350 6-71 blower motor rebuild, I could use some advice. - Chevelle Tech

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post #1 of 22 (permalink) Old Apr 22nd, 10, 6:31 PM Thread Starter
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Dennis
 
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350 6-71 blower motor rebuild, I could use some advice.

Trying to help my father-in-law out on his engine.

His 350 - kb pistons (hypers), summit cam (224/234@.050"), stock 882 heads with z28 springs, 6-71 blower (6% overdriven) and 2 out of the box eddy carbs 750cfm and just to add his old school ways of just a plain jane points distributor- just didn't make it down the track, he broke 4 pistons and cracked the block. He got 2 passes out of this combo before it really sounded like crap, of course it never sounded good going down the track first time spitted and popping. e.t. 13.5 102mph



His new combo, fresh block, same crank and rods with new pistons speed pro 21.10 dish pistons .030 over, howard solid FT cam 262/274 @.050", dart aluminum pro 1 heads (180cc runners 72cc chamber complete heads) and maybe re-adjust blower speed.

here are his parts
http://www.summitracing.com/parts/HRS-112101/
http://www.summitracing.com/parts/TRW-WL2441F30/
http://www.speedwaymotors.com/Dart-A...ign=GoogleBase

he already bought the heads, pistons, cam and lifters.
this is in the vw bug with a 4 speed behind it. he spent over 25,000 to build this car
and he really wants some help this time out on the engine.

I figure his head and piston combo should put him about 7.9 to 1 he is using some mls head gaskets that are .040" thick. and about .020 down the hole (guess).

what should he be spinning the blower at?
what about fuel?
spark? trying to get him away from that points dist.
what would his dynamic compression be?

any info I could pass on to him would help, maybe I can print and show him as well so he doesn't think I'm out of my mind for trying to steer him in the right direction, I would have to edit this part, I tried to tell him first time, but he was the wiser one and I didn't know nothing "back in the day this is how we ran it" now that he has a pile of broken parts he told me he can't afford to do this every other week and asked me what I thought.

What about ring gap? bearing clearence? If he sees others recommending things to do he will be more apt to apply them. And it's just not coming from ME.

thanks for any help.

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post #2 of 22 (permalink) Old Apr 22nd, 10, 9:04 PM
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Re: 350 6-71 blower motor rebuild, I could use some advice.

Dennis,
BDS has a ton of good info on their web site http://www.blowerdriveservice.com/

Bill Koustenis
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post #3 of 22 (permalink) Old Apr 22nd, 10, 10:18 PM
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Re: 350 6-71 blower motor rebuild, I could use some advice.

go to www.bigalstoybox.com give Al a call, real nice guy, he can answer all questions

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post #4 of 22 (permalink) Old Apr 22nd, 10, 11:18 PM
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post #5 of 22 (permalink) Old Apr 23rd, 10, 12:12 AM
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Re: 350 6-71 blower motor rebuild, I could use some advice.

Quote:
Originally Posted by ddeennis View Post
Trying to help my father-in-law out on his engine.

His 350 - kb pistons (hypers), summit cam (224/234@.050"), stock 882 heads with z28 springs, 6-71 blower (6% overdriven) and 2 out of the box eddy carbs 750cfm and just to add his old school ways of just a plain jane points distributor- just didn't make it down the track, he broke 4 pistons and cracked the block. He got 2 passes out of this combo before it really sounded like crap, of course it never sounded good going down the track first time spitted and popping. e.t. 13.5 102mph



His new combo, fresh block, same crank and rods with new pistons speed pro 21.10 dish pistons .030 over, howard solid FT cam 262/274 @.050", dart aluminum pro 1 heads (180cc runners 72cc chamber complete heads) and maybe re-adjust blower speed.

here are his parts
http://www.summitracing.com/parts/HRS-112101/
http://www.summitracing.com/parts/TRW-WL2441F30/
http://www.speedwaymotors.com/Dart-A...ign=GoogleBase

he already bought the heads, pistons, cam and lifters.
this is in the vw bug with a 4 speed behind it. he spent over 25,000 to build this car
and he really wants some help this time out on the engine.

I figure his head and piston combo should put him about 7.9 to 1 he is using some mls head gaskets that are .040" thick. and about .020 down the hole (guess).

what should he be spinning the blower at?
what about fuel?
spark? trying to get him away from that points dist.
what would his dynamic compression be?

any info I could pass on to him would help, maybe I can print and show him as well so he doesn't think I'm out of my mind for trying to steer him in the right direction, I would have to edit this part, I tried to tell him first time, but he was the wiser one and I didn't know nothing "back in the day this is how we ran it" now that he has a pile of broken parts he told me he can't afford to do this every other week and asked me what I thought.

