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4t80e rehash and custom engine mods


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Just wanted to bring up a relatively old subject. I have a 2005 Pontiac GXP which I am tweaking beyond the mods that were available when it was new. I realize it's not a Cadillac, but with the Northstar engine, I believe I can be forgiven for posting here.

Currently I have Madtuner.com PCM, K&N filter in a homemade cold air box ( properly sealed from the engine bay) , modified MAF intended for an LS1 engine, polyurethane sway bar links, Monroe coil shock conversion, ( ask me about my homemade ride height compressor solution.) a pair of higher flowing aftermarket cats with twin 2 1/2" factory shaped pipes, modified "Y" pipe and roll on 20" wheels. Still have the stock Helmholtz resonators but looking at mufflers and listening to YouTube sounds for the tone I want.

I have been attempting to contact Comp Cams for a regrind, hoping to have one of the milder Ford 4.6 DOHC profiles or Ecotec profiles ( the Ecotec is very similarly the N*, including 1.68 follower ratio so they should be able to do a N*) ground on my cams. I have a set of all the factory cams from 00-05 for starting points, ( including a set of " rough idle " cams that were never replaced under warranty by the original cars owner ) depending on which profile gives them the most material to start with. Comp did the Wheel to Wheel cams back on the Tim the Tool Man days, but these cams are not quite what I am looking for in a DOHC. Also lobe profile technology has greatly improved in the time since these were done. I have been having trouble getting a response and 99-999-3 , custom grind part number, is no longer listed in the catalog, imterestinly, they still advertise custom cam grinding. CHRFAB says they can regrind 2nd gen cams and Elgin seems to have a pretty comprehensive regrind order form but I have always run Comp. Just seems to have worked out that way, so I trust their lobe philosophy, no other specific reason. If all else fails I will run some 03 L37 cams timed for performance instead of emissions. I doubt I will see any loss of low end since these cams are almost as small as the original LD8 profiles but have more lift due to the 1.68 ratio followers. I am also trying to find a junked Ford DOHC to see if their 1.8 follower will fit the N*.

I have been trying to find the " raw " cam specs for an LH2 but no one seems to have spec'd them. I haven't been able to figure out how to retro- fit the heads and VVT to my LD8 but the cams themselves might have good numbers, I would probably need to pin the gears. Surprisingly, the bottleneck is not PCM programming but the oiling changes to the LH2 block. I suppose I could use the whole engine but I really don't want to try to fit a longitudal engine in a transverse installation. I'm not that good. I am also currently researching injector spray patterns so I can install injectors cable of handling the power increases.

I have a " fair " budget, my car was " totaled in January but if I purchased it back for under $500 because it is such a good runner and the engine is worth more than the buy back. Using salvage yard parts and skipping the paint job for now ( I have tri-color Caddy white, holy crap it's expensive to get sprayed ) ,I am left with some unexpected coin and I can do a fair amount of fabrication so this is not really "pipe dreaming" .

Contrary to some older information the Northstar is not " maxed out " from the factory. Checking factory cam specs show that the power level for my LD8 has remained the same as the original, even though I have the smallest cams ever used. You can't really make the cam smaller, keep the same power level and say the engine is at it's full potential. The real problem has always been the crossover pipe. At its smallest dimension it seems to be about 2" which means the L37's probably made different HP on the front and rear banks ( approximately 144 front and 156 rear ) . Using my test block/ trans and subframe, it seems I can just about squeeze a pair of 1 7/8" pipes side by side by using heat wrap and lowering the skid plate a negligible amount. This would allow a " real " 400 engine HP, which is fine for me, my target is slightly lower. Of course I would need the headers to be tri- y or 180 degree, since I have to make them anyway it really doesn't matter to me. The Fiero guys have been making sweet headers for years. I bought a U build box of header bends etc to make things easier. I am also looking for flow numbers for 2nd gen heads. I have heard the intakes flow better but the exhaust are " worse " ( as far as a DOHC having " bad " flowing ports. I don't think I will need porting on the intake but maybe extrude honing the exhaust. I won't know until I see the numbers and it is unlikely I can pop for flow testing. I have read most of the poppycock regarding the porting of N* heads and while I realize the info comes from a former GM engineer, it comes from a source that had little incentive to encourage the average car owner to do this. Additionally, if stock injectors were used, they were probably duty cycle beyond their intended max. I doubt the Shelby ran stock ports and injectors and nobody seems to complain about CHRFAB or BPE ported Northstar heads so no worries. Technology is also light years ahead of what could be accomplished back then.

Finally, the 4t80e, I had wanted to swap in a 6t80e and enjoy the lower first gear ( possibly allowing a more radical camshaft) while maintaining the a similar final drive ratio in overdrive, with my 3.71s.( I don't mind a street car with poor manners ) and a better exhaust crossover situation. We all know that might not be so feasible until some 2014s show up in the salvage yards. One of the performance 4t65es would be ideal, but outside my budget. I have decided to stick with the 4t80e and install some of the newer 06-11 hard parts. If there was some way to swap the sun and planet gear tooth count, I could acheive a 4.16 ratio in the final drive to compensate for any stupidity I might suffer from cam selection. Small engines need RPM's and I love to hear my N* scream. Overdrive ratio would only jump from 2.52 to 2.83, hardly a deal breaker. Back in the day (TH350) we considered that a " fuel economy " ratio. I have access to a supplier of gears and such. There may just be an off the shelf solution, it will just take some time and careful measurements. Torque management is disabled on my tune and it spanks the tires nicely on the 1-2 shift. I have seen the original 305lbs/ft rating, which means it actually can handle at least 400 allowing for the standard engineering rule of 25% under rating for warranty purposes. Also, this rating was never updated as the factory made it's improvements. I was wondering if any one remembered the weak link that the guy ( Mark ? ) with the awesome turbo setup had, just in case I want to stock a spare.

Sorry for the long post, but this is the place I think I can get my answers. I am a grownup, not a dreaming teenager, and my intended mods are more than possible for the average person who fabricates his/ her own parts on a regular basis. Thanks in advance for any tips, help or even critisisms. I realize this is old material, but it's what I have and what I want to mod.

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I would trust CHRFAB more than anyone for Northstar mods, since they have so much experience, albeit not in Cadillacs. Sounds like an interesting project.

Bruce

2016 Cadillac ATS-V gray/black

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