I've been told before by others that the Valve spring rate on the 4.5L allante engines is actually higher than the 4.9L caddy engines. Can anyone verify this with factory specs? i have the factory spring rate specs for the 4.9L engine, and they are:

Free length 49.5mm
Pounds required to compress
to 44mm (1.73")(valve closed)
68-76
Pounds required to compress
to 34.3mm (1.35")(valve open)
214-232

Does anybody have the factory specs for the 4.5L allante valve springs?

damn.. 21 views and no replies so far?

hmm, I think that is a myth but I'm gonna do some digging.

quote Originally posted by collinwestphal: hmm, I think that is a myth but I'm gonna do some digging.

wow, collin, you respond to my posts but not to my PMs or my emails.. fascinating.

you have a PM. and I did not have any luck finding out the spring rates.

I thought that 4.5 Allante heads had an extra dampener spring which accounted for the extra 500 or so rpm higher redline. 4.5's had three valve springs per valve and 4.9's had two valve springs per valve.
Thought I read it here or the other Fiero site....

Dragon1/Brian

hmm, thats interesting. I wonder is it a dual spring, or is it a two spring damper? and if it was a dual spring would they fit on a 4.9L head?

we need somebody with an allante engine to take pics!

[This message has been edited by collinwestphal (edited 01-26-2005).]

I think it was a spring with two dampeners.....

Dragon1/Brian

quote Originally posted by Dragon1: The Allante did have a stronger rocker arm pivot support made of steel.(pn 1641338) The 4.9 rocker arm pivot support is cast aluminum. The Allante also used a different valve spring ( pn 1646891) that has a higher seat pressure and a longer free length than the 4.9. This valvespring has since been discontinued by GM. It is nothing special, but it did allow a maximum 5200 RPM compared to the standard 4.9 valve spring. So swapping to 4.5 Allante valve springs should help a little...

yes, the steel rocker arm supports are the only NOTICEABLE difference in the valvetrain on the Allante engine. Other than that, they both LOOK indentical.

I have a new 4.9L longblock, with a mustang E303 profile cam made for it according to the specs on Rockcrawl's site, and I also have a '91 Allante engine. I was planning on swapping the entire intake setup from the allante onto the 4.9L, as well as the rocker arm pivots. I need verifiable exact figures on the spring rates for the allante valve springs, to see wether or not it is worth swapping them onto the 4.9L. Someone just saying the allante valve springs have a higher seat pressure and a longer free length still doesn't provide adequate information. And, furthermore, the 4.9L engine from the factory also has a 5200 rpm redline, as the ECM is set to that, so saying the allante revved to 5200 rpm is inconclusive. I appreciate this inoformation very much, but I am hoping someone has more conclusive data to contribute to this thread

I am pulling my engine out next week to put my Delta Cam in and my extra set of heads are at the shop being prepped.
You can not use the Caddy springs with anything over .400 lift without getting coil bind. You must also machine the tops of the valve guides to avoid contact with the valve retainer.

To answer your question about the Allante vs standard Caddy springs, I just walked out to the garage and looked at a set of regular 4.9s next to the Allantes and saw no difference.
They are a single spring with no damper on both heads. They look the same, but I did not mic them to see if they were the same diameter or not.

Gene

quote Originally posted by scrabblegod: To answer your question about the Allante vs standard Caddy springs, I just walked out to the garage and looked at a set of regular 4.9s next to the Allantes and saw no difference. They are a single spring with no damper on both heads. They look the same, but I did not mic them to see if they were the same diameter or not. Gene

they ARE different, that much has been established. just because two springs look alike doesnt mean they are in fact, alike. spring rates can very based on the way the spring is tempered. anyways.. i read up on the ASG 5.0L stage 2 engines, and contacted the company. the cam profile they use is pretty much maxed out, and they machine the stock rocker arm's fulcrum to allow movement for all the extra lift, and yet they use the stock 4.9L valve springs, and achieve a 6000 RPM redline, and just before anyone questions this, yes, it has MAXIMUM HP at this rpm, 320 HP to be precise with the custom superchips program and upgraded 24 lb injectors that it was programmed with, and 290 HP with the stock caddy ECM and injectors. so anyways.. the cam profile i chose for mine makes power from 1500 to 5500 rpm, and i have the allante springs here. I figured that if they do indeed have a higher spring rate, it would be worth it to swap them over. anyways.. i hope somebody in this forum comes forward with the specs.

From the 1989 Allante Service Information Manual:

Valve Springs

Free Length........54mm
Pounds required to compress to 44mm (1.73") (Valve Closed)....93-103#
Pounds required to compress to 32.5mm (1.28") (Valve Open)....204-221#

Somewhat different than the 4.9.

