Need some help from experienced nitrous people........I was previously running a 150 shot on this motor when it was stock before I totally went through and redid everything. It did fine then but I'm kinda scared to use it now and i'm wondering if I even should. Here's the setup:

1974 Low compression caddilac 500 block
1979 rebuilt ported, polished, milled .040 425 heads, 85 CC chambers (1974 500 chambers are around 125 CC)
Edlebrock performer caddy intake,
600cfm vacuum secondary holley
Comp Cams 268 hi energy custom caddy grind cam, .490 lift, 218/218 duration
stock manifolds
performance stock diameter converter
TH350 tranny, shift kit,
factory 1978 Grand Prix 7.5inch 10 bolt with 2.41 gears
No AC, no heater, no interior, Summit racing seats, ect......weighs.......3,200 without driver??



Right now, it has a cranking compression of 210+psi and detonation is a problem since the cam I picked is obviously way too small to bleed off the compression. I am going to put a 230/238 duration cam in the motor......but until then, if I wanted to run nitrous, would it be safe on race gas? The motor just BARELY wants to run right with 92 octane pump gas and octane booster with the total timing set to 25 degrees. I can't turn the timing up anywhere past that or it detonates.
The funny thing is, with the odd combination of huge torque monster 500 with 2.41 gears and the rather small cam and high compression, the car actually HAULS ***. I can get about 6-7 car lengths on just about any LS1 6 speed car I can find on Speedway, but obviously from a stop or slow roll I'm toast cuz the tires will go up in flames. The rearend is welded "posi" but it doesn't help much with over 550 torque on tap. What would you guys recommend I do before running nitrous? Wait for the bigger cam? Gears? Would it be safe to just keep the timing where it is (25 degrees) and run straight race gas to use the N20? FYI even with high CR cammed 500 caddy's the most gear advisable is 3.42 according to Al at MTS motorsports....so actually 2.41 isn't as bad as it sounds. Unfortnately I haven't run the car at the track but I do have Gtech #'s from before I redid the motor:

13.7@109 N/A

12.3@119 150 shot

Now with the new motor setup the car is DEFINITEY faster on the motor that it was before on nitrous, I know this because my buddies 65 Chevelle with brownsfield headed 350 runs 12.1's and it would run neck and neck with his car on the bottle, and now it runs just the same on the motor.

 

First thing you have to do is get it to hook up. if you cant you are sunk. IMO, this is what you need to work on next.

then, find out what it goes through the traps @. if you are close to your red line. leave it along. if you are 1500 RPM from it, then either go up on the rear end gear or put the bottle back on it.

There is no difference in running the bottle in this engine than the last. Do plug checks, & keep it a bit on the fat side. if you do that & you dont rev the thing to 10K it ought to hold together (but now you are back into a traction problem, hope you did it right in step 1, or you are back to step 1).

thats my2c
BW

 

When are you taking that beast to Speedway again?

 

On the nitrous subject you should be ok on straight race gas, but I'd pill down to a 75 shot first and slowly work up from there just to make sure. I've got a couple other recommendations for ya as well.

Well first thing is get that beast to hook up, check out the adjustable control arms from www.bmrfabrication.com, they're a lot cheaper than the hotchkis units, and I like 'em better. You may also want to check out www.g-body.org, I used to ahve a tech article on this suspension set up there, dunno if it still is.

Your set up for that engine is gonna be similar to mine on my cutlass, both the olds 455 and caddy 500 are major torque monsters. I'd recommend around 3.23 gears. That should put you right about your redline at the end of the quarter (with the smaller cam, go to the bigger cam and you'll be a bit under it, but you'll be fine).
If you run straight race gas you'll have a lot less detonation issue, people run 13:1 and higher on race gas. Race gas is also usually formulated for a faster burn so you might actually get a bit of power there. And you can probably bump the timing back up, I seem to remember that those 500's like a lot of timing so that's probably hurting you.
You definitly need a bigger cam, remember more displacement will accept longer duration, so that 268 cam on that 500 is just plain TINY. With 11:1 compression I'd think that cam your looking at is just about right. If it was a higher revving motor I'd go higher, but with the caddy's you don't want to rev very high. Right now I'd bet your putting out well over 500 ft/lbs at 2000 rpm. The bigger cam will bleed some of that off and increase your higher end.
I'd also say that that 600 carb is too small, go up to an 850 you'll see around 15 hp at the top end.

get your traction problems solved and I'd bet on you being in the high 11's on just the motor. Get a set of DOT slicks maybe? Get the nitrous going, and the other changes you might see mid 10's (once again with traction). That's pretty much right where I run with my cutlass. With AC, full interior, basically the full car. Oh your car probably only ways 3400 fully stock, so with all that stripped off you may weigh in less than you think, cause the caddy engine is only a little heavier than a small block chevy. If you've added rollcages and stuff that'll add of course. Good Luck

 

You'll need high octane gas for N/A and NOS with 11:1 cr
regardless of the cam timing. The detonation may be reduced at low rpm, but will still be there at high rpm with a bigger cam.
Unless you retard the ignition timing, which will kill the power.
That tini tiny air cleaner really has to go..... LOL

Water/ methanol injection may help....

 

I know its a sickness but I love caddy motors too, but the large bore and poor combustion chaimber design require that race gas. not just 110 but maybe the 114-116 variety might be required to quell detonation concerns even with timing retarded a little. an EFI caddy would be the shiz-nit!

