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Overbuilt 383?

6K views 68 replies 26 participants last post by  pockets 
#1 ·
Wondering if I overbuilt my last motor. Was intended to be a street/strip car and now is entirely a street car. Its a 67 Chevelle with a 383/4 speed/3:55 rear gear. Was going to be a 4:10 rear gear, but changed it to a 3:55 when it became a street car. We are running 15 x 7 with 235 60's on the front and 15 x 8 with 255 60's on the rear.

The bottom end is good until about 500 horse. It has a cast Eagle crank with something like SIR rods I think with -12 dished hyper pistons in it. Compression came out around 10 to 1, maybe a slush under it at 9:9 to 1. It has 195 cranking compression. The cam is very mild...its a UDHarold design at 280/288 and 226/234 @ .050 with .536/.536 lift on a set of 1.52 roller rockers. The cam is installed at 109 ICL and is on a 112 lsa. Not sure why the builder chose that as the cam card called for 106 ICL. The heads is where I think its overbuilt...for the street...we had a set 200 Dart Conquest ported and flow very well for what they are....they flow at .500 270 and at .600 they flow 285. We used a second hand Edelbrock RPM intake with a Holley 3310 on it. Motor runs fine with the exception of a rocker getting loose from time to time. Our timing is at 18* initial with a 16* mechanical curve for a total all in of 34* around 2100. The can adds another 12* for a total of 48* at cruise.

The car has a 160 thermostat in it here in Florida and runs about 180 to 190 in the Florida summer heat. Fans come on to keep it in this this area, but then go off. Really pleased with the cooling.

I feel the cam would run better on a 108 lsa there is no doubt about that, but I also feel that we should of left the heads alone and run them unported and run a 2.05 valve for the street to keep up velocity. However, Eric Weingartner did the work on them thinking it would be a strip/strip motor. The motor is a little sluggish to me down low for a mild cam, but really seems to run really well at above 3000 to 6500. Seems to pull very nice up there. We want more bottom end with a shift point of around 5800 to 6000 to make it more like a strong street motor....but its all good in that it runs good for a cruiser.

Anyone want to add there opinions to the discussion?
 
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#2 ·
Take Eric's word for it on the heads. Not many better than him available.

sounds like the ignition is set up pretty good.

where does it feel sluggish? off the line? how does it run at WOT in the mid-range?

Have you tried giving it a little more advance? 2-3 degrees?

Have you tried giving it a little more pump shot? like going from a 28 to a 31. quick, easy and cheap. Pump adjusted correctly? no slop in the linkage at closed throttle.

Seems like that would be a pretty hard running combo.
 
#3 ·
Yeah, Tom...I really like Erics work. He has has done a lot of good work for me. He has done my heads on my track s10.

Yes, pleased with the ignition.

It feels a little sluggish off idle and off the line...with the 255's on the back it doesn't really just bust the tires loose....it just seems to go....but if you push the clutch in and bring it up to around 2200 to 2500 it will spin the tires. .

Runs very strong at WOT in the mid range...nothing to complain about.

I haven't done anything to the 3310. I just told a local racer who rebuilt the 3310 what the motor had and he jetted and tuned it according....we have not had it on a dyno yet or at the track...never checked the plugs. I do think it has a yellow spring in it.

It does run very well...just thought that a 383 with that small of a tire would break the tires loose off idle with easy.
 
#4 ·
I have a similar cam, 221/235 .544/.544 lift with 1.6 rockers. 108LSA. Brodix IK180 heads, Holley single plane that I’m going to switch back to my air gap. Four speed with 3.73s. 357 with 10:1 compression. Fun motor pulls great form down low easily to 6000
 
#5 ·
Justin, I have a 350 with a similar combo as yours. It runs great. I run the same cam in 350 as the 383. It is cut on a 108 lsa and installed at 104 ICL. Everything else is the same as yours....Brodix Iron Killer 180s and a RPM Air Gap with 10.3 compression....this motor ran 12:50's in my 67 Chevelle with a 4 speed and 4:10 gears.
 
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#7 · (Edited)
I’d spend some time at the track dialing in you ignition and carb before swapping cam. Seat of the pants is often inaccurate and shouldn’t by itself be the basis for expensive changes. If you live fairly close to s track there is no reason not to go. Since it’s a 4 speed, don’t necessarily judge your car by its 60ft, pay attention to the time between each incremental on the time slip and the mph at the 1/8th and 1/4 mile.