What about ring gap? bearing clearence? If he sees others recommending things to do he will be more apt to apply them. And it's just not coming from ME.

thanks for any help.
Ditch the eddy's and the dist. The eddy's could work but...they are difficult to set up for this app. Not that it can't be done, but not many people know how to. So he's better off going with a holley or demon type carb. The distributor is a no brainer...first, this is the year 2010. The technology has come a long way (and for a reason), second, you want spark reliability. You don't want to start misfiring a boosted (or nitrous) engine...it just isn't good, and it probably caused alot of the popping and fartin' it was doing before.

Fuel? Fuel is everything...he needs to decide what he wants to run (pump gas,race gas,alcohol). That can dictate everything else (boost level, timing,). If he goes with primium pump gas with almost 8:1 I wouldn't go any more than 10 psi boost. Race gas might sound good but even though you can boost higher because of the octane, you are still heating the charge more. You probably wouldn't effectivly spin the blower to get more than 17-18 psi before heating the charge to the point where the adiabatic efficientcy is in the toilet. In which case you need alcohol, or nitrous, or run a bigger blower...

Other than that...run a bigger ring gap. Go with the manufacturers recommendation. Err on the side of wide...things get hot rings get bigger-cylider holes don't.

Bearing clearences should be a little bigger. More important is using a good bearing that is designed more specifically for blower applications.

Just remind him that "back in the day" doesn't fly today. There are a lot of street cars 'today' that could wax the top performers of "back in the day"...Have fun with it!!
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post #6 of 22 (permalink) Old Apr 23rd, 10, 12:57 AM
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Mike
 
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Re: 350 6-71 blower motor rebuild, I could use some advice.

I can help. I was bitting my lip when I read the parts list of the first motor.. At 6% overdriven.. it did exactly what one would expect.. who knows what the timing was, and he had way too much boost on cast pistons. Those eddy carbs will work but need tweaking for a blower (you can't use their jetting out of the box), and those Z28 valve springs are way, way to weak on the seat to hold the boost and will hang the valves open resulting in an intake explosion.

He is already starting to make big mistakes with his new engine and needs serious guidance. His new combo should have bigger heads.. 180cc is a bit small for that blown SBC.. he should go with 195-200cc runners at the least for the 355ci. You can return them to Summit. Stop with that cam.. it is way way too big (unless this is a track only car) and you are trying to use it together with a small head.. doesn't make any sense.. he should go with a solid flat tappet with a 230-234 intake, 240-246 exhaust at .050 duration cam with 112-114 LSA. Use EDM lifters, please!, and break in carefully with the right oil. For that solid flat tappet, use 130-140lbs seat and not more than 360lbs open pressure. Be anal about these valve spring pressures.. a little too little, a little too much and you will be sorry one way or another with that blower motor. The springs on the heads he just bought cant even handle the lift of the cam he just bought. He is cutting way too many corners here that will cost him more money and misery in the end. A cheap 4340 forged Scat crank and H-beam rod would have been better. I wouldnt push more than 7lbs boost on the cast crank.

I dont know how tight his blower is but an average 6-71 at 6% overdrive on a 350ci engine will put you at 17.1lbs boost!! The engine was probably a higher compression all cast stocker and this suggests that advice is sorely needed before another gross blunder. He should start at 16% underdrive and not spin faster than 14% underdrive and not exceed 10lbs boost without more investment in the lower end. Actually I would advise he keep it to 8 lbs boots with 93 octane sunoco or the like

I have carb settings for those exact Eddy 750 carbs posted somewhere on this site that you should refer too as I used them on my blown 6-71 355ci.

Just make sure your static compression is ~8:1 or less.. I think you will be in the ball park with 72cc chambers and the 21cc dish pistons... that's about 7.9:1 compression.

Go for a Mallory pointless distributor (no vacuum advance) and proper ignition. Set initial timing at 18-20 degrees and do not exceed 32* total timing until you get a better handle on what you are doing and invest in an all forged lower end.

What fuel pump and fuel line size?? A mechanical will work fine here.

4 bolt main? using studs on the mains?

What oil pump?

You will want 1.75" primary tube headers.

If you PM me, I will guide you through this.

mike

1973 RS Z28: 401ci Dart Little M, Littlefield 8-71 supercharger @14lbs boost, Callies Magnum crankshaft, Lunati Pro-Mod rods, JE pistons, 7.8:1 compression, AFR 227 Comp heads, T&D 1.6 shaft rockers. Reed solid FT cam (240/250@.050, .523/.542 lift, 112 LSA), QFT 750 carbs, Tremec TKO-500, Lemons headers, Moser 12 bolt, 33 spline axles & 3.42 gears
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post #7 of 22 (permalink) Old Apr 23rd, 10, 3:57 AM
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Re: 350 6-71 blower motor rebuild, I could use some advice.

