Convertibel1970

Hi!

I hope you guys can help by your experience.

I have an original NM ZQ3 300HP small block in my Vette.
It is mildly modified:

-Edelbrock Thunder AVS 650 carb
-Edelbrock 2101 Performer Plus mild cam
-Pro Comp dual-plane intake manifold Edelbrock Performer clone
-Summit mid-length ceramic headers
-2,5" Corvette Central Magnaflow exhaust system
-Pertronix breakerless ignition and high voltage coil
-K&N air filter

I found 186 heads on my engine.
My car has got the economy G81 option with the 3.08 Posi rear end.

I´m not satisfied with the acceleration and feel that my current engine setup needs revs above 2500rpm for a good "kick".
So i´m considering to change the ratio to 3.36.
(My Posi seems to be worn anyway)
Or do you think 3.55 is better?

What are the gear ratios of my original Muncie 4speed shifter?
Is it close or wide ratio?

I like to swap the Edelbrock for a brand new Street Demon 625cfm spread bore.
I had problems with the Edelbrock AVS right out of the box... Maybe bad workmanship.
The Edelbrock has got square bore and the Street Demon spread bore. The spread bore should improve the low rev torque, right? I also like to switch from the cheap Pro Comp intake manifold to an air gap intake for cooling down the air mixture.


Thanks,

Andreas

Matt Gruber

IMO something is wrong, but it is a popular complaint.
I have a 3.08 and just put larger radius tires on, which makes it like a 2.87 and it frys the tires BUT i have a TH400 and the stock converter DOUBLES torque.
.
so the typical causes of it having weak torque
1. slow curve, not enough base tming
2. wrong carb base gasket,(open center instead of 4 hole), air-gap cut down divider, that new carb u like, all cause too much cross flow, allows exhaust to be sucked in during overlap, kills torque
3. wrong cam. anything bigger than the xe262 or 270H(stick) is asking for a low end turd.
.
and in your case, using a close ratio w/3.08 would be bubba. that was not allowed by GM but unless u bought it new, anything is possible.

Convertibel1970

My Performer Plus specifications:



RPM Range: Idle-5500

DURATION AS ADVERTISED INTAKE: 278° EXHAUST: 288°
DURATION @ .050 INTAKE: 204° EXHAUST: 214°
LIFT @ CAM (Lobe) INTAKE: 0.28" EXHAUST: 0.295"
LIFT @ VALVE INTAKE: 0.42" EXHAUST: 0.442"
LOBE SEPERATION: 112° INTAKE CENTERLINE: 107° IDLE VACUUM @ 1000 RPM: 14"

The information below is for verification of
opening and closing events.
INTAKE TIMING @ .050" LIFT: Opens: 5° ATDC
Closes: 29° ABDC
EXHAUST TIMING @ .050" LIFT: Opens: 44° BBDC
Closes: 10° BTDC

Street Rat

Put the 3.55s out back.

Convertibel1970

Sorry, I don´t understand what you mean?!? (I´m German......)

Matt Gruber

Well, steep gears only give the illusion of more power. Sure they help lots at the DRAGS on SLICKS, but say u are going 35 and want to blast past a slow car. The steep gear does NOTHING except change which gear u use to do the pass. It adds no HP. In fact, chassis dyno tests show LESS hp everytime, at the rear wheels, due to increased friction from more teeth.
.
Now that cam is awful. easy to add 35-50hp by using the xe262. According to dyno tests by Joe Sherman it "adds power everywhere, not just top end"

Street Rat

Matt is correct. If you want more seat of the pants feel, the cam has to go. If you are planning on a gear swap ONLY, I'd put the 3.55 gears in. How much highway driving do you do? The higher numerically that you go in a gear set the more rpms the engine will be turning. That equates to burning more fuel and a possible exhaust drone that you may not want to live with at highway speeds.

Convertibel1970

I´m living nearby Berlin.
In the countryside I drive around 70mph maximum, not faster.
Longer trips on the highway are very seldom. Sometimes in a US car convoy or a trip through the mountains...

My original engine block seems to be in good shape.
If it´s worn I´ll stroke it, but keep it in my car for NM.

fishslayer143

if you need to rebuild the differential anyway, a shiney new set of 3.55 gears will give you a better launch and make it more fun to drive..true, .it does not add horsepower but it does add torque multiplication, and on the street, it feels like it .. later factory L82 cars all came with 3.55 ratios to give better performance to a basically weak *** motor.. and they are still very driveable on interstate hiways at 70mph .. they are a good overall choice for non-overdrive cars...add a little better cam and you ll be smiling

MCMLXI

I had a '72 ZQ3 (base motor) with a wide ratio 4-speed and 3:36 gears. That was a nice setup for quick starts and low highway rpm's.

