FAQ |
Members List |
Social Groups |
Calendar |
Search |
Today's Posts |
|
#1
|
|||
|
|||
Too Much Compression ?
I bought a 1967 Firebird 400 convertible out of an estate. The deceased owner had the drivetrain build mostly done. I finished the body and now I'm going to tune the engine for the street. I have a thick notebook of all the parts used.
It has a 1975 400 block. Edelbrock 60599 Heads 72 cc Edelbrock Cam Duration at 0.006" Lift: Intake: 278° Exhaust: 288° Duration at 0.050" Lift: Intake: 204° Exhaust: 214° Lift at Cam: Intake: 0.280" Exhaust: 0.295" Lift at Valve: Intake: 0.420" Exhaust: 0.442" Timing at 0.050" lift: Open Close Intake: 3° ATDC 27° ABDC Exhaust: 42° BBDC 8° BTDC Centerlines: Lobe Separation - 110° Intake Centerline - 105° COMP Cams Aluminum Roller Rocker Arms Rocker Arm Ratio: 1.5 Rocker Arm Style: Full roller Stud Size: 7/16 in. Rocker Arm Material: Aluminum Slot Width (in): 0.562 in. Maximum Spring Diameter (in): 1.500 in. Rocker Arm Finish: Red anodized Edelbrock Performer Intake Manifold Edelbrock 1411 Carb Doug's Headers Super Muncie 4 Speed 3:36 Rear Gears Posi Funtional Ram Air I just finished a compression test. On both #1 and #2, cold and dry, 215 psi. What can I expect for street performance? What octane am I going to need to use? Any suggestions on tuning are greatly appreciated. Thanks! |
#2
|
||||
|
||||
Cranking PSI is too high.
I'd swap the cam, intake and carb. |
#3
|
|||
|
|||
Quote:
I thought the pressure was high too. Had to get another gage just to make sure. Is that about 11:1? Must have been decked? Why the cam, intake and carb swap? What would you swap to? Thanks again for your help. |
#4
|
||||
|
||||
A larger cam will better use the heads and help manage your compression.
I'm partial to solid cams but for a hydraulic flat, maybe a Voodoo 703. Assuming you are around 400 cubes. As Steve said, the Performer intake is limiting. RPM is much better. |
#5
|
|||
|
|||
Quote:
I drove it last summer. It would pull good up until about 5000K and then it just runs out of pull. It's just not as quick and fast as it should be. All the parts in the build check out. Compression test shows good compression. I'm going to look a little closer at the timing and the distributor. |
#6
|
|||
|
|||
My cold and dry compression is between 185 and 215 on all 8 cylinders.
It is a 1970 455, #48 heads, and a '65 intake. Unknown bore, stroke, and cam, specs with timing at 12 initial and 32 total. I need to run 91 octane with a 16 oz. bottle of boostane. Even with this, I may have issues on hot days. Without the boostane, the engine diesels when turned off.
__________________
1965 Pontiac GTO 455/469 w/ #48 Heads, '65 Tri-Power 9.25:1 CR Stump Puller Cam Muncie M22W 1st-2.56 2nd-1.75 3rd-1.37 4th-1.00 3.55 Rear Differential Front: 225/60R15 Height: 25.6" Rear: 275/60R15 Height: 28" |
#7
|
|||
|
|||
Quote:
|
#8
|
|||
|
|||
My 455 with 48s and dished pistons for 9.5 CR and as I remember pumped 180s run fine on 91 at 36 degrees total.FWIW,Tom
|
#9
|
||||
|
||||
The question comes down to does the block still have the 1975 stock Pistons with the chamfer around its OD, if it does then you will have no isuue with compression being too high as you will be lucky to have 9.2 to 1 .