Steve R
 
#8 ·
I was a little confused by the cam talk there, but if I read that the cam is in "straight up", and Harold's cams "always" run better advance 4 or so. I'd rephase the cam to +4 or and feel the bottom come back in. 105-106 ICL. Heck even 104. This will increase the intake" ram" effect and "shrink" them heads a freckle.
 
#9 ·
Gene..Harolds cam card calls for the 112 lsa cam to be installed at a 106 ICL. Its installed at 109 ICL...only three degrees advance. Do, a 106 would be 6* of advance. I think, if Im right.
 
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#10 ·
Which 4 speed are you using? If its a Muncie with a 2.20 first gear, and coupled with a 3.55 gear it may feel a little lacking down low.
 
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#11 ·
I gave up years ago trying to tune drag motors for street use. Today I just use big cubes with stock heads and low compression but run high initial (22-26) with 10 to 14 mechanical in late like 2800.. Starts without issue, idles nice and smooth, power brakes work great.. I'm into suspensions now, making them handle well.. 9 out of 10 old cars out there have suspensions that cant handle the power trains they carry... Frankly on the street, the stock big cube motors feel much faster then the small drag motors I used to slave over, probably just my imagination but I enjoy this much more.. :thumbsup:
 
#21 ·
Jeff

Are you talking about big inch small blocks or big blocks?

What all kinds of suspension upgrades do you do?
 
#13 ·
Aaron, I agree with your thoughts that the heads are a mismatch for the combination. It’s causing you a loss of port velocity which translates in to a little laziness until you get the engine well up in the RPM range. I’d be looking for another set of heads first. (My opinion is they need more cubes, cam and compression.)

I’d be afraid to advance the cam which might make you a noticeable change on the bottom but is likely to take the heads out of their operating realm.
 
#18 ·
Couldn't agree more with this post.
Also Aaron, I've read many of your posts over the years, so this ain't your first rodeo. And I know you've heard, "build you engine around your gears".

You originally built this combination for a higher rpm application, but then decided to add 3:55 gears into the equation (BTW, one of my favorite street gears).
You could possibly gain something on the low end with a cam timing adjustment, as some have suggested, but it seems that would just be a band aide on a possible parts mis-match.

Back in 1982 when I was 19 I had a phenomenal street 396 in a 66 SS Chevelle, 4-spd with 3:31's. The low & mid-range torque was thru the roof, and great throttle response via a 750 DP. I was in my glory.
I decided that I was going to put some rectangular port heads on it because bigger is better, right? (I know you see where I'm going with this).
The local mechanic who had tuned my car told me I was stupid. Well, those big port heads ended up basically moving the power band into a higher rpm range - it was sluggish down low and would no longer boil the tires at the lower rpms.
I'll never forget that old mechanic telling that I now needed 4:10 gears.

Long story short - those oval port heads were back on within 2 weeks, because of my particular application.
Change the gears or the heads.

Good luck
 
#14 ·
I would try a couple more degrees of timing. If it has the yellow spring, try the brown one. My 355 ran quicker with the brown over the yellow.
 
#24 ·
George, how is your car coming?

I think it might like 2 to 4 more degrees of timing...I will play with it some.
 
#15 ·
All my SBC from 355 on up have gone quicker and faster with a 106° but if you are going to run a lot on the street the 112-114 cams idle better and are much more driveable. On a BBC it seems to be different as one does not need as much low end tq. so a wider LCA seems to broaden out the tq. curve and help out top end.
 
#17 ·
Aaron: my 383 has exactly the bottom end you're looking for....although many will say that 170/180cc heads don't belong on a 383 SBC. I completely disagree.

However, I strongly (and strenuously) recommend that you get your car to a dyno tuning session with someone who knows what he's doing. You need to dial in what you have first....and then think about making changes.

Your motor should still melt the tires at will down low.

Personally, I prefer a dyno tuning session over track runs to help tune an engine. You're taking driver technique and whether out of the equation. You can also accomplish in one session what would take weeks at the track.

Best of luck!
 