I now have a '61 with a close ratio 4-speed and 3:70 gears. This has a similar feel around town, but the rpm's are higher on the highway.

Matt Gruber

The trick to having strong low end is, in part, having a cam with a short seat to seat duration. the xe262 is 262/270
the OP's cam is 278/288.
Way too much seat to seat duration. If the valve isn't CLOSED it can't build compression at low rpm.
This is the #1 reason why my 72 spins the tires w/3.08. It makes plenty of power at low rpm.

johnt365

I agree with the others. The drive line gearing must work with the power band of the cam. I had 3.08's with a xe268h cam and it was a slug with the th400. I changed the rear to 3.55's and it was great. However, the autobahn may be a drag if you are turning 4000 rpms just to keep up.

How easy is it to get parts for these old american cars in Berlin? If a cam change to an xe262 lowers your powerband to where you can enjoy it, that might be cheapest.

Can you easily get a corvette differential or what about an overdrive transmission like a 700R4 in your area

Convertibel1970

Hi, happy New Year!

These are the specs of the XE262H-10:

Grind # XE262H-10
Duration @ 0.006": 262° / 270° Duration
@ 0.050": 218° / 224°
Max Lift w/ 1.5RR: .462" / .469"
Lobe Separation: 110°
Lobe ID#'s: 5442 / 5201
Intake Centerline: 106°
Engine Type: Chevrolet 350 Small Block

These are again the specs of my current Edelbrock Performer Plus cam:

DURATION AS ADVERTISED INTAKE: 278° EXHAUST: 288°
DURATION @ .050 INTAKE: 204° EXHAUST: 214°
LIFT @ CAM (Lobe) INTAKE: 0.28" EXHAUST: 0.295"
LIFT @ VALVE INTAKE: 0.42" EXHAUST: 0.442"
LOBE SEPERATION: 112°
INTAKE CENTERLINE: 107°

The information below is for verification of
opening and closing events.
INTAKE TIMING @ .050" LIFT: Opens: 5° ATDC
Closes: 29° ABDC
EXHAUST TIMING @ .050" LIFT: Opens: 44° BBDC
Closes: 10° BTDC


You have to consider the maximum lift of my original 1970 ZQ3 300HP small block with "186 heads, big valves and flat pistons.
The garage told me 0,45" lift is the max for my engine. is that right?


BR

Andreas

Convertibel1970

Take a look at this:

http://www.superchevy.com/technical/...der_heads.html

They used a mild PowerMax hydraulic flat-tappet piece from Crane Cams. A dual-pattern with 0.427/0.454 lift split, 204/216-degree duration split (at 0.050), all ground on a 110-degree lobe separation angle.

Except the lift the specs are not too different compared to the Edelbrock Performer Plus cam, right?

fishslayer143

there are as many cams available on the market as there are opinions about them.. your cam is pretty mild , not much lift, power is down low, probably very smooth idle, basically an RV cam... changing your cam and nothing else will be a small improvement .. and with your current gear ratio, hardly noticeable ..thats just my opinion, but I ve been working on these cars for 40 years

johnt365

Play around with this calculator http://tri-5.chevyrides.com/rpm.php

3.08's are more highway gears than performance. 3.55's will get you off the line and a different torque converter (if automatic) may help too.

Convertibel1970

Hi!

A friend of mine has got an engine simulation program.
The Comp Cam XE262 increased by 10HP around 5000rpm, only!
I think I just swap the differential to a 3.55 ratio and let an experienced garage check my cylinder heads, the timing and the carb.
If the engine is worn I´ll stroke it, add a suitable cam and buy better TFS heads.
Do you think it makes sense to port my double hump "186 heads?
I don´t know if any pre-owner installed the hardened valve seats.
Our gas is not plumbed...

BR

Andreas

Convertibel1970

Actually I don´t know if I have the Muncie close or wide ratio 4speed manual transmission.
I have the 1970 "G81" economy option with 3.08 rear end and the ZQ3 300HP small block. Does anyone know more exactly???

TheSkunkWorks

Ich würde wählen 3,55:1.

Dustup7T2