Good post.

Quote:
This post is a duplicate of a post that you have posted in the last five minutes.
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post #8 of 22 (permalink) Old Apr 23rd, 10, 7:30 AM
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Re: 350 6-71 blower motor rebuild, I could use some advice.

first thing he needs to do is get the blower 10-15% underdriven-cam is huge, prob way out of a useful RPM
not sure what hes trying to accomplish with this thing, lol
i would get it into a more boost friendly RPM, esp with the parts he has
ring gaps need to be opened up per manf. specs, timing your gonna want to start out low and work up, good ign, maybe even a boost retard-i have used the Edelbrocks with good
results, but you kind of have to know how they work to make them work, lol
if he likes old school, i have a Vertex mag, lol
get the balancer with the proper press fit to the crank-i hope its an aftermarket balancer
hard to change someones mind if their stuck on an idea, lol

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post #9 of 22 (permalink) Old Apr 23rd, 10, 7:39 AM
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Richard
 
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Re: 350 6-71 blower motor rebuild, I could use some advice.

Lots of good advise here. IMO, the Pistons ruined the engine the first time around. Get a Real Blower piston. 6AL ignition box, and real blower carbs.

462 forged internals, Dart iron 308cc, Crower cam (Small 545 lift.) solid flat tappet, Weiand team G, Hooker comps, 565 hp/tq. All in a tight bundle of American steel called a 69 C-10.
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post #10 of 22 (permalink) Old Apr 23rd, 10, 12:09 PM Thread Starter
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Dennis
 
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Re: 350 6-71 blower motor rebuild, I could use some advice.

Quote:
Originally Posted by Tokyo Torquer View Post
I can help. I was bitting my lip when I read the parts list of the first motor.. At 6% overdriven.. it did exactly what one would expect.. who knows what the timing was, and he had way too much boost on cast pistons. Those eddy carbs will work but need tweaking for a blower (you can't use their jetting out of the box), and those Z28 valve springs are way, way to weak on the seat to hold the boost and will hang the valves open resulting in an intake explosion.

He is already starting to make big mistakes with his new engine and needs serious guidance. His new combo should have bigger heads.. 180cc is a bit small for that blown SBC.. he should go with 195-200cc runners at the least for the 355ci. You can return them to Summit. Stop with that cam.. it is way way too big (unless this is a track only car) and you are trying to use it together with a small head.. doesn't make any sense.. he should go with a solid flat tappet with a 230-234 intake, 240-246 exhaust at .050 duration cam with 112-114 LSA. Use EDM lifters, please!, and break in carefully with the right oil. For that solid flat tappet, use 130-140lbs seat and not more than 360lbs open pressure. Be anal about these valve spring pressures.. a little too little, a little too much and you will be sorry one way or another with that blower motor. The springs on the heads he just bought cant even handle the lift of the cam he just bought. He is cutting way too many corners here that will cost him more money and misery in the end. A cheap 4340 forged Scat crank and H-beam rod would have been better. I wouldnt push more than 7lbs boost on the cast crank.

I dont know how tight his blower is but an average 6-71 at 6% overdrive on a 350ci engine will put you at 17.1lbs boost!! The engine was probably a higher compression all cast stocker and this suggests that advice is sorely needed before another gross blunder. He should start at 16% underdrive and not spin faster than 14% underdrive and not exceed 10lbs boost without more investment in the lower end. Actually I would advise he keep it to 8 lbs boots with 93 octane sunoco or the like

I have carb settings for those exact Eddy 750 carbs posted somewhere on this site that you should refer too as I used them on my blown 6-71 355ci.

Just make sure your static compression is ~8:1 or less.. I think you will be in the ball park with 72cc chambers and the 21cc dish pistons... that's about 7.9:1 compression.

Go for a Mallory pointless distributor (no vacuum advance) and proper ignition. Set initial timing at 18-20 degrees and do not exceed 32* total timing until you get a better handle on what you are doing and invest in an all forged lower end.

What fuel pump and fuel line size?? A mechanical will work fine here.

4 bolt main? using studs on the mains?

What oil pump?

You will want 1.75" primary tube headers.

If you PM me, I will guide you through this.

mike
His old block was a 4 bolt main studded block with forged crank and stock rods with arp bolts and kb hyper flat tops.

he will be reusing the crank, since it is double keyed and forged and rods. he bought those forged pistons posted above in the parts list.

He built his own headers, since this was a custom VW build, not sure on the size.

he uses a fuel cell and electric pump and i believe 3/8" fuel line

his new pistons should put him around 7.9 to 1

he has the pulleys to get 12% underdriven thats the ones that came with the blower new. after a few passes and engine plugs damaged he thought he need more boost to fix the problem, so he installed the 6% overdrive pulleys.

he now says he's not married to the % , he said he would buy new pulleys to make it right if needed.

