The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > General Truck Forums > Engine & Drivetrain

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 10-15-2010, 03:15 AM   #26
cppursell
Registered User
 
cppursell's Avatar
 
Join Date: Dec 2008
Location: San Francisco, CA
Posts: 144
Re: High compression engine and pinging

Quote:
Originally Posted by Ticker View Post
See this post; long-winded but pretty good and although it looks a little intimidating it's not all that hard to do - and well worth a couple hours investment.

http://67-72chevytrucks.com/vboard/s...d.php?t=290498
It sounds like a weekend project. I'll see if I can get to it. Hopefully it'll make a positive difference.
cppursell is offline   Reply With Quote
Old 10-15-2010, 03:22 AM   #27
cppursell
Registered User
 
cppursell's Avatar
 
Join Date: Dec 2008
Location: San Francisco, CA
Posts: 144
Re: High compression engine and pinging

Quote:
Originally Posted by nd72c10 View Post
Do you know anything about the engine that you just stuck these random heads onto? cam part #?

What is the casting number from the cylinder heads? How was it determined that they are small chambered 283 heads?
Don't know about the cam (I didn't put it together) but the head # is 3795896 or
3884520 determined by the single triangle symbol, per this guide:
http://www.chevellestuff.com/qd/head...ng_by_year.htm

Only word I got on the cam right now is that it isn't stock.
cppursell is offline   Reply With Quote
Old 10-15-2010, 03:33 AM   #28
cppursell
Registered User
 
cppursell's Avatar
 
Join Date: Dec 2008
Location: San Francisco, CA
Posts: 144
Re: High compression engine and pinging

Quote:
Originally Posted by SSedan64 View Post
I think you have the wrong Heads for the engine. 283 Heads have tiny 1.72" Intake valves & chambers. Larger chamber & valve needed.
Yeah, well I guess the experiment with this engine is how efficient and lean it can run, so I guess my cousin's idea with putting these heads on was to see if the higher compression (and small intake) would equal +MPG.
I think the heads are great so far, 'cause I got this thing on the freeway and it accelerates more than my old (stock) 350 with powerpack heads.
cppursell is offline   Reply With Quote
Old 10-15-2010, 03:35 AM   #29
cppursell
Registered User
 
cppursell's Avatar
 
Join Date: Dec 2008
Location: San Francisco, CA
Posts: 144
Re: High compression engine and pinging

Quote:
Originally Posted by LEEVON View Post
Just a thought...have you checked total timing? Could it be that you have too much mechanical and vacuum advance? Adjustable vacuum canisters are cheap, you can dial it back and get the total timing correct. I agree with the others, bring your initial back to about 12 degrees and see what happens. I run about 10.5:1 in my 350 and don't have detonation but then I make sure the total timing is in range too.
I agree, I definitely need to time my engine more accurately. I just haven't had time yet (school). I'll try to get to it this weekend.
cppursell is offline   Reply With Quote
Old 10-15-2010, 03:36 AM   #30
cppursell
Registered User
 
cppursell's Avatar
 
Join Date: Dec 2008
Location: San Francisco, CA
Posts: 144
Re: High compression engine and pinging

Quote:
Originally Posted by Ticker View Post
Cool - but my only suggestion is stop experimenting until you get the timing set right as I noted previously.

It's not just about the initial timing but the total timing including advance, which from your description is where the issue is.
Thank you ticker for your previous link. Yes, I'll try to get to that this weekend.
cppursell is offline   Reply With Quote
Old 10-15-2010, 03:38 AM   #31
cppursell
Registered User
 
cppursell's Avatar
 
Join Date: Dec 2008
Location: San Francisco, CA
Posts: 144
Re: High compression engine and pinging

Quote:
Originally Posted by bradh View Post
If you get the total timing set and it still knocks try a cooler plug. If I'm not mistaken that's a .375 reach gasket type plug on 283 heads. A Champion RJ12YC should be in the ballpark.
I have new AC Delco plugs in the engine. My cousin set the gap but he kept it modest.

Last edited by cppursell; 10-15-2010 at 03:56 AM.
cppursell is offline   Reply With Quote
Old 10-15-2010, 04:31 PM   #32
Bad70sbchevy
Registered User
 
Bad70sbchevy's Avatar
 
Join Date: Aug 2009
Location: Newberry,FL
Posts: 277
Re: High compression engine and pinging

Quote:
Originally Posted by Ticker View Post
As previously noted, a cam with a lot of overlap on an engine making less than about 1.4 HP/CID just wastes power, gas and driveability. Your engine would make significantly more power (on the order of 10-15% or more) with a lower static CR and the RIGHT cam. And it would make far more power where it spends most of it's time - below 4500 RPM.

