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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
I am reliving my past with the purchase of a 1985 Z28 exactly like I purchased through the PX in Germany in 1985. With the only exception being that this car is a 5 speed.
I have decided to make a few performance modifications to the car; Trick Flow 23 175 cc heads, hydraulic roller cam (retrofit) perhaps Howards or Comp Cams??, and Hawks Y-Pipe (off road), and Jet Performance chip. I understand that the factory exhaust manifolds are quite restrictive, but I am not too keen on fighting headers leaks and obtrusive noise (I'm a little old).
Thank you in advance for your thoughts and recommendations regarding my cam selection.
Cam recommendations and EFI (that's an assumption) don't necessarily mix for me (there are others here with plenty of personal experiences but I'm a carb guy) but the headers are essential in order to realize any real performance gains. Little sense in a cam upgrade if the exhaust is holding back any potential.
I'm with you on the headers leaks. I've tried many different types of gaskets however since I've been using Remflex gaskets, leaks have been zero. And that's over thousands of miles. Something to consider.
Thank you Sir for your prompt reply. I should have made mention that this is a carb (LG4) car. I have considered the Hooker exhaust system as an option, but wanted to try the y-pipe 1st to retain the factory stock look. In an effort to maintain the factory look, intend to paint the aluminium heads black as well.
Your decision to stick with manifolds notwithstanding (although results from any cam/heads upgrade is gong to be limited by that choice) base your components around parts that are compatible.
I run a small head like the 175cc Trick Flows you posted albeit with 355 cubic inches. With that, I worked towards a compression ratio that was street friendly and worked with my cam choice.
A few other details are needed and I'd have to look them up in order to refine any kind of cam spec.
Without asking what your intentions are with the car, and by that I mean that it's taken into account that you want greater performance without going outside of the "street" envelope, then targeting a static compression ratio of around 10:1 combined with a cam that will build some decent compression pressure and a noticeable difference in torque and power will be the result.
What I don't have is the compression ratio and piston type of the 1985 LG4. I believe around that time there was switch to a flat top pistons and CR was probably close to 9:1. Up from the early days of 8.6:1.
A head with a 56 cc chamber, combined with a .026 gasket (about as thin as you can go with getting into the finicky shim style gaskets) and an assumed flat top piston should yield around 9.7:1. That CR works well with a cam in or around the 218 @ .050" mark. Comps XR270HR would be a good fit.
The 1985 LG4 was factory rated at 9.5 compression up from 8.5 in 84. I really like your head gasket recommendation. It should work excellent with the small combustion chamber.
Beginning with the end in mind; this car will be 99% street driven and rarely if ever drag raced (5 speed).
I read the article and really like the cam recommendation. It is seemly exactly what I am looking for.
In regards to the CC quadrajet; I intend to send it to the Carb Shop in Onterio, California for rebuild and calibration/tuning.
You may want to consider a better intake manifold and eventually...headers. It's really the only way to go. And while it's been some time since I've worked on any quadrajet I do know that they can be made into an excellent performing carb. Get a wide band O2 sensor and AFR gauge to go along with it. That makes any additional tuning much easier.
Those elements combined should be able to produce around 1.1 - 1.2 HP/C.I.
That said, I would choose the XR270HR over the XM270HR (from the article). Slightly better specs when considering the LSA if nothing else.
I utilized the XR lope profile on my stroker ls build with excellent results. Thanks for the suggestion. I really wish that I could find a Weiand 8001 intake manifold, but it's no longer made and hard to find.
Ja85..,
If you're going to stick with exhaust manifolds, at least upgrade to a set from a TPI or L69 car. In fact, a complete exhaust system for TPI/L69 would accomodate a big performance increase with 305 cu in.
See my sig for what a complete TPI exhaust system accommodates even behind 350 cu in.
I just recently learned from talking with the previous owner that he had done some grinding work inside the TPI manifolds before installing them. BUT......YOU can do the same!
Go with the XR-type cam that skinny mentioned, but I'd keep the duration a bit shorter for only 305 cubes with 9.7'ish CR and manifolds, certainly no more than 212 duration on the intake. I'm running only a 208 dur cam in the 350 in my sig, and as you can see, it's no slouch. It's about the limit of what the unmodified E4ME carb wants to deal with at idle and light throttle cruise. With an XR264 cam on a 110 LSA, your vacuum signal will be lower and I would tell the guys at the Carb Shop to set it up to deal with about a 15" idle vacuum rather than the stock 19-20"
Gorgeous car! TPI manifolds, better y-pipe, 3 in exhaust, mild cam, maybe some 3.73 gears, and you should have a very fun car to drive. I love the color scheme.
Excellent advice gentlemen and it is genuinely appreciated. I have been eyeballing a Howards hydraulic roller cam 213/217 @ .050 485/495 on a 110 lsa. Please don't hold back with your opinion.
Have you determined what your final compression will be taking into account: piston dish/valve relief volume, piston at TDC to block deck distance (deck height), combustion chamber volume and head gasket thickness/volume?
This will ultimately determine the suitability of any cam you might choose.
