Not really a tow truck but I do get some funny looks when pulling my enclosed trailer behind my car...

But I have your attention hopefully!! I have a 98 CNG bi-fuel cavalier. I tow a trailer with it since I have no trunk. I love this little car and want at least 5 more years out of it. Sure, I could go plop down cash for a new truck, but why? I save money in the bank every time I turn the key on this car, its a workhorse, and lets be honest it gets chicks.

Recently I swapped in a 5 speed, GREAT mod. Right after we took it to Canada and it did great, except I lost oil pressure, the new clutch is slipping, and the fuel pump failed. So time for an engine build, clutch, external fuel pump etc.

One VERY important fact: I CAN NOT TUNE THIS ENGINE!!!!! Again, NO TUNING.

If you look at my ecm with hptuners the CNG run file is a format that can NOT be modified or viewed. This car burns two different types of fuel, but I always burn CNG, which is nice with its 130 octane rating, but I do burn fuel occasionally when there are not pumps in the area, Idaho for instance.

So on the engine my goals are NO TUNE, and 15-20 horse and ft/lbs. Right now it is all stock, not even a muffler.

My basic ideas:
Either a used engine or rebuild my current.
Bump compression with either pistons (which are stupidly expensive) or zero deck the block and pull .020 off the head if its a used motor
As much cam as I can
Correct pushrod lengths depending on machine work, stock rockers and springs if possible
Port and polish, valve job, stock valve size
Research a bigger throttle body
Maybe open up the intake
Pacesetter header
Maybe a muffler, I dont want ANY "ricer" sound
A decent clutch

I am sure I am missing a few things but I have some questions.
First the cam, I see the stage 1 and 2 from IPP, they seem expensive considering a grind should be less than $150 from crane but I havent a clue where to start on specs, it obviously cant be much, duration will cause missing issues I think and to high lift will obviously mess with my lack of tuning ability. Anyone have a decent cam recommendation?

Compression, say I do rebuild, is there anyone out there charging a SANE price for pistons? I mean come on, I have a 450 horse motor in my rockbuggy and 8 forged pistons were as much as these sites show for 4. I will want a basic speed pro or keith black with a 10 or 10.5 rating, I see no reason why Hypereutectic would not work. The slight gain in displacement and compression will be beneficial and should not cause any tuning issues.

If I buy a used engine I will need to do some research on the zero decking, I have not seen that one yet.

Valve train, I will assume my stock rockers will be fine, obviously with the cam change added lift will not be necessary. What about lifters and springs, can I keep them stock? I see where you guys are pocketing the springs and going LS, I cant really understand why, seems a matched set of springs with proper pressure would work fine, hopefully stockers. Push rods will have to go, with a grind, or the decking, or milling, something there will change, what interference are you guys running between the valves and pistons? I measured for push rods once, put on light springs, went tdc on the cylinder, and used a dial indicator to check for clearance, but it was a long time ago.

I am not a big fan of bigger valves for a motor geared towards torque, which this will be, I dont want to start lightening anything, the higher mass stays rotating better imo, good for towing. Maybe a slight bigger tb, pacesetter seems to be getting good reviews and I will throw it up on the rack and try a few mufflers off the shelf and find the quietest, I also think my cat is plugged so chuck that.

Any recommendations on a clutch? I havent owned a manual since my LT1 camaro in high school. Used Centerforce back then, recently heard some bad things, well 3-4 years ago heard they were going to hell.

Bearings if I rebuild, why are the Clevites so much freaking money? Seems ridiculous.

So these are some of my goals, basically need to start ordering parts and make a decision on what to do with the block. Going to call Crane and get a idea if they have opened the shop back up for grinds, if not maybe Lunati.

With this build can I stay away form tuning? I dont think this is too unreasonable for the stock fuel trims.

Right now the car runs decent, I can almost pull hills in 5th on fuel, have to use 4th on CNG. I want that full 5th gear on CNG. That is my goal.

And by the way, because of the CNG I do a tailpipe emissions, check engine lights are irrelevant, light is on anyways due to the auto pcm with the manual trans, only issue is a code every 5 days with a trans slipping code.

Thanks for any help, cant wait to see if I can get 10% more out of this little thing.

So I have done alot more reading today.

I am looking at cam choices, the crane HR206-313 looks like a decent cam that would allow me to use the stock rockers and valve springs. I found a reference that the lift of that cam is pushing the limits of the stock springs, but I dont think I want to go to the effort of machining the spring pockets. Then I will mill the head .030, port and polish, change pushrod lengths and put it in the car with an exhaust update and a new clutch. Thinking of buying a used engine and tearing it down to do this combo. For what I am gaining the costs of a rebuild by the time you do everything doesnt seem worth it. I will also change the oil pump and check the timing chain. Should give me a decent gain, anyone have any input?

You trailer, I wouldnt even dream of putting an aftermarket cam in. All you're going to do is move the power band up. A better rocker ratio would help with some breathing without hurting your towing. I'm not an LN2 guy though so there might be some better opinions.


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Spent more time again today. Didnt get a chance to call Crane.

Decided I am going to buy a low mileage engine and put it on the stand.
Have the new cam on hand (need to decide specs, handle stock springs so .460 lift MAX I think?)
First check all bearing clearances on the rods and mains
Then mock up the new cam and check for intake and exhaust valve to piston clearance and rough idea on rocker geometry
Then pull the head and check the block for how much can be decked
Using that info I can determine how much to mill off everything, max on the block, the rest on the head, I think .090 and .135 for clearance minimum
Then I will check the valves for how well they are seating, determine if a valve job is necessary and if so decide on +1 valves
Then port and polish the head
Then I will tear the engine down and take it and the head to be milled and cleaned
Then I will install the stock used bottom end in the block (assuming all clearances were ok)
Install a new oil pump for sure and chain if necessary
Reassemble the top end with stock springs, lifters and rockers
Measure for exact pushrod length
Final assemble motor

2.3 throttle body
Header
No cat
30 inch resonator
Dbx Muffler
Build a very basic intake

Now with this build will I need to tune? I also need to decide on cam specs and find a solid lifter and soft valve springs to take measurements with.

Max lift on stock springs should be kept below .500 if I remember right. Some people have probably gone over, but that's a safe amount. You'll also want higher ratio rockers. Honestly, I wouldn't dare run an aftermarket cam without a tune, at least not for any amount of time.

Really, even a very mild cam will need a full tune? That will be a major issue, I am in no ways knowledgeable about the limitations of the stock tune. Say I can not run a different cam, can I run 1.6 roller rockers instead? Still open everything up and then bump the compression and run it?

Quote:

So on the engine my goals are NO TUNE, and 15-20 horse and ft/lbs.

I understand why you're stuck but yea... good luck with that.

Trust me I will dyno when we are done, just to know. It will be fun. I have a line on a few used engines, I am trying to find the lowest cheapest best bargain.

man i agree with you i have a 10 foot long 5.5 foor wide trailer i tow my dirtbike with and it works amazing at 115kmh ,
im replying to your clutch concern i have had 3 go through my car and slipping almost a month to the day, what i found was the slave cylinder is internal and has been over extending,
the fix for it was a new flywheel and clutch, but find and spen the money on the slave as it is internal to the car and really expensive my stock replacement was 360.00.
if you dont do the flywheel ull pull the trans again for overextending the slave and then all components are soaked in brake fluid.
the car tows grate for me and it hasent effected gas economy enuf to bother saying
other mods, pacesetter header, cold air intake, lots of suspension,