David Breeze

------------------

Pantera Rebody Kits

[This message has been edited by opm2000 (edited 01-27-2005).]

Those specs are interesting because they show the Allante having a higher lift cam if you look at the valve open specs.
It also shows a higher closed pressure but a lower open pressure. This makes you wonder which set of specs are incorrect.

Gene

From the same 1989 Allante FIM:

Camshaft

Valve Lift
Intake.....9.75mm (.384")
Exhaust..10.06mm (.396")

Duration
Intake.....277Deg
Exhaust..273deg

David Breeze

quote Originally posted by opm2000: From the same 1989 Allante FIM: Camshaft Valve Lift Intake.....9.75mm (.384") Exhaust..10.06mm (.396") Duration Intake.....277Deg Exhaust..273deg David Breeze

cool.. and the cam specs for the 4.9L are:

Intake lift (at valve) 9.75mm (.384")
Exhaust lift (at valve) 10.06mm (.396")
Intake duration 278 deg
Exhaust duration 274 deg
Overlap 49 deg

the lift specs are the same for both cams, but the duration is 1 degree more for both the intake and exhaust on the 4.9L.

[This message has been edited by aaronrus (edited 01-27-2005).]

Some more measurements actually observed.

4.9 spring
50.1mm length
4.95mm wire size

Allante spring
55.1mm length
4.57mm wire size

Tomorrow, I hope to get on and off seat values for each spring.

Gene

GOOD work scrabblegod,

what is the solid(compressed) height of each of the springs?

i'm curious to know at what amount of lift each of the springs would coil bind.

I am going to try to get the lift for coilbind tomorrow also.

Gene

quote Originally posted by scrabblegod: I am going to try to get the lift for coilbind tomorrow also. Gene

thanks alot gene, i appreciate the help.

quote Originally posted by scrabblegod: Some more measurements actually observed. 4.9 spring 50.1mm length 4.95mm wire size Allante spring 55.1mm length 4.57mm wire size Tomorrow, I hope to get on and off seat values for each spring. Gene

There is no substitute for an actual spring measurement for coilbind.
However, you can get a close estimate by multiplying the wire diameter by the number of coils.
As both springs appear to have 6 full coils,
the 4.9 spring would be 4.95mm x 6 = 29.7mm ( 1.170")
the Allante spring would be 4.57mm x 6 = 27.42 ( 1.080")

To eliminate coil bind in an installation, you would add a minimum of .060" to both of these total heights to determine the maximum lift each spring could accomodate.

This gives 1.230" for the 4.9 and 1.140" for the Allante, which would approximate the maximum allowable compression of each spring when installed.

On paper, the Allante spring can handle .090" more lift at the valve, using the same spring retainer.

Again, this is just a quick comparison to be confirmed and/or adjusted by actual spring coil bind measurements.

Kerry

quote Originally posted by scrabblegod: I am going to try to get the lift for coilbind tomorrow also. Gene

hey gene, any luck measuring the solid ( compressed) spring height of the 4.9L and the 4.5L allante springs? i look forward to hearing the results so i can figure out how much lift i am limited to for an aftermarket cam using stock springs. do you think it would be possible to take pics of the measurement as you take it?

We tested several springs, and they all coiul bound between .512 and .518.
Whlie it seems they would work with a hotter cam, the problem is the low seat pressure.
By the time you shim them enough to get good seat pressure, you end up with coil bind at about .460 lift.

We ended up not using the 2.8 performance springs. The inner coil does not really sit properly on the retainer. It would work, but he felt in the long run it may cause the inner spring to be wedged between the coils of the outer. I should say he builds big buck racing engines and may be overly concerned for a lower RPM street engine.

We tried various springs he had at the shop and finally ended up using a set from a late model chevy fast burn cyl head.
If you are interested, I will ask him the exact application. This spring gave 125lbs on the seat and 265lbs at .502 lift.

Gene

what is the downside to using springs with a higher spring pressure?

in other words, why wouldn't GM use these in the stock engines?

I realize you are getting these to use with a hotter cam, but are there downsides to using a stiffer spring with a stock cam?

A stiffer spring requires more HP to operate.
It can also cause accelerated wear on components.
They design a spring to operate in the stock rpm range.