#34 ·
2-4* more initial should make a difference in off idle, as long as it likes it. It does in both my locked out 388 and also the hei/ vacuum advance equipped 454 wagon.
 
#36 ·
I'd try tuning what you have now before changing any parts. I'm running a 388 SBC with 220cc heads on the street with 3.73 gears and it will destroy the tires off idle. I do have a 700R4, so gearing is on my side off the line. My combo likes 36 degrees timing, I run 26 initial with 10 degrees of mechanical advance. Vac adds another 15 degrees or so for highway cruising. I'm running a 750 DP Holley. I've played with vacuum secondary carbs before and it just always runs better with mechanical secondaries.
My cam is a 242/248 .608/.614 solid roller with a 110 lobe separation.
 
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#42 ·
Chris, I appreciate the advice...very good advice I might add. Looks like I will be playing with some timing first and go from there. May need to replace the modified factory HEI I have with something like a MSD unit that has a tunable mechanical advance.
 
#39 ·
I would talk to the head porter and see what he says I bet a change in camshaft could make a nice difference. anyway seems like the build changed once the engine was done.
 
#45 ·
Jeff, I will consult with him. No, the cam and compression was selected first and had to band aide the heads to make out built work some. This combo would do better with more compression...Im at a 8.0 DCR right now. The cranking compression is at 195 psi. I could switch out the pistons and run flat tops and get it up to around 11 to 1 and then advance the cam to 106 ICL and have probably 205 psi cranking compression.
 
#40 ·
Aaron,

I had a similar 383 back in the day. 10.3:1 compression with AFR 220 Race Ready heads that only flowed ~260 cfm. Big slow port that didn't move any air by today's standards. I ran a quite a bit bigger solid roller cam.

You need as much initial timing as you can get away with and it is probably going to want 36-38 degrees total. I ran mine locked out at 36 degrees with an MSD start retard.

That old combo would light off 275/60R15 street tires at anything under 50 MPH even with a converter that was too tight.

I put about 300 passes on that old combo. About 200 of them I was testing and learning.

For what you are doing something around a 200-210 cc head would probably be optimal, but what you have can be made to work with some tweaks. You might just have to dig for it a little.

PS - 2 degrees of timing on my current 450 SBC was 50+ HP.
 
#46 ·
Jason, thanks for the solid advice. I have a track 383 in a s10 with a similar head and cam combo. I do agree that 260 flow numbers are very dated...back to around the mid 90's. I have my flow numbers posted above.

I may need to take my welded up factory HEI and replace with a MSD that is more tuneable.

I will start playing with just adding some total timing first before doing anything else...maybe find some more power.
 
#47 ·
Well, I have formed a game plan without spending much money.

1. Add some timing first to get how it like it and responds.

2. Change out the pump cam, play with the squirters, and change the spring to see if anything gets freed up

3. Get it on a chassis dyno.

4. Advance the cam 3 degrees when it comes out

5. Change the cam to a 108 lsa if result aren't acceptable.

6. Switch to a 4:10 gear or go to unported head like a stock 195 or 200 runner, maybe even a 180 ported head.
 
#48 ·
Forgot to add that my goal is to try to improve the low end.

The upper end is fine...just need to improve the low end some...idle to 2000 rpms.
 
#50 ·
Jeff65SS

Im at 30 degrees at idle....I have 16* of mechanical advance and 12* of vacuum advance.

My mechanical initial is 18* with 16* of mechanical for a mechanical total of 34*.

When I plug in the vacuum advance I get 30*. That's 18* of initial plus 12* of vacuum for a total of 30*. At cruise I have 34* total with 12* of vacuum advance for a total of 48*.
 
#51 ·
Jeff is right. This is only testing to see if 1000-2000 improves, do not run it beyond. Your vac advance goes away on full throttle, so you do not include that on base timing. I also think it will run better with locked mech advance, and then you could still keep vac advance for cruising.
 
#54 ·
Clarify what you mean by "testing to see if 1000 to 2000 improves, do not run it beyond."

This is misleading and or confusing to me.
 
#52 ·
From idle to 2000 rpms, I wouldnt re-phase a cam. Whomever said that advancing would not "match" the heads well, Harold Brookshire had me advance a cam ( it went +7 by accident) to improve the "ram effect" through my rectangular port heads on a 427. So, someone got it sort of backwards. Changing cam phasing changes the pulse harmonics thru ports. But this, I now beleive, is irrelevant.

