Vast Engine Problems
Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,841
Likes: 0
From: Inver Grove Minnesota
Vast Engine Problems
Ok, I started out with a fairly new lower end. About 15,000 miles on it. I striped it down to the block with pisions still in. Then I added the holley systemax 2 kit.
http://store.summitracing.com/partde...5&autoview=sku
It contains:
68cc aluminum heads with 68cc exhaust and 184 cc intake runners
Street dominator dual plane intake
Lunati cam with 235°/240° duration at .050, .490/.490 in. lift, and 112° lobe
Also pushrods and lifters.
I'm using lunati aluminum 1.5 roller rockers:
http://store.summitracing.com/partde...5&autoview=sku
It is all toped off by a Holley 750 dual inlet carb. Currently with 70 jets in it.
I seem to have an issue with it at low rpm's and whenever I hit the throttle hard. If I am at a stand still and I am not very careful on the throttle it will hesitate and die. And if I nail it down it will backfire and die. But if I'm moving along usually above 2000 rpms and I hit it I will get a backfire. Then I let off in fear.
I have tried disconnecting all of the vac lines and pluging them but it doesn't help. I'm running a newer accel HEI a curve kit. The initial timing is 12. I am at 36 by about 2500-2600 rpms. I use the vac advance but this still doesn't seem to help.
My build is summed up here:
http://24.118.233.41/jebu.html
Thanks in advance, Justin
http://store.summitracing.com/partde...5&autoview=sku
It contains:
68cc aluminum heads with 68cc exhaust and 184 cc intake runners
Street dominator dual plane intake
Lunati cam with 235°/240° duration at .050, .490/.490 in. lift, and 112° lobe
Also pushrods and lifters.
I'm using lunati aluminum 1.5 roller rockers:
http://store.summitracing.com/partde...5&autoview=sku
It is all toped off by a Holley 750 dual inlet carb. Currently with 70 jets in it.
I seem to have an issue with it at low rpm's and whenever I hit the throttle hard. If I am at a stand still and I am not very careful on the throttle it will hesitate and die. And if I nail it down it will backfire and die. But if I'm moving along usually above 2000 rpms and I hit it I will get a backfire. Then I let off in fear.
I have tried disconnecting all of the vac lines and pluging them but it doesn't help. I'm running a newer accel HEI a curve kit. The initial timing is 12. I am at 36 by about 2500-2600 rpms. I use the vac advance but this still doesn't seem to help.
My build is summed up here:
http://24.118.233.41/jebu.html
Thanks in advance, Justin
Race Director
Joined: Mar 2001
Posts: 11,322
Likes: 1
From: Living in the Hartland
Sounds like a carb tuning issue, make sure gas comes out the squirter as soon as you pull the throttle
BTW you do not have a DP carb, they have mech secondaries and an acc pump for both mains and sec's thus 'double pumper' name; looks like you have a 4160 with vac sec since there is no meter block just a metering plate in the sec side
BTW you do not have a DP carb, they have mech secondaries and an acc pump for both mains and sec's thus 'double pumper' name; looks like you have a 4160 with vac sec since there is no meter block just a metering plate in the sec side
Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
hummm I wonder what color accelerator pump cam opens the accelerator pump quicker, and these big 50cc diaphragms, and all
of these bigger nozzles, and these power valve sizes, maybe a
phone call to holley tech line would help me. A $20 book on holley
carbs.
of these bigger nozzles, and these power valve sizes, maybe a
phone call to holley tech line would help me. A $20 book on holley
carbs.
Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,841
Likes: 0
From: Inver Grove Minnesota
BTW you do not have a DP carb
make sure gas comes out the squirter as soon as you pull the throttle
ummm I wonder what color accelerator pump cam
Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,841
Likes: 0
From: Inver Grove Minnesota
Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
Holley tech line phone # 270-781-9741 8:00 to 5:00 CST. monday-
friday. I heard thru the grapevine that if someone calls holley
tech for information and you ask a question they don't like, they
have GODZILLA chained up in there warehouse they go get him
and he bites the callers head off thru the phone.
friday. I heard thru the grapevine that if someone calls holley
tech for information and you ask a question they don't like, they
have GODZILLA chained up in there warehouse they go get him
and he bites the callers head off thru the phone.
Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,841
Likes: 0
From: Inver Grove Minnesota
Ha, I got some new cams. I put on the one that gave me the most squirt. It still doesn't seem to run right. I might have to give them a call. Maybe I have a faulty carb.
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Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Suggest that Lunati might be too much camshaft ... can't see piston pics too well ... nothing else to go by in your "buildup" expose ... pistons seems like 4vr flattops? ... looks like 4bolt mains so guessing 30over L82 which had 4vr flattops ... even so, unlikely CR over 9.5:1 w/ 68cc ALUM heads (probably closer to 9.4:1). So, maybe too much camshaft? ... 235*/240* ... and maybe too much carb.
Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,841
Likes: 0
From: Inver Grove Minnesota
Why would my CR be 9.5 it should be around 10:1 i thought. It hasn't been machined. It was a GM crate engine. So it shouldn't be 30 over I don't think. Gee, I sure hope they are not bent. But I m getting pretty pissed off over here from the lack of progress.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Originally Posted by JustinD
Why would my CR be 9.5 it should be around 10:1 i thought. It hasn't been machined. It was a GM crate engine. So it shouldn't be 30 over I don't think. Gee, I sure hope they are not bent. But I m getting pretty pissed off over here from the lack of progress.
BTW ... over bore will raise CR ... without it ... it's less.
And is it flattop or dished?
BTW ... it's after midnite for half the nation ... and bristol qualifying is on
Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,841
Likes: 0
From: Inver Grove Minnesota
No part number all I know is it was installed in 83. No no, I'm not pissed at you guys. I'm pissed at myself. I've been screwing with this thing for months. BTW They are flat tops.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
I agree that it SHOULD be 10:1 (or better) to work with what you've bought ... but I doubt it's more than 9.4:1.
Run the numbers yourself. Piston dome volume probably about MINUS 6.1cc, pistons probably 0.022" down in hole (deck height) gasket probably 0.038" thick. STANDARD? bore = 4.000", stroke = 3.48"
http://www.campbellenterprises.com/R...o%20calculator
Run the numbers yourself. Piston dome volume probably about MINUS 6.1cc, pistons probably 0.022" down in hole (deck height) gasket probably 0.038" thick. STANDARD? bore = 4.000", stroke = 3.48"
http://www.campbellenterprises.com/R...o%20calculator
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Originally Posted by JustinD
Ok, I see what your saying. So I'm screwed right?
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Originally Posted by JustinD
With a smaller cam I'm gonna be making crap for power. I could pull my motor and mill the block put in new pistions and what not.
You sure can deck block/change pistons ... that'll get compression up ... just a matter of time & $. Your call.
Safety Car
Joined: Jul 2002
Posts: 3,770
Likes: 3
From: St Louis MO
You don't need new cam, you just need some carb tuning. Make sure the screw/spring on the accelerator pump arm is adjusted so that you get a squirt THE INSTANT the throttle is moved. I can't stress that enough.
Brett
Brett