 

Yeah I'd have to agree that traction was something I failed to mention and yes it is quite a problem, HOWEVER............I do have the spider gears welded together, and its been working quite nicely, from a 30 mph 1st gear roll the car hooks incredibly hard, enough to lift the frontend WAY up and to the left, but the car still kinda feels like its on ice so I know it still spins bad.....The suspension is pretty much stock, although the tires are massive 295 variety. I was thinking maybe boxing the stock control arms and getting an air bag. I was playing with the timing today and added some of that NOS octane booster and got it to run at 30 degrees total without hearing any pinging, MAN what a difference those couple degrees made! I can now smoke my buddies 12.3 second chevelle. Sweet DAmnit if I could only make it track legal Needs a battery cutoff, battery hold down bolts welded, rear firewall, fuel line, power steering leak fixed, ect...........doh!

 

Its there pretty much every Fri./Sat. at Coach's or cruising. Raced a C5 on Pima last week. That was funny

 

What colour was the C5? I saw a C5 at the gas station on Alvernon/Speedway that was cruising.

I might head out there Friday night and look for you at Coach's. I hate cruising up and down Speedway because I get that "I'm in rush hour traffic and I need to get home and get laid" mentality. And that gets me tickets.

Ya need a set of headers.

 

headers would be nice, but they are practically impossible to fit, you'll see when I show you the motor in person, that caddy literarly fills the engine bay. However the car does have a good 3inch mandrel exhaust so its not suffering too bad. I've seen a hot rod caddy dyno and they only gained like 12HP and 20 torque from a $700 set of custom made big block chevy converted headers

 

c5 was white with different ( I think they were different than stock) chrome 18inch rims

 

Hehe...even with the spiders welded..If he hooks with that motor..that 10 bolts gonna chuck..

In all seriousness, solving your traction problems is going to kill that 7.5, just too much torque available. I would start with replacing that rear with a 9 inch or a A-Body rear with Southside arms. Then replace your stock arms with the arms of your choice, I'm currently swapping a 9 inch from a Lincoln into my Malibu using stock lower mounts and spring mounts and fabbing up new arms myself with custom mounts on top. Also I am adding a panhard bar to keep the rear square, and working on some brackets to mount 11" SVO discs. I believe an airbag in the pass side spring helps too. Love the sleeper look. cheers, Bob

 

If it's the C5 I'm thinking about (white with red stripes), I ran him at SIR last time. He runs only about 14.2 @ 102.

I took a closer look at the engine pic, if that's your steering shaft practically touching your exhaust manifold, I understand why you don't have headers. I'll let you get by on that one.

 

Very True Saturn, though I just swapped in a rear end from a T-type and it's holding up pretty well. Course I'm not putting out 500+ torque at 2000 rpm either, I don't get that high til 3000. But your right a rearend upgrade is a must.

 

This one didnt' have stripes

In order for me to even be able to steer the car I had to grind down the driver side manifold about 1/2inch in one spot (on a bump) but it still rubs sometimes, and when I am racing people and I floor it, the frame starts to flex up quite a bit from the torque and sometimes the steering joint locks up on the exhaust manifold as the motor torques over. NOT fun

On the subject of the rear...........I have a spare 12 bolt 2.56 geared rear from a 65 chevelle that would bolt pretty much straight in (with some control arm rigging), but I'm gonna wait and buy some gears and a locker, or just weld the sucker like this one

 

Hmmmm that should be a 8.5 10 bolt. if it came from a turbo buick. with some prep a mighty fine rear end. cheers, Bob

 

Because extra fuel is added in a N2O setup, this idea won't help with that. But I would second rhuarc30's recomendation of going to a bigger carb. Personally I have always thought of a 600 being borderline for a 350 for certain setups. I would suggest at least a 750.

 

you know, its interesting people are recommending I go bigger on the carb, because at least on this caddy motor for some reason, bigger doesnt' seem to be better. I had a 750 double pumper on the car before the 600, and it just didn't spit out the torque it does now, or the HP. In fact the day I swapped to the 600 vacuum secondary carb it was like the car gained 2 seconds!! It almost felt like I added another engine. Either something was totally fubared with that 750, or caddy's just like smaller vacuum carbs better. I'd gather to say that with a 850 Demon vacuum secondary carb it might be a different story. I think auto's, ****ty gears and double pumper's don't mix too well.

 

Hey John.....whats that camaro run like?? That sounds pretty similar to the motor I'm building right now for my bird, I just got all the parts gathered and will start slapping it together tommorow morning, should have it running by Saturday........I can't wait.

 

double pumps and autos, and crappy gears don't mix well, A 750 3310 Holley would respond much better than it's DP brother. I haven't run a Holley in years, and always ran 600 VS on my GT's and was very happy as far as Holleys go...lol

Yeah, I'd be looking at swapping your 12 bolt soon... cheers, Bob

 

Yeah, I should have said vacuum secondary carb, I hate double pumpers. I actually run a modified quadrajet on my 455, and I love it, great throttle response, decent gas mileage, and when those secondaries open, hold on.

 

I love double pumpers....but I still know thier place. No converter heavy car and crappy gears ain't it. Step that thing up to liek an 850VS carb.

 

Chris, I love the setup I have. I still have a stock suspension, and that is a big problem. The only way I have found to make a good run on the street is to heat the tires real good, and then short shift 2nd, after I launch. I don't have any times, but I can beat my room mates 2001 Camaro by a good margin. If I could get some good fuel, and advance the timing a little more, I think I could do even better. I haven't been driving it lately b/c I'm in the process of getting all my Autometer gauges installed. After that the car will be up for sale.

 

Ok, I'll display how naive I am when it comes to SBC carbs.

What's the difference between a double pumper and a vacuum secondary?

All my carb experience is with Solexes and Webers.

 

double pumps squirt fuel from all 4 barrels, primary and secondarys at once where vacuum secondarys open seperatly from the primaries. cheers Bob