Here's my situation:

I flew to buy a used car with LS1 shortblock, GTP 5.3L heads, and a 225/225, 589/589 112LSA cam. On the test drive, a valve spring broke. I found out that there are between 30-40,000 miles on this setup and these stock-like springs. The current owner is not familiar with engine work. In fact the last two owners of this car just bought it to drive it. They were enthusiasts who changed oil religiously and took care of the car cosmetically, but werent aware that things like springs need to be checked/changed on camm'ed cars.

Anyway, his mechanic is not familiar with LS1's, but is old-school. He replaced the broken valvespring with a new LS1 stock spring, AFAIK. They compression tested the motor afterward and all cylinders are even.

I'm concerned about the motor and told him I'd like to have it dyno'd to make sure it's still making the power he advertised it to (430whp/401wtq).

I'm going to buy the car regardless (It has all the paint, body, wheels/tires/suspension that I want on it and that saves me big dough), but we've agreed that if it's down more than 10-15% on power, we'd negotiate a lower price.

The problem is that I'm afraid to run it up to 6500rpm or whatever with the remaining fifteen 30-40k mile old springs that may have never been upgraded from stock. If I break another spring on the dyno at WOT in the high revs, BYE BYE motor.

It seems like the easy answer is DO NOT DYNO IT. I don't have the tools to change out the springs beforehand as I'm flying 600 miles to get the car. I have a set of brand new PAC 1518 springs for the car and had planned on changing them and buying new pushrods (to set my lifter preload where I want it) when I get home.

Am I just screwed? If I pay full price for this car, drive it home gently, change the springs/PRs and go dyno it and it dyno's low I just have to eat the cost of rebuilding the motor. If I chance it on the dyno before I drive it home with the old springs and the motor goes, I'll have to fork out $1000 to have the car shipped home and who knows what will need to be replaced, much less rebuilt, and we sort of agreed to knocking only $2500 off the price.

FWIW, after changing the broken spring, the compression test numbers were 150-160psi across all 8 cylinders on a COLD test.

What would YOU do?

 

Buy the car, drive it home, change the springs. If it has lost 10-15% im sure it still will be too much for the suspension thats on the car, If Im right in assuming its stock seeing as the last 2 owners were just enthusiasts and just did general maintenance. Plus those numbers will be fine for a while then you will be wanting more.

 

Suspension is not stock, and it's not an F-Body It's an FD RX7. 3.90 LSD rear end and Koni Yellows with Eibach Prokits all around and delrin bushings. 275 street tires don't get a lot of mercy, I'm sure, but it has been run this way, at this power level for 4 years with no problems.

Car went 11.1@127mph a few years back.

I'm leaning more and more towards just driving it back and not risking the dyno with the old springs.

C'est la vie, right? I suppose my LS1 teardown skills need work anyway, it'll be a fun break from all the turbo fours I've built in the past.

 

I think that is the correct plan. I would not risk the motor on the dyno with those weak springs. Even if they don't break, you would likely have some float in the upper rpms anyway. This does have a little bit of risk involved, but really good deals often do. Good luck, sounds like a fun ride.

 

Chances are those numbers are generous. A 225/225 with that lift and 5.3 heads will most likely not make that much power.

I'd check it out, buy it, then replace the springs immediately. If you put it on a dyno and you break a spring you could drop a valve and cause yourself all sorts of headaches.

 

The heads are GTP stage 2 ported 5.3's. The cam is either a 225/225 or a 228/228, the owner is not exactly sure and the original builder of this car isn't either, as he's built about 10 of them since this one was built. The car is well done in almost every aspect except the interior, and it's a good price. I guess I'll just limp her home.

Do I have anything to worry about keeping the revs under 3000 driving it home with that one stock spring? I know stock springs aren't rated to handle .589 lift, but driving it 600 easy miles does that involve any crazy risk to the motor?

FWIW, here is the original dyno:



Sorry, I know the image kinda sucks but it's the only one I have.

 

You'd be surprised what some GTP 4.8/5.3's will do with a small cam...most of his stuff has great air speed and killer mid-lift numbers on mild port work overall with a runner that's kept sane. You just don't hear about them anymore since all the budget CNC and nice aftermarket stuff got big.

And you really don't need tons of lift to make power. I built some cars back in '05 with those heads, a fast, and low 230's cams with .580" that all made 460/400-ish. Sure with a nasty lobe and another .040" lift, it might have picked up 10-15 but at a cost of significantly reduced component longevity from my experience.

To the OP, try and at least replace the stocker if you can before you go to driving it far. It would suck to drop a valve. You def selected a good spring to replace them with in the 1518. Sounds like you have a good street car combo that will be a blast in a RX7.

 

Thanks! We decided to ship the car instead. It arrived at my house last night and I will be changing out the springs on Sunday.

The tech who put the one stock spring in the car decided to change both springs for that cylinder, I guess. He put the un-broken second spring in the box with the brand new PAC 1518's.

It appears the springs that were/are on the car are a good 1/4" shorter. Is this normal? I guess my main concern is, "Do PAC 1518 springs drop straight into 5.3L heads?"

Am I missing something?

 

SSP Racing...GTP speced my buddie a set-up...it SUCKS. Only made 404rwhp...his cam, and worked to hell heads. The heads that were on the previous car, w/ a different cam speced by our tuner made a good bit more power. MY cam only car makes more power. He told him this set-up would make 465 ALL day long.

To the OP good luck w/ the car...sounds cool! Def. change those springs before u go driving it.

 

The Pac should be installed at 1.800 height. You get a spring micrometer and install on 1 valve, twist untill snug all the way as far as micrometer will go. Read height. If more than 1.800 then you need to shim the difference.

 

This is a basically stock setup (stock valves, seats, retainers, rockers, lifters, pr's)... is that really necessary? I thought the comp 918s/Pac 1518's were drop-in springs?

Also... the pac looks taller... wouldn't that mean I'd need the OPPOSITE of shims? Won't a taller free standing spring be closer to coil bind than a shorter spring?

 

That sucks...I've ran his heads on a dozen setups from H/C to strokers and always had consistently good results. Not record breaking $3k ported AFR or TFS numbers, but very good for the $ spent. Sounds like something major got overlooked in the combination or somethings broken.

 

Nothing broken...brand new motor 0 miles.
He speced the combo!
I'm just saying if i made 404 w/ heads and cam...i'd be PISSED.

 

I probably would too. Fortunately, this setup with a mild cam on 91 octane tune made 430/405.