__________________
Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
#10
|
|||
|
|||
Quote:
The test showed 215 psi. Probably not 9:2:1 correct? The receipts show that they used TRP forged pistons. Everything is new on this build, except the block. |
#11
|
||||
|
||||
My guess would be about 10.75:1 CR
Stan
__________________
Stan Weiss/World Wide Enterprises Offering Performance Software Since 1987 http://www.magneticlynx.com/carfor/carfor.htm David Vizard & Stan Weiss' IOP / Flow / Induction Optimization - Cam Selection Software http://www.magneticlynx.com/DV Download FREE 14 Trial IOP / Flow Software http://www.magneticlynx.com/DV/Flow_..._Day_Trial.php Pontiac Pump Gas List http://www.magneticlynx.com/carfor/pont_gas.htm Using PMD Block and Heads List http://www.magneticlynx.com/carfor/pont_pmd.htm |
#12
|
|||
|
|||
Great info. Thanks Stan.
|
#13
|
||||
|
||||
That was just a guess on my part, but why I said 10.75
Head Gasket Thickness = 0.028" Head Gasket Bore = 4.160" Combustion Chamber Volume = 72 cc's Dome Volume = -7 cc's Zero Deck CR = 10.752 Stan
__________________
Stan Weiss/World Wide Enterprises Offering Performance Software Since 1987 http://www.magneticlynx.com/carfor/carfor.htm David Vizard & Stan Weiss' IOP / Flow / Induction Optimization - Cam Selection Software http://www.magneticlynx.com/DV Download FREE 14 Trial IOP / Flow Software http://www.magneticlynx.com/DV/Flow_..._Day_Trial.php Pontiac Pump Gas List http://www.magneticlynx.com/carfor/pont_gas.htm Using PMD Block and Heads List http://www.magneticlynx.com/carfor/pont_pmd.htm |
#14
|
|||
|
|||
Was this correct? With L2262FSTD pistons? With standard block?
Last edited by TAQuest; 04-08-2019 at 06:29 PM. |
#15
|
||||
|
||||
Quote:
Stan
__________________
Stan Weiss/World Wide Enterprises Offering Performance Software Since 1987 http://www.magneticlynx.com/carfor/carfor.htm David Vizard & Stan Weiss' IOP / Flow / Induction Optimization - Cam Selection Software http://www.magneticlynx.com/DV Download FREE 14 Trial IOP / Flow Software http://www.magneticlynx.com/DV/Flow_..._Day_Trial.php Pontiac Pump Gas List http://www.magneticlynx.com/carfor/pont_gas.htm Using PMD Block and Heads List http://www.magneticlynx.com/carfor/pont_pmd.htm |
#16
|
|||
|
|||
What if it was not decked, what would it be?
|
#17
|
|||
|
|||
So it's set up like a ram air IV?
|
#18
|
||||
|
||||
That cam is the Eddy Perfomer.
https://www.summitracing.com/parts/e...7/make/pontiac Are you sure you have Full battery voltage to the Dizzy. Appropriate spark plugs? Last edited by STEELCITYFIREBIRD; 04-02-2019 at 06:34 PM. |
#19
|
||||
|
||||
Quote:
I'd keep total mechanical timing to 32 or less with that much cylinder pressure... till you sort out problem, less you create much a larger scale problem. And check timing as Steve25 called out for , and at higher RPM. Then unplug your tach recheck timing, they can cause odd problems if bad or incompatible with your dizzy. A vacuum gauge can tell you a lot about the base engine. I'd expect it to be ~18-20+ at idle with that cam and CR.. Careful setting valves,push rod spin is an acquired feel, zero play is a good description. Some pictures of your valvetrain, close up of valve end/retainers open and closed may show if there is some bad geometry or interference going on. It's an ignition problem, my best guess with the info so far. HTH Last edited by STEELCITYFIREBIRD; 04-03-2019 at 11:04 AM. |
#20
|
|||
|
|||
Originally Posted by steve25
"You do not have any issues to look for in regards to the springs on those heads limiting the motors rpm if it will rev passed 3200 out of gear so stop going back and bringing that up." His current valve springs may not be the specific issue at hand in his situation but once he gets it all sorted out those cheap Edelbrock single coil springs set up 0.250" away from coil bind is NOT optimum ! That was the point. That said, with the tiny cam it will peak out at such a low rpm anyway so no big deal. Onward. EDIT: to add NOT optium .
__________________
'70 TA / 505 cid / same engine but revised ( previous best 10.63 at 127.05 ) Old information here: http://www.hotrod.com/articles/0712p...tiac-trans-am/ Sponsor of the world's fastest Pontiac powered Ford Fairmont (engine) 5.14 at 140 mph (1/8 mile) , true 10.5 tire, stock type suspension https://www.youtube.com/watch?v=qDoJnIP3HgE Last edited by Steve C.; 04-03-2019 at 11:13 AM. |
Reply |
|
|