Ignition Timing. 14 degrees VAC ADV is way too much unless it a pooch compression engine showing 130-150 psi. I had 205 in the 427 and even limited to 10 degrees VAC ADV would sometimes ping on the highway. Mark Joens prefers I DO NOT run VAC ADV on that 600 hp beast he built for me, even though I've used the Crane cam to limit it to maybe 5 degrees. ( he simply dosent want me to ruin all that exemplary machine work for 1 mpg)

Aaron, I am no pro, but think if you cut your VAC ADV down ( which btw, goes AWAY at that low speed part throttle area you 're wanting to improve on. ) to 6-10 degrees, and add that back into the mechanical advance you may have a good solution. Better minds than I have been saying that here, and once i read you are running 12 degrees VAC I knew they were onto something. You want to guarantee it, put a 095 or 105 PV in the primary side of the Holley AND tweak your ignition timing, limiting your mech adv to 12 and adding it back to initial.

I'm think she looses all of that 12 deg vac , and you're feeling it. Especially if you have a mech curve that comes in later than 2000 rpms.

Dave Ray, where are you!? I'd like independent corraboration or dispute.
 
#56 ·
Gene, so your against making a advancement of the cam if its just soggy off idle to 2000? Again, the cam is retarded....to a 109 ICL from Harolds cam card of 106 ICL.

Gene, I don't have 14* of vacuum advance...I have 12*

Gene, this motor has 195 psi cranking compression and a 9.9 to 1 static compression and a DCR of 8.0.

Are you saying to use a 9 1/2 or a 10 1/2 power valve? I follow you what your saying about the mechanical advance of 10* to 12* with a can that adds 10*. That would put me back at 46* to 48* of timing at cruise.

I think Im going to have to get a new distributor...this GMPP distributor cant be done this way without more custom work. It originally had a 22* mechanical curve. I welded custom stops to limit it to 18*. I read and followed the IGNITION 101 thread and followed what vvroom suggested for a performance cam.
 
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#57 ·
Ray, going to have to look at another distributor more than likely....this GMPP one I have has had a lot of custom work to it already to control the mechanical advance.
 
#60 ·
If you have 195 psi of cranking compression, I don't think pump gas will stand much more than that, so advancing the cam more might not help, unless you plan to use octane boost or mix race gas

Sent from my SM-T817V using Tapatalk[/QUOTE

Your right, this is a concern...I have run as much as 215 cranking compression on 92 octane without issue. This is a topic that is hotly debated.
 
#61 ·
To simplify it Aaron, I was thinking only that you may consider limiting the vac adv back a few degrees, but then putting that into the total as INITIAL not mechanical. So its "ON" all the time, not just at rpm.

I am also ASSUMING the full mechanical curve is not in by 2000 rpm. So once again, some more base timing may ease the low end sluggishness all by itself. But with that much squeeze, you'll have to limit it elsewhere.
and yes 095 105 are the 9.5"Hg and 10.5" Hg power valves. As long as the idle circuit is working and the blades arent open enough to pull fuel off the boosters, it will work even at a 8" Hg idle. I only went back to a 085 from teh 105 since every gear change ( Muncie) would drop Hg" to 9-ish" and open that PV. I had to go just below that part throttle shift vacuum reading to keep it from being too rich.

Each engine is different, but my 427 @ 205psi was a little "finicky" about fuel. Ignition timing , therefore, aalso gets "finicky". PS I truly enjoy the Crane adjustable vacuum advance Dave Ray installed on his distributor. I never had highway "pinging" with the vacuum limited to 7-8 degrees, but did with my GM oem Pertronix fired distributor, and it has some sort of hipo GM can on it but gives 10+. Too much for a 200 psi engine, imho. 46 total was on the edge.
 
#63 ·
Hey Aaron as you might remember my dad's Vega runs the same cam in his 406. Its a mild camshaft but the lil sucker packs a good punch! I agree with the others to put more timing in it. Currently running 38 total in dad's 406. Something that was not talked about was what are your headers primary tube size?? For a real torque beast 383 some 1 5/8's work killer. My dad's has puny 1.5" shorty conversion headers on it.
 
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