HEI upgrade options - street car 350

fstarocka

Member
Feb 1, 2013
75
Seattle
Hi all.. i got a 77 with a vortec 350 9:1 qjet roller GM hotcam, 16gb of ram, 3k stall, headers, intake, L31 heads - etc etc - drives gr8 but seems to float when I mash it - im planning a 383 blower build later on but wondering if the MSD 6A would help me along in the spark division - wanna do it on the cheap.. and what else do i need if i get a control box? the MSD coil too? or is the HEI in cap one ok - or can I just upgrade the HEI module? This is a street toy -

sorry for the questions but about the last thing to upgrade on my ride is the ignition
 

larrylarry

Veteran Member
Dec 22, 2011
1,615
San Antonio Tx
I don’t think a MSD 6A would be much help on your present motor, on a blower motor yes it would help. I have 3 different kinds of HEI coils, hi performance to stock. I can’t tell the difference between them. Ign. module, if it’s working just leave it alone, after a lot of research I’ve done on modules you won’t see any gain in HP. Your float or hesitation problem is a carburetor problem I bet! I’m not well versed on Qjets. You won’t need anything else except for some better spark plug wires if you get a new spark box, they come with everything needed. If you do get a spark box use a resettable 3 amp fuse on the 12volt power wire that way you won’t burn it up like I did.
 

Zspoiler

Veteran Member
May 6, 2012
4,365
Federal Way, Washington
I have a 1979 Z-28 with a supercharged 377 cubic inc small block with all the "toys". I a DUI ignition coil and a Crane HI-6 TR ignition box .with MSD 8MM ignition wires .All which are not cheap. You can check on an MSD type set up as well. And or check the swap meets and such.But that mean it works. I took my time to save my money to get mine . Just to
 

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fstarocka

Member
Feb 1, 2013
75
Seattle
reason im asking is because ive read the hEI kinda falls off around 4-4.5k - thats what ive "read" -not experienced.. the 6a units are found cheap so was wondering - im trying to eliminate possible issues one at a time.

Can someone explain what valve float feels like? When i mash it from say 10-15mph.. it takes off but soon after it kinda starts floating, like the trans jumped into neutral (im talking pedal to the floor / WOT) with a 3k stall.. the carb seems to run well - i get 23mpg highway and it has some nice power but the top end issue is odd..

when i put in the hotcam i matched a set of single street springs, i didnt want to go dual springs cos the hotcam isnt THAT crazy on the ramps etc - or am i wrong? i used the comp tool and my micrometer to cut down the guide bosses almost equal..

Very informative articel here:

https://www.chevelles.com/forums/10-1999/2995-msd-vs-stock-hei-2.html
 
Last edited:

larrylarry

Veteran Member
Dec 22, 2011
1,615
San Antonio Tx
Valve float is caused by weak/worn out valve springs. Don’t get fixated like I do sometimes by thinking it’s valve float when it’s really something else. Your transmission may be shifting slowly. Check the transmission module, it has a vacuum line going to it, see if it’s leaking. Put a shift kit in it. I did that to my TH350 an it really woke it up! Readjust the rocker arms but read up on how to do it correctly first. Recheck your timing. 80% of the time it’s something simple.
HEI’s do kind of poop out above 5 grand but how much do you push it to 5 grand? I hardly ever get up to 5500 rpm’s but I don’t drag race either.
 

450bench

Veteran Member
Feb 25, 2002
3,716
memphis, tn-shelby
I'm running a bone stock GM Delco Remy HEI in my big block car. I changed one stock spring to a lighter one. Car revs all day to 6500. Tough to beat the old stock GM hei.

I've got the cheap eBay Chinese $50 hei on the shelf as well. Never had an issue with them either.
 

biker

Veteran Member
Gold Member
Dec 7, 2014
5,304
Canada
HEI works so well if it isn't worn out. I have a DUI unit, second one in 25 years. Easy 7000 rpm, great customer service when u need to modify or recurve. Expensive but worth it. A good stock one curved properly with a hot coil works well too.

Are you starving for air or fuel at high RPM? When I upgraded my engine, I couldn't rev above 5000 at wide open with the stock short air filter.
 

1980RS

Veteran Member
Jun 17, 2006
6,559
MN
Best thing ever made for an HEI is a MSD 6AL, just make sure you put a low resistance button under the coil or it will burn through the rotor. Mine did. Make sure you get a good coil as it will help a lot. I can spin my HEI to 7K but my distributor now needs to be replaced as it has too much shaft side clearance.
 




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