Can'tHave2MuchHP

Not on a C3 but figured this would be a good place to start. Engine is in my 73 Z28.

The build:
Chevy Small Block 383 Stroker
Full Forged Internals, H Beam, Roller Rockers etc.
Comp Cams XR282 230/236 @ .050" retro-fit hydraulic roller
Patriot 64cc 195 Aluminum Heads
Edelbrock RPM Air Gap Intake Manifold
Holley Street Avenger 770 Carb
Dynatech Headers

Car went to the tuner running pretty solid but the idle was staying at 1300 despite all the adjusting I could do. He basically just changed the timing a bit, adjusted the corner screws and that's it. Idle is still at 1200 or so. Which is really annoying and can't hear the cam at all. It put down 364 RWHP/365 RWTQ. Power dropped off quickly after 6000, not sure if that's accurately portrayed on the graph below or if he let off at 6000. Wondering if it's running out of spark, needs an MSD box or coil maybe.

I think the power is a bit low as well. I expected 400 RWHP as most people running similar setups are getting that consistently. This is through a 5 speed manual too.

Also need to start a thread on getting this Holley 770 to idle down. I'm guessing it's transfer slots that need adjustment. I was hoping the tuner would know how to deal with it. There's no vacuum leaks that I can find or the tuner saw. The throttle cable is free and returns to zero easily.

gkull

I can't find out anything on Patriot aluminum 195 cc heads. What are the valve sizes and port flow cfm? H-rollers are rpm limited by the valve train weight. You might be valve float limited at 6000 rpm. You have a small cam and if combined to small valves and cfm flow rate it is starved out at 6000. I'm also not sure of an rpm air gaps ability to supply 383 ci over 6000. When they rate a manifold to say 6500 rpm they are taking about on a common 350 ci.

There is something wrong if you can't dial your rpm down with the idle rpm set screw. Maybe you have a vacuum leak because it is getting air from somewhere.

If you really read up on multi spark ignition boxes. They only multi spark at 3000 or less rpm where it is most needed.

NewbVetteGuy

The Patriot heads were covered in the HotRod cylinder heads under $1,000 showdown a while back and did pretty well. I think they've changed names a few times in the past few years..

NewbVetteGuy

Op: See if you can find the CFM Flow #'s from somewhere and post back here. I've found 3 sets of supposed flow #'s for these and they're ALL different...

If you went with the comp cams retro roller lifters, which ones? (They have a low bleed-down series that's designed for higher RPMs.) Also what weight oil are you running?


Also, given that you're running a CompCam, you can go download Comp's CamQuest software, which is a modified version of the 2nd from the newest version of the DesktopDyno software that only lets you model Comp cams. It would be a good way to pretty easily play around with the numbers.
http://www.compcams.com/downloads/register.asp



Adam

sstonebreaker

Good point about the valve float. Normally you can hear that happening, but maybe they weren't paying attention. On the manifold, if it was limiting air flow the horsepower would most likely level out, not drop off, wouldn't you think? I'm leaning towards valve float or possibly running out of spark. Not sure about the MSD box, first thing I would try is a better coil.

HeadsU.P.

I believe they are now ProMaxx. NO relation to ProComp. I have a set of ProMaxx and am impressed with the performance and machining.

HeadsU.P.

As far as the high idle; what type of secondaries does that Holley have? I too chased an idle issue for several weeks. Blamed the IGN, blamed vac leak. Turned out to be the secondary linkage (after-market base). There is a small non-adjustable rod that connects the throttle brackets with the secondary throttle blades. In my case, it was binding and holding the secondaries open ever so slightly. My RPMs were 700 then 1200, 700, 1200. With all cables, rods and linkage removed I found the issue.
A little tweaking of the rod with some channel-locks did the trick.
Also some Holleys have a adjustable secondary screw hidden on the base plate to crack open the blades. Look for that procedure on YouTube.

Jebbysan

I think you are running lean......the A/F should be 12.0 or so under WOT for max power........the 770 Street Avenger runs notoriously lean out of the box.
If that A/F is correct on the Dyno sheet....you are leaving your 35 horsepower you are looking for on the table.

Jebby

stingr69

On the carb, Turn it upside down and look at the idle transfer slots. With the primary butterflly adjusted right they should look like a square, not rectangular. Secondary butterfly stop might be closed up a bit to lower the idle.

Cam might be too small. Carb could be too small.

