ditch that ignition with the springs and weights, and go with a programmable digital 7 with boost retard curve. They said this would clean up the launch of the car a lot. The extreme velocity carb hat with dropping the secondaries down 5 jet sizes and giving the idle circuit more fuel seemed to help out a lot. Surging is almost gone and little blurps on throttle are much more crisp.

First things first is a innovate wideband system. then digital 7. Hopefully this gets me to where i need to be. Other wise I might have to look into the FAST system more seriously. Can a fast system be used with a digital 7. The good news is I have an extra labtop sitting around the house waiting for software! I was on their site and the program looks very extensive. Whats the learning curve on it?

[Turbo Hen]

I use the digital 7.....its VERY easy to use & EXTREMELY user friendly.

if you goto MSD's website, download the "ProData" software & start playing with it....you can know it inside out before you even buy the Digital 7.

-Carm

[bigdaddyvu]

I have a turbo charged camaro with a blow through holley 750 dbl pumper. I have or had similar problems with my setup. when you get a holley style carb or have one modified make sure it has neo fill floats or they will collapse under pressure, remove and mill choke, anti blow power valve they like to rip apart under uneven pressure, modified air bleeds, vacuum fittings on all extrenal throttle shafts bushing and having a vaccum line attacted to the plenum ( holley style carbs always leak power at the throttle shafts) special metering block gaskets (rubberize coated style) seal off all unused vacuum fitting with epoxy or solder don't use rubber cabs or vacuum lines with a bolt stuck in it. reduce your primaries and inrichen your secondaries. and mod your metering blocks. or you can buy a carb already setup for blow throughs for atleast 800 bucks. and another thing check the nuts and bolt on the carb they like to loosen up with the hot and cold ( i blew a gasket on my float bowl cuz one bolt was loose)

I also use a aeromotive fuel pressure regulator. with a progressive line signal. run your pressure at least 4 psi and should always be atleast 4psi above boost psi or the boost will push the fuel back into the tank (4 psi @ idle no boost psi to 18 psi of fuel 14 psi of boost)

I use a mallory hyfire vi 685 advance box. it features boost psi retard. beings everyone knows you can't run a advancing dizzy on a boosted engine or detenation occurs (hestitates or popping just before boost). i modified a hei dizzy with a lockout advance and have it set at 24 degrees i use the hyfire feature by using a stock gm map sensor and hooking it up to the plenum now i can retard the timing. basic rule for boosted is for every pound of psi retard the timing a degree or two. and since i have the dizzy solid advance i also use other feature the under 500 rpm to retard timing to get the engine started easier.

if you don't believe me read the book Maxinum Boost by corky bell

i have a 86 z28 junkyard 350 s-10 headers flipped, t-70 turbo, ford power strok intercooler, holley 750 blow through, spohn 8 point roll cage 6 point legal, sub fram, and other misc stuff. 4000 dallors get me going 10.69 @124 mph in a qtr

[Supervette]

Nice! I believe you.. I gotta get rid of this ignition system this week. Msd digital 7 for sure now. Also the innovate wideband is it okay to run one band and switch it to the other side for tuning.. I can't see spending an extra $400 for another sensor.

[slocobra]

try www.theturboforums.com and check in teh carb+boost forum. there you will find everything you ever wanted to know and alot of guys that will help you even though you have a blower

[Supervette]

Okay so i decided to stick with the blow through setup. I purchased the innovative wideband today and sent in my specs for the csu carb. Its six weeks out though:eek:. Im gonna finish installing the rack and pinion setup and then install this wideband and let the car sit for a bit until i get the carb done. He says that I should also do the boost retard curve 38 to 40 degrees and then slowly drop degrees of timing as boost comes in.

[whytry]

Kevin told me the same thing, Lock it out @ 40 and retard with BTM, but I am finding out the BTM is not as accurate as the dial indicates....

[WELTERRACER]

Im running a procharger prepped holley 750. 75/85 jets.. it runs very good, probobly not perfect by some of your standards but very good.. (i gave someone on the site a ride in it and i think he was impressed)

I am running 36degrees total timing and no cintrifical advance..

[Supervette]

Well Im back with an update. i had a carb worked over by Kevin at CSu and I must say im very happy with it so far. I brought it down to the dyno and it idles nice and has a wonderful wide open throttle with some minor jet changes. Now that Im out on the street. Im noticing I have a lean spot on partial throttle. When I bring the rpms up slowly get ready to crack on it at 3200 to 3500 and my wideband starts to show a lean condition. i think this attributed to my pump cam. I have the green ones in there now at position one. Im not sure which way to go from here. I had it sneeze once on me. Now I just cruise around watching the wideband so I dont make it sneeze. Anyone have any ideas on what type of pump cam to put in this. Maybe I need a bigger shooter possibly. Any ideas would be appreciated.

Almost there Mike

[Supervette]

I changed the pump cams to the brown ones from the green ones and she launched perfect. wheels and procharger spinning. A shout out to kevin and CSU for the help with the e85 conversion. Time to go racing!

[Supervette]

oh yeah and Hi tech motorsports for there dyno time and knowledge. They have some of the best facilities I've seen.:6gears: great people to work with.

[NEokcTERROR]

I am glad you got this all worked out. I read this post thoroughly and kept thinking I was going to have to post. "STOP DROPPING JET SIZES that's not where the problem is." Kevin did mine and so far 3 years later so good.

I thought at one time I had a carb problem when I tried lowering the boost. I took the carb apart and stood in awe of the modifications. I have over 20 yrs experience with Holley carbs and I have to say Kevin's attention to detail and phone support are second to none. I would say the phone support alone is worth the expenditure on the carb. Got any RWHP numbers with new carb yet?