This isn't intended to be harsh, but using DCR to run a high static CR is just bad engine design on a low-power, low-RPM engine. It's a crutch to make a bad combo work - but it doesn't work well. 1 point of CR is worth maybe 1.5 - 3% MAX on an engine making less than 1.4 HP/CID or so...so shooting for high CR for a street engine *does not* make power. It's a design technique for high-powered racing engines that has made it's way into street design.
I agree, a big cam is NOT good for engines seeing low rpms, but a big cam will make more power, it just happens at a higher rpm due to overlap helping cylinder scavenging thus increasing volumetric efficiency. Also on engines, shouldnt you always shoot for the highest compression ratio possible (without detonation) since it results in higher efficiency thus leading to more power? Any time you raise compression you should always see a power gain (in theory), even if its a little bit. I wouldnt call it a bad combo, just probably not for a PURE street engine.
__________________
1970 Chevrolet C-10 w/355sbc
2010 Silverado Daily Driver
1971 Mercedes 280sl project car
Bad70sbchevy is offline   Reply With Quote
Old 10-15-2010, 04:37 PM   #33
pockets
Registered User
 
pockets's Avatar
 
Join Date: Sep 2010
Location: Broken Arrow, OK
Posts: 428
Re: High compression engine and pinging

i agree that running a larger cam to reduce DCR isn't a great idea, just that it can work. a real street engine that never/rarely sees the track will be far better off with the right cam and compression.

I also agree that a higher compression ratio will generally mean more power, assuming the cam is up to the task as well as the fuel. Race engines use high compression to make more power, but they also have the fuel to compensate.
__________________
Project Bad Karma
pockets is offline   Reply With Quote
Old 10-15-2010, 05:51 PM   #34
Ticker
Account Suspended
 
Join Date: Oct 2009
Location: Sammamish, WA
Posts: 2,404
Re: High compression engine and pinging

Quote:
Originally Posted by Bad70sbchevy View Post
I agree, a big cam is NOT good for engines seeing low rpms, but a big cam will make more power, it just happens at a higher rpm due to overlap helping cylinder scavenging thus increasing volumetric efficiency. Also on engines, shouldnt you always shoot for the highest compression ratio possible (without detonation) since it results in higher efficiency thus leading to more power? Any time you raise compression you should always see a power gain (in theory), even if its a little bit. I wouldnt call it a bad combo, just probably not for a PURE street engine.
A big cam isn't going to make more power unless the heads can flow to the level of that lift. As an example, a big cam with 882 heads even if they're ported to a crazy extent isn't going to make power at high RPM...it just can't flow enough to use what the cam offers. And overall - a big cam making power at a crazy RPM level doesn't really do any good unless the car is regularly at that RPM level.

Compression ratio does improve volumetric and combustion efficiency...but again, only if the engine can make use of it. The more flow the engine can consume, then the more important CR becomes. Premium pump gas limits CR to around 10.2 with full ignition advance and an .040 quench....that's just as far as we can go on the toilet water we have for gas today. Going higher than that means giving up power - backing off on ignition advance or the previously mentioned DCR. For an engine running on pump gas, that 10.2 or so is the Golden Rule for a GEN I. We can push that a fair bit on a GEN II or LS due to the dramatically better combustion chamber shape, and even a bit with top-notch heads on a GEN I...but the gains are minimal unless it's a very hot engine. Vizard has an interesting chart that shows the benefits based on HP/CID - I'll see if I can scan and post it.

I would call the OP's engine a really bad combo. It can be made to work, but it's never going to work particularly well. The only thing we can do is figure out the crutches it's going to take to make it work without coming apart, and there have been a lot of good suggestions around that...but if budget is not an object, swapping the heads to get the CR into a reasonable place is the best choice.

Again, not trying to be but this is the way it is
Ticker is offline   Reply With Quote
Old 10-19-2010, 04:49 PM   #35
cppursell
Registered User
 
cppursell's Avatar
 
Join Date: Dec 2008
Location: San Francisco, CA
Posts: 144
Re: High compression engine and pinging

Thanks for everyone's replies and advice. I simply don't have time to work on my truck 'cause of school, so I have my timing set to as advanced it will get without pinging, 15. It's a quick and dirty solution for now, but I still plan to take everyone's advice when I get the chance.
Thanks again and good trucking!
cppursell is offline   Reply With Quote
Reply

Bookmarks

Tags
283, 350, fuel, heads, octane

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 01:23 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright 1997-2022 67-72chevytrucks.com