JasonAndrew

Being a so called stroker, the engine should be putting out at least more torque than power.

cv67

W/Jebby
Get a wideband (AEM) in there see what the engine is doing, then find someone who can tune it .
Valve float can happen long before you hear it but one thing at a time, get your tune right first
(You do need a good spring with the fast ramp cams or they will float upstairs)

Has the distributor been curved? Know an old timer with a Sun machine?
MSD is a complete waste of money imo.

Youll get it sorted, be patient.

Bet you got a simple vacuum leak minimum if you cant idle it down that low.

Can'tHave2MuchHP

Wow thanks for all the info guys. This has been the quickest responded to thread I've had on here. I'll go through and quote/reply to each...

Can'tHave2MuchHP

Unfortunately, I wasn't paying attention when my dad was taking this thing apart and speccing this new engine setup about 8 years ago. I do not know what the numbers are. I will try to find out. Yes he heard about them in the Hot Rod Magazine...https://www.hotrod.com/articles/ccrp...m-heads-64-cc/

Wasn't aware of the Air Gap's ceiling on a 383, again new to this stuff, and didn't spec this myself. From a quick glance on their website, it would appear the one I have is their most extreme street intake manifold short of the super tall Victor and Pro-Flo (Which would never fit under the hood).
Correct.
I'll try to find the flow numbers, probably won't be able to though.

Not sure on the lifters either, will have to dig up receipts...Oil I'll get back with you on.

Thanks.
Yeah my dad read about them in Hot Rod and thought they sounded good. I wasn't paying attention at the time.
Will check into that.
That's the first thing I thought but was told that 14.0-14.5 is ideal for this SBC. I'm used to AFRs in the 11.8-12.8 range on my modern stuff, which I'm much more familiar with. You think I'll pick up that much power by fattening it up? It certainly would be safer.
Yeah I will check that, that's what I read last night. I'm pretty sure the 770 is more than enough for my setup, the heads and cam are pretty mild judging by what I've been told here. I do with I had a much larger cam but I didn't spec this setup. Trying to straighten it out for my dad.
It did, by 1.6 *sarcasm*. Definitely not impressed with the tuner nor the setup so far. It's just overall too mild. Don't need drivability in a weekend hot rod like this. They got my 454 in my 70 running awesome. Great power and drivability. Same for a 79 442. But they blew it on this one.

I'll keep mining for info and am willing to try whatever need be. As of right now it runs great in every measure except the idle pisses me off. I'll have to take the carb off and fiddle with it. The AFR scares me too. Might take it right back and have them get it into the mid 12s.

Jebbysan

14.7 is Stoichiometric ratio for optimum efficiency at light load.......it is NOT the correct ratio for WOT and heavy load. You need to fatten this motor up.
That is not a large cam......this engine with the parts you describe would make about 450 horsepower....maybe a tad more.
As mentioned....the optimum curve in the distributor is critical as well for good numbers.
Do the distributor first.....timing it, tighten it down and LEAVE it......35-36 degrees total is your number. Then fatten the carb up........

Jebby

maj75

Can'tHave2MuchHP

Tuner put the timing at 35 degrees and ti dropped power, gained the most at 29 total. Had something like 25 or so when I brought it in. Claimed 35 degrees picked up zero power over what it was when I brought it. Is that due to the lack of fuel?

Going to end up tuning this thing myself I guess. Anybody point me in the direction of a complete process?

Can'tHave2MuchHP

I'm aware of this. I've done lots of late model builds, just unfamiliar with the old school carbed SBC/BBC engines.

Jebbysan

I just mentioned the plan above.......and yeah...no more power because no more fuel. But something is suspect as unless it is running boost......NO small block wants only 29 degrees of lead, unless it is under boost.
Read member "Lars" paper on timing on such....it is so well written that for me to say anything about it would be redundant.
You need more timing and more fuel.......assuming the dyno is reading accurately.

Jebby

bobs77vet

it seems to me that carb may be need to set up for more flow....it may be a bit on the small size for your build. can you add some 02 sensors and see what the A/F ratio is?

427Hotrod

I agree....lots left in it.

I would expect timing to be higher than 29* also.
Compression ratio?
Definitely needs lot more fuel. Maybe it being so lean is why it didn't respond to added timing?
Fuel pump keeping up?
Double ck what valve springs are on those heads.
Intake will be OK. I've had those intakes making 540'ish on a pump gas 400" deal.
What octane fuel was in it?
What other loads? Fan?
Was hood open or closed?
Did anyone monitor if secondary's were opening all the way? I've picked up 30+ RWHP by manually opening them when the vacuum can wasn't calibrated properly.
Was air filter on it? how big is it? How tall?

JIM