Gene

quote Originally posted by scrabblegod: A stiffer spring requires more HP to operate. It can also cause accelerated wear on components. They design a spring to operate in the stock rpm range. Gene

now, gene, if im using the E303 mustang cam profile on my 4.9L , which has .498 x .498 lift, and around 280 duration( makes power from 2500 to 5500 rpm ).., would the stock 4.9L springs provide adequate enough seat pressure for street use? i have a set of 4.5L allante springs also, do they have a slightly higher seat pressure than the 4.9L or about the same? i dont knwo if referencing the stock numbers on both springs would help you determine that, but here it is:

Allante:
Free Length........54mm
Pounds required to compress to 44mm (1.73") (Valve Closed)....93-103#
Pounds required to compress to 32.5mm (1.28") (Valve Open)....204-221#

4.9L:
Free length 49.5mm
Pounds required to compress to 44mm (1.73")(valve closed) 68-76#
Pounds required to compress to 34.3mm (1.35")(valve open) 214-232#

now, it would appear from these numbers, that the 4.5 Allante would have a slightly higher seat pressure than the 4.9L, but did your REAL world measurements produce a different result?

[This message has been edited by aaronrus (edited 02-17-2005).]

That is the same cam I am using.
I checked the lift on the cam with a mic, and mine comes out at .502 lift which matches what was listed on the cam card he sent back.

Now keep in mind these were used springs (75,000 for the Allante and 160,000 for the 4.9)
The Allante springs averaged 98lbs on the seat at the factory installed height. The lowest was 94 and the highest was 101.
The 4.9 springs averaged 71lbs

At .384 lift, the Allantes averaged 212lbs and the 4.9s averaged 216.

The Allantes are longer than the 4.9s, but have a smaller wire diameter.

At .500 lift, both sets came in around 240lbs, and were ~.015 away from coil bind.
These types of spring pressures are marginal with the quick ramp on this cam, and when you consider the tolerances in the factory rockers and the chance of a lifter pumping up, it is to close to coil bind for comfort to me.
If you are increasing the rev limiter at all. I think the higher spring pressures are needed.

Gene

quote Originally posted by scrabblegod: That is the same cam I am using. I checked the lift on the cam with a mic, and mine comes out at .502 lift which matches what was listed on the cam card he sent back. Now keep in mind these were used springs (75,000 for the Allante and 160,000 for the 4.9) The Allante springs averaged 98lbs on the seat at the factory installed height. The lowest was 94 and the highest was 101. The 4.9 springs averaged 71lbs At .384 lift, the Allantes averaged 212lbs and the 4.9s averaged 216. The Allantes are longer than the 4.9s, but have a smaller wire diameter. At .500 lift, both sets came in around 240lbs, and were ~.015 away from coil bind. These types of spring pressures are marginal with the quick ramp on this cam, and when you consider the tolerances in the factory rockers and the chance of a lifter pumping up, it is to close to coil bind for comfort to me. If you are increasing the rev limiter at all. I think the higher spring pressures are needed. Gene

do you recall what the actual measured height of the spring itself was for both the 4.9L and the allante springs, when they were fully compressed? based on the numbers posted before, it looked like the allante springs were shorter when fully compressed, which would give me better room to work with. This is the last bit of info I'll need from you. I'm raising the fuel cutoff redline to 5600 in the ecm, up from 5200 limit, that is stock for the 4.9L. I have a set of allante springs here, and if you think they are a better match for the e303 .498x.498 cam than the stock 4.9L springs, i'll use those, but i've decided against buying aftermarket springs, simply because i dont plan revving it past 5600.

ohh.. one more request.. you wouldnt happen to have a picture of a stock 4.9L rocker arm, one that is laying around. i need to see the length of the slot for the stock rocker supports..I appreciate the help. The machine shop i used for the work supposedly lengthened the rocker arm's slot to allow for the extra lift. ijust wanted to compare the two to make sure the work was done right.

Give me about 2 hours, and I will get you the picture of the rocker along with the actual length of the slot.
I will also get the spring lengths.

Gene

quote Originally posted by scrabblegod: Give me about 2 hours, and I will get you the picture of the rocker along with the actual length of the slot. I will also get the spring lengths. Gene

thanks again gene, you dah man!

The height of the Allante springs at coilbind was 1.262.
The 4.9s were 1.268.
This corresponds to .518lift for the Allante and .512lift for the 4.9.

I have not modded my rockers yet so this is a picure of a stock rocker and the slot is .830 in length.

Gene

quote Originally posted by scrabblegod: The height of the Allante springs at coilbind was 1.262. The 4.9s were 1.268. This corresponds to .518lift for the Allante and .512lift for the 4.9. I have not modded my rockers yet so this is a picure of a stock rocker and the slot is .830 in length. Gene

cool... if i use the allante springs, this will give the acceptable allowance of .020 using the E303 cam.

would wider retainers fit?

The inside id of the caddy spring is .960 and the od ~1.40

The springs in my new heads are from a late model chevy fast burn cyl head.
I am not sure of the inside id, but the outside id varies from 1.31-.133 and they work fine with the stock caddy retainers.
I will get the exact application today.

Gene

you may be talking about the same spring? This is from a 96' chevy corvette.

I tried to find an inside diameter of the spring, but couldnt.