Thread: 70 Monte 454 Fuelie Bad Combo Questions:(

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Hello all!
First post here. Looking for answers to a poor running 454 combo.
70 Monte Carlo 454 Turbo 400 2500 stall. Car is resto-custom frame off. Around 4000 lbs.
Started with a marine block (pass perf Mk4 cast in rear). Stock bore size (never bored).
Forged GM crank (not nitrided...forgot part number but IIRC it's a good one!)
New GM performance rods with 7/16 rod bolts.
TRW Speed Pro forged pistons L-2465F. 10.2 -1 compression is what I had it figured at 5 years ago when I built it.
GM performance aluminum heads with the large valves 12363390 2.25 intake valves oval port
Lunati 50266 Roller Cam Hydraulic http://www.lunatipower.com/CamSpecCa...rtNumber=50266
Accel Gen7 fuel management dual sync dist, sequential fuel control. Accel intake oval port aluminum, I spent 10 hours match porting the intake to the heads on a milling machine. 1350 CFM oval blade throttle body.
Holley ignition box (since discontinued).
Long tube headers 2 inch homemade. 28-34 inch primaries. Dual Random Technology CATS going into 2.5 inch dual exhaust 40 series mufflers.

I forget all the specs, I'll keep adding. My issue is a terrible spark knock that starts around 2200 RPM. I've pulled the timing down to 8 degrees in this area. Fuel 12.5-1 WOT with wide band O2. Things are ok if you can get thru this bad spot although this engine doesn't feel like it is making more than 350-375 HP. It should make just under 500. I have added a 2500 stall converter which did help, now I am custom tuning the shift points with a governor weight/spring kit.
This engine burns oil. I knew it would use a bit of oil but not this much.
At this point the engine has about a thousand miles on it and my next step is cylinder leakdown, compression cranking tests to reveal leakage. If so I'll tear it out.
I thought my cam choice would be ok for a street, strip car. not sure now.
93 octane gas may NOT be enough for this pig....wondering.
Please help with next steps. My thoughts are to throw an HEI and carb on this to be sure that some of my issue aren't tune related. My tuning background is small block with Holley Commander 950 and LS1,2 stuff and EFIlive. Have taken 2 tuning courses (1 with Greg Banish).
My background is European automotive and no problems doing engine/transmission work (until now).

Thanks for reading. I'll dig up more specs. Labor of love at this point.

John

Sounds like your compression is right on the cusp of being to high. If it's burning as much oil as you say, the oil is taking up space in the cylinder volume thus increasing your overall compression ratio. It sounds like the engine knocks under load, ask me how I know.

Keith

first work on the oil if you say your burning that much oil thats not helping what breathers do you have on the valve covers ?are you sucking oil up the intake check for good seal? whats vacuum @idle. that cam is abit small so with 10to1? cr your going to have to run good fuel have you try that? did you check that the piston are not hitting the new chevy heads?

Cheap Chinese Ebay tall valve covers with baffles. One of the first things I checked was oil through the PCV hose. It's dry as a bone, unlike LS1 stuff.

I dropped the timing to zero at this area where knock occurs. NO difference.
Starting to think I have an ignition issue but still going ahead with leakdown, compression when I get a bit of time. Please keep me in mind for the "proper" cam selection to work with these heads and single plane intake.

Thanks!

John

You'll need much higher octane with 12.5:1 compression and that short duration cam. Even with longer cam you'll want to run standard (110) or at least 100. The oil problem is another story and probably result of detonation/preignition... Comp/leakdown test first then either lower CR or big cam and higher converter and more octane.

-Chris

Sorry... I misread that. You have 10.2:1 CR and 12.5:1 AFR. Still a fairly short cam for that compression. My old 10.2:1 motor I ran 240@.050 and it ran ok on premium but preferred 100 octane and I have the "luxury" of no air at this altitude

Added Speed-Prop L-2465F piston number to first posts.
Last night i pulled the plugs and performed cranking compression then leakdown. The results surprised me as this is quite tight.
#1 compression 198 leakdown 2%
2 190 2%
3 195 2%
4 195 2%
5 185 2.5%
6 195 2%
7 187 3%
8 192 2%


Engine idles @ 60KPA vacuum 20 degrees advance @ idles seems perfect.

No I haven't tried Race Gas.

Not sure of next move....Try an HEI distributor temporarily or a cam swap. I'm thinking about boring and lowering compression but will not make this same mistake twice.
Lead me on Gents...Open ears here. If nothing else it sounds like my cam choice is poor huh?