Anything I can scrap up from anyones personel experience or even anyones combo that working good for them that would be close to what he is trying to do would help,

I told him holley's when he started this project, I have the tuning parts everywhere and I know how to tune them. He should already know that since i run a tunnel ram on the street that super smooth.

His response, I shouldn't have to tune, I spend that much on carbs they need to work out of the box, so I'm getting eddy's, I don't have to do nothing with them.

I told him a nice set of aluminum heads in the beginning about 200cc.

His reply, this is a blower motor you don't need fancy heads , you are pushing air thru them, if you need more air to go thru just crank up the blower speed more those other heads are just a waste of money.

i told him about nice dist. with msd box of some sort.

You don't need those, back in the day all we had was points, nothing has changed since. if they ran with points back then it will run with points today.

I came to a point I gave up and I stopped going to his house to help, He would not take any advice and now I see him struggling to try and get this VW down the track and my heart goes out to him, he has spent lots of money, but stuck in his old ways and this is a PURE RACE CAR built from ground up

So it seems he is kinda taking advice and I'm trying to get him as much info as I can.

He is kinda set on the HOWARDS cam, his heads are good for 520 lift and the cam is .488/.510 net after you subtract the lash off the GROSS lift.

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post #11 of 22 (permalink) Old Apr 23rd, 10, 12:38 PM
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Re: 350 6-71 blower motor rebuild, I could use some advice.

doesn't sound like he's taking ANY advice at all......if he can't accept that there's been HUGE advancement over the years then your wasting your time....nice try and good effort but sometimes you can't fix xxxxxx......no dis-respect intended

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post #12 of 22 (permalink) Old Apr 23rd, 10, 12:41 PM
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Re: 350 6-71 blower motor rebuild, I could use some advice.

"...and he really wants some help this time out on the engine."

From what you just posted it doesn't really sound like it. There's some really good info here from those that have successful blown combinations. He can't approach a blower engine like an N/A one, simple as that. Carbs will rarely work perfect out of the box. Ignition has to produce a top-notch spark at the correct timing. Cam are very specific in design. Plus, you can often get away with larger than normal runners, not the other way around. In addition to the websites and articles listed above, have him take a look at the "Street Supercharging" book a lot of us started out with and I still use as a reference.

Jim

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post #13 of 22 (permalink) Old Apr 23rd, 10, 6:51 PM
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Mike
 
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Re: 350 6-71 blower motor rebuild, I could use some advice.

re the heads comment.. blower motors allow a few minor mismatches but this is a bit much. bust on your guage measures the what is backed up in the intake. small port hads will see boost in the intake tall of which is not making it through the ports. this is plain leaving easy performance on the table. 180cc and 200cc heads cost the same, but the 180 cc heads come with puny valve springs I bet.

mike

1973 RS Z28: 401ci Dart Little M, Littlefield 8-71 supercharger @14lbs boost, Callies Magnum crankshaft, Lunati Pro-Mod rods, JE pistons, 7.8:1 compression, AFR 227 Comp heads, T&D 1.6 shaft rockers. Reed solid FT cam (240/250@.050, .523/.542 lift, 112 LSA), QFT 750 carbs, Tremec TKO-500, Lemons headers, Moser 12 bolt, 33 spline axles & 3.42 gears
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post #14 of 22 (permalink) Old Apr 23rd, 10, 7:18 PM
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Re: 350 6-71 blower motor rebuild, I could use some advice.

I read this thread when it was first posted, started to respond and then though to myself "why?". It takes a lot of effort and thought to post a detailed reply and 9 times out of 10 people don't want to listen. You have had several experienced guys suggest a better or correct way to build a blown engine. You can't just throw these things together without planning and thought or you end up with a bunch of broken parts (as you now know). That first engine was a granade with the pin pulled.

Don't take this wrong I am not bashing the OP (original poster). You need to have your father read this thread. There is a lot of knowledgable blower guys that would love to help out but, only if the advice is going to be followed.

One other suggestion, find one of the guys on this board you want to listen to and follow his advice to a T. Do not take a little advice from each guy and make your own recipe or you may be sorry (again).

I also suggest ditching the Eddy carbs, even when tuned they are not going to compare to a properly tuned Holley in a blower application.

Good luck.

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post #15 of 22 (permalink) Old Apr 23rd, 10, 8:08 PM
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Re: 350 6-71 blower motor rebuild, I could use some advice.

Sorry, but he followed his own advice the first time around and built an expensive grenade. Time to listen to what these guys are trying to tell him or another explosion is imminent.

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