Last edited by skinny z; 03-01-2017 at 01:01 PM.
Reason: correcting poor grammar
Getting to 10:1 SCR might be a bit of a stretch if it's only the heads and gasket that you're changing.
With a standard bore and stroke (3.736" x 3.48"), .025" piston below deck (optimistic), a flat top piston with 5cc valve relief (also optimistic), a 56cc cylinder head and a .026" x 4.120" gasket (about as thin as I would go), the CR works out to 9.8:1. Pretty close but likely to be lower as the piston is probably closer to .030" down. That's 9.67. I can't say what the piston type is but you see where this is going. It's entirely possible that you can reduce the combustion chamber volume to 54cc. That pushes the value up to 9.9:1 so it is doable but I would suggest having the heads off and taking some measurements before ordering parts.
However if you work with the 10:1 target, then the cam as suggested would be a good fit (in my opinion). The dynamic compression ratio, which is the number that really counts when discussing compression (if you're asking me), comes in at 8.26:1. (The typically acepted range for a pump gas street engine with this particular architecture is 7.5 - 8.5 :1).
With iron heads, I'd say that's an excellent number. With aluminium heads, it's also good and with room to spare. That room will help to ensure that you stay out of detonation. That, and good engine management.
As an example, my iron headed 355 dialed in once at 10.4:1 SCR and 8.4 DCR. It didn't work well with pump gas. Even using 94 octane premium, I had to take out lots of ignition timing. Something I've learned from that experience and have since followed up on is that an engine responds much better to timing to timing than it does to compression.
All of that said, 10:1 and that cam and I'd say you'll probably be happy with the results. Even at a lower SCR of 9.6:1, the compression pressure should be reasonable as the DCR is still above 8.0:1.
It's not just about power production either. The increased compression pressure will help the overall torque production and the fuel economy sees a boost as well. I have as much pride of ownership with 20+ mpg on the highway as I did running mid 12's with an old school carbed 350.
Originally Posted by 86LG4Bird
It's about the limit of what the unmodified E4ME carb wants to deal with at idle and light throttle cruise. With an XR264 cam on a 110 LSA, your vacuum signal will be lower and I would tell the guys at the Carb Shop to set it up to deal with about a 15" idle vacuum rather than the stock 19-20"
That's something I can't comment on as I have zero experience with the cc version of the Quadrajet.
Originally Posted by dmccain
...maybe some 3.73 gears...
The gearing will make a difference in the overall driveability.
I just like crunching numbers.
Please keep in mind that I'm only relating my experiences and am by no means any kind of expert.
I have a handful of engine analysis calculators and a couple of software programs that keep me amused. My only real claim to fame was the over-achieving Vortec headed 350 I built to start my second go around with hotrodding several years ago. Stock heads, little cam and yet with the right gearing and converter it performed surprisingly well at the track and on the highway. I've been trying to re-capture that recipe ever since but with a move more towards racing than street driving, it's not quite as simple.
...... Something I've learned from that experience and have since followed up on is that an engine responds much better to timing to timing than it does to compression.
All of that said, 10:1 and that cam and I'd say you'll probably be happy with the results. Even at a lower SCR of 9.6:1, the compression pressure should be reasonable as the DCR is still above 8.0:1.
It's not just about power production either. The increased compression pressure will help the overall torque production and the fuel economy sees a boost as well. I have as much pride of ownership with 20+ mpg on the highway as I did running mid 12's with an old school carbed 350.
.........
The gearing will make a difference in the overall driveability.
Those statements are spot on.
Even running 87 octane fuel, I'm amazed at the timing I can throw at my example in sig to give it VERY snappy response. It's about 8.1:1 DCR.
Yes, the '86 Firebird. Actually my daughter's car.
"Now: 250k mile L31 motor with new rod bearings, timing set, ZZ3 cam, Performer manifold, and Edge 2800 TC..... 12.91 @ 105.0 on street tires
Still with TPI manifolds and exhaust."
The only time it gets 93 octane is when it's being flogged in summer temps.
.
Makes me want to step back from my current build.
I either need another full point of compression or a smaller cam. Cranking compression came out to a rather disappointing 165 psi (at 2200' elevation) despite the 10.2:1 SCR. DCR works out to less than 8:1...But I'm in it now. I lucked out in that the torque converter I picked up over the winter is a step up from the 10" I currently have. I'm hoping the extra stall (reportedly to be about another 500 RPM or so) will help cover up what I know will be an under-performer at lower engine speeds.
A stroker crank would fix all of that though.
(Thanks for the hi-jack Jay)
I am having a good time bench racing! The only thing that has me a little disappointed is that it appears that Trick Flow 23 175cc head is the only aftermarket game in town for an aluminum ready-head.
There is the option of taking just about any 64cc (nominal) head and flat milling or angle milling to get to the desired volume.
For example, AFR's 180cc head can be angle to 55cc. Granted this can invite other problems with fitment but the option is there. http://www.airflowresearch.com/180cc...cylinder-head/
02-28-2017, 09:40 AM