Thanks, John

Have not had much time but bad weather soon arrives in this part of the country.
I realize there is an oil consumption issue that must be addressed. My thinking is to replace current camshaft with one that would work better with 10-1 compression but also would be fine with 9-1. This way I would try another grind this Fall. When installing I will check valve guides/seals in an attempt to remedy the oil burning.
If the new grind does not remedy the detonation I would tear this engine down this Winter and get it bored, lower the compression to 9-1 or something more street-worthy. Obviously I should have had it bored the first time around.

Could you guys take a stab at a roller cam grind that would work with this combo?

Thanks, John

OK...Tearing it out.
Starting over.
I won't screw it up the second time!

John

Originally Posted by ssvolvo

My issue is a terrible spark knock that starts around 2200 RPM.

Pat McCarthy and Jerry Clayton, among others, have way more experience building big block Chevies than I do, but I enjoy sitting down and figuring out what's going on and how to fix it. In the end, every motor out there is just a big ole air pump that responds to pretty much the same parts and procedures as the next one.

First thing I see is that the squish isn't tightened up as much as it could be. Also, that big lump of dome on the piston is gettin' in the way of flame propogation. And the static compression ratio is too high for pump gas and the cam you're using.

The piston you have used has a compression height of 1.640". Add a 6.135" rod and a 2.000" stroke radius and you have a stack of 9.775" in a ~9.800" block deck height, leaving you with a 0.025" piston deck height. Add a nominal 0.040" head gasket to that and the squish measures 0.065". You can't use a thinner gasket because of the aluminum heads, so you have to do whatever else you can to fix the situation.

If we were to cut the block decks 0.010", registering off the centerline of the main bearing bore and use pistons with a taller compression height, like SRP forged #141635 that measure 1.645", you could improve the squish by 0.015" and arrive at a ~0.050" squish. The other plus side of using this piston is that the dome is 14 cc's instead of the 25.7 cc dome you have in the motor now, so flame propogation across the chamber should work a lot better.
Static compression ratio should end up at 9.72:1 and I'd bet that would work pretty well on pump gas with the Lunati cam you're using.

The SRP pistons are designed to work with the Edelbrock Recti-Oval heads you have. Here is a blurb about them....

"SRP big block Chevy small dome profile pistons are designed to fit Edelbrock 110cc and GM Signature series heads. They're 4032 low-expansion, high-silicon aluminum alloy that's heat-treated to SRP specifications. CNC-machined domes with radiused valve reliefs provide optimum flame travel. They include pin fitting, double Spiro locks, and wrist pin."
http://www.competitionproducts.com/p...?number=141635

Here are the volumes I used in computing the SCR....
4.280" x 4.000" = 943 cc's
Chambers +/- 110 cc's
Pistons 14 cc's
Piston deck height (block deck height 9.790", piston deck height 0.010") 2.4 cc's
0.039"/0.040" composition gasket for aluminum heads 9.7 cc's.

Deduct the dome from the chamber. 110 less 14 = 96 cc's. This is what we use for chamber volume. Piston volume is now zero.

Figured thusly....
943 (cylinder) + 96 (chamber) + 0 (piston) + 2.4 (piston deck height) + 9.7 (head gasket) = 1051.1 cc's.

96 + 0 + 2.4 + 9.7 = 108.1

Divide 1051.1 by 108.1 and find 9.723:1 static compression ratio.

Oh, and by the way, your present static compression ratio is 10.55:1

Also, I ran into a blurb somewhere that said the valve guides are semi-finished as produced. Check with whomever finished the guides. That may be where the oiling is coming from. Just a thought. Also, when you pull the motor apart, look closely at the intake gaskets to see if they are pinched all the way around. If you were pulling crankcase air into the ports from the bottom side because of a mis-match at the sealing surfaces, the motor could have been going lean and you'd never be able to find it.

You spent a bunch of time on this for me.
Thank-You.


John

Disassembling this weekend. Still have not found the oil consumption problem but will check the guides/seals.

It's obvious that piston domes are pretty high for these chambers which are called "semi-open".

My biggest mistake was letting a salesman from Sgoggin-Dickey choose the pistons for me because I wasn't sure.

John

that piston is fine but them heads are not working with that cam re hone rering re cam heads maybe to big for your build

so how much oil did it use in how many miles?
Did you use lite oil rings?
The block notch for the intake valve shows a lot of ring---has it been made bigger for some reason??
Hone pattern and size??
Lalve guide size and seals--Are they 11'32 valve with 3/8 seals?

walls look like there is no cross hatch look to be glazed over for a new engine . yes to start at a STD bore with new pistons is a very bad idle less bores are very nice .most all the time there not. at the least re ring some one may have put the ring s in upside down engine was getting alot fuel in the oil . what did you